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James IV of Scotland

James IV (17 March 1473 – 9 September 1513) was King of Scotland from 11 June 1488 until his death at the Battle of Flodden in 1513. He inherited the throne at the age of fifteen on the death of his father, James III, at the Battle of Sauchieburn, following a rebellion in which the younger James was the figurehead of the rebels. James IV is generally regarded as the most successful of the Stewart monarchs. He was responsible for a major expansion of the Scottish royal navy, which included the founding of two royal dockyards and the acquisition or construction of 38 ships, including the Michael, the largest warship of its time.

James was a patron of the arts and took an active interest in the law, literature and science. With his patronage the printing press came to Scotland, the University of Aberdeen and the Royal College of Surgeons of Edinburgh were founded, and he commissioned the building of the Palace of Holyroodhouse and Falkland Palace. The education act passed by the Parliament of Scotland in 1496 introduced compulsory schooling. During James's twenty-five-year reign, royal income doubled, the Crown exercised firm control over the Scottish church, and by 1493 had overcome the last independent Lord of the Isles. Relations with England improved with the Treaty of Perpetual Peace in 1502 and James's marriage to Margaret Tudor in 1503, which led to the Union of the Crowns in 1603.

The long period of domestic peace after 1497 allowed James to focus more on foreign policy, which included the sending of several of his warships to aid his uncle, John of Denmark, in his conflict with Sweden; amicable relations with the Pope, Holy Roman Emperor Maximilian I and Louis XII of France; and James's aspiration to lead a European naval crusade against the Turks of the Ottoman Empire. James was granted the title of Protector and Defender of the Christian Faith in 1507 by Pope Julius II.

When Henry VIII of England invaded France in 1513 as part of the Holy League, James chose the Auld Alliance with the French over the "Perpetual Peace" with the English, and led a large army across the border into England. James and many of his nobles were killed at the Battle of Flodden on 9 September 1513, fighting against the English forces of Catherine of Aragon, Henry VIII's wife and regent. James was the last monarch in Great Britain to be killed in battle and was succeeded by his son James V.

Early life
Born on 17 March 1473 at Stirling Castle, James was the eldest son of King James III and Margaret of Denmark. As heir apparent to the Scottish crown, he became Duke of Rothesay at birth. James probably spent most of his infancy and youth at Stirling Castle in the care of his mother, along with his two younger brothers, James and John. In 1478, Queen Margaret was officially entrusted with the custody and education of the Duke of Rothesay. Not much is known about James's early life, but it is known that he received a good education from Archibald Whitelaw, the humanist scholar and secretary of state, and the theologian John Ireland, under the direction of his mother. In addition to Scots, James became fluent in Latin and Spanish, also learned French, German, Flemish and Italian, and was the last Scottish monarch known to have spoken Gaelic. The surviving exchequer records show that Prince James was taken from Stirling to visit Edinburgh in the summers of 1474 and 1479, and that his nurse in the 1470s was Agnes Turing, the wife of an Edinburgh burgess.

In October 1474, James III agreed a peace treaty with Edward IV of England, the foundation of which was to be a marriage between Prince James and Edward's daughter, Cecily of York, when they both reached marriageable age. The treaty marked the beginning of James III's pursuit of friendship with England, a policy which was unpopular in Scotland. This policy would see further prospective English brides proposed for his son: Anne de la Pole (niece of Richard III of England) in 1484 and an unspecified daughter of Edward IV in 1487. James III was an unpopular king: he faced two major rebellions during his reign, and alienated members of his close family, especially his younger brother, Alexander, Duke of Albany. James III's unpopular pro-English policy rebounded badly upon him when the peace with England broke down in 1480. This led to the invasion of Scotland and capture of Berwick in 1482 by Richard, Duke of Gloucester, in the company of the Duke of Albany. When James III attempted to lead his army against the invasion, his army rebelled against him and he was briefly imprisoned by his own councillors. During James III's imprisonment, Albany visited Queen Margaret and the young Duke of Rothesay at Stirling Castle to discuss the crisis with them.

For the nine-year-old heir to the throne, the crisis of 1482 had shattered the calm of his youthful existence at Stirling. Following the death of Margaret of Denmark in July 1486, Prince James may have viewed the king's deliberate promotion of his second son — the 1486 and 1487 proposals to marry him to one of the younger daughters of Edward IV of England, and the conferring on him of the dukedom of Ross in January 1488 — with apprehension. There is no explanation of why James III seemed to be favouring his second son over his heir, although it has been suggested that James III's suspicion and distrust of his heir arose from the young Duke of Rothesay's meeting with the Duke of Albany during the 1482 crisis.

On 2 February 1488, the Duke of Rothesay departed from Stirling Castle, without the king's knowledge. This defection saw the start of another major rebellion against James III, led by the earls of Angus and Argyll, and the Home and Hepburn families. Pitscottie claimed that the prince defected as he had heard that his father was approaching Stirling with a large army to imprison him. The prince became the figurehead of the rebels, who claimed that they had removed him from Stirling to protect him from his vindictive father, who had surrounded himself with wicked Anglophile counsellors. Like Prince James, many of the rebels also feared for their safety if James III continued to rule. Matters came to a head on 11 June 1488, when the royal and rebel armies fought outside Stirling at the Battle of Sauchieburn. The royal army was defeated and James III was killed during the battle, though several later sources claimed that the Duke of Rothesay had forbidden any man to harm his father. James IV bore intense guilt for the indirect role which he had played in the death of his father. He decided to do penance for his sin, constantly wearing an iron belt around his waist, next to the skin, to which he added weight every year throughout his life.

Early reign

The victorious rebels moved swiftly to consolidate their power, and on 12 June, only a day after Sauchieburn, the new king issued his first charter. Edinburgh and Stirling castles were secured, as were the late king's money and jewels, and the rebel leaders were rewarded with offices of state and posts in the royal household. James IV's coronation took place on 24 June 1488 at Scone Abbey. The Archbishop of St Andrews, William Scheves, a favourite of James III, did not officiate during the coronation ceremony, with the new king being instead crowned by Robert Blackadder, Bishop of Glasgow. A few days later, James IV attended the burial of his father at Cambuskenneth Abbey, a scene later portrayed in James IV's book of hours. The new king also hosted his maternal great-uncle, Gerhard VI, Count of Oldenburg, who arrived at Leith with a Danish fleet in August, and remained in Scotland until the following year.

James IV quickly proved to be a wise and effective ruler, and entrusted the running of his government to Patrick Hepburn, 1st Earl of Bothwell, Archibald Douglas, 5th Earl of Angus, and William Elphinstone, Bishop of Aberdeen. He defeated a major rebellion led by the Master of Huntly, the Earl of Lennox and Lord Lyle in 1489, laying siege to Crookston, Duchal and Dumbarton castles, and defeating a rebel army at Gartloaning in Stirlingshire. James also took a direct interest in the administration of justice, brought the feud between the Murrays and the Drummonds in Strathearn to an end, and went out on justice ayres across the kingdom throughout his reign. A tax of £5,000 was granted by the Parliament of Scotland to fund an embassy to France and Spain to search for a foreign bride for the king. Pope Innocent VIII conferred the Golden Rose on James in 1491, and the alliance with France was renewed in 1492. Treaties were also made with Denmark and Spain, and truces were negotiated with Henry VII of England in 1493 and 1494. In 1494 James received the Sceptre of Scotland as a papal gift from Pope Alexander VI. James IV met with Hugh Roe O'Donnell, King of Tyrconnell in June 1495 in Glasgow. O'Donnell was the most powerful northern Irish magnate and a committed enemy of Henry VII's government in Ireland, and the Scottish and Irish kings made a defensive alliance. They also discussed Perkin Warbeck, the pretender to the English throne, who O'Donnell had been a supporter of for years.

James IV received Warbeck in Scotland in November 1495. The attraction of Warbeck to James lay in the recognition of Warbeck's claim to the English throne by Maximilian, King of the Romans, Ferdinand II and Isabella I of Spain (the Catholic monarchs), Philip, Duke of Burgundy, and Margaret of York. Embracing Warbeck's cause would give James IV international leverage to seek European alliances, and threatening Henry VII with Warbeck would surely produce a much more attractive offer of alliance from the English king. As Ferdinand and Isabella were negotiating an alliance with Henry VII, James knew that Spain would help him in his struggles with England in order to prevent the situation escalating into war with France. Spanish ambassadors arrived in Edinburgh, and later Pedro de Ayala was established as a resident ambassador during the crisis.

In September 1496, James IV invaded England alongside Warbeck, destroying Tillmouth, Duddo, Branxton and Howtel towers, and Twizell Castle and Heaton Castle. However, the army quickly retreated when resources were expended, and hoped-for support for Perkin Warbeck in Northumberland failed to materialise. The Scottish army left on 25 September 1496 when an English army commanded by Lord Neville approached from Newcastle. When news of this invasion reached Ludovico Sforza, Duke of Milan, on 21 October 1496, he wrote to his ambassador in Spain, to request the Spanish monarchs make peace between England and Scotland. The peace mission was entrusted to the Spanish ambassador in Scotland, Pedro de Ayala. Later, wishing to be rid of Warbeck, James IV provided a ship called the Cuckoo and a hired crew under a Breton captain, Guy Foulcart. Horses were hired for 30 of Perkin's companions to ride to the ship at Ayr on 5 July 1497, where Perkin sailed to Ireland. In August 1497, James invaded England once more and laid siege to Norham Castle with a huge artillery train, including Mons Meg, a huge medieval bombard or cannon.

Peace with England

James IV's use of war as a forceful extension of his diplomacy with England, and Henry VII's realisation of how vulnerable the Anglo-Scottish border was, saw Henry treat for peace with James. The Treaty of Ayton was signed on 30 September 1497, agreeing to a seven-year truce between Scotland and England. Shipping and trade were to be conducted according to the 1464 Treaty of York, and Border wardens on either side were given new powers to execute cross-border murderers after 20 days detention and punish thieves caught red-handed, and neither king should harbour the other's rebels. The Spanish monarchs Ferdinand and Isabella were appointed to arbitrate future disputes and unresolved issues such as redress for damages caused by the recent invasions. The possibility was also raised of strengthening the peace between both kingdoms with the marriage of James IV to Henry VII's eldest daughter, Margaret.

Following several years in which the Treaty of Ayton held, Scottish and English commissioners met at Richmond Palace on 24 January 1502. They agreed the marriage between James IV and Margaret, with a dowry of £35,000 Scots, and a peace treaty between the two kingdoms. Under the terms of the Treaty of Perpetual Peace, there was to be "good, real and sincere, true, sound, and firm peace, friendship, league and confederation, to last all time coming" between England and Scotland, neither king or their successors were to make war against the other, and if either king broke the treaty, the Pope would excommunicate him. In a ceremony at the altar of Glasgow Cathedral on 10 December 1502, James confirmed the Treaty of Perpetual Peace with Henry VII, the first peace treaty between Scotland and England since 1328. The marriage was completed by proxy on 25 January 1503 at Richmond Palace in the presence of the king and queen of England, the Earl of Bothwell standing as proxy for the Scottish king. Margaret left Richmond for Scotland on 27 June and, after crossing the border at Berwick upon Tweed on 1 August 1503, was received at Lamberton by the Archbishop of Glasgow and the Bishop of Moray. On 8 August 1503, the marriage of the 30-year-old Scottish king and his 13-year-old English bride was celebrated in person in Holyrood Abbey. The rites were performed by Robert Blackadder, Archbishop of Glasgow and Thomas Savage, Archbishop of York. Their wedding was commemorated by the gift of the Hours of James IV of Scotland, and was portrayed as the marriage of The Thrissil and the Rois (the thistle and rose — the flowers of Scotland and England, respectively) by the poet William Dunbar, who was then resident at James's court.

Margaret did not bear her first child until 1507 when she was seventeen. James IV's marriage to Margaret meant that only the future Henry VIII stood between the Scottish king and the English succession, as Henry's lack of an heir made it possible that either James or one of his successors might succeed if the Tudors failed to produce heirs. Margaret's first pregnancy resulted in the birth of James, Duke of Rothesay at the Palace of Holyroodhouse in February 1507. However, this heir to the throne died a year later in February 1508. At this point Margaret was already pregnant with a second child, a daughter whose name is unknown, and who was born and died in July 1508. In October 1509, a second son was born and named Arthur, a name recalling Margaret's late brother, Arthur, Prince of Wales, and reminding the still heirless Henry VIII that, if he were unable to produce a legitimate son to succeed him, it might be a son of Margaret Tudor who would succeed.

Policy in the Highlands and Isles

From the perspective of the new administration in the early 1490s, the Western Highlands and the Hebrides were regarded as a problem area and a threat to the rest of the kingdom. By that period the Lordship of the Isles was fracturing as rivalries in Clan Donald disrupted the authority of John of Islay, Lord of the Isles. John was a weak leader whose authority had been damaged in 1476 when he had forfeited the earldom of Ross and his lands in Knapdale and Kintyre to James III due to the treasonous Treaty of Westminster he had agreed with Edward IV of England. After this, Ross-shire was continually invaded by the MacDonald islanders. In 1491, Alexander MacDonald of Lochalsh, heir to the lordship of the Isles, attempted to recover the earldom of Ross by raiding Ross-shire in alliance with Clan Cameron and Clan Chattan. They marched to Inverness, where they stormed Inverness Castle, and clashed with Clan Mackenzie before being routed. In consequence of this insurrection, at a meeting of parliament in Edinburgh in May 1493, the title and possessions of John MacDonald, Lord of the Isles were declared to be forfeited to the Crown. In August 1493, King James made his first expedition to the western Highlands. Accompanied by Chancellor Angus, Bishop Elhinstone, the Earl of Bothwell, Lord Home, and Secretary of State Archibald Whitelaw, James IV sailed to Dunstaffnage Castle, where the local chiefs, including John MacLean of Lochbuie and John MacIain of Ardnamurchan, made their submissions of loyalty to him. John of Islay surrendered and was brought back to the royal court and given an annual pension of £133 6s 8d.

The following year, Sir John MacDonald of Dunnyveg rebelled, and in July the king sailed with an army from Dumbarton to Tarbert Castle, before sailing south to Dunaverty Castle in Kintyre. The royal forces repaired both castles and soon afterwards Sir John was summoned for treason committed in Kintyre. Sir John ignored the summons and continued to reside at Islay, but was later captured by John MacIain of Ardnamurchan and brought to Edinburgh to be hanged for treason. In 1495 King James sailed on his third and final expedition to the Isles to find and reward supporters of the Crown within the forfeited lordship, sailing to Mingary Castle, where Lachlan Maclean of Duart, Alan Cameron, and MacNeil of Barra came in to Mingary to submit and offer their allegiance to the king in person, who confirmed them in their lands and offices.

In October 1496, the Privy Council ordered that the clan chiefs in the region would be held responsible by the king for crimes of the islanders. This act for the governance of the region was unworkable, and after the Act of Revocation of 1498 undermined the chiefs' titles to their lands, resistance to Edinburgh rule was strengthened. James waited at Kilkerran Castle at Campbeltown Loch to regrant the chiefs' charters in the summer of 1498. Few of the chiefs turned up. At first, Archibald Campbell, 2nd Earl of Argyll, was set to fill the power vacuum and enforce royal authority, but he met with limited success in a struggle with his brother-in-law, Torquil MacLeod of Lewis.

After this defiance, Alexander Gordon, 3rd Earl of Huntly, was granted Torquil's lands. He raised an army in Lochaber and also cleared the tenants of that area, replacing them with his supporters. After the parliament of 1504, a royal fleet sailed north from Ayr to attack the Castle of Cairn-na-Burgh, west of Mull, where it is thought that Maclean of Duart had Domhnall Dubh in his keeping. As progress at the siege was slow, James sent Hans the royal gunner in Robert Barton's ship and then the Earl of Arran with provisions and more artillery. Cairn-na-Burgh was captured by June 1504 but Domhnall Dubh remained at liberty. In September 1507, Torquil MacLeod was besieged at Stornoway Castle on Lewis. Domhnall Dubh was captured and imprisoned for 37 years until he was released in 1543 and died in 1545 in Ireland; Torquil MacLeod died in exile in 1511. The Earl of Huntly was richly rewarded for his troubles, a price that James was prepared to pay.

Parliament
James IV's reign saw a decline in the holding of parliaments, which was a departure from the practice of previous reigns. While ten meetings of the three estates were held between 1488 and 1496, there were only three during the remaining seventeen years of the reign, with no parliaments held in the eight years between 1496 and 1504. There was also a substantial reduction in the numbers of those attending parliaments as the reign progressed. This development matched that of the English and European monarchies in the playing down of the role of their representative assemblies, and placing more reliance on conciliar government: Edward IV of England only held six parliaments during his twenty-three-year reign, and Henry VII held seven in his twenty-four years on the throne. In France, the Estates General were not summoned again for seventy-six years after 1484.

With the ending of the conflicts with England in 1497, the Crown no longer needed Parliament to grant extraordinary revenue in the form of taxation, with Parliament no longer being summoned with the same regularity as a result. In the decade before 1496, successive parliaments had presided over, or sanctioned, regicide or rebellion, and failed foreign embassies to find the king a bride. With this experience of parliaments, perhaps James IV considered the frequent calling of parliaments inimical to good royal government.

The absence of parliaments between 1496 and 1504 may also have been due to James's discovery of other methods of raising revenue, and his reluctance to summon meetings of the three estates due to their propensity for dissent. The last three parliaments of James IV's reign in 1504, 1506 and 1509 were all called to address the administration of justice and the forfeiture of rebels following further risings in the western Highlands. James IV managed to govern effectively without regular parliaments from 1496 onwards due to his use of general councils (a sister institution to Parliament) in 1497, 1498, 1502, 1511 and 1512, and the use of greatly enlarged sessions of the Privy Council in 1508, 1511 and 1513.

Finances

From the beginning of his reign, one of James's objectives was to increase the relatively limited Crown income by extracting larger returns from all available sources of revenue. The king had to fund all government expenses out of his own income, which came from the revenue from Crown lands, and from burgh customs, mails, tolls and duties. The annual revenues of the Crown from these sources remained constant throughout James's reign (around £5–6,000 Scots). However, the king only received a small amount of the income from burgh revenues, as the majority of that income was alienated to provide annuities to reward numerous nobles and Crown servants.

Taxation imposed by Parliament offered the king greater opportunities to raise income. Between 1488 and 1497, Parliament voted taxation almost annually to support diplomacy and war, including embassies to the continent, the king's naval expeditions to the western Highlands, and the 1496–97 conflicts with England. However, James soon learned that using taxation extensively as a means of generating revenue was likely to provoke resistance without bringing in the sums required. Following the failure to raise the huge sum of £12,000 Scots from the three estates (clergy, nobility and burghs) in 1502–1504 to fund the sending of a naval expedition and a small army to Denmark, no further taxation was imposed until 1512, and even then the tax which brought in almost £7,000 was only imposed on the clergy.

James's annual income increased remarkably between 1497 and 1513, due to several sources of revenue. In 1497 he received a substantial windfall from the death of Archbishop William Scheves of St Andrews. James appointed his younger brother, the Duke of Ross, to fill the vacant see of St Andrews, bringing the highest office of the Scottish church within the royal family, with the appointment generating an annual income of around £2,500 for the Crown from the revenues of the archbishopric. Although Bishop Elphinstone protested against this scandalous appointment, it was a shrewd move by the king as it removed any potential dynastic threat which his legitimate younger brother might pose in the future. James also appointed Ross as abbot of Holyrood (1498), Dunfermline (1500) and Arbroath (1503). These offices, in combination with his appointment to the chancellorship in 1501, gave the Duke of Ross the highest status after the king. Following the death of the Duke of Ross in 1504, James IV appointed his eleven-year-old illegitimate son, Alexander, as archbishop, thereby ensuring that the Crown would continue to receive the revenues of St Andrews.

In 1498, James IV reached the age of twenty-five and was entitled to make a formal act of revocation of all grants made by him during his minority. Although James could — in theory — cancel all grants of lands and offices which had been made since his accession, the purpose of the revocation was only to assert royal authority by re-granting lands and offices surrendered to the Crown, and raise thousands of pounds in revenue, as their holders paid compensation to the Treasurer to receive confirmation of their holdings. The payment of Margaret Tudor's dowry between 1503 and 1505 also brought in a relatively meagre £10,000 sterling. By the end of the reign the Treasurer's annual receipts had increased — due to feudal payments made to the Crown by the holders of land, and judicial fines for criminal offences — from around £4,500 in 1496–1497 to a huge £28,000 by 1512. When these receipts are added to income from ecclesiastical properties and the rental income from Crown lands, James IV may have received a total income of around £44,500 by 1513, although by that time there was an annual deficit of around £7,000.

Military

James IV took a close interest in the development of the Royal Scots Navy, viewing a strong fleet as a means of protecting Scottish shipping, gaining international prestige, and providing him with an outlet to pursue foreign policies in alliance with either England or France. In the course of his reign, James commissioned or acquired a total of at least thirty-eight ships. His naval building programme was large, especially so for the ruler of a small kingdom. Naval spending was by far the greatest single item of royal expenditure in the later years of his reign. In the early years, the annual average spent on ships was about £140 Scots. By the early 1510s it was £8,710.

In 1491, James determined to address the many attacks on Scottish shipping in the vicinity of the Firth of Forth from the English and other pirates. He erected fortresses at Largo and Inchgarvie, and made extensive repairs to Dunbar Castle, to defend the firth from hostile attacks. In 1493 James ordered every burgh to provide the Crown with a boat of 20 tons, and to conscript able men to crew them. The forfeiture of the Lordship of the Isles was followed by James's naval expeditions to Argyll and the Hebrides in 1492–1495 and 1498, and in May 1502 James sent a fleet of five ships and 2,000 troops under the command of James Hamilton, 1st Earl of Arran to Denmark to aid his uncle, John, King of Denmark, who had appealed to James for aid during the Dano-Swedish War. The expedition was a failure, arriving too late to help Queen Christina hold Stockholm. The Danish expedition seems to have concentrated James IV's mind on naval expansion: shipwrights and craftsmen were recruited from across Scotland, and from France, Flanders, Denmark and Spain; timber for shipbuilding was felled in Lanarkshire and the Highlands and imported from Norway and France. James was also responsible for the founding of new dockyards on the Forth at Newhaven in 1504, and Pool of Airth in 1506. The king also wore the insignia of an Admiral — a whistle and a chain of gold.

The Margaret, built at Leith and launched in 1506, weighed around 600–700 tons, was armed with four falconets, a cannon and twenty-one other guns, and cost the king an estimated £8,000 — more than a quarter of his annual income. The carrack Great Michael was the largest warship of its time. Built at Newhaven and launched in 1511, it measured between 150 ft and 180 ft in length, weighed around 1,000 tons, and was supposed to have cost around £30,000. Armed with twenty-four bronze cannons and three basilisks, it marked a shift in design as it was designed specifically to carry a main armament of heavy artillery. The navy's core of four large ships (the Treasurer, the Margaret, the James and the Michael) were supported by a number of smaller craft and privately owned merchant ships.

Like his grandfather and father, James IV also took an enthusiastic interest in artillery, and from early in his reign he added to James III's French train of artillery. In 1507 he shot some "great guns" at Holyrood Abbey with three of his gunners, and the following year it is recorded that he held shooting matches with hand culverins in the great halls of Holyrood Palace and Stirling Castle. James also took a culverin to stalk deer in the park of Falkland Palace and shot at sea birds with one from a row boat off the Isle of May. James IV imported guns, shot and powder from France, and in 1511 the royal gun foundry was moved from Stirling Castle to Edinburgh Castle, where Scots, Dutch, German, and French gunmakers worked under the master gunner, Robert Borthwick, in what was the earliest significant foundry for producing large bronze guns in the British Isles. Their output included guns for the Michael, and the Seven Sisters, a set of cannons captured by the English at Flodden. James's artillery also included arquebus à croc (mounted heavy arquebuses), hand culverins and falconets.

Culture and patronage

James IV was a true Renaissance prince and a patron of the arts, including many literary figures, most notably the Scots makars. Poets associated with his court include William Dunbar, Walter Kennedy and Gavin Douglas. James patronised music at Restalrig using rental money from the King's Wark, and gave his backing to the foundation of King's College, Aberdeen, by his chancellor, William Elphinstone, and St Leonard's College, St Andrews, by his illegitimate son, Alexander, Archbishop of St Andrews, and John Hepburn, Prior of St Andrews. In 1496, partly at Elphinstone's instance, he also passed what has been described as Scotland's first education act, which introduced compulsory education at grammar school for the eldest sons and heirs of all barons and freeholders of substance.

James was both highly intelligent and well educated. In July 1498, Spanish ambassador, Pedro de Ayala, reported to Ferdinand II of Aragon and Isabella I of Castile:

"The King is 25 years and some months old. He is of noble stature, neither tall nor short, and as handsome in complexion and shape as a man can be. His address is very agreeable. He speaks the following foreign languages: Latin, very well; French, German, Flemish, Italian, and Spanish; Spanish as well as the Marquis, but he pronounces it more distinctly. He likes, very much, to receive Spanish letters. His own Scots language is as different from English as Aragonese from Castilian. The King speaks, besides, the language of the savages who live in some parts of Scotland and on the islands. It is as different from Scots as Biscayan is from Castilian. His knowledge of languages is wonderful. He is well read in the Bible and in some other devout books. He is a good historian. He has read many Latin and French histories, and profited by them, as he has a very good memory. He never cuts his hair or his beard. It becomes him very well."

James also ensured that the very best education was given to his illegitimate son, Alexander, who was tutored by Erasmus in Padua, Siena and Rome. James IV allegedly conducted a language deprivation experiment in which two children were sent to be raised by a mute woman alone on the island of Inchkeith, to determine if language was learned or innate.

James IV had a wide range of intellectual interests and took an interest in practical and scientific matters. He patronised the establishment of Scotland's first printing press, Chepman and Myllar Press, in 1507, and granted the Incorporation of Surgeons and Barbers of Edinburgh a royal charter in 1506. James was also interested in dentistry, an interest which began in 1503 when the king summoned a "barbour" to extract one of his teeth for the sum of 14 shillings. In 1504, he sought more practical experience of dentistry and purchased two gold toothpicks suspended from a chain, and "ane turcase [pincer] to tak out teith". It is recorded that James pulled two teeth from one of his own barber-surgeons, for which the king paid him 14 shillings, and also tried bloodletting on patients, and treating and dressing ulcer wounds. He also took an interest in other sciences which are now less creditable, establishing an alchemy workshop at Stirling Castle, where alchemist John Damian looked for ways to turn base metals into gold. The project consumed quantities of mercury, golden litharge, and tin. A goldsmith, Matthew Auchinleck, provided the alchemists with a still made of silver. Damian also researched aviation and undertook a failed experiment to fly from the battlements of Stirling Castle, an event which William Dunbar satirised in two separate poems.

James poured large amounts of money into the construction or remodelling of several royal residences. He commissioned the construction between 1501 and 1505 of the Palace of Holyroodhouse. The impetus for the work probably came from his marriage to Margaret Tudor, which took place in Holyrood Abbey in August 1503. James also commissioned the construction of Falkland Palace in Fife between 1501 and 1513, on a site to the south of Falkland Castle. At Stirling Castle, James commissioned the construction of the great hall and a new royal lodging (the present-day King's Old Building), the remodelling of the chapel royal, and the reconstruction of the principal defences on the southern and eastern sides of the castle. He also commissioned the construction of the great hall at Edinburgh Castle, rebuilding at Linlithgow Palace, Rothesay Castle, and Dunbar Castle, and furnished his palaces with tapestries.

The first evidence of whisky production in Scotland comes from an entry in the Exchequer Rolls for 1494 where malt is sent "To Friar John Cor, by order of the king, to make aquavitae", enough to make about 500 bottles. James IV reportedly had a great liking for whisky, and in 1506 the town of Dundee purchased a large amount of whisky from the Guild of Barber-Surgeons, which held the monopoly on production at the time.

African presence at the Scottish court
James IV's court and royal household were cosmopolitan, containing assorted foreign peoples including French, Italian and German minstrels, Flemish metalworkers, and Spanish dancers. The court also hosted a number of Africans, some working as servants or (possibly) slaves, but others appearing to have been courtiers, invited guests or musicians. In 1504, two African women, who were later christened as Margaret and Helen or Elen More, are mentioned in the Accounts of the Lord High Treasurer of Scotland. The women were visible in court life and Helen More became the presumed subject of the poem "Of Ane Blak-Moir" by William Dunbar describing an African woman offered as a prize in jousting tournaments. The poem is critical of her appearance and status as a black woman in a predominantly white court and country.

An African drummer referred to as the "More taubronar" travelled with James around Scotland. "Peter the Moor" was an African man whose travel and expenses were paid for by royal funds. He first appears in records in 1500 and some historians believe he and other Africans arrived in Scotland initially as "human booty" captured by Scottish privateers from Portuguese cargo ships. Records show that Peter the Moor was a companion to King James in his various trips across the country, appearing in the records until August 1504, when he received a large and final payment. Historian Imtiaz Habib argues that Peter was "clearly a favourite companion to the monarch" and was "well accepted" into the court culture. The status of the Africans in James IV's court is contested, with some historians taking the view that the two women Elen and Margaret More were "enjoying in the royal service a benevolent form of ... black slavery". Other historians emphasise that these individuals were treated as "court curiosities" rather than being in control of their own lives, and were most likely enslaved to some extent.

Diplomacy and war
James was granted the title Protector and Defender of the Christian Faith in 1507 by Pope Julius II, and in April 1507 at Holyrood Abbey he received the Blessed sword and hat. In 1508 James IV made plans to go on pilgrimage to Jerusalem, after a journey to Venice, before sailing from there to Jaffa in a Venetian ship. James's uncle, King John of Denmark, protested against his projected pilgrimage to Jerusalem in a letter written to the Archbishop of Glasgow in July 1507, remarking that the Scottish king should think first of his young wife and his country. Archbishop Blackadder left Scotland in February 1508 to set out on pilgrimage to the Holy Land, probably as a reconnaissance for the king's pilgrimage. Blackadder's death on 28 July 1508, presumably from an infectious illness, on board a ship from Venice to Jaffa appears to have convinced James IV of the inadvisability of sailing to Jerusalem. In 1507–1508, Louis XII of France was endeavouring to have James renew the Franco-Scottish alliance, and James wrote to Louis raising the idea of a joint Franco-Scottish crusade to the Holy Land. James's maintenance of Scotland's traditional good relations with France occasionally created diplomatic problems with England. In April 1508, Thomas Wolsey was sent to Scotland discuss Henry VII's concerns over rumours that James would renew the Auld Alliance with France. Wolsey found "there was never a man worse welcome into Scotland than I. ... They keep their matters so secret here that the wives in the market know every cause of my coming." Wolsey was unable to persuade James to abandon the Auld Alliance, but Anglo-Scottish relations nonetheless remained stable until the death of Henry VII in 1509.

Relations between Scotland and England deteriorated with the accession of Henry VIII of England in April 1509. Unlike his father, Henry had no interest in appeasing James, because his focus was on France. Henry VIII also believed that whatever the implications of the Treaty of Perpetual Peace, the King of Scotland owed him obedience. At the core of the increasing hostility between James and Henry was James IV's position in relation to the English throne. From his accession in 1509 until the birth of his daughter Mary in 1516 — apart from the short life of his son Henry, Duke of Cornwall in 1511 — Henry was childless and had no recognised heir. Through his wife Margaret, James IV was an heir to the English throne. When Margaret gave birth to a son in October 1509, the baby was christened Arthur, not after Margaret and Henry's elder brother, but to advertise the Scottish claim to the Arthurian legend and as a British name for a potential British king. Then on 10 April 1512, Margaret gave birth to another boy, to be called James. This boy, the future James V, was still alive and well a year later, while his uncle continued to remain childless.

As a result of the Italian Wars, in October 1511 Pope Julius II created a Holy League against France. The new alliance included the Papacy, Venice, Spain and the Holy Roman Empire. In November 1511, England also joined the League, with Henry VIII deciding to use the occasion as an excuse to conclude the Treaty of Westminster — a pledge of mutual aid against the French — with Ferdinand II. Relations between the Scottish and English kings continued to deteriorate with the passing of the Subsidy Act by the English parliament in 1512, with the act preamble declaring that the King of Scotland was "the very homage and obedience of right to your Highness [Henry VIII]". This assault on Scotland's independence was a reassertion of claims to English overlordship which had been implicitly revoked on a permanent basis by the 1502 Treaty of Perpetual Peace. The English justification of the claim was that James IV had broken the peace, and was preparing for war. This was completely specious as James had by then not even acceded to Louis XII's urgent requests to renew the Franco-Scottish alliance. In theory, there was a "court of appeal" which had the power to adjudicate such differences between the parties to the treaty: the Papacy. But Pope Julius II was now an ally of England, and far from being an honest broker. James IV had so far refused the French king's requests to renew the Franco-Scottish alliance as Louis XII was not offering a sufficient benefit in return. However, Henry VIII's increasingly belligerent stance effectively ensured that the Auld Alliance would be renewed. James gave formal agreement to the renewal of the alliance in July 1512, but this was a gesture rather than a commitment of active support against England, and it was still possible that Scotland would remain neutral in any Anglo-French war.

Before his death in February 1513, Pope Julius II had been persuaded by the Archbishop of York, Christopher Bainbridge, to impose an interdict as a general censure against the Scottish people. He also threatened to excommunicate the Scottish king if he was judged to have broken the treaty with England, and granted Bainbridge the power to excommunicate James is such circumstances. James IV sent Andrew Forman, the Bishop of Moray, to Rome to try and persuade the new Pope, Leo X, to countermand the interdict, but without success. Leo sent a letter to James, threatening him with ecclesiastical censure for breaking peace treaties, and in the summer of 1513 the king was excommunicated by Bainbridge. On 30 June, Henry VIII invaded France, his troops defeating a French army at the Battle of the Spurs, before capturing Thérouanne and Tournai. James IV summoned the Scottish army, and sent a naval fleet of twenty-two vessels, including the Great Michael, to join the ships of Louis XII of France. The fleet, commanded by James Hamilton, 1st Earl of Arran, departed from the Firth of Forth on 25 July and sailed around the north of Scotland. It first created a diversion in Ireland, where it attacked the English royal garrison at Carrickfergus and burnt the town, with support from Hugh Duff O'Donnell. The Scottish fleet then joined the French at Brest, from where it might cut the English army in France's line of communication across the English Channel. However, the fleet was so badly delayed that it played no part in the war; James had sent most of his experienced artillerymen with the expedition, a decision which was to have unforeseen consequences for his land campaign.

Flodden

Led by James IV, the Scottish army, numbering some 42,000 men, and including a large artillery train, crossed the River Tweed into England near Coldstream around 22 August. The Scottish troops were unpaid and were only required by feudal obligation to serve for forty days. Once across the border, a detachment turned south to attack Wark on Tweed Castle, while the bulk of the army followed the course of the Tweed downstream to the northeast to invest the remaining border castles. Norham Castle was taken and partly demolished, and the army then moved south, capturing the castles of Etal and Ford. On 8 September the Scottish army took up position against an English army commanded by Thomas Howard, Earl of Surrey on Branxton Hill in Northumberland. James's army, somewhat reduced from the original 42,000 by sickness and desertion, still amounted to about 34,000, outnumbering the English force by 8,000. The Scottish infantry had been equipped with 18 ft pikes by their French allies; a new weapon which had proved devastating in continental Europe, but required training, discipline and suitable terrain to use effectively. The Scottish artillery, consisting mainly of heavy siege guns, included five great curtals and two great culverins, together with four sakers and six great serpentines. The English infantry were equipped with traditional polearms, mostly bills which were the favoured pole arm of the English infantry. There was also a large contingent of well-trained archers armed with the English longbow. The English artillery consisted of light field guns of rather old-fashioned design, typically firing a ball of only about 1 lb, but easy to handle and capable of rapid fire.

James IV began the battle with an artillery duel, but his heavy guns did not perform well, contemporary accounts putting this down to the difficulty for the Scots of shooting downhill, another factor being that their guns had been hastily sited instead of the careful emplacement which was usually required for such heavy weapons, slowing their rate of fire. This allowed the light English guns to turn a rapid fire on the massed ranks of Scottish infantry. The Scottish left, under Lord Home and the Earl of Huntly, then advanced downhill towards the English army. The Scots had placed their most heavily armoured men in the front rank so that the English archers had little impact. The outnumbered English formation was forced back and elements of it began to run off before Surrey ordered the intervention of Dacre's light horsemen. The eventual result was a stalemate in which both sides stood off from each other and played no further part in the battle.

In the meantime, James had observed Home and Huntly's initial success and ordered the advance of the next formation in line, commanded by the earls of Errol, Crawford and Montrose. At the foot of Branxton Hill, they encountered an unforeseen obstacle, an area of marshy ground, made worse by days of heavy rain. As they struggled to cross the waterlogged ground, the Scots lost the cohesion and momentum on which pike formations depended for success. Once the line was disrupted, the long pikes became an unwieldy encumbrance, and the Scots began to drop them. Reaching for their side-arms of swords and axes, they found themselves outreached by the English bills in the close-quarter fighting that developed. It is unclear whether James had seen the difficulty encountered by the earls formation, but he followed down the slope regardless, making for Surrey's formation. James has been criticised for placing himself in the front line, thereby putting himself in personal danger and losing his overview of the field. He was, however, well known for taking risks in battle, and it would have been out of character for him to stay back. Encountering the same difficulties as the previous attack, James's men nevertheless fought their way to Surrey's bodyguard. The fierce fighting continued, centred on the contest between Surrey and James. As other English formations overcame the Scottish forces they had initially engaged, they moved to reinforce the Earl of Surrey. An instruction to English troops that no prisoners were to be taken explains the exceptional mortality amongst the Scottish nobility. James IV himself was killed in the final stage of the battle, having fought to within a spear length of the Earl of Surrey.

The Battle of Flodden was one of Scotland's worst military defeats: the loss of not only a popular and capable king but also a large portion of the political community, was a major blow to the realm. James IV's son, James V, was crowned three weeks after the disaster at Flodden but was only one year old, and his minority was to be fraught with political upheaval.

Death of the king

The body of James IV was found the following day amongst the thousands of Scottish dead on the battlefield, having been identified by two Scottish soldiers captured by the English, and by Thomas Dacre, 2nd Baron Dacre. James's lower jaw had been pierced by an arrow, an injury which would have disabled him sufficiently for the attacking English soldiers to move in and slash him with their bills, almost severing his left hand and slicing his throat open. James's body was taken to Berwick-upon-Tweed, where it was embalmed, sealed in a lead-lined coffin, and transported to Sheen Priory in Surrey, where it remained unburied. James's slashed and bloodstained surcoat was sent to Henry VIII (then on campaign in France) by his queen, Catherine of Aragon.

As James had been excommunicated prior to his death, he could not be buried in consecrated ground until the Pope remitted the sentence. Although Henry VIII obtained a dispensation from Pope Leo X on 29 November 1513 to have the Scottish king buried in St Paul's Cathedral in London, James IV remained unburied. His coffin remained above ground at Sheen Priory, as the decades passed and the priory was dissolved in 1539 during the English Reformation, becoming the secularised estate of Henry Grey, 1st Duke of Suffolk. During the reign of Edward VI of England the antiquarian John Stow was shown the coffin, lying in a store room: "since the dissolution of the House I have been shewed the same body (as was affirmed) so lapped in lead throwne into an old wast roome, amongst old timber, stone, lead, and other rubble". James IV's coffin was rediscovered during the reign of Elizabeth I of England when it was opened and his body became a plaything, John Stow writing that "Workmen there for their foolish pleasure hewed off his head." The body disappeared, its last-known resting place at Sheen now lying under the fairway of the 14th hole of the Royal Mid-Surrey Golf Course. Elizabeth I's master glazier, Lancelot Young, is said to have kept James's "sweetly scented" head (still identifiable as James by its red hair and beard) as a curio at his home in Wood Street in the City of London, before giving it to the sexton of the local church, St Michael's. The head was then buried in a charnel pit in St Michael's churchyard. The church was later demolished, and the site redeveloped many times.

Rumours persisted that James IV had survived and was seen riding back across the Tweed; that he had gone on pilgrimage to Jerusalem; or that his body was buried in Scotland. Two castles in the Borders are claimed as his resting place. The legend ran that, before the Scottish charge at Flodden, James had ripped off his surcoat to show his nobles that he was prepared to fight as an ordinary man-at-arms. Border legend claimed that during the battle, four Home horsemen or supernatural riders swept across the field snatching up the king's body, or that the king left the field alive and was killed soon afterwards. In the 19th century, when the medieval well of Hume Castle was being cleared, the skeleton of a man with a chain round his waist was discovered in a side cave; but this skeleton has since disappeared. Another version of this tale has the skeleton discovered at Hume a few years after the battle and re-interred at Holyrood Abbey. The same story was told for Roxburgh Castle, with the skeleton there discovered in the 17th century. Yet another tradition is the discovery of the royal body at Berry Moss, near Kelso. Fuelling these legends, Robert Lindsay of Pitscottie, writing in the 1570s, claimed that a convicted criminal offered to show John Stewart, 2nd Duke of Albany the king's grave ten years after the battle, but Albany refused.

Fictional portrayals
James IV has been depicted in historical novels, short stories and media portrayals. They include the following:
 * The Yellow Frigate (1855) by James Grant, also known as The Three Sisters. The main events of the novel take place in the year 1488, covering the Battle of Sauchieburn, the assassination of James III, the rise to the throne of James IV, and the plots of the so-called English faction in Scotland. James IV and Margaret Drummond are prominently depicted. Andrew Wood of Largo and Henry VII of England are secondary characters;
 * In the King's Favour (1899) by J. E. Preston Muddock, which covers the last few months of James IV's reign and ends with the Battle of Flodden.
 * The Arrow of the North (1906) by R. H. Forster. The novel mainly depicts Northumberland in the reigns of Henry VII and Henry VIII. It covers the Flodden campaign of the Anglo-Scottish Wars and the finale depicts the battle that ended James IV's life.
 * The Crimson Field (1916) by Halliwell Sutcliffe, which also covers the Anglo-Scottish Wars. It features James IV and ends with a full account of the Battle of Flodden;
 * King Heart (1926) by Carola Oman. The story depicts Scotland in the time of James IV. The king himself is depicted in an epilogue featuring the Battle of Flodden;
 * Gentle Eagle (1937) by Christine Orr, an account of the king's life;
 * Sunset at Noon (1955) by Jane Oliver, an account of the king's life;
 * Chain of Destiny (1964) by Nigel Tranter, an account of the king's life, from Sauchieburn to Flodden;
 * Falcon (1972) by A.J. Stewart, an unusual work by an author claiming to be a reincarnation of the king;
 * The Shadow of the Tower television drama where he was played by Derek Anders;
 * Three Sisters, Three Queens (2016) by Philippa Gregory, written from the point of view of Margaret Tudor, extensively featuring James;
 * The Spanish Princess (2020) by Philippa Gregory, with James portrayed by actor Ray Stevenson;
 * James IV – The Queen of the Flight (2022), a play by Rona Munro, centred on the life of Ellen More at his court.

title: James IV of Scotland


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Phytoplankton

Phytoplankton are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater ecosystems. The name comes from the Greek words φυτόν (phyton), meaning 'plant', and πλαγκτός (planktos), meaning 'wanderer' or 'drifter'.

Phytoplankton obtain their energy through photosynthesis, as trees and other plants do on land. This means phytoplankton must have light from the sun, so they live in the well-lit surface layers (euphotic zone) of oceans and lakes. In comparison with terrestrial plants, phytoplankton are distributed over a larger surface area, are exposed to less seasonal variation and have markedly faster turnover rates than trees (days versus decades). As a result, phytoplankton respond rapidly on a global scale to climate variations.

Phytoplankton form the base of marine and freshwater food webs and are key players in the global carbon cycle. They account for about half of global photosynthetic activity and at least half of the oxygen production, despite amounting to only about 1% of the global plant biomass. Phytoplankton are very diverse, varying from photosynthesizing bacteria to plant-like algae to armour-plated coccolithophores. Important groups of phytoplankton include the diatoms, cyanobacteria and dinoflagellates, although many other groups are represented.

Most phytoplankton are too small to be individually seen with the unaided eye. However, when present in high enough numbers, some varieties may be noticeable as colored patches on the water surface due to the presence of chlorophyll within their cells and accessory pigments (such as phycobiliproteins or xanthophylls) in some species.

Types

Phytoplankton are photosynthesizing microscopic protists and bacteria that inhabit the upper sunlit layer of marine and fresh water bodies of water on Earth. Paralleling plants on land, phytoplankton undertake primary production in water, creating organic compounds from carbon dioxide dissolved in the water. Phytoplankton form the base of — and sustain — the aquatic food web, and are crucial players in the Earth's carbon cycle.

"Marine photosynthesis is dominated by microalgae, which together with cyanobacteria, are collectively called phytoplankton." Phytoplankton are extremely diverse, varying from photosynthesizing bacteria (cyanobacteria), to plant-like diatoms, to armour-plated coccolithophores.

Ecology

 * Red = diatoms (big phytoplankton, which need silica)
 * Yellow = flagellates (other big phytoplankton)
 * Green = prochlorococcus (small phytoplankton that cannot use nitrate)
 * Cyan = synechococcus (other small phytoplankton)

Phytoplankton obtain energy through the process of photosynthesis and must therefore live in the well-lit surface layer (termed the euphotic zone) of an ocean, sea, lake, or other body of water. Phytoplankton account for about half of all photosynthetic activity on Earth. Their cumulative energy fixation in carbon compounds (primary production) is the basis for the vast majority of oceanic and also many freshwater food webs (chemosynthesis is a notable exception).

While almost all phytoplankton species are obligate photoautotrophs, there are some that are mixotrophic and other, non-pigmented species that are actually heterotrophic (the latter are often viewed as zooplankton). Of these, the best known are dinoflagellate genera such as Noctiluca and Dinophysis, that obtain organic carbon by ingesting other organisms or detrital material.

Phytoplankton live in the photic zone of the ocean, where photosynthesis is possible. During photosynthesis, they assimilate carbon dioxide and release oxygen. If solar radiation is too high, phytoplankton may fall victim to photodegradation. Phytoplankton species feature a large variety of photosynthetic pigments which species-specifically enables them to absorb different wavelengths of the variable underwater light. This implies different species can use the wavelength of light different efficiently and the light is not a single ecological resource but a multitude of resources depending on its spectral composition. By that it was found that changes in the spectrum of light alone can alter natural phytoplankton communities even if the same intensity is available. For growth, phytoplankton cells additionally depend on nutrients, which enter the ocean by rivers, continental weathering, and glacial ice meltwater on the poles. Phytoplankton release dissolved organic carbon (DOC) into the ocean. Since phytoplankton are the basis of marine food webs, they serve as prey for zooplankton, fish larvae and other heterotrophic organisms. They can also be degraded by bacteria or by viral lysis. Although some phytoplankton cells, such as dinoflagellates, are able to migrate vertically, they are still incapable of actively moving against currents, so they slowly sink and ultimately fertilize the seafloor with dead cells and detritus.

Phytoplankton are crucially dependent on a number of nutrients. These are primarily macronutrients such as nitrate, phosphate or silicic acid, which are required in relatively large quantities for growth. Their availability in the surface ocean is governed by the balance between the so-called biological pump and upwelling of deep, nutrient-rich waters. The stoichiometric nutrient composition of phytoplankton drives — and is driven by — the Redfield ratio of macronutrients generally available throughout the surface oceans. However, across large areas of the oceans such as the Southern Ocean, phytoplankton are limited by the lack of the micronutrient iron. This has led to some scientists advocating iron fertilization as a means to counteract the accumulation of human-produced carbon dioxide (CO2) in the atmosphere. Large-scale experiments have added iron (usually as salts such as ferrous sulfate) to the oceans to promote phytoplankton growth and draw atmospheric CO2 into the ocean. Controversy about manipulating the ecosystem and the efficiency of iron fertilization has slowed such experiments.

Phytoplankton depend on B vitamins for survival. Areas in the ocean have been identified as having a major lack of some B Vitamins, and correspondingly, phytoplankton.

The effects of anthropogenic warming on the global population of phytoplankton is an area of active research. Changes in the vertical stratification of the water column, the rate of temperature-dependent biological reactions, and the atmospheric supply of nutrients are expected to have important effects on future phytoplankton productivity.

The effects of anthropogenic ocean acidification on phytoplankton growth and community structure has also received considerable attention. The cells of coccolithophore phytoplankton are typically covered in a calcium carbonate shell called a coccosphere that is sensitive to ocean acidification. Because of their short generation times, evidence suggests some phytoplankton can adapt to changes in pH induced by increased carbon dioxide on rapid time-scales (months to years).

Phytoplankton serve as the base of the aquatic food web, providing an essential ecological function for all aquatic life. Under future conditions of anthropogenic warming and ocean acidification, changes in phytoplankton mortality due to changes in rates of zooplankton grazing may be significant. One of the many food chains in the ocean – remarkable due to the small number of links – is that of phytoplankton sustaining krill (a crustacean similar to a tiny shrimp), which in turn sustain baleen whales.

The El Niño-Southern Oscillation (ENSO) cycles in the Equatorial Pacific area can affect phytoplankton. Biochemical and physical changes during ENSO cycles modify the phytoplankton community structure. Also, changes in the structure of the phytoplankton, such as a significant reduction in biomass and phytoplankton density, particularly during El Nino phases can occur. The sensitivity of phytoplankton to environmental changes is why they are often used as indicators of estuarine and coastal ecological condition and health. To study these events satellite ocean color observations are used to observe these changes. Satellite images help to have a better view of their global distribution.

Diversity
The term phytoplankton encompasses all photoautotrophic microorganisms in aquatic food webs. However, unlike terrestrial communities, where most autotrophs are plants, phytoplankton are a diverse group, incorporating protistan eukaryotes and both eubacterial and archaebacterial prokaryotes. There are about 5,000 known species of marine phytoplankton. How such diversity evolved despite scarce resources (restricting niche differentiation) is unclear.

In terms of numbers, the most important groups of phytoplankton include the diatoms, cyanobacteria and dinoflagellates, although many other groups of algae are represented. One group, the coccolithophorids, is responsible (in part) for the release of significant amounts of dimethyl sulfide (DMS) into the atmosphere. DMS is oxidized to form sulfate which, in areas where ambient aerosol particle concentrations are low, can contribute to the population of cloud condensation nuclei, mostly leading to increased cloud cover and cloud albedo according to the so-called CLAW hypothesis. Different types of phytoplankton support different trophic levels within varying ecosystems. In oligotrophic oceanic regions such as the Sargasso Sea or the South Pacific Gyre, phytoplankton is dominated by the small sized cells, called picoplankton and nanoplankton (also referred to as picoflagellates and nanoflagellates), mostly composed of cyanobacteria (Prochlorococcus, Synechococcus) and picoeucaryotes such as Micromonas. Within more productive ecosystems, dominated by upwelling or high terrestrial inputs, larger dinoflagellates are the more dominant phytoplankton and reflect a larger portion of the biomass.

Growth strategies
In the early twentieth century, Alfred C. Redfield found the similarity of the phytoplankton's elemental composition to the major dissolved nutrients in the deep ocean. Redfield proposed that the ratio of carbon to nitrogen to phosphorus (106:16:1) in the ocean was controlled by the phytoplankton's requirements, as phytoplankton subsequently release nitrogen and phosphorus as they are remineralized. This so-called "Redfield ratio" in describing stoichiometry of phytoplankton and seawater has become a fundamental principle to understand marine ecology, biogeochemistry and phytoplankton evolution. However, the Redfield ratio is not a universal value and it may diverge due to the changes in exogenous nutrient delivery and microbial metabolisms in the ocean, such as nitrogen fixation, denitrification and anammox.

The dynamic stoichiometry shown in unicellular algae reflects their capability to store nutrients in an internal pool, shift between enzymes with various nutrient requirements and alter osmolyte composition. Different cellular components have their own unique stoichiometry characteristics, for instance, resource (light or nutrients) acquisition machinery such as proteins and chlorophyll contain a high concentration of nitrogen but low in phosphorus. Meanwhile, growth machinery such as ribosomal RNA contains high nitrogen and phosphorus concentrations.

Based on allocation of resources, phytoplankton is classified into three different growth strategies, namely survivalist, bloomer and generalist. Survivalist phytoplankton has a high ratio of N:P (>30) and contains an abundance of resource-acquisition machinery to sustain growth under scarce resources. Bloomer phytoplankton has a low N:P ratio (<10), contains a high proportion of growth machinery, and is adapted to exponential growth. Generalist phytoplankton has similar N:P to the Redfield ratio and contain relatively equal resource-acquisition and growth machinery.

Factors affecting abundance
The NAAMES study was a five-year scientific research program conducted between 2015 and 2019 by scientists from Oregon State University and NASA to investigated aspects of phytoplankton dynamics in ocean ecosystems, and how such dynamics influence atmospheric aerosols, clouds, and climate (NAAMES stands for the North Atlantic Aerosols and Marine Ecosystems Study). The study focused on the sub-arctic region of the North Atlantic Ocean, which is the site of one of Earth's largest recurring phytoplankton blooms. The long history of research in this location, as well as relative ease of accessibility, made the North Atlantic an ideal location to test prevailing scientific hypotheses in an effort to better understand the role of phytoplankton aerosol emissions on Earth's energy budget.

NAAMES was designed to target specific phases of the annual phytoplankton cycle: minimum, climax and the intermediary decreasing and increasing biomass, in order to resolve debates on the timing of bloom formations and the patterns driving annual bloom re-creation. The NAAMES project also investigated the quantity, size, and composition of aerosols generated by primary production in order to understand how phytoplankton bloom cycles affect cloud formations and climate.

Factors affecting productivity

Phytoplankton are the key mediators of the biological pump. Understanding the response of phytoplankton to changing environmental conditions is a prerequisite to predict future atmospheric concentrations of CO2. Temperature, irradiance and nutrient concentrations, along with CO2 are the chief environmental factors that influence the physiology and stoichiometry of phytoplankton. The stoichiometry or elemental composition of phytoplankton is of utmost importance to secondary producers such as copepods, fish and shrimp, because it determines the nutritional quality and influences energy flow through the marine food chains. Climate change may greatly restructure phytoplankton communities leading to cascading consequences for marine food webs, thereby altering the amount of carbon transported to the ocean interior.

The diagram on the right gives an overview of the various environmental factors that together affect phytoplankton productivity. All of these factors are expected to undergo significant changes in the future ocean due to global change. Global warming simulations predict oceanic temperature increase; dramatic changes in oceanic stratification, circulation and changes in cloud cover and sea ice, resulting in an increased light supply to the ocean surface. Also, reduced nutrient supply is predicted to co-occur with ocean acidification and warming, due to increased stratification of the water column and reduced mixing of nutrients from the deep water to the surface.

Role of phytoplankton

In the diagram on the right, the compartments influenced by phytoplankton include the atmospheric gas composition, inorganic nutrients, and trace element fluxes as well as the transfer and cycling of organic matter via biological processes. The photosynthetically fixed carbon is rapidly recycled and reused in the surface ocean, while a certain fraction of this biomass is exported as sinking particles to the deep ocean, where it is subject to ongoing transformation processes, e.g., remineralization.

Phytoplankton contribute to not only a basic pelagic marine food web but also to the microbial loop. Phytoplankton are the base of the marine food web and because they do not rely on other organisms for food, they make up the first trophic level. Organisms such as zooplankton feed of these phytoplankton which are fed on by other organisms and so forth until the fourth trophic level is reached with apex predators. Approximately 90% of total carbon is lost between trophic levels due to respiration, detritus, and dissolved organic matter. This makes the remineralization process and nutrient cycling performed by phytoplankton and bacteria important in maintaining efficiency.

Phytoplankton blooms in which a species increases rapidly under conditions favorable to growth can produce harmful algal blooms (HABs).

Aquaculture
Phytoplankton are a key food item in both aquaculture and mariculture. Both utilize phytoplankton as food for the animals being farmed. In mariculture, the phytoplankton is naturally occurring and is introduced into enclosures with the normal circulation of seawater. In aquaculture, phytoplankton must be obtained and introduced directly. The plankton can either be collected from a body of water or cultured, though the former method is seldom used. Phytoplankton is used as a foodstock for the production of rotifers, which are in turn used to feed other organisms. Phytoplankton is also used to feed many varieties of aquacultured molluscs, including pearl oysters and giant clams. A 2018 study estimated the nutritional value of natural phytoplankton in terms of carbohydrate, protein and lipid across the world ocean using ocean-colour data from satellites, and found the calorific value of phytoplankton to vary considerably across different oceanic regions and between different time of the year.

The production of phytoplankton under artificial conditions is itself a form of aquaculture. Phytoplankton is cultured for a variety of purposes, including foodstock for other aquacultured organisms, a nutritional supplement for captive invertebrates in aquaria. Culture sizes range from small-scale laboratory cultures of less than 1L to several tens of thousands of litres for commercial aquaculture. Regardless of the size of the culture, certain conditions must be provided for efficient growth of plankton. The majority of cultured plankton is marine, and seawater of a specific gravity of 1.010 to 1.026 may be used as a culture medium. This water must be sterilized, usually by either high temperatures in an autoclave or by exposure to ultraviolet radiation, to prevent biological contamination of the culture. Various fertilizers are added to the culture medium to facilitate the growth of plankton. A culture must be aerated or agitated in some way to keep plankton suspended, as well as to provide dissolved carbon dioxide for photosynthesis. In addition to constant aeration, most cultures are manually mixed or stirred on a regular basis. Light must be provided for the growth of phytoplankton. The colour temperature of illumination should be approximately 6,500 K, but values from 4,000 K to upwards of 20,000 K have been used successfully. The duration of light exposure should be approximately 16 hours daily; this is the most efficient artificial day length.

Anthropogenic changes

Marine phytoplankton perform half of the global photosynthetic CO2 fixation (net global primary production of ~50 Pg C per year) and half of the oxygen production despite amounting to only ~1% of global plant biomass. In comparison with terrestrial plants, marine phytoplankton are distributed over a larger surface area, are exposed to less seasonal variation and have markedly faster turnover rates than trees (days versus decades). Therefore, phytoplankton respond rapidly on a global scale to climate variations. These characteristics are important when one is evaluating the contributions of phytoplankton to carbon fixation and forecasting how this production may change in response to perturbations. Predicting the effects of climate change on primary productivity is complicated by phytoplankton bloom cycles that are affected by both bottom-up control (for example, availability of essential nutrients and vertical mixing) and top-down control (for example, grazing and viruses). Increases in solar radiation, temperature and freshwater inputs to surface waters strengthen ocean stratification and consequently reduce transport of nutrients from deep water to surface waters, which reduces primary productivity. Conversely, rising CO2 levels can increase phytoplankton primary production, but only when nutrients are not limiting.

Some studies indicate that overall global oceanic phytoplankton density has decreased in the past century, but these conclusions have been questioned because of the limited availability of long-term phytoplankton data, methodological differences in data generation and the large annual and decadal variability in phytoplankton production. Moreover, other studies suggest a global increase in oceanic phytoplankton production and changes in specific regions or specific phytoplankton groups. The global Sea Ice Index is declining, leading to higher light penetration and potentially more primary production; however, there are conflicting predictions for the effects of variable mixing patterns and changes in nutrient supply and for productivity trends in polar zones.

The effect of human-caused climate change on phytoplankton biodiversity is not well understood. Should greenhouse gas emissions continue rising to high levels by 2100, some phytoplankton models predict an increase in species richness, or the number of different species within a given area. This increase in plankton diversity is traced to warming ocean temperatures. In addition to species richness changes, the locations where phytoplankton are distributed are expected to shift towards the Earth's poles. Such movement may disrupt ecosystems, because phytoplankton are consumed by zooplankton, which in turn sustain fisheries. This shift in phytoplankton location may also diminish the ability of phytoplankton to store carbon that was emitted by human activities. Human (anthropogenic) changes to phytoplankton impact both natural and economic processes.

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title: Phytoplankton


text:
Zooplankton

Zooplankton are the animal (or heterotrophic) component of the planktonic community (the "zoo-" prefix comes from ζῷον), having to consume other organisms to thrive. Plankton are aquatic organisms that are unable to swim effectively against currents. Consequently, they drift or are carried along by currents in the ocean, or by currents in seas, lakes or rivers.

Zooplankton can be contrasted with phytoplankton (cyanobacteria and microalgae), which are the plant-like component of the plankton community (the "phyto-" prefix comes from φῠτόν, although taxonomically not plants). Zooplankton are heterotrophic (other-feeding), whereas phytoplankton are autotrophic (self-feeding), often generating biological energy and macromolecules through chlorophyllic carbon fixation using sunlight — in other words, zooplankton cannot manufacture their own food, while phytoplankton can. As a result, zooplankton must acquire nutrients by feeding on other organisms such as phytoplankton, which are generally smaller than zooplankton. Most zooplankton are microscopic but some (such as jellyfish) are macroscopic, meaning they can be seen with the naked eye.

Many protozoans (single-celled protists that prey on other microscopic life) are zooplankton, including zooflagellates, foraminiferans, radiolarians, some dinoflagellates and marine microanimals. Macroscopic zooplankton include pelagic cnidarians, ctenophores, molluscs, arthropods and tunicates, as well as planktonic arrow worms and bristle worms.

The distinction between autotrophy and heterotrophy often breaks down in very small organisms. Recent studies of marine microplankton have indicated over half of microscopic plankton are mixotrophs. A mixotroph is an organism that can behave sometimes as though it were a plant and sometimes as though it were an animal, using a mix of autotrophy and heterotrophy. Many marine microzooplankton are mixotrophic, which means they could also be classified as phytoplankton.

Overview

Zooplankton are heterotrophic (sometimes detritivorous) plankton. The word zooplankton is derived from ζῷον; and πλᾰγκτός.

Zooplankton is a categorization spanning a range of organism sizes including small protozoans and large metazoans. It includes holoplanktonic organisms whose complete life cycle lies within the plankton, as well as meroplanktonic organisms that spend part of their lives in the plankton before graduating to either the nekton or a sessile, benthic existence. Although zooplankton are primarily transported by ambient water currents, many have locomotion, used to avoid predators (as in diel vertical migration) or to increase prey encounter rate.

Just as any species can be limited within a geographical region, so are zooplankton. However, species of zooplankton are not dispersed uniformly or randomly within a region of the ocean. As with phytoplankton, 'patches' of zooplankton species exist throughout the ocean. Though few physical barriers exist above the mesopelagic, specific species of zooplankton are strictly restricted by salinity and temperature gradients, while other species can withstand wide temperature and salinity gradients. Zooplankton patchiness can also be influenced by biological factors, as well as other physical factors. Biological factors include breeding, predation, concentration of phytoplankton, and vertical migration. The physical factor that influences zooplankton distribution the most is mixing of the water column (upwelling and downwelling along the coast and in the open ocean) that affects nutrient availability and, in turn, phytoplankton production.

Through their consumption and processing of phytoplankton and other food sources, zooplankton play a role in aquatic food webs, as a resource for consumers on higher trophic levels (including fish), and as a conduit for packaging the organic material in the biological pump. Since they are typically small, zooplankton can respond rapidly to increases in phytoplankton abundance, for instance, during the spring bloom. Zooplankton are also a key link in the biomagnification of pollutants such as mercury.

Ecologically important protozoan zooplankton groups include the foraminiferans, radiolarians and dinoflagellates (the last of these are often mixotrophic). Important metazoan zooplankton include cnidarians such as jellyfish and the Portuguese Man o' War; crustaceans such as cladocerans, copepods, ostracods, isopods, amphipods, mysids and krill; chaetognaths (arrow worms); molluscs such as pteropods; and chordates such as salps and juvenile fish. This wide phylogenetic range includes a similarly wide range in feeding behavior: filter feeding, predation and symbiosis with autotrophic phytoplankton as seen in corals. Zooplankton feed on bacterioplankton, phytoplankton, other zooplankton (sometimes cannibalistically), detritus (or marine snow) and even nektonic organisms. As a result, zooplankton are primarily found in surface waters where food resources (phytoplankton or other zooplankton) are abundant.

Zooplankton can also act as a disease reservoir. Crustacean zooplankton have been found to house the bacterium Vibrio cholerae, which causes cholera, by allowing the cholera vibrios to attach to their chitinous exoskeletons. This symbiotic relationship enhances the bacterium's ability to survive in an aquatic environment, as the exoskeleton provides the bacterium with carbon and nitrogen.

Size classification
Body size has been defined as a "master trait" for plankton as it is a morphological characteristic shared by organisms across taxonomy that characterises the functions performed by organisms in ecosystems. It has a paramount effect on growth, reproduction, feeding strategies and mortality. One of the oldest manifestations of the biogeography of traits was proposed over 170 years ago, namely Bergmann's rule, in which field observations showed that larger species tend to be found at higher, colder latitudes.

In the oceans, size is critical in determining trophic links in planktonic ecosystems and is thus a critical factor in regulating the efficiency of the biological carbon pump. Body size is sensitive to changes in temperature due to the thermal dependence of physiological processes. The plankton is mainly composed of ectotherms which are organisms that do not generate sufficient metabolic heat to elevate their body temperature, so their metabolic processes depends on external temperature. Consequently, ectotherms grow more slowly and reach maturity at a larger body size in colder environments, which has long puzzled biologists because classic theories of life-history evolution predict smaller adult sizes in environments delaying growth. This pattern of body size variation, known as the temperature-size rule (TSR), has been observed for a wide range of ectotherms, including single-celled and multicellular species, invertebrates and vertebrates.

The processes underlying the inverse relationship between body size and temperature remain to be identified. Despite temperature playing a major role in shaping latitudinal variations in organism size, these patterns may also rely on complex interactions between physical, chemical and biological factors. For instance, oxygen supply plays a central role in determining the magnitude of ectothermic temperature-size responses, but it is hard to disentangle the relative effects of oxygen and temperature from field data because these two variables are often strongly inter-related in the surface ocean.

Zooplankton can be broken down into size classes which are diverse in their morphology, diet, feeding strategies, etc. both within classes and between classes:

Microzooplankton
Microzooplankton are defined as heterotrophic and mixotrophic plankton. They primarily consist of phagotrophic protists, including ciliates, dinoflagellates, and mesozooplankton nauplii. Microzooplankton are major grazers of the plankton community. As the primary consumers of marine phytoplankton, microzooplankton consume ~ 59–75% daily of the marine primary production, much larger than mesozooplankton. That said, macrozooplankton can sometimes have greater consumption rates in eutrophic ecosystems because the larger phytoplankton can be dominant there. Microzooplankton are also pivotal regenerators of nutrients which fuel primary production and food sources for metazoans.

Despite their ecological importance, microzooplankton remain understudied. Routine oceanographic observations seldom monitor microzooplankton biomass or herbivory rate, although the dilution technique, an elegant method of measuring microzooplankton herbivory rate, has been developed for almost four decades (Landry and Hassett 1982). The number of observations of microzooplankton herbivory rate is around 1600 globally, far less than that of primary productivity (> 50,000). This makes validating and optimizing the grazing function of microzooplankton difficult in ocean ecosystem models.

Mesozooplankton
Because plankton are rarely fished, it has been argued that mesoplankton abundance and species composition can be used to study marine ecosystems' response to climate change. This is because they have life cycles that generally last less than a year, meaning they respond to climate changes between years. Sparse, monthly sampling will still indicate vacillations.

Protozoans
Protozoans are protists that feed on organic matter such as other microorganisms or organic tissues and debris. Historically, the protozoa were regarded as "one-celled animals", because they often possess animal-like behaviours, such as motility and predation, and lack a cell wall, as found in plants and many algae. Although the traditional practice of grouping protozoa with animals is no longer considered valid, the term continues to be used in a loose way to identify single-celled organisms that can move independently and feed by heterotrophy.

Marine protozoans include zooflagellates, foraminiferans, radiolarians and some dinoflagellates.

Radiolarians
Radiolarians are unicellular predatory protists encased in elaborate globular shells usually made of silica and pierced with holes. Their name comes from the Latin for "radius". They catch prey by extending parts of their body through the holes. As with the silica frustules of diatoms, radiolarian shells can sink to the ocean floor when radiolarians die and become preserved as part of the ocean sediment. These remains, as microfossils, provide valuable information about past oceanic conditions.

Foraminiferans
Like radiolarians, foraminiferans (forams for short) are single-celled predatory protists, also protected with shells that have holes in them. Their name comes from the Latin for "hole bearers". Their shells, often called tests, are chambered (forams add more chambers as they grow). The shells are usually made of calcite, but are sometimes made of agglutinated sediment particles or chiton, and (rarely) silica. Most forams are benthic, but about 40 species are planktic. They are widely researched with well-established fossil records which allow scientists to infer a lot about past environments and climates.

Dinoflagellates
Dinoflagellates are a phylum of unicellular flagellates with about 2,000 marine species. Some dinoflagellates are predatory, and thus belong to the zooplankton community. Their name comes from the Greek "dinos" meaning whirling and the Latin "flagellum" meaning a whip or lash. This refers to the two whip-like attachments (flagella) used for forward movement. Most dinoflagellates are protected with red-brown, cellulose armour. Excavates may be the most basal flagellate lineage.

Mixotrophs
A mixotroph is an organism that can use a mix of different sources of energy and carbon, instead of having a single trophic mode on the continuum from complete autotrophy at one end to heterotrophy at the other. It is estimated that mixotrophs comprise more than half of all microscopic plankton. There are two types of eukaryotic mixotrophs: those with their own chloroplasts, and those with endosymbionts—and others that acquire them through kleptoplasty or by enslaving the entire phototrophic cell.

The distinction between plants and animals often breaks down in very small organisms. Possible combinations are photo- and chemotrophy, litho- and organotrophy, auto- and heterotrophy or other combinations of these. Mixotrophs can be either eukaryotic or prokaryotic. They can take advantage of different environmental conditions.

Many marine microzooplankton are mixotrophic, which means they could also be classified as phytoplankton. Recent studies of marine microzooplankton found 30–45% of the ciliate abundance was mixotrophic, and up to 65% of the amoeboid, foram and radiolarian biomass was mixotrophic.

Phaeocystis species are endosymbionts to acantharian radiolarians. Phaeocystis is an important algal genus found as part of the marine phytoplankton around the world. It has a polymorphic life cycle, ranging from free-living cells to large colonies. It has the ability to form floating colonies, where hundreds of cells are embedded in a gel matrix, which can increase massively in size during blooms. As a result, Phaeocystis is an important contributor to the marine carbon and sulfur cycles.

A number of forams are mixotrophic. These have unicellular algae as endosymbionts, from diverse lineages such as the green algae, red algae, golden algae, diatoms, and dinoflagellates. Mixotrophic foraminifers are particularly common in nutrient-poor oceanic waters. Some forams are kleptoplastic, retaining chloroplasts from ingested algae to conduct photosynthesis.

By trophic orientation, dinoflagellates are all over the place. Some dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey (phagotrophy). Some species are endosymbionts of marine animals and other protists, and play an important part in the biology of coral reefs. Others predate other protozoa, and a few forms are parasitic. Many dinoflagellates are mixotrophic and could also be classified as phytoplankton. The toxic dinoflagellate Dinophysis acuta acquire chloroplasts from its prey. "It cannot catch the cryptophytes by itself, and instead relies on ingesting ciliates such as the red Myrionecta rubra, which sequester their chloroplasts from a specific cryptophyte clade (Geminigera/Plagioselmis/Teleaulax)".

Metazoa (animals)

Free-living species in the crustacean class Copepoda are typically 1 to 2 mm long with teardrop-shaped bodies. Like all crustaceans, their bodies are divided into three sections: head, thorax, and abdomen, with two pairs of antennae; the first pair is often long and prominent. They have a tough exoskeleton made of calcium carbonate and usually have a single red eye in the centre of their transparent head. About 13,000 species of copepods are known, of which about 10,200 are marine. They are usually among the more dominant members of the zooplankton.

In addition to copepods the crustacean classes ostracods, branchiopods and malacostracans also have planktonic members. Barnacles are planktonic only during the larval stage.

Ichthyoplankton
Ichthyoplankton are the eggs and larvae of fish ("ichthyo" comes from the Greek word for fish). They are planktonic because they cannot swim effectively under their own power, but must drift with the ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into juvenile fish. Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals.

Gelatinous zooplankton
Gelatinous zooplankton include ctenophores, medusae, salps, and Chaetognatha in coastal waters. Jellyfish are slow swimmers, and most species form part of the plankton. Traditionally jellyfish have been viewed as trophic dead ends, minor players in the marine food web, gelatinous organisms with a body plan largely based on water that offers little nutritional value or interest for other organisms apart from a few specialised predators such as the ocean sunfish and the leatherback sea turtle.

That view has recently been challenged. Jellyfish, and more gelatinous zooplankton in general, which include salps and ctenophores, are very diverse, fragile with no hard parts, difficult to see and monitor, subject to rapid population swings and often live inconveniently far from shore or deep in the ocean. It is difficult for scientists to detect and analyse jellyfish in the guts of predators, since they turn to mush when eaten and are rapidly digested. But jellyfish bloom in vast numbers, and it has been shown they form major components in the diets of tuna, spearfish and swordfish as well as various birds and invertebrates such as octopus, sea cucumbers, crabs and amphipods. "Despite their low energy density, the contribution of jellyfish to the energy budgets of predators may be much greater than assumed because of rapid digestion, low capture costs, availability, and selective feeding on the more energy-rich components. Feeding on jellyfish may make marine predators susceptible to ingestion of plastics." According to a 2017 study, narcomedusae consume the greatest diversity of mesopelagic prey, followed by physonect siphonophores, ctenophores and cephalopods.

The importance of the so-called "jelly web" is only beginning to be understood, but it seems medusae, ctenophores and siphonophores can be key predators in deep pelagic food webs with ecological impacts similar to predator fish and squid. Traditionally gelatinous predators were thought ineffectual providers of marine trophic pathways, but they appear to have substantial and integral roles in deep pelagic food webs.

Role in food webs
Grazing by single-celled zooplankton accounts for the majority of organic carbon loss from marine primary production. However, zooplankton grazing remains one of the key unknowns in global predictive models of carbon flux, the marine food web structure and ecosystem characteristics, because empirical grazing measurements are sparse, resulting in poor parameterisation of grazing functions. To overcome this critical knowledge gap, it has been suggested that a focused effort be placed on the development of instrumentation that can link changes in phytoplankton biomass or optical properties with grazing.

Grazing is a central, rate-setting process in ocean ecosystems and a driver of marine biogeochemical cycling. In all ocean ecosystems, grazing by heterotrophic protists constitutes the single largest loss factor of marine primary production and alters particle size distributions. Grazing affects all pathways of export production, rendering grazing important both for surface and deep carbon processes. Predicting central paradigms of ocean ecosystem function, including responses to environmental change requires accurate representation of grazing in global biogeochemical, ecosystem and cross-biome-comparison models. Several large-scale analyses have concluded that phytoplankton losses, which are dominated by grazing are the putative explanation for annual cycles in phytoplankton biomass, accumulation rates and export production.

Role in biogeochemistry
In addition to linking primary producers to higher trophic levels in marine food webs, zooplankton also play an important role as “recyclers” of carbon and other nutrients that significantly impact marine biogeochemical cycles, including the biological pump. This is particularly important in the oligotrophic waters of the open ocean. Through sloppy feeding, excretion, egestion, and leaching of fecal pellets, zooplankton release dissolved organic matter (DOM) which controls DOM cycling and supports the microbial loop. Absorption efficiency, respiration, and prey size all further complicate how zooplankton are able to transform and deliver carbon to the deep ocean.

Sloppy feeding and release of DOM

Excretion and sloppy feeding (the physical breakdown of food source) make up 80% and 20% of crustacean zooplankton-mediated DOM release respectively. In the same study, fecal pellet leaching was found to be an insignificant contributor. For protozoan grazers, DOM is released primarily through excretion and egestion and gelatinous zooplankton can also release DOM through the production of mucus. Leaching of fecal pellets can extend from hours to days after initial egestion and its effects can vary depending on food concentration and quality. Various factors can affect how much DOM is released from zooplankton individuals or populations. Absorption efficiency (AE) is the proportion of food absorbed by plankton that determines how available the consumed organic materials are in meeting the required physiological demands. Depending on the feeding rate and prey composition, variations in AE may lead to variations in fecal pellet production, and thus regulates how much organic material is recycled back to the marine environment. Low feeding rates typically lead to high AE and small, dense pellets, while high feeding rates typically lead to low AE and larger pellets with more organic content. Another contributing factor to DOM release is respiration rate. Physical factors such as oxygen availability, pH, and light conditions may affect overall oxygen consumption and how much carbon is loss from zooplankton in the form of respired CO2. The relative sizes of zooplankton and prey also mediate how much carbon is released via sloppy feeding. Smaller prey are ingested whole, whereas larger prey may be fed on more “sloppily”, that is more biomatter is released through inefficient consumption. There is also evidence that diet composition can impact nutrient release, with carnivorous diets releasing more dissolved organic carbon (DOC) and ammonium than omnivorous diets.

Carbon export
Zooplankton play a critical role in supporting the ocean's biological pump through various forms of carbon export, including the production of fecal pellets, mucous feeding webs, molts, and carcasses. Fecal pellets are estimated to be a large contributor to this export, with copepod size rather than abundance expected to determine how much carbon actually reaches the ocean floor. The importance of fecal pellets can vary both by time and location. For example, zooplankton bloom events can produce larger quantities of fecal pellets, resulting in greater measures of carbon export. Additionally, as fecal pellets sink, they are reworked by microbes in the water column, which can thus alter the carbon composition of the pellet. This affects how much carbon is recycled in the euphotic zone and how much reaches depth. Fecal pellet contribution to carbon export is likely underestimated; however, new advances in quantifying this production are currently being developed, including the use of isotopic signatures of amino acids to characterize how much carbon is being exported via zooplankton fecal pellet production. Carcasses are also gaining recognition as being important contributors to carbon export. Jelly falls – the mass sinking of gelatinous zooplankton carcasses – occur across the world as a result of large blooms. Because of their large size, these gelatinous zooplankton are expected to hold a larger carbon content, making their sinking carcasses a potentially important source of food for benthic organisms.

title: Zooplankton