Majid Pourkerman
email: pourkerman@yahoo.com

Nick Marriner
email: nick.marriner@univ-fcomte.fr

Christophe Morhange

Morteza Djamali

Hamid Lahijani

Sedighe Amjadi

Matteo Vacchi

Mohammad E Jelodar

Giorgio Spada

Hossein Tofighian

| Nick Marriner

| Sedighe Amjadi

Abdolmajid N Beni

Etemad Zadeh

Late Holocene relative sea-level fluctuations and crustal mobility at Bataneh (Najirum) archaeological site, Persian Gulf, Iran

Keywords: ancient harbour, crustal mobility, geoarchaology, Najirum, Persian Gulf, relative sea level

| INTRODUCTION

The Persian Gulf is located between the Zagros Mountains to the northwest and the Arabian Platform to the southeast. Collision of the Arabian and Eurasian continents played out during the Tertiary. At the end of the Oligocene, the opening of the Red Sea separated Arabia from Africa and produced an uplift of the Arabian Shield, exposing the Precambrian crystalline basement. The main fault systems trend N-S from the Qatar Arc and the SE boundary of the shield. During the evolution of the Zagros orogenic system, evolution of the Arabian Plate was flexed, leading to the formation of the Mesopotamian foreland basin and the Persian Gulf in front of the Zagros Mountains [START_REF] Konert | Paleozoic stratigraphy and hydrocarbon habitat of the Arabian Plate[END_REF]. The asymmetry of the Persian Gulf has been accentuated due to the tilting of the Arabian Peninsula, associated with an opening of the Red Sea in the Neogene.

Zagros is one of the most active collisional belts in the world, and much of the deformation and seismicity of the Zagros Mountains and high-relief topography on the northeastern margin of the Persian Gulf are related to its active tectonics. On the southern margin of the Gulf, the aseismic low relief is consistent with a tectonically static region (US Geological Survey, 2011).

The Zagros tectonic setting and halokinesis control the Persian Gulf basin and its coastal morphology. According to [START_REF] Pourkerman | Geoarchaeology as a tool to understand ancient navigation in the northern Persian Gulf and the harbour history of Siraf[END_REF] classification, the Persian Gulf coast can be subdivided into three morphological zones with different tide levels: (i) gently sloping marshland coasts with permanent rivers (Zone 1); (ii) diapiric uplifting coastal salt domes (Zone II) and (iii) rocky coasts with steep coastal slopes (Zone III) (Figure 1 and Table 1).

Several studies have been carried out in the Persian Gulf to reconstruct Holocene relative sea-level (RSL) changes [START_REF] Aqrawi | Stratigraphic signatures of climatic change during the Holocene evolution of the Tigris-Euphrates delta, lower Mesopotamia[END_REF][START_REF] Kassler | The structural and geomorphological evolution of the Persian Gulf[END_REF][START_REF] Lambeck | Shoreline reconstructions for the Persian Gulf since the last glacial maximum[END_REF][START_REF] Lokier | Late Quaternary sea-level changes of the Persian Gulf[END_REF][START_REF] Mcclure | Holocene shorelines and tectonics movements in Eastern Saudi Arabia[END_REF][START_REF] Paul | Holocene marine hardground formation in the Arabian Gulf: Shoreline stabilisation, sea level and early diagenesis in the coastal sabkha of Abu Dhabi[END_REF][START_REF] Williams | Late Quaternary highstand deposits of the southern Arabian Gulf: a record of sea-level and climate change[END_REF]. [START_REF] Uchupi | Late Quaternary stratigraphy, paleoclimate and neotectonism of the Persian (Arabian) Gulf region[END_REF] suggested that the Holocene marine transgression has accelerated basin subsidence in the axial zone and that local uplift occurred, especially in the northeast of the Persian Gulf.

Coastal uplift in the United Arab Emirates happened under the influence of Holocene RSL rise and halokinesis [START_REF] Wood | Rapid late Pleistocene/Holocene uplift and coastal evolution of the southern Arabian (Persian) Gulf[END_REF]. By contrast, [START_REF] Stevens | Eustatic control of late Quaternary sea-level change in the Arabian/Persian Gulf[END_REF] believed that RSL in the southeast of the Persian Gulf is controlled by eustatic sea-level changes and that local halokinesis and neo-tectonics have not had any impacts on RSL and coastal elevation changes.

An understanding of ancient maritime trade in the Persian Gulf must be based on a proper contextualisation of the physical factors involved in shipping goods from one place to another [START_REF] Caspