E Di Franco

P Pierson

L Di Iorio

A Calò

J M Cottalorda

B Derijard

A Di Franco

A Galvé

M Guibbolini

J Lebrun

A Di Franco

F Micheli

F Priouzeau

C Risso-De Faverney

F Rossi

C Sabourault

G Spennato

P Verrando

P Guidetti

Effects of marine noise pollution on Mediterranean fishes and invertebrates: a review

Keywords: marine noise pollution, stress responses, behavioral alterations, population and ecosystem impacts, sustainable development

Introduction

The marine noise generated by human activities has increased drastically since the first Industrial Revolution, especially after the second world war [START_REF] Frisk | Noiseonomics: The relationship between ambient noise levels in the sea and global economic trends[END_REF]. Nowadays, the ocean is reported to be 2-10 times louder compared to the pre-industrial period [START_REF] Hildebrand | Anthropogenic and natural sources of ambient noise in the ocean[END_REF][START_REF] Frisk | Noiseonomics: The relationship between ambient noise levels in the sea and global economic trends[END_REF]. This trend is likely to continue in the future due to increasing human population, coastal urbanization, maritime traffic, oil extraction and other ocean-based energy production systems (e.g. wind and wave farms, wave energy).

Pollution is generally defined as the direct or indirect introduction into the environment of substances or energy (MSDF;EU, 2008) resulting from anthropogenic activities potentially threatening living resources and ecosystems. The locution "marine noise pollution" (hereafter MNP) has been coined to define any source of anthropogenic sound occurring in the marine environment capable of producing deleterious effects on marine life (MSDF;EU, 2008). MNP is today considered as an emerging and remarkable source of pollution by national and international legislations, including the United Nations Convention on the Law of the Sea (UNCLOS; ICP-19, https://undocs.org/A/73/124) and the European Marine Strategy Framework Directive 56/2008 CE (MSFD; EU, 2008).

MNP is reported to interfere with 1) vocalizations emitted by many animals to communicate with their conspecifics e.g., for mate attraction/selection, avoiding predators or alerting about the presence of threats [START_REF] Hatch | Quantifying Loss of Acoustic Communication Space for Right Whales in and around a U.S. National Marine Sanctuary: Hatch et al[END_REF][START_REF] Erbe | Communication masking in marine mammals: A review and research strategy[END_REF]; 2) natural sounds that animals perceive and use as clues for orientation in space, movements in search of food, migration to reproductive areas, and detection of appropriate habitats for settlement [START_REF] Simpson | Small-Boat Noise Impacts Natural Settlement Behavior of Coral Reef Fish Larvae[END_REF]. MNP can thus alter behaviors and interfere with many vital processes (Erbe et al., 2016;[START_REF] Rako-Gospić | Underwater Noise: Sources and Effects on Marine Life[END_REF], as well as cause physiological impacts ranging from mild stress to internal bleeding and ultimately death [START_REF] Fernández | Gas and Fat Embolic Syndrome" Involving a Mass Stranding of Beaked Whales (Family Ziphiidae) Exposed to Anthropogenic Sonar Signals[END_REF][START_REF] Aguilar De Soto | From physiology to policy: A review of physiological noise effects on marine fauna with implications for mitigation[END_REF][START_REF] Hawkins | Effects of Man-Made Sound on Fishes[END_REF].

Originally, studies of the impact of MNP mainly focused on physiology and behavior of marine mammals (e.g., [START_REF] Aguilar De Soto | From physiology to policy: A review of physiological noise effects on marine fauna with implications for mitigation[END_REF][START_REF] Erbe | Underwater noise of whale-watching boats and potential effects on killer whales (Orcinus orca), base on an acoustic impact model[END_REF][START_REF] Nowacek | Responses of cetaceans to anthropogenic noise[END_REF][START_REF] Wright | Do Marine Mammals Experience Stress Related to Anthropogenic Noise?[END_REF][START_REF] Götz | Acoustic deterrent devices to prevent pinniped depredation: efficiency, conservation concerns and possible solutions[END_REF][START_REF] Weilgart | Din of the Deep: Noise in the Ocean and Its Impacts on Cetaceans[END_REF]. In the last decade, however, there has been a considerable increase in research on MNP as an important source of stress for other marine animals, like many species of fish and invertebrates capable of producing and detecting sounds [START_REF] Tolimieri | Ambient sound as a cue for navigation by the pelagic larvae of reef fishes[END_REF][START_REF] Popper | Acoustic detection and communication by decapod crustaceans[END_REF][START_REF] Montgomery | Larval orientation to reefs and reef sound[END_REF][START_REF] Amorim | Diversity of sound production in fish[END_REF][START_REF] Hu | Acoustically evoked potentials in two cephalopods inferred using the auditory brainstem response (ABR) approach[END_REF][START_REF] Patek | The acoustics and acoustic behavior of the California spiny lobster (Panulirus interruptus)[END_REF][START_REF] Holt | Can you hear the dinner bell? Response of cyprinid fishes to environmental acoustic cues[END_REF][START_REF] Ladich | Ecology of sound communication in fishes[END_REF].

Understanding the impact of MNP on fish and invertebrates is crucial because both these groups include species that are threatened or have a significant socio-economic importance, e.g. for fisheries and aquaculture [START_REF] Holmlund | Ecosystem services generated by fish populations[END_REF][START_REF] Anderson | Sound, stress, and seahorses: The consequences of a noisy environment to animal health[END_REF][START_REF] Eddy | Ecosystem effects of invertebrate fisheries[END_REF]. Also, many species of invertebrates and fish play key roles: 1) some species occupy, within food webs, a range of trophic positions from primary consumers to apex predators, in some cases as keystone predators (like some coastal fishes and lobsters; [START_REF] Hammerschlag | Ecosystem Function and Services of Aquatic Predators in the Anthropocene[END_REF]; 2) other species contribute considerably to carbon and nitrogen cycles [START_REF] Pinnegar | Why the damselfish Chromis chromis is a key species in the Mediterranean rocky littoral -a quantitative perspective: CHROMIS CHROMIS IN THE MEDITERRANEAN SEA[END_REF]; 3) other species, finally, are habitat-forming species, e.g. some bivalve mollusks and corals [START_REF] Peirano | The coral Cladocora caespitosa (Anthozoa, Scleractinia) as a bioherm builder in the Mediterranean Sea[END_REF][START_REF] Tolley | THE ROLE OF OYSTERS IN HABITAT USE OF OYSTER REEFS BY RESIDENT FISHES AND DECAPOD CRUSTACEANS[END_REF][START_REF] Pitacco | The Mediterranean stony coral Cladocora caespitosa (Linnaeus, 1767) as habitat provider for molluscs: colony size effect[END_REF]. Therefore, as many fish and invertebrates play key ecological roles contributing to shape whole communities,. Uunderstanding the possible impacts of MNP on these organisms is vital to design and adopt appropriate management, conservation and restoration measures [START_REF] Slabbekoorn | A noisy spring: the impact of globally rising underwater sound levels on fish[END_REF][START_REF] Hawkins | Responses of free-living coastal pelagic fish to impulsive sounds[END_REF][START_REF] Tidau | Review on behavioral impacts of aquatic noise on crustaceans[END_REF][START_REF] Weilgart | THE IMPACT OF OCEAN NOISE POLLUTION ON FISH AND INVERTEBRATES[END_REF][START_REF] Rako-Gospić | Underwater Noise: Sources and Effects on Marine Life[END_REF].

There are two distinct types of MNP, depending on the intensity and duration: 1) acute MNP, characterized by sounds with high intensity and short duration, often emitted repeatedly and over a wide frequency band (e.g. sonar, explosions, pile driving, air guns); 2) chronic MNP, generally characterized by a lower intensity but a longer duration, to which animals are exposed regularly or over longer time lapses (e.g. boat traffic; Rako-Gospić and [START_REF] Rako-Gospić | Underwater Noise: Sources and Effects on Marine Life[END_REF]. Chronic MNP is much more widespread than acute MNP and is widely considered as the main contributor to the increase in ocean background noise ( MSFD EU, 2008;[START_REF] Hildebrand | Anthropogenic and natural sources of ambient noise in the ocean[END_REF]. These different types of MNP can co-occur and interact in producing their impact on marine life. Two components of noise may influence the relationships between sounds and living beings: 1) particle motion, i.e. the back-and-forth motion of particles in the medium; 2) sound pressure, i.e. the pressure fluctuations with zones of high and low pressure in the medium (see https://dosits.org/decision-makers/tutorials/science/what-is-sound/ for a visual representation of these two components). Fish mainly produce sounds at frequencies <4000 Hz (in most cases below 1000 Hz). Their hearing abilities can differ substantially depending on the species: 1) most species, called "hearing generalists", perceive the sound as particle motion;

2) other species, called "hearing specialists", possess gas-filled cavities like the swim bladder, which resonate with sounds. This condition allows "hearing specialist" fishes to perceive both particle motion and sound pressure, covering a larger frequency band of sound.

Hearing specialist fishes are generally more sensitive to MNP, essentially because the vibration of their gas-filled cavities in the presence of noise can lead to rupture of these cavities and cause damages to the surrounding organs [START_REF] Halvorsen | Effects of exposure to pile-driving sounds on the lake sturgeon, Nile tilapia and hogchoker[END_REF]. Invertebrates do not have gas-filled cavities and are likely to just perceive the particle motion component of sound. Fish and invertebrates hearing is mostly sensitive to sounds <2000 Hz, which correspond to the frequency band of most anthropogenic noises [START_REF] Hawkins | Effects of Man-Made Sound on Fishes[END_REF], and are therefore likely to be sensitive to and potentially affected by MNP (being most of the energy produced by MNP <1000 Hz; [START_REF] Hildebrand | Anthropogenic and natural sources of ambient noise in the ocean[END_REF].

The Mediterranean Sea is a temperate and semi-enclosed basin crossed by some of the most important marine trade routes (Fig. 1), where coastal areas are highly urbanized, and fishery resources heavily exploited and multiple threats concentrate making it a sea "under siege" [START_REF] Micheli | Cumulative Human Impacts on Mediterranean and Black Sea Marine Ecosystems: Assessing Current Pressures and Opportunities[END_REF]. The Mediterranean Sea is thus likely to be particularly affected by MNP, suggesting the urgent need to develop more investigations for improveing our understanding of its effects on marine life and mitigateing its ecological impacts.

The aims of this review, therefore, are: i) to synthesize the available and sparse information about the impact of MNP on Mediterranean fishes and invertebrates; ii) to identify knowledge gaps and priorities for future research guiding the design and adoption of management and mitigation measures.

Materials and methods

Google Scholar (https://scholar.google.com/) and Web of Science (https://webofknowledge.com) were used to perform a systematic search of the literature following the PRISMA review protocol (http://www.prisma-statement.org/, see Supplementary figure 1 for visual flowchart). Results were limited to peer-reviewed articles published in international journals between January 1990 and December 2019. The specific search terms were "fish" OR "invertebrate/s" AND "marine noise" OR "noise pollution" OR "anthropogenic noise" AND "behavior" OR "stress" or "physiology" AND "Mediterranean".

Additional peer-reviewed articles were identified by screening references cited in the selected primary literature.

In the present review, we considered both field and laboratory studies because they offer different and often complementary information. Field observational studies are generally useful to collect correlative evidence about the effects of MNP under natural conditions. However, field investigations have the disadvantage that the multiple sources of variation (other than MNP) possibly influencing the response variables under study cannot be controlled, so that the putative effects of MNP cannot be disentangled from other sources of variation. In contrast, experiments conducted in controlled conditions (e.g. in mesocosms) allow to control other possible sources of variations. They thus allow to directly assess the effects of MNP, even though they may suffer from the bias introduced by experimental artifacts [START_REF] Parvulescu | The acoustics of small tanks[END_REF][START_REF] Akamatsu | Empirical refinements applicable to the recording of fish sounds in small tanks[END_REF][START_REF] Duncan | Issues associated with sound exposure experiments in tanks[END_REF][START_REF] Rogers | Parvulescu Revisited: Small Tank Acoustics for Bioacousticians[END_REF], while generally omitting natural complexity and variability (e.g. daily, seasonal) of a number of factors (e.g. temperature, salinity, pH) possibly affecting the response variables (see [START_REF] Underwood | Experiments in ecology: their logical design and interpretation using analysis of variance[END_REF] for generalities and more details about experimental logics). This literature search first produced 652 results, which decreased to 506 after having removed duplicates. The articles' abstracts were then reviewed to select field or in aquaria/mesocosm studies with the main focus on the effects of MNP on Mediterranean fish and/or invertebrate species (i.e. species native of the Mediterranean, whose distribution range is not necessarily limited to the basin). Forty-five studies finally met the selection criteria. These articles were then classified based on the taxonomic group, the type of noise (i.e. acute vs. chronic), the origin of the noise (e.g. ships, pile-driving), the experimental setup (i.e. field vs. mesocosms), the intensity and frequency of the noise, its duration and the location where field studies have been carried out (see Supplementary Table 1 for further details).

Results and discussion

Among the forty-five studies selected, fifteen were conducted in the field (six of them have been actually carried out in the Atlantic waters, North Sea or Baltic Sea on species living also in the Mediterranean basin, while nine have been conducted in Mediterranean waters), mostly in the west part of the Mediterranean basin and in the Adriatic Sea (Fig. 1).

The literature review showed an increasing trend in the number of studies about MNP, especially in the last decade. Specifically, up to 2004 only 2 (4%) studies had been published on the impact of MNP on Mediterranean fishes and invertebrates, 4 (8%) between 2005 and 2009, 15 (33%) between 2010 and 2014 and 24 (53%) between 2015 and 2019 (Fig. 2 A).

The analysis of the published articles highlighted that: 1) 24 (53%) studies focused on chronic MNP, 20 (45%) on acute MNP and 1 (2%) investigated both MNP types (Fig. 2 B);

2) 21 (47%) studies investigated the effects of MNP produced by ships/vessels, 6 (13%) by pile driving, 1 (2%) by both, 1 (2%) by air guns, 1 (2%) by pingers normally used as marine mammals' deterrent and 15 (34%) by a computer replicating one or many of the previously mentioned noise sources (Fig. 2 C); 3) 30 (67%) studies were conducted on fishes and 15 (33%) on invertebrates (8 (18%) on crustaceans, 6 (13%) on cephalopods and 1 (2%) on cnidarians) (Fig. 2 D); 4) 30 (67%) studies were conducted under controlled conditions (e.g. aquaria) and 15 (33%) in the field, either using caged or free-living individuals (Fig. 2 E); 5) 23 (51%) studies assessed the impact of MNP on behavior, 14 (31%) on physiology and 8 (18%) on both (Fig. 2 F).

We analyzed more in depth the studies for their specific contents by classifying them based on two criteria: taxonomic group impacted (fish vs invertebrates) and MNP type (acute vs chronic). Results are reported here below.

Impact of MNP on fishes

Thirty out of the 45 studies focused on fish. Approximately half of them (13) analyzed the response of two species, the European seabass (Dicentrarchus labrax) and the gilthead seabream (Sparus aurata). These two species represent more than 90% of the European marine aquaculture production (FEAP 2016, http://feap.info/). The remaining studies dealt with flat (the common sole Solea solea, the European plaice Pleuronectes platessa), pelagic (the wild sprat Sprattus sprattus, the mackerel Scomber scombrus, the Allis shad Alosa alosa, the Atlantic bluefin tuna Thunnus thynnus), cryptobenthic (the red-mouthed goby Gobius cruentatus, the Common goby Pomatoschistus microps, the lusitanian toadfish Halobatrachus dydactilus, the long-snouted seahorse Hippocampus guttulatus) and other coastal/demersal species (the black seabream Spondyliosoma cantharus, the whiting-pout Trisopterus luscus, the thicklip grey mullet Chelon labrosus, the brown meagre Sciaena umbra, the damselfish Chromis chromis and the European eel Anguilla anguilla). See Table 1 for a summary of the response variables tested for each species.

In Table 1 of Supplementary Material more details about the studied species, the noise features (type, level, duration and frequency) and the locations where the studies included in this review have been conducted, are reported.

Acute MNP

The available studies showed fairly heterogeneous results. Seven studies have been carried out on the potential impact of pile driving, either in the field or in controlled conditions (mesocosms or aquaria). Studies on juvenile European seabass [START_REF] Debusschere | Acoustic stress responses in juvenile sea bass Dicentrarchus labrax induced by offshore pile driving[END_REF][START_REF] Radford | Repeated exposure reduces the response to impulsive noise in European seabass[END_REF], larvae of common sole [START_REF] Bolle | Common Sole Larvae Survive High Levels of Pile-Driving Sound in Controlled Exposure Experiments[END_REF] and adults of European plaice (Bruintjes et al., 2016b) did not report any detectable effect from pile driving noise in terms of instantaneous or delayed mortality, long term effects on ventilation rate or oxygen uptake by organisms. Available evidence suggests that pile driving does not have any significant effect on the investigated species, development stages or variables measured.

These results could be related to the experimental settings not representative of real conditions (see [START_REF] Akamatsu | Empirical refinements applicable to the recording of fish sounds in small tanks[END_REF][START_REF] Rogers | Parvulescu Revisited: Small Tank Acoustics for Bioacousticians[END_REF], and/or also to a rapid recovery, an increase in tolerance or a change in hearing sensitivity, resulting in an absence of permanent/detectable effects on the measured variables. Other studies showed that juvenile and adult European seabass, and adult black seabream exposed to pile driving noise, displayed a decrease or increase of oxygen consumption rate (Bruintjes et al., 2016b;[START_REF] Debusschere | Acoustic stress responses in juvenile sea bass Dicentrarchus labrax induced by offshore pile driving[END_REF], which is indicative of a stress-induced response. Pile driving has also been reported to affect the structure and dynamics of shoals of juvenile seabass that tend to be less cohesive, less directionally ordered and less coordinated in speed and directional changes [START_REF] Herbert-Read | Anthropogenic noise pollution from pile-driving disrupts the structure and dynamics of fish shoals[END_REF]. [START_REF] Hawkins | Responses of free-living coastal pelagic fish to impulsive sounds[END_REF] exposed schools of wild sprat and mackerel to sequences of acute noises simulating strikes from pile driving and showed that sprat schools were more likely to disperse and mackerel schools more likely to change swimming depth.

Significant effects of pile driving noise on oxygen consumption and grouping behavior have been mostly detected on confined individuals following exposure to the "real" pile driving noise in the natural environment [START_REF] Santulli | Biochemical Responses of European Sea Bass (Dicentrarchus labrax L.) to the Stress Induced by Off Shore Experimental Seismic Prospecting[END_REF]Bruintjes et al., 2016a;[START_REF] Debusschere | Acoustic stress responses in juvenile sea bass Dicentrarchus labrax induced by offshore pile driving[END_REF][START_REF] Hawkins | Responses of free-living coastal pelagic fish to impulsive sounds[END_REF]. On the contrary, the studies where no effect has been observed used playbacks records of real noises emitted either in aquaria or in the field [START_REF] Bolle | Common Sole Larvae Survive High Levels of Pile-Driving Sound in Controlled Exposure Experiments[END_REF][START_REF] Debusschere | In Situ Mortality Experiments with Juvenile Sea Bass (Dicentrarchus labrax) in Relation to Impulsive Sound Levels Caused by Pile Driving of Windmill Foundations[END_REF]Bruintjes et al., 2016b;[START_REF] Radford | Repeated exposure reduces the response to impulsive noise in European seabass[END_REF]. The two exceptions reviewed here are the case of European plaice directly exposed to the real pile driving noise, where no detectable effects on oxygen consumption have been reported (Bruintjes et al., 2016b), and the modification of structure and dynamics of shoals of European seabass reported in aquaria [START_REF] Herbert-Read | Anthropogenic noise pollution from pile-driving disrupts the structure and dynamics of fish shoals[END_REF]. [START_REF] Santulli | Biochemical Responses of European Sea Bass (Dicentrarchus labrax L.) to the Stress Induced by Off Shore Experimental Seismic Prospecting[END_REF] investigated the potential effects of another type of acute noise, the air gun acoustic waves. The authors showed a biochemical response in caged European seabass exposed to this type of stress. Such a response consisted of transient alterations of cortisol, glucose, lactate, AMP, ADP, ATP and cAMP in blood and different tissues, which went back to normality within 72h post-exposure.

To test whether intermittency, amplitude fluctuation, repetition interval regularity and the presence of 'ramp-up' have the potential to impact fish behavior, [START_REF] Neo | Temporal structure of sound affects behavioural recovery from noise impact in European seabass[END_REF][START_REF] Neo | Impulsive sounds change European seabass swimming patterns: Influence of pulse repetition interval[END_REF][START_REF] Neo | Sound exposure changes European seabass behaviour in a large outdoor floating pen: Effects of temporal structure and a ramp-up procedure[END_REF] exposed adults of European seabass to multiple types of artificial noises. They reported multiple behavioral responses including increased group cohesion, swimming speed and depth, startle response (i.e., sudden change in swimming direction and acceleration). All these behavioral changes could be due to the perception of the noise by fish, considered as a potential threat.

Effects of acute noises with higher frequency and much lower intensities compared to pile driving and air gun have also been tested. [START_REF] Kastelein | Effects of acoustic alarms, designed to reduce small cetacean bycatch in gillnet fisheries, on the behaviour of North Sea fish species in a large tank[END_REF] investigated, in outdoor tanks, the effects of the noise of different dolphin anti-depredation pingers on adults of three Mediterranean fish species, i.e. European seabass, Whiting-pout and thicklip grey mullet.

While exposed to this noise, these fishes displayed pinger-and species-specific alterations in terms of swimming-speed and -depth. An increase in swimming speed (possibly related to an escape reaction; [START_REF] Wilson | Allis shad ( Alosa alosa) exhibit an intensity-graded behavioral response when exposed to ultrasound[END_REF] has been observed in adults of Allis shad in response to ultrasounds [START_REF] Wilson | Allis shad ( Alosa alosa) exhibit an intensity-graded behavioral response when exposed to ultrasound[END_REF]. This species can perceive these frequencies that correspond to the sounds produced by some of their natural predators (i.e. sea mammals), which are similar to those of sonars or boat propellers.

Chronic MNP

All the studies we have found about chronic MNP dealt with boat noise, produced by recreational or fishing vessels, ships and ferries. Thirteen studies investigated the effects of chronic noise exposure, either through playbacks in aquaria (n=7) or directly in the field on wild fish (n=6).

Studies that employed playback records in aquaria provided evidence that boat noise can alter hearing threshold, affect physiological response, induce behavioral modifications, and mask communication in fishes [START_REF] Hawkins | Effects of Man-Made Sound on Fishes[END_REF]).

An increase in hearing thresholds (defined as the limit in decibels (dB) under which a sound is not perceived) has been observed in adults of brown meagre, damselfish and redmouthed goby, by using playbacks of boat noise. Such increases in hearing thresholds were associated with a decrease in hearing and communication range [START_REF] Codarin | Effects of ambient and boat noise on hearing and communication in three fish species living in a marine protected area (Miramare, Italy)[END_REF]. Celi et al. (2016) showed an increase in stress-related plasma variables (ACTH, cortisol, glucose, lactate, cholesterol, triglycerides, Hsp70, hematocrit and osmolarity) in adults of gilthead seabream after 10 days exposure in aquaria to a sound loop consisting of seven recreational vessels, a hydrofoil, a ferry and a fishing boat. [START_REF] Filiciotto | Impact of aquatic acoustic noise on oxidative status and some immune parameters in gilthead sea bream Sparus aurata (Linnaeus, 1758) juveniles[END_REF] have reported changes in immune parameters, such as higher levels of lysozyme activity, antiprotease activity and white blood cells together with a lower albumin/globulin ratio in gilthead seabream after 40 days of exposure to a loop of recordings of different types of boats. [START_REF] Buscaino | Impact of an acoustic stimulus on the motility and blood parameters of European sea bass (Dicentrarchus labrax L.) and gilthead sea bream (Sparus aurata L.)[END_REF] found that the exposure of juvenile European seabass and gilthead seabream to linear sweeps in the frequency band in which most of the boat noises are produced induced an increase in lactate and hematocrit levels, as well as an increased mobility in both species, while a decrease in glucose was observed in gilthead seabream. [START_REF] Vazzana | Noise elicits hematological stress parameters in Mediterranean damselfish ( Chromis chromis , perciformes): A mesocosm study[END_REF] exposed caged adult damselfishes during two minutes to an artificial noise consisting of pure tones aimed at reproducing the main acoustic energy produced by boat, ships and ferries. They found that this exposure induced an increase in stress biomarkers in blood, such as glucose, lactate, total proteins and Hsp70.

Resident adults of red-mouthed goby, a small-sized territorial benthic fish, were found to be more submissive and won less encounters while fighting against conspecific intruders in the presence of noise playbacks of a 5 m-fiberglass boat [START_REF] Sebastianutto | How boat noise affects an ecologically crucial behaviour: the case of territoriality in Gobius cruentatus (Gobiidae)[END_REF]. [START_REF] Alves | Boat noise reduces acoustic active space in the lusitanian toadfish Halobatrachus didactylus[END_REF] showed that masking induced by the presence of boat noise caused a reduction in the distance at which adult lusitanian toadfish were able to detect a conspecific from 6 m to 2.5-4 m and from 13 m to 7-8.5 m, depending on the call and the type of boat noise.

The noise produced by boats at sea can affect individual and schooling behavior. Two field studies conducted on adult brown meagre showed that boat noise caused an increase both in the rate of vocalizations, probably to compensate communication masking [START_REF] Picciulin | Brown meagre vocalization rate increases during repetitive boat noise exposures: A possible case of vocal compensation[END_REF], and in flight duration and frequency of hiding behaviors, followed by a rapid recovery after exposure (La [START_REF] Manna | Behavioral response of brown meagre ( Sciaena umbra ) to boat noise[END_REF]. [START_REF] Bracciali | Effects of Nautical Traffic and Noise on Foraging Patterns of Mediterranean Damselfish (Chromis chromis)[END_REF] reported an increased escape duration, the alterations of physiological conditions (Body Condition Index = Total weight / Standard length 3 ) and a decrease in feeding frequency in adult damselfish exposed to boat noise in comparison to a navigation-restricted area. [START_REF] Palma | Effects of anthropogenic noise as a source of acoustic stress in wild populations of Hippocampus guttulatus in the Ria Formosa, south Portugal[END_REF] observed the displacement in 37.5% and an increased respiration rate in 87% of adult long-snouted seahorse during passages of motorboats over the specimens. A decrease in anti-predator response and an increase in startle latency has also been reported as a behavioral reaction to boat noise in adult European eel (Bruintjes et al., 2016a). [START_REF] Purser | Condition-dependent physiological and behavioural responses to anthropogenic noise[END_REF] also investigated the anti-predatory response and ventilation rate in juveniles of European eels. Their results were similar to those reported by Bruintjes et al. (2016a), but only when the fish were in bad body conditions. [START_REF] Blom | Continuous but not intermittent noise has a negative impact on mating success in a marine fish with paternal care[END_REF] showed that continuous broadband noise, increased latency to female nest inspection and spawning, and decreased spawning probability in adult Common goby. [START_REF] Sarà | Effect of boat noise on the behaviour of bluefin tuna Thunnus thynnus in the Mediterranean Sea[END_REF] observed that adults of Atlantic bluefin tuna caged in a tuna trap modified their schooling behavior during the passage of ferry boats next to the trap, suggesting that migration patterns to spawning and feeding grounds could be affected by boat noise. By using time-budget analyses during playbacks of a ferry boat and a fiberglass boat, [START_REF] Picciulin | In situ behavioural responses to boat noise exposure of Gobius cruentatus (Gmelin, 1789; fam. Gobiidae) and Chromis chromis (Linnaeus, 1758; fam. Pomacentridae) living in a Marine Protected Area[END_REF] reported a significant decrease in the time spent caring their nests in adults of damselfishes and an increase in the time spent sheltering in adults of red-mouthed goby. Similar behavioral changes have the potential to affect, besides the single individuals, whole populations, by decreasing offspring survival in damselfishes or decreasing the time dedicated to feeding and mating in red-mouthed goby. Finally, González [START_REF] Correa | Recreational boat traffic effects on fish assemblages: First evidence of detrimental consequences at regulated mooring zones in sensitive marine areas detected by passive acoustics[END_REF] found that fish call rates and complexity were higher in a location where mooring was not allowed compared to regulated mooring locations where motorboat noise was higher.

Impact of MNP on invertebrates

MNP has been found to induce multiple negative effects on invertebrates [START_REF] Carroll | A critical review of the potential impacts of marine seismic surveys on fish & invertebrates[END_REF]. In the Mediterranean Sea, fifteen studies assessed potential effects of anthropogenic noise on marine invertebrates: six dealt with physiology, seven with behavior and two evaluated both; eight concerned crustacean species (the hermit crab Pagurus bernhardus, the spiny lobster Palinurus elephas, the common prawn Palaemon serratus), six cephalopods (the European squid Loligo vulgaris, the common cuttlefish Sepia officinalis, the common octopus Octopus vulgaris, the southern shortfin squid Illex coindetii) and one cnidarians (the Mediterranean jellyfish Cotylorhiza tuberculata, the barrel jellyfish Rhizostoma pulmo). See table 2 for a summary of the response variables tested for each species.

In Table 1 of Supplementary Material more detail is provided about the studied species, the noise features (type, level, duration and frequency) and the location where the studies used in this review have been conducted.

Acute MNP

One study assessed the impact of acute MNP on crustaceans, and was conducted on adults of the hermit crab. [START_REF] Roberts | Sensitivity of Pagurus bernhardus (L.) to substrate-borne vibration and anthropogenic noise[END_REF] showed that an experimental apparatus generating noise types similar to anthropogenic activities, such as blasting and pile driving, may induce the retraction of antennas and reduce locomotion of the hermit crab in aquaria.

MNP studies on cephalopods in the Mediterranean Sea focused on four species: European squid, common cuttlefish, common octopus and southern shortfin squid. [START_REF] André | Lowfrequency sounds induce acoustic trauma in cephalopods[END_REF] exposed adults of these four species to high-intensity low-frequency sounds, mimicking acute sounds produced by human activities like pile driving and air guns. These authors reported permanent and substantial alterations of the sensory hair cells of the statocysts, responsible for the animals' sense of balance and position in space, with damages increasing with time of exposure. These results were confirmed by Solé et al. (2013aSolé et al. ( , 2013b) ) who exposed adults of the same four species to the same sound sweeps, and observed typically noise-induced lesions in the statocysts, whose seriousness was correlated with time of exposure. [START_REF] Solé | Offshore exposure experiments on cuttlefish indicate received sound pressure and particle motion levels associated with acoustic trauma[END_REF] observed the same damages on statocysts by exposing caged adults of common cuttlefish to different noises at different distances from the source in the field. [START_REF] Samson | Graded behavioral responses and habituation to sound in the common cuttlefish Sepia officinalis[END_REF] assessed the response of juvenile and adult common cuttlefish exposed to pure-tone pips in aquaria and reported an escape response from sounds. The intensity of the response was related to the stimulus amplitude and sound frequency. After repeated exposure, some evidence of habituation was observed but a total response inhibition never occurred.

The only study focusing on cnidarians is the one of [START_REF] Solé | Evidence of Cnidarians sensitivity to sound after exposure to low frequency noise underwater sources[END_REF], which reported injuries in the statocyst sensory epithelium in two medusa jellyfish species (Mediterranean and barrel jellyfishes) after two hours of exposure to low frequency and high intensity sweeps. [START_REF] Filiciotto | Behavioural and biochemical stress responses of Palinurus elephas after exposure to boat noise pollution in tank[END_REF] showed that adult spiny lobster exposed in controlled conditions to 30 min of boat noise playbacks recorded next to a harbor, display an increase in stressrelated haemolymphatic biomarkers (glucose, total proteins, Hsp70 and heamatocrit) and in locomotory activity reflecting a potential disturbance. Boat noise was also involved in the alteration of immune response (with a decrease in total haemocyte count and in phenoloxydase activity in cell-free haemolymph) and the increase in Hsp27 expression in haemocyte lysate of spiny lobsters [START_REF] Celi | Shipping noise affecting immune responses of European spiny lobster (Palinurus elephas)[END_REF]. These results showed that boat noises may induce stressful conditions at both cellular and biochemical levels. The 30 mins exposure to boat noise on adult specimens of common prawn elicited an increase in protein concentration, Hsps 27 and 70 expressions, DNA fragmentation, and a decrease in locomotory activity as well as in the time spent for sheltering [START_REF] Filiciotto | Underwater noise from boats: Measurement of its influence on the behaviour and biochemistry of the common prawn ( Palaemon serratus , Pennant 1777)[END_REF]. These impacts could decrease the probability of survival in the presence of a predator and lower the number of mate encounters, thus decreasing the reproductive success. Exposure to playbacks of boat noise, either produced by a large shipping vessel or a small outboard craft, can affect the behavior of the hermit crab inducing a greater response latency to a stimulus of looming predator, thus increasing predation risk and mortality by predation [START_REF] Nousek-Mcgregor | Does Noise From Shipping and Boat Traffic Affect Predator Vigilance in the European Common Hermit Crab?[END_REF]. Moreover, in two studies, Tidau andBriffa (2019a, 2019b) reported that the hermit crab displays clear grouping preferences with other individuals that is dependent on shell suitability (crabs with optimal shells prefer to stay in pairs, while crabs with suboptimal shells do not show any group preference). While exposed to boat noise, grouping preferences disappear or strongly change, and shell selection ability decreases (hermit crabs are less capable to select an optimal shell). Finally, [START_REF] Walsh | Noise affects resource assessment in an invertebrate[END_REF] investigated the impact of white noise on the hermit crab in aquaria ; this type of noise is produced by combining different frequencies together, effectively simulating broadband noise like the noise produced by distant ships. In a noisy environment, shell selection was more rapid, with hermit crabs approaching faster the shells, decreasing the time spent for inspecting and entering the shells. This could induce a sub-optimal shell selection potentially decreasing individual survival probability.

Chronic MNP

For cephalopods, [START_REF] Kunc | Anthropogenic Noise Affects Behavior across Sensory Modalities[END_REF] reported that playbacks of ship noise can induce an increase in the frequency of livery (body coloration patterns) change in adult common cuttlefish.

Conclusions, knowledge gaps and perspectives

There is increasing evidence worldwide that MNP may represent a serious threat to marine life. Our review indicates that acute and chronic MNP can cause, in fact, a wide variety of effects on marine invertebrates (chiefly mollusks and crustaceans) and vertebrates (fishes and mammals) [START_REF] Carroll | A critical review of the potential impacts of marine seismic surveys on fish & invertebrates[END_REF][START_REF] Rako-Gospić | Underwater Noise: Sources and Effects on Marine Life[END_REF]. Effects encompass behavioral alterations (e.g. swimming and gregarious patterns, anti-predator responses, mating and spawning patterns), auditory damage, communication masking (mostly intra-specific), stress-related non-auditory physiological responses, changes in habitat use (e.g. shelter frequentation), migration and displacement (e.g. towards less noisy places), or immediate death (e.g. as a consequence of severe internal organs' damages) [START_REF] Aguilar De Soto | From physiology to policy: A review of physiological noise effects on marine fauna with implications for mitigation[END_REF][START_REF] Cox | Sound the alarm: A meta-analysis on the effect of aquatic noise on fish behavior and physiology[END_REF][START_REF] Hawkins | Effects of Man-Made Sound on Fishes[END_REF].

The present review summarizes the available evidence about MNP effects specifically on Mediterranean fish and invertebrates. Fewer studies concerned marine invertebrates, while most of them dealt with fishes. Among the 30 reviewed studies assessing the effects of MNP on Mediterranean fish species, four did not detect any effect and 26 reported that MNP may have detectable negative repercussions. Negative effects ranged from mild modifications in physiological variables to extremely stressful conditions associated with decreased immune capacities and degraded body conditions. Behavior can also be impacted, with effects ranging from short displacements and slight changes in swimming behavior to compromising feeding and nest caring behaviors. These negative effects could impact both single individuals and entire populations. Such individual-to population-wide impacts have the potential to affect entire communities, especially when species playing key ecological roles are impacted (e.g. high-level predatory fishes; [START_REF] Guidetti | Marine Reserves Reestablish Lost Predatory Interactions And Cause Community Changes In Rocky Reefs[END_REF]. This review also showed that MNP can have impacts on physiology of many invertebrates (crustacean decapods, cephalopod mollusks and cnidarians), that can range from an increase in stress-related variables to permanent structural damages, possibly having fatal effects. Crustaceans and cephalopods, also, showed different degrees of potentially harmful behavioral responses, ranging from changes in movement patterns to increased latency in response against predators, possibly affecting individual reproductive success and survival. Most studies we have found are individual-based, but the effects of MNP could have population-wide repercussions, particularly when MNP is intense and/or chronic. Community-and ecosystem-wide effects may occur whenever MNP affects species that have crucial roles, such as habitat-former mollusks (e.g. oysters; [START_REF] Charifi | Noise pollution limits metal bioaccumulation and growth rate in a filter feeder, the Pacific oyster Magallana gigas[END_REF] and high-level fish predators [START_REF] Guidetti | Marine Reserves Reestablish Lost Predatory Interactions And Cause Community Changes In Rocky Reefs[END_REF][START_REF] Sarà | Effect of boat noise on the behaviour of bluefin tuna Thunnus thynnus in the Mediterranean Sea[END_REF].

MNP has the potential to affect a variety of species and among them some key species providing ecosystem goods and services, which justifies the increasing attention paid to marine noise pollution (MSFD;EU, 2008). This review showed that until now the available evidence for the Mediterranean was largely anecdotal, and limited to a few species (marine mammals excepted; see https://www.frontiersin.org/research-topics/8654/impacts-ofshipping-on-marine-fauna), a few variables (while marine noise may potentially impact from cells to ecosystems) and to snapshot or short-term studies carried out at a few locations. There is thus a clear need for more research and systematic monitoring to exhaustively assess the risks generated by MNP to marine life. Data gathering should be expanded in space and time, and should integrate multiple species and multiple variables, so to be capable of capturing information on both early symptoms and long-term permanent effects. Also, MNP has generally been assessed without taking into account the variety of interactions it can have with other sources of environmental disturbance at sea, such as overfishing, climate change, acidification, chemical pollution and other forms of anthropogenic disturbance that can combine to ultimately influence the marine biodiversity in complex ways [START_REF] Côté | Interactions among ecosystem stressors and their importance in conservation[END_REF][START_REF] Micheli | Combined impacts of natural and human disturbances on rocky shore communities[END_REF]. [START_REF] Purser | Condition-dependent physiological and behavioural responses to anthropogenic noise[END_REF], from this point of view, observed that only eels in bad health conditions were adversely affected by MNP, which suggests how important is to consider the potential synergistic effectsinteractions (synergies, antagonisms and additive effects, [START_REF] Côté | Interactions among ecosystem stressors and their importance in conservation[END_REF] of different sources of disturbance at sea. Environmental agencies, authorities, policy makers and legislators at all levels (e.g. at EU or at the Mediterranean scale) strongly need data to take proper management decisions, but presently there are still lots of unknown aspects about MNP [START_REF] Erbe | International regulation of underwater noise[END_REF]. More complete and integrated data would provide crucial information to set appropriate conservation and management/mitigation measures, which should be accompanied by effective educational campaigns and supporting legislations.

Based on our literature review we identified the following gaps in knowledge about the potential effects that MNP may have on Mediterranean fish and invertebrates: 1) some categories of marine organisms have been little investigated or totally ignored, such as i) invertebrates (especially groups like annelids and echinoderms), ii) elasmobranchs (in spite they are the most threatened fish group in the Mediterranean Sea and worldwide; see [START_REF] Ferretti | Loss of Large Predatory Sharks from the Mediterranean Sea: Large Sharks in the Mediterranean[END_REF][START_REF] Ferretti | Patterns and ecosystem consequences of shark declines in the ocean: Ecosystem consequences of shark declines[END_REF] and [START_REF] Casper | Are Sharks Even Bothered by a Noisy Environment?[END_REF]), iii) early life stages (generally more sensitive to impacts than adults, see e.g. [START_REF] Simpson | Small-Boat Noise Impacts Natural Settlement Behavior of Coral Reef Fish Larvae[END_REF]);

2) some biological variables/mechanisms have been little investigated or totally ignored as well, such as i) the hearing sensitivity of organisms (that has been investigated for a few species, so we do not actually know for how many species MNP can impair hearing and mask communications), ii) the bio-physiological mechanisms triggering the observed behavioral responses, iii) the ways MNP affects populations, communities and ecosystems, iv) the physiological variables potentially impacted by MNP stress (which is crucial, e.g., to properly evaluate energy metabolism changes, to characterize concentration variations for hormones potentially implied in stress responses), and v) omics (which could be useful to study long term adaptation of species subject to MNP stress);

3) a few studies assessed the potential of recovery, habituation and adaptation to MNP in relation e.g. to species' mobility, which is fundamental to understanding whether some responses are permanent or temporary; 4) most available studies focus on chronic MNP (almost all on boat noise), which is the most widespread type of MNP monitored by the MSFD, but not a priori the most impacting one; 5) methodologically speaking, many aspects would deserve to be investigated more in depth, such as i) the advantages of coupling field and laboratory approaches (whose lack often prevents the possibility to draw reliable and robust conclusions about the effects of the different types of MNP on the investigated species), ii) the limits to use organisms (especially fish) coming from aquaculture (which could be less sensitive or responsive than wild animals because of potential habituation or because they descend from cultured lineages exposed since birth to the noise of aquaculture facilities), iii) the effects of the acoustic configuration of the experimental units (e.g. aquaria) or the sea bottom (potentially hindering, modifying or stopping the noise stimulus produced, perceived or emitted by animals; see [START_REF] Rogers | Parvulescu Revisited: Small Tank Acoustics for Bioacousticians[END_REF]), and iv) the spatial distribution of field studies (few field studies have been conducted in the Mediterranean Sea, and most of them are concentrated in the western sector or in the northern Adriatic Sea, while the rest of the basin and particularly some sectors that are likely to be "noise hotspots", like in the proximity of the Suez Canal, have not been investigated yet); 6) unusual sources of MNP and multi-stressors' interactions also would deserve more attention, such as i) the sources of noise generated by typically terrestrial human activities that are likely to propagate in the sea (e.g. by railway tracks or airports and heliport installations near the sea; see [START_REF] Urick | Noise Signature of an Aircraft in Level Flight over a Hydrophone in the Sea[END_REF] and [START_REF] Erbe | Underwater noise from airplanes: An overlooked source of ocean noise[END_REF] for non-Mediterranean examples), and ii) the potential of climate change (which is going to modify the physical properties of marine waters) to increase the ambient noise levels in the future [START_REF] Hester | Unanticipated consequences of ocean acidification: A noisier ocean at lower pH[END_REF]; 7) finally, more effort should be dedicated to improve regulations that, in the Mediterranean region, are limited to the obligation of Mediterranean EU countries to monitor the MNP in the framework of the MSFD and to swiftly enforce the limitations or use of silent engines in a few marine protected areas.

Even though gaps of information are still relevant, some measures aimed at mitigating if not locally eradicating MNP have already been proposed [START_REF] Würsig | Development of an air bubble curtain to reduce underwater noise of percussive piling[END_REF][START_REF] Dähne | Effects of pile-driving on harbour porpoises ( Phocoena phocoena ) at the first offshore wind farm in Germany[END_REF]. As for other sources of pollution (e.g. plastic or chemical compounds), preventing the noise to be transmitted through the aquatic medium is a difficult task (conventional methods for physically reducing noise pollution on land, like noise barriers, can hardly work at sea).

MNP can sometimes be mitigated, however, by reducing it at the source (see [START_REF] Merchant | Underwater noise abatement: Economic factors and policy options[END_REF].

Vessel circulation can be locally banned or re-routed away from sensitive sites and ecosystems, vessel numbers and/or speed can be reduced, e.g. within or in some parts of marine protected areas [START_REF] Buscaino | Temporal patterns in the soundscape of the shallow waters of a Mediterranean marine protected area[END_REF]. Also, more silent motors, generators, hulls and propellers could be developed, combining such technical solutions with specific educational programs and laws implementing speed limits. Especially for acute MNP (e.g. construction works), bubble curtains have been used to effectively limit noise propagation (see e.g. [START_REF] Würsig | Development of an air bubble curtain to reduce underwater noise of percussive piling[END_REF]. Even though evidence is limited and research is still in its infancy, recent studies report that some marine vegetation could contribute to reducing MNP [START_REF] Wilson | Seagrass meadows provide an acoustic refuge for estuarine fish[END_REF][START_REF] Johnson | Low frequency acoustic properties of Posidonia oceanica seagrass leaf blades[END_REF]. Finally, resource prospection methods could be switched to more silent ones (e.g. marine vibroseis to replace noisy air guns; [START_REF] Smith | Acquiring and processing marine vibrator data in the transition zone[END_REF].

In conclusion, taking into account i) that the interest in the economic potential of the oceans is escalating [START_REF] Bennett | Towards a sustainable and equitable blue economy[END_REF][START_REF] Jouffray | The Blue Acceleration: The Trajectory of Human Expansion into the Ocean[END_REF], ii) that many human activities at sea causing significant MNP as a by-product (e.g. maritime traffic) keep increasing [START_REF] Sardain | Global forecasts of shipping traffic and biological invasions to 2050[END_REF] and iii) that the Mediterranean Sea is densely populated and is a crucial crossroad for many maritime routes, there is no reason to expect that MNP will decrease in the next future, unless innovative technical solutions, specific rules/laws and/or good practices are systematically adopted. It is, therefore, imperative that effective measures are fairly rapidly adopted, hopefully based on a clear internationally-based/shared legislation. This goes along with an enhancement of ecological awareness via education programs, in order to address the problem of MNP at the Mediterranean scale and mitigate its effects on marine life, from individual marine organisms to whole ecosystems.

Figure 1 :

 1 Figure 1: Map representing the main routes of maritime traffic in the Mediterranean Sea and the distribution of field studies (blue dots) (data from MarineTraffic -Global Ship Tracking Intelligence; www.marinetraffic.com).

Figure 2 :

 2 Figure 2: Summary schemes of the studies considered in this review. A) Temporal trend of published studies on the impact of noise pollution on Mediterranean fishes and invertebrates ; B) Type of noise; C) Source of noise pollution; D) Taxonomic group investigated; E) Experimental conditions; F) Category of variable considered.

Table 1 :

 1 Response variables assessed for fish studies

			Response variable
	Noise type	Species	Behavior	Physiology	Reference

Acknowledgements:

This work has been partially supported by MarineTraffic (MarineTraffic -Global Ship Tracking Intelligence www.marinetraffic.com)

This work has been supported by the French government, through the UCA JEDI Investments in the Future project managed by the National Research Agency (ANR) with the reference number ANR-15-IDEX-01. It was carried out in the framework of the "Nautilus Project", supported by the Academy of Excellence 3 ("Space, Environment, Risk and Resilience").

Acute

Alosa alosa

Swimming


Valentina Costa
email: vale.costa@gmail.com

Antonio Mazzola

Salvatrice Francesca Rossi

Salvatrice Vizzini

Decomposition rate

Keywords: seagrass detritus, litterbag, benthic invertebrate, carbon, nitrogen. Highlights

come

Introduction

Seagrass meadows are ecologically important because of their high primary productivity, provision of habitat and supporting of high biodiversity levels [START_REF] Hemminga | Seagrass ecology[END_REF]. Seagrasses with mangroves and saltmarshes, trap and sequester carbon, that in the last years has been referred as 'Blue Carbon' [START_REF] Nellemann | Blue carbon: the role of healthy oceans in binding carbon: a rapid response assessment[END_REF]. The estimates of organic carbon (C org ) sequestered in seagrass meadows, have recognized them as global hotspots in the Blue Carbon global balance [START_REF] Fourqurean | Seagrass ecosystems as a globally significant carbon stock[END_REF]). In the Mediterranean Sea, the endemic species Posidonia oceanica (L.) Delile covers only 1-2% of the seabed (25,000-50,000 km 2 , [START_REF] Pasqualini | Mapping of Posidonia oceanica using aerial photographs and side scan sonar: application off the island of Corsica (France)[END_REF], but produces up to 3,499 million tons of carbon annually [START_REF] Pergent | Fate of primary production in Posidonia oceanica meadows of the Mediterranean[END_REF]) and represents the largest recognized polls of C org stored in living seagrass [START_REF] Fourqurean | Seagrass ecosystems as a globally significant carbon stock[END_REF]. In seagrass meadows, the grazing pathway is highly variable, depending on the study site and time of sampling, with a range between ∼3% and 100% of net primary production directly consumed by herbivores (Heck & Valentine 2006 and reference herein). The amount of primary production not directly used becomes litter, which can enter the brown food web or be buried into the sediment [START_REF] Cebrián | Detrital stocks and dynamics of the seagrass Posidonia oceanica (L.) Delile in the Spanish Mediterranean[END_REF][START_REF] Boudouresque | The necromass of the Posidonia oceanica seagrass meadow: fate, role, ecosystem services and vulnerability[END_REF]. Therefore, seagrasses act as a significant source of C org also beyond the area directly occupied by the meadows, through the detrital biomass. [START_REF] Duarte | Export from Seagrass Meadows Contributes to Marine Carbon Sequestration[END_REF] pointed out as the potential sequestration of seagrass carbon exported beyond the meadows may approach 30% of the carbon sequestered within meadows. Detritus act as faunal magnets [START_REF] Duggins | Islands in the stream: kelp detritus as faunal magnets[END_REF][START_REF] Remy | Effects of an experimental resource pulse on the macrofaunal assemblage inhabiting seagrass macrophytodetritus[END_REF], attracting fungi and bacteria, but also benthic invertebrates that use them as food and shelter [START_REF] Heck | Trophic Transfers from Seagrass Meadows Subsidize Diverse Marine and Terrestrial Consumers[END_REF][START_REF] Remy | Seagrass organic matter transfer in Posidonia oceanica macrophytodetritus accumulations[END_REF]. Detritus undergoes decomposition and recycling that allows it to be channeled to higher trophic levels [START_REF] Michel | Dominant amphipods of Posidonia oceanica seagrass meadows display considerable trophic diversity[END_REF]. The pathway undertaken by detrital leaves is a crucial component of the flow of energy and matter regulated by seagrass meadows [START_REF] Romero | Nutrient dynamics in seagrass ecosystems[END_REF].

Despite the recognition of the importance of the detritus, a real estimate of the contribution of this compartment to the Blue carbon global balance is unknown.

Biotic and abiotic variables regulate seagrass decomposition rate (e.g. [START_REF] Enríquez | Patterns in decomposition rates among photosynthetic organisms: the importance of detritus C:N:P content[END_REF][START_REF] Mateo | Evaluating seagrass leaf litter decomposition: an experimental comparison between litter-bag and oxygen-uptake methods[END_REF]. Litter quality, such as carbon and nitrogen concentration, influence its decomposition and palatability for consumers [START_REF] Enríquez | Patterns in decomposition rates among photosynthetic organisms: the importance of detritus C:N:P content[END_REF][START_REF] Apostolaki | Fish farming impact on decomposition of Posidonia oceanica litter[END_REF]. Abiotic conditions are known to affect decomposition both directly, by influencing rates of biological reactions, and indirectly by modifying leaf quality and/or consumer communities [START_REF] Nicastro | Direct and indirect effects of tidal elevation on eelgrass decomposition. Mar Ecol Prog Ser Norkko A, Bonsdorff E[END_REF]). Among physical variables, the reduced hydrodynamics typical of coastal basins may decrease the mechanical action on the detritus, slowing down the decomposition process, while the increase in nutrients and rise in temperature may stimulate and facilitate the activity of heterotrophic bacteria [START_REF] Mateo | Evaluating seagrass leaf litter decomposition: an experimental comparison between litter-bag and oxygen-uptake methods[END_REF][START_REF] Lopez | The effect of nutrient additions on bacterial activity in seagrass (Posidonia oceanica) sediments[END_REF]), accelerating the decomposition, but with probably inverse effects at high temperature [START_REF] Pedersen | Temperature effects on decomposition of a Posidonia oceanica mat[END_REF]. Moreover, the high environmental variability of coastal basins, in terms of daily and seasonal variation [START_REF] Kjerfve | Coastal lagoon processes[END_REF], can affect invertebrate community composition. Evolution selects a small number of taxa capable of tolerating this stressful condition, lowering community diversity while abundance and biomass increase [START_REF] Arias | Structure and production of the benthic macroinvertebrate community in a shallow lagoon in the Bay of Cadiz[END_REF][START_REF] Mistri | Redundancy of macrobenthos from lagoonal habitats in the Adriatic Sea[END_REF], with potential consequences for the ecosystem functions. The role of benthic invertebrates as direct detritus shredders and enhancers of microorganism activity is well recognized [START_REF] Graca | Patterns and processes in detritus-based stream systems[END_REF], despite invertebrate abundance and decomposition rate are not always positively correlated [START_REF] Dye | Inhibition of the decomposition of Zostera capricornii litter by macrobenthos and meiobenthos in a brackish coastal lake system[END_REF], as the macrofauna abundance seem to follow an exponential trend with an upper limit related to the litter quality [START_REF] Fazi | Effects of macro-detritivores density on leaf detritus processing rate: a macrocosm experiment[END_REF]. As the distribution of invertebrates in confined waters, like lagoons and coastal basins, is strongly influenced by water movement [START_REF] Guelorget | Le domaine paralique: expressions géologiques, biologiques et économiques du confinement[END_REF][START_REF] Constable | Ecology of benthic macro-invertebrates in soft-sediment environments: A review of progress towards quantitative models and predictions[END_REF], seagrass decomposition rate and therefore nutrients dynamics may respond in the same way.

In this experimental study, we deliberately added P. oceanica leaf litter across a gradient of hydrodynamics in a Mediterranean semi-enclosed coastal basin and simultaneously followed the decomposition process, the nutrient dynamics and the colonisation by benthic invertebrates. The specific objectives of the research were (1) to test the null hypothesis of no significant differences of seagrass decomposition and invertebrates colonization across a hydrodynamic gradient; (2) to analyse organic carbon and nitrogen dynamics during seagrass decomposition.

Methods

Study sites and experimental set-up

The study was conducted in the Stagnone di Marsala, a semi-enclosed coastal basin (surface of 20 km 2 ; average depth of 1 m) in western Sicily (Italy) (Fig. 1). The basin is connected to the Mediterranean Sea by a northern and a southern opening, the former narrower and shallower (400 m wide, 0.3-0.4 m deep) than the latter (1200 m wide, 1.0-1.5 m deep). The sandy-muddy sediments are colonised by the seagrass Cymodocea nodosa (Ucria) Ascherson. P. oceanica patches are present in the central part of the basin and a natural P. oceanica reef emerges in the southern region [START_REF] Tomasello | Seagrass meadows at the extreme of environmental tolerance: the case of Posidonia oceanica in a semi-enclosed coastal lagoon[END_REF], creating two geomorphologically different sub-basins. The entire area is oligotrophic [START_REF] Sarà | Spatial and temporal changes of suspended matter in relation to wind and vegetation cover in a Mediterranean shallow coastal environment[END_REF]). Three sites were chosen according to their hydrodynamic regime with the same depth (0.8 m), vegetation coverage (C. nodosa with P. oceanica patches) and sediment grain-size (sand 80-90%, silt/clay 5-15%, gravel 0-5%): Site 1 (N37° 52.284' E12° 27.517') in the central-northern basin, Site 2 (N37° 50.453' E12° 27.198') in the southern basin and Site 3 (N37° 51.613' E12° 26.339') outside the basin (Fig. 1). The exposure level to the open sea in the three sites was obtained from the Intertidal Dispersion Coefficient (IDC, La Loggia et al., 2004). The IDC (m 2 s -1

) is a useful tool for characterising the dispersion of a point in the water body, integrating data of, among others, water current velocity, wind shear stress and fetches: when the IDC is high, water exchange is strong (hence residence time is short) [START_REF] Cheng | Dispersion in tidally averaged transport equation[END_REF]. A clear difference was shown between the central-northern and the southern sub-basins (Fig. 1), with the latter showing higher IDC values (about 23.8 m 2 s -1

) than the former (about 11.2 m 2 s -1

) [START_REF] Loggia G La | Influence of hydrodynamic conditions on the production and fate of Posidonia oceanica in a semi-enclosed shallow basin (Stagnone di Marsala, Western Sicily)[END_REF]). Since the selected sites were located along a well-documented gradient within the basin, we used the factor Site as a proxy of the hydrodynamic condition of the area.

Seagrass leaves were collected close to P. oceanica patches within the Stagnone di Marsala in May 2010.

Adult leaves naturally detached from the plants (due to ageing or mechanical action) were cut into 10 cmlong fragments and only the central section was used, to minimise heterogeneity in thickness and toughness [START_REF] Mancinelli | To bite, or not to bite? A quantitative comparison of foraging strategies among three brackish crustaceans feeding on leaf litters[END_REF]. Aliquots of leaf fragments were dried at 60°C to constant weight, weighed (3.000 ± 0.001 g initial dry mass) and enclosed in 1 mm mesh litterbags (10x10 cm). The mesh size of the litterbags was chosen to reduce the amount of detritus lost from mechanical fragmentation but not limiting macroinvertebrates colonization [START_REF] Walker | Seagrass decomposition[END_REF]. Twenty-four litterbags were added to each site and tethered to steel rods anchored to the bottom.

Sampling and laboratory procedures

The litterbags were deployed on June 11 th 2010. After 6 hours, three bags per site (time 0) were collected.

Remaining bags were collected in triplicate at each site after 3, 7, 14, 47, 101, 152 and 221 days. Each bag was carefully enclosed underwater in a plastic bag and preserved in a cooler for transportation to the laboratory. At each sampling time, temperature (resolution: ±0.01°C), salinity (±0.01) anddissolved oxygen concentration (DO, ±0.01 mg l -1

) were measured in the seawater column above the litterbags in triplicate with a HYDROLAB DS5 multiparametric probe.

In the laboratory, litterbags were gently washed and invertebrates inside the litterbags were carefully removed. P. oceanica leaf fragments from each bag were dried (60°C, 72 h) and weighed (Dry Mass, DMDM, ± 0.001 g). Subsamples were grounded and analysed for organic carbon (C%) and nitrogen (N%) concentration using a Flash EA 1112 Thermo-Electron analyser.

Invertebrates were counted and identified at species level. Organisms were dried (60°C, 72 h) and weighed (DM). List of all species identified was included in Table 1.

Data elaboration and statistical analysis

Differences in the mass loss, seagrass leaf litter variables (%C, %N and C:N ratio) and density and biomass for each invertebrate group between sites during the experiment were tested via a one-way repeatedmeasures ANOVA (RM-ANOVA): Site (3 levels) was the between-subject factor and Time (i.e. sampling events) the repeated-measures (within-subject) factor.

Decomposition rate was estimated as the loss of dry mass during time and fitted to the exponential curve [START_REF] Petersen | Leaf processing in a woodland stream[END_REF]:

W t = W 0 * e -kt
, where W t is the dry mass (g) remaining at time t (days), W 0 is the initial dry mass, and k is the decomposition constant (day -1

). We used one-way ANOVA with Site (3 levels) as categorical factor to assess the statistical significance of the effect of Site (3 levels, t=221 days) on decomposition rate.

Prior to ANOVAs, all data were checked for normality and homoscedasticity. In the event of significant effects on the factors investigated, post-hoc comparisons were performed using Tukey's Honest Significant Difference [START_REF] Zar | Biostatistical analysis[END_REF]. Univariate statistical analysis were performed with R version 3.5.1.

Differences in density and biomass of invertebrates species during the experiment were investigated at a multivariate level, through analysis of variance based on permutations (PERMANOVA, [START_REF] Anderson | PERMANOVA: a FORTRAN computer program for permutational multivariate analysis of variance[END_REF], using a two-way model with factors Site (3 levels, fixed) and Time (8 levels, random). Data were square-root transformed to build a matrix of Bray-Curtis similarity coefficients. When the number of random permutations in the PERMANOVA analysis was not sufficient to allow a reasonable permutation test, the p-value was obtained using a Monte Carlo random sample from the asymptotic permutation distribution [START_REF] Anderson | PERMANOVA: a FORTRAN computer program for permutational multivariate analysis of variance[END_REF].

The similarity percentage routine (SIMPER) was used to highlight which invertebrate species provided the largest contribution to dissimilarities between groups [START_REF] Clarke | Change in marine communities: an approach to statistical analysis and interpretation[END_REF]. Multivariate analyses were performed with PRIMER v6 software [START_REF] Clarke | Change in marine communities: an approach to statistical analysis and interpretation[END_REF].

Results

Seawater column variables

Seawater parameters were measured in the water column during the experiment. Temperature showed a clear seasonal trend with a range of 13.3-27.9°C and with average higher values at Site 1 than at Site 2 and Site 3 (23.4±4.9, 22.8±4.5 and 22.1±4.1°C, respectively). Salinity ranged from 38.0 to 48.0, with higher values at Site 1 (overall mean: 44.8±4.0) than at Sites 2 and 3 (40.4±1.4 and 39.2±0.7, respectively).

Dissolved oxygen concentration (DO) ranged from 5.5 to 8.9 mg l -1 with the same average value in the three sites 7.3±0.9 mg l -1

.

Seagrass leaf litter decomposition was significantly affected by the factor Site (RM-ANOVA, F 2,14 =4.03, p<0.05). A rapid mass loss of P. oceanica leaf litter was observed at the first sampling date (0 days), with an overall mean remaining weight of 2.3 ± 0.1 g (mean ± s.d.) and no differences between sites (Tukey test, p>0.05). More than 60 and 70% of leaf mass loss occurred after 221 d in Sites 2 and 3 respectively, compared with a loss of only 40% in Site 1 (Fig. 2).

Overall, the decomposition process followed an exponential decay, with decomposition rate coefficients (k 221 ) significantly higher in Sites 2 (0.0030 ± 0.0004 day -1 , r 2 of the exponential regression line = 0.90) and 3 (0.0044 ± 0.0003 day -1

, r 2 = 0.96) than in Site 1 (0.0011 ± 0.0003 day -1

, r 2 = 0.60) (ANOVA, F 2,6 =76.34, p<0.001; Tukey test, p<0.01). No differences were observed between Sites 2 and 3.

Seagrass leaf litter features

Changes in nutrient concentrations (%C, %N and C:N ratio) were observed in seagrass leaf litter during the experiment (Fig. 3). Despite the hydrodynamic condition did not affect C concentration of the detritus during the decomposition (RM-ANOVA, F 2,14 =1.89, p>0.05), the overall initial C concentration (average 38.2%) decreased slightly, and at day 221 a lower C concentration was recorded at Site 3 (33.2 ± 0.3%) than at Sites 1 and 2 (37.1 ± 0.7 and 35.0 ± 1.1%, respectively) (Fig. 3; Tukey test, p<0.01). N concentration showed a very narrow range of variation from 0.8±0.1% (Site 1, 101 days) to 1.3±0.2% (Site 2, 152 days) with no significant differences between sites during the experiment (RM-ANOVA, F 2,14 =3.48, p>0.05). C:N ratio ranged from 29.1 ± 5.1 (Site 2, 152 days) to 49.0 ± 4.0 (Site 1, 101 days) with significant differences between sites during the experiment (RM-ANOVA, F 2,14 =5.24, p<0.05). At the beginning of the experiment C:N ratio averaged 35.5 while at the end higher values were recorded at Site 1 than at Sites 2 and 3 (39.2 ± 1.8, 32.8 ± 1.9 and 32.1 ± 2.7, respectively) (Fig. 3; Tukey test, p<0.05).

Invertebrate densities and biomass

A total of 1964 individuals (379, 948 and 637 respectively at Site 1, 2 and 3) belonging to 3 Phyla were recovered and identified: the Arthropoda was the phylum with the highest number of taxa (46 crustacean species grouped in 3 orders, 40 species of Amphipoda, 4 species of Isopoda and 2 species of Tanaidacea), followed by Mollusca (8 species grouped in 2 classes, 1 species of Bivalvia and 7 species of Gastropoda)

and Anellida (2 species belonging to Polychaeta class) (Tab. 1).

Density and biomass of the entire invertebrate community were significantly affected by the interaction Site x Time (PERMANOVA, Tab. 2). Pairwise tests for the term Site x Time for Site factor showed significant differences from 47 to 152 days, with Site 1 showing significantly lower values than the others (P(MC) <0.05). In general, the average dissimilarity, in terms of density and biomass data, was always higher between Site 1 and the others than between Sites 2 and 3 (SIMPER; Tab. 3). The invertebrate groups mostly responsible for differences between sites belong to the Arthropoda for both density and biomass data: the amphipod Gammarus aequicauda (Martynov, 1931) contributes always for more than 10% and 7% to this dissimilarity, respectively for density and biomass data, followed by the tanaidacean Chondrochelia savignyi Linnaeus, 1758)], respectively at Sites 2 and 3 (Fig. 4). Total density ranged from 0.1 ± 0.2 to 13.4 ± 6.3 (Site 1, 0 and 101 days), from 0.0 to 77.8 ± 27.9 (Site 2, 0 and 101 days) and from 0.0 to 49.8 ± 18.5 (Site 3, 0 and 152 days) individuals g -1 DM of seagrass detritus (Fig. 4). Total biomass ranged from 0.2 ± 0.3 to 4.7 ± 0.9, from 0.0 to 30.7 ± 33.7 and from 0.0 to 22.4 ± 15.2 mg g -1 DM respectively at Site 1, 2 and 3 (0 and 221 days) (Fig. 5). Univariate analysis showed that the density of organisms changed during the experiment, with significant differences between sites only for the Amphipoda group (RM-ANOVA, F 2,14 =3.97, p<0.05) (Fig. 4), while no significant differences in biomass data were reported (RM-ANOVA, p>0.05) (Fig. 5).

(
The invertebrate community was dominated by the Arthropoda both in terms of density (up to 106 ind. g

Discussion

Seagrass leaf litter decomposition and nutrient dynamics

Seagrass meadows are recognized as some of the most productive of the Earth's ecosystems [START_REF] Fourqurean | Seagrass ecosystems as a globally significant carbon stock[END_REF]), but most of the primary production is exploited only through detrital routes [START_REF] Cebrián | Detrital stocks and dynamics of the seagrass Posidonia oceanica (L.) Delile in the Spanish Mediterranean[END_REF]. Accordingly, in the Stagnone di Marsala, the bottom of which is covered by a dense C. nodosa meadow and patchy P. oceanica, there is evidence for the role of seagrass-derived organic matter for consumers through detrital pathways [START_REF] Vizzini | Trophic transfer of trace elements in an isotopically constructed food chain from a semi-enclosed marine coastal area (Stagnone di Marsala, Sicily, Mediterranean)[END_REF].

In this area, leaf litter decomposition rates (from 0.001 to 0.004 day -1

) were in the range reported for seagrasses (from 0.001 to 0.110 day -1

; [START_REF] Harrison | Detrital processing in seagrass systems: A review of factors affecting decay rates, remineralization and detritivory[END_REF], despite the decomposition rate recorded for the central part of the Stagnone was lower than previously observed values for P. oceanica (from 0.003 to 0.017 day -1

; [START_REF] Romero | The Detritic Compartment in a Posidonia oceanica Meadow: Litter Features, Decomposition Rates, and Mineral Stocks[END_REF][START_REF] Mateo | Evaluating seagrass leaf litter decomposition: an experimental comparison between litter-bag and oxygen-uptake methods[END_REF][START_REF] Cebrián | Magnitude and fate of the production of four cooccurring Western Mediterranean seagrass species[END_REF]). The high variability of seagrass decomposition rates reported in the literature may be ascribed to the different experimental conditions in decomposition studies. As summarised by [START_REF] Harrison | Detrital processing in seagrass systems: A review of factors affecting decay rates, remineralization and detritivory[END_REF], the length of the study (from days to years), the use of different types of detritus (fresh or dried leaves), leaf age (green leaves lose mass faster than old ones) and also the mesh size (smaller mesh reduce the amount of particles lost but affect colonization) are among the conditions that may affect the decay rates. Leaf litter decomposition rates in this study exhibited a high spatial heterogeneity that was not imputable to the experimental conditions (i.e. type of detritus, leaf age), which were homogeneous at the beginning of the experiment. The P. oceanica decomposition rate was 2x and 4x higher respectively in the southern and in the external sites than in the central-northern site.

Despite, the low decomposition rate in the Site 1 could be ascribed to different experimental conditions compared to other studies, this result highlights a clear spatial pattern in the decomposition dynamics within the basin.

Based on C and N concentration in seagrass leaf litter, loss of organic nutrients from the detritus on a daily basis was calculated as the total mass x nutrient concentration at the beginning of the experiment minus that at the end divided by the number of experimental days [START_REF] Wardle | Linkages between plant litter decomposition, litter quality, and vegetation responses to herbivores[END_REF]). Carbon release rates were 0.09 ± 0.01, 0.21 ± 0.01 and 0.26 ± 0.01 mgC g -1 d -1 in Sites 1, 2 and 3 respectively, showing the same spatial pattern as for litter decomposition rates, with a higher loss outside the basin than in the internal sites. In contrast, nitrogen released by seagrass detritus was constant at all sites (0.01 ± 0.00 mgN g -1 d -1

).

Leaf detritus is a source of nutrients which return in soluble forms through decomposition [START_REF] Harrison | Detrital processing in seagrass systems: A review of factors affecting decay rates, remineralization and detritivory[END_REF][START_REF] Romero | Nutrient dynamics in seagrass ecosystems[END_REF]), but the dynamics of carbon and nitrogen regeneration during the decay process is rather complex and, as suggested in the literature, there is no common pattern to nutrient loss (see references in [START_REF] Romero | Nutrient dynamics in seagrass ecosystems[END_REF], highlighting the uncoupling between nutrient release and the negative exponential trend of mass loss [START_REF] Petersen | Leaf processing in a woodland stream[END_REF]. As summarised in [START_REF] Romero | Nutrient dynamics in seagrass ecosystems[END_REF], during the first phase of decomposition (leaching), the labile components release nutrients that can be assimilated by microbes colonising the detritus; when all the labile substrates are processed, nutrients from the dead leaf tissues are released in inorganic and/or organic forms (which can be assimilated again by microbes) by means of bacteria exoenzyme attack; during the last phase of decomposition, the refractory portion decomposes very slowly, releasing only nitrogen, while most of the carbon remains [START_REF] Kristensen | Decomposition of macroalgae, vascular plants and sediment detritus in seawater: Use of stepwise thermogravimetry[END_REF].

These expected dynamics of nutrients were partially matched in our study: the initial phase of labile nutrient release was probably bypassed by the pre-drying treatment of leaf litter as organic molecules become less easily degraded [START_REF] Harrison | Detrital processing in seagrass systems: A review of factors affecting decay rates, remineralization and detritivory[END_REF];the slow release of C (from ~38% to ~33%) was coupled with the stable condition reported for the N concentration (from ~1.3% to ~0.8%), with the decrease of C related to the decomposition of mobilizable carbohydrates, and the stable N values probably related to the accumulation of microbial biomass that can be responsible for a high portion (75-100%) of the total nitrogen content in decaying litter [START_REF] Newell | Established and potential impacts of eukaryotic mycelial decomposers in marine/terrestrial ecotones[END_REF]. In addition, the slower loss of organic matter was previously reported for dead leaves (used in this study) compared to fresh material [START_REF] Harrison | Detritus formation from eelgrass (Zostera marina L.): The relative effects of fragmentation, leaching, and decay[END_REF] This dynamic of nutrient release also explains the fact that the C:N ratio of detritus was remarkably high, exhibiting a wide range of variation from ~30 to ~50, but was within the range reported for seagrass detritus (14-75; [START_REF] Enríquez | Patterns in decomposition rates among photosynthetic organisms: the importance of detritus C:N:P content[END_REF]. Moreover, the higher C:N reported for the internal site during the experiment indicates that seagrass detritus here becomes more recalcitrant to decomposition [START_REF] Pirc | Seasonal Changes in Nitrogen, Free Amino Acids, and C/N Ratio in Mediterranean Seagrasses[END_REF] and more refractory to digestion by consumers than in the other sites. Accordingly, the seagrass-derived organic matter largely contributes to the sedimentary organic matter pool in the central part of the Stagnone di Marsala, as shown by stable isotope data [START_REF] Vizzini | Trophic transfer of trace elements in an isotopically constructed food chain from a semi-enclosed marine coastal area (Stagnone di Marsala, Sicily, Mediterranean)[END_REF], pinpointing the role of the basin as a sink of organic carbon.

Role of invertebrate community in seagrass leaf litter decomposition

Leaf litter, as a particular benthic substrate, provides food to invertebrates and refuge from predators, channelling marine macrophyte production to higher trophic levels through the detritus-based food web [START_REF] Lepoint | Food sources of two detritivore amphipods associated with the seagrass Posidonia oceanica leaf litter[END_REF]. Most of the invertebrates living in P. oceanica detritus belong to the typical community found in the meadows [START_REF] Gambi | Depth and Seasonal Distribution of Some Groups of the Vagile Fauna of the Posidonia oceanica Leaf Stratum: Structural and Trophic Analyses[END_REF][START_REF] Sánchez-Jerez | Comparison of the epifauna spatial distribution in Posidonia oceanica, Cymodocea nodosa and unvegetated bottoms: Importance of meadow edges[END_REF], despite the fact that some species show specific adaptations to the detritus habitat (e.g. different body colouration for the isopod Idotea sp. and the shrimp Hyppolyte inermis, [START_REF] Gallmetzer | Macrofauna diversity in Posidonia oceanica detritus: distribution and diversity of mobile macrofauna in shallow sublittoral accumulations of Posidonia oceanica detritus[END_REF].

Despite the limitation due to the mesh size of the litterbags, colonization of the detritus by invertebrates is generally a rapid process (Norkko & Bonsdorff 1996), as also shown in our study (overall colonization started after three days), with the dominance of motile taxa (e.g. amphipods, isopods and tanaidaceans). During the experiment, Amphipoda and Isopoda were responsible for among-site differences in the invertebrate assemblages both in terms of density and biomass. The dominance of crustaceans in detritus accumulation is well-documented [START_REF] Gallmetzer | Macrofauna diversity in Posidonia oceanica detritus: distribution and diversity of mobile macrofauna in shallow sublittoral accumulations of Posidonia oceanica detritus[END_REF], with amphipods and isopods being the main constituents of the crustacean community of P. oceanica detritus [START_REF] Wittmann | Some laboratory experiments on the activity of the macrofauna in the fragmentation of detrital leaves of Posidonia oceanica (L.) Delile[END_REF][START_REF] Remy | Seagrass organic matter transfer in Posidonia oceanica macrophytodetritus accumulations[END_REF]. Crustaceans, and in particular amphipods and isopods, are an abundant, widely distributed and ecologically important component of benthic communities, exhibiting a high degree of niche specificity [START_REF] Mancinelli | The Influence of Allochthonous Leaf Detritus on the Occurrence of Crustacean Detritivores in the Soft-bottom Macrobenthos of the Po River Delta Area (northwestern Adriatic Sea)[END_REF], De-La-Ossa-Carretero et al. 2012). In our study, G. aequicauda was responsible for among-site differences in the macrofaunal assemblages both in term of densities and biomass. Within the amphipods, the Gammarus genus is a highly opportunistic feeder group (defined as a facultative shredder by [START_REF] Cummins | Sensitivity of amphipods to sewage pollution[END_REF], but with a certain degree of selectivity probably related to environmental characteristics [START_REF] Friberg | Feeding plasticity of two detritivore-shredders[END_REF][START_REF] Mancinelli | The Influence of Allochthonous Leaf Detritus on the Occurrence of Crustacean Detritivores in the Soft-bottom Macrobenthos of the Po River Delta Area (northwestern Adriatic Sea)[END_REF]. Based on stable isotope and/or gut content analysis, some species were reported to directly feed on P. oceanica leaf litter within these species the amphipods G. aequicauda and Gammarella fucicola [START_REF] Remy | Seagrass organic matter transfer in Posidonia oceanica macrophytodetritus accumulations[END_REF]), but also isopods of the genera Idotea and Cleantis [START_REF] Lepoint | Food sources of two detritivore amphipods associated with the seagrass Posidonia oceanica leaf litter[END_REF][START_REF] Sturaro | Trophic diversity of idoteids (Crustacea, Isopoda) inhabiting the Posidonia oceanica litter[END_REF]) and some echinoderms as the holothurian Holothuria tubulosa Gmelin [START_REF] Costa | Holothuria tubulosa Gmelin 1791 (Holothuroidea, Echinodermata) enhances organic matter recycling in Posidonia oceanica meadows[END_REF]. In particular, G. aequicauda relied up to 80% of its diet on P. oceanica leaf detritus [START_REF] Michel | Dominant amphipods of Posidonia oceanica seagrass meadows display considerable trophic diversity[END_REF][START_REF] Remy | Seagrass organic matter transfer in Posidonia oceanica macrophytodetritus accumulations[END_REF], highlighting the crucial role of this species not only during the fragmentation process but also in the transfer of seagrass detritus organic matter in the food chain.

Low density and biomass of the invertebrate community were recorded in the central part of the Stagnone di Marsala, where carbon released by detritus was lower, seagrass detritus more recalcitrant (high C:N ratios)

and resistant to degradation [START_REF] Enríquez | Patterns in decomposition rates among photosynthetic organisms: the importance of detritus C:N:P content[END_REF]) and, hence, the decomposition rate was reduced. The central part of the Stagnone is characterised by reduced hydrodynamic condition [START_REF] Loggia G La | Influence of hydrodynamic conditions on the production and fate of Posidonia oceanica in a semi-enclosed shallow basin (Stagnone di Marsala, Western Sicily)[END_REF]), which may influence seagrass decomposition both directly and indirectly. Hydrodynamic is known to contribute to detritus fragmentation through direct mechanical action on seagrass leaves, increasing the surface available for microbial colonization [START_REF] Mateo | Detritus dynamics in the seagrass Posidonia oceanica: elements for an ecosystem carbon and nutrient budget[END_REF][START_REF] Romero | Nutrient dynamics in seagrass ecosystems[END_REF]. Moreover, reduced hydrodynamic could act not only limiting the loss of fine particles through the litterbag but also reducing the aeration of the litter through water movement in very shallow basins is also responsible for wide variability in seawater variables which, in combination with the poor nutritional value of detritus, may have limited invertebrate (but also microbial) colonization and slowed down the decomposition process.

Conclusions

Seagrass decomposition rate varied at a small spatial scale in a semi-enclosed coastal basin, resulting faster in the sites that are more exposed to the open-sea than in the internal part of the Stagnone di Marsala. The Stagnone seems to act as a sink of organic matter wherein the slow recycling process enhances the accumulation of refractory materials. Moreover, the peculiar environmental characteristics of the internal site constrain invertebrate abundance and the more recalcitrant and refractory condition of the detritus results in slower decomposition. Consequently, low decomposition rates of seagrass leaves in internal sites characterised by low hydrodynamic forces may promote organic matter burial and carbon stocks, emphasising the role of coastal basins such as ponds and lagoons as blue carbon areas [START_REF] Nellemann | Blue carbon: the role of healthy oceans in binding carbon: a rapid response assessment[END_REF]). , 3, 7, 14, 47, 101, 152, 221 days in the three sites. Exponential decay fitting lines were reported as black dotted (Site 1), grey dotted (Site 2) and black full (Site 3) lines.

  biomass (up to 65 mg g -1 DM): Amphipoda density and biomass increased gradually reaching the maximum at the end of the experiment at Site 2 (Figs.4, 5); Isopoda showed the highest density at 101 days at Site 2, while Tanaidacea showed the highest density and biomass at 101 days at Site 3 (Fig.4, 5). Density for Anellida was always below 8 ind. g -1 DM, with the highest values of density and biomass at Site 3 at the end of the experiment (Fig.4, 5). Mollusca Bivalvia showed no changes during the experiment in terms of density and biomass, while Gastropoda density showed high values at 101 days and the highest biomass at the end of the experiment at Site 3 (Fig.4, 5).

Figure captions Figure 1 .

 captions1 Figure captions

Figure 2 .

 2 Figure2. Dry mass (g) of P. oceanica leaf detritus remaining in the litterbags after0, 3, 7, 14, 47, 101, 152,

Figure 3 .

 3 Figure 3. Mean (±s.d.) C%, N% and C:N of P. oceanica leaf detritus remaining in the litterbags after 0, 3, 7, 14, 47, 101, 152, 221 days in the three sites.

Figure 4 .

 4 Figure 4. Total density (ind. g -1 DM of detritus, mean±s.d.) and mean density (ind. g -1 DM) of each invertebrate group (A, Anellida Polychaeta; B, Arthropoda Amphipoda; C, Arthropoda Isopoda; D, ArthropodaTanaidacea; E, Mollusca Bivalvia; F, Mollusca Gastropoda) found in the litterbags during the experiment in the three sites.

Figure 5 .

 5 Figure 5. Total biomass (mg g -1 DM of detritus, mean±s.d.) and mean biomass (mg g -1 DM) of each invertebrate group (A, Anellida Polychaeta; B, Arthropoda Amphipoda; C, Arthropoda Isopoda; D, ArthropodaTanaidacea; E, Mollusca Bivalvia; F, Mollusca Gastropoda) found in the litterbags during the experiment in the three sites.

Fig. 4

 4 Fig. 4

  Fig. 5 514

  Krøyer, 1842), and the caprellid Caprella acanthifera(Leach, 1814) for density data and the isopod Cymodoce truncate (Leach, 1814), the polychaetes Nereis sp. and the amphipod Lysianassa caesarea for biomass data. (Tab. 3). Other species generally contributed less than 8% to the average dissimilarity between sites (Tab. 3).Colonization of litterbags started with the Gastropoda Tricolia pullus at Site 1 (day 0), while at 3 days with

Amphipoda [G. aequicauda and Melita palmata (Montagu, 1804)], Isopoda (C. truncate) and Tanaidacea (C. savignyi) and Amphipoda [Aora gracilis (Bate, 1857), C. acanthifera, G. aequicauda, Lysianassa costae (Milne Edwards, 1830), Pseudoprotella phasma (Montagu, 1804)], Tanaidacea (L. savignyi) and Gastropoda [Melarhaphe neritoides (

Table 2 .

 2 PERMANOVA results for the effects of factors Site and Time on density (individuals g

	1	2	3

Table 3 .

 3 Results of the SIMPER analysis on density (ind. g -1 DM) and biomass (mg g -1 DM) data showing the contribution of invertebrate species to dissimilarity between sites during the experiment: AD/SD, ratio of the average dissimilarity to the standard deviation of dissimilarity for the particular species; Contr(%), percentage contribution to the dissimilarity. Cut-off: cumulative percentage 60%.

	Density (ind. g	-1 DM)			Biomass (ind. g	-1 DM)
		Average				Average
	Species	Dissimilarity	AD/SD Contr(%)	Species	Dissimilarity	AD/SD Contr(%)
	Site 1 vs 2	65.59			Site 1 vs 2	74.39
	Gammarus aequicauda			0.91	13.29	Gammarus aequicauda	0.69	9.12
	Chondrochelia savignyi			1.04	9.2	Cymodoce truncata	0.57	7.34
	Joeropsis brevicornis			0.93	8.15	Lysianassa caesarea	0.7	7.31
	Gnathia phallonajopsis			0.63	7.97	Nereis sp.	0.82	6.79
	Tricolia pullus			0.22	6.93	Tricolia pullus	0.22	6.11
	Caprella acanthifera			0.64	6.92	Chondrochelia savignyi	0.63	5.75
	Maera sodalis			0.74	5.51	Caprella acanthifera	0.58	5.37
						Gnathia phallonajopsis	0.73	5.26
						Maera sodalis	0.7	5.22
	Site 1 vs 3	63.38			Site 1 vs 3	74.38
	Gammarus aequicauda			0.74	12.19	Gammarus aequicauda	0.63	9.26
	Chondrochelia savignyi			1.29	11.78	Nereis sp.	0.82	8.09
	Tricolia pullus			0.23	7.54	Tricolia pullus	0.25	6.97
	Caprella acanthifera			0.56	7.11	Maera sodalis	0.64	6.56
	Maera sodalis			0.71	5.94	Caprella acanthifera	0.59	5.93
	Nereis sp.			0.85	5.22	Lysianassa costae	0.74	5.39
	Lysianassa costae			0.77	4.72	Quadrimaera inaequipes	0.61	5.17
	Quadrimaera inaequipes			0.64	4.6	Chondrochelia savignyi	0.66	5.08
						Lysianassa caesarea	0.52	4.07
	Site 2 vs 3	54.07			Site 2 vs 3	68.4
	Gammarus aequicauda			1.1	10.43	Gammarus aequicauda	0.89	7.93
	Caprella acanthifera			0.62	8.41	Lysianassa caesarea	0.65	7.32
	Gnathia phallonajopsis			0.69	8.27	Cymodoce truncata	0.57	6.52
	Joeropsis brevicornis			1.02	7.95	Caprella acanthifera	0.63	5.79
	Chondrochelia savignyi			0.95	7.94	Gnathia phallonajopsis	0.73	5.34
	Lysianassa costae			0.73	5.23	Gammarella fucicola	0.7	5.05
	Gammarella fucicola			0.71	4.69	Lysianassa costae	0.68	4.44
	Quadrimaera inaequipes			0.72	4.22	Chondrochelia savignyi	0.62	4.34
						Quadrimaera inaequipes	0.72	4.2
						Elasmopus pocillimanus	0.46	3.65
						Cerithium sp.	0.57	3.59

This study was supported by the Flagship Project RITMARE-Italian Research for the Sea-funded by the Italian Ministry of Education, University and Research. We are grateful to A. Savona for field assistance and E. A. Aleo for help with laboratory analyses.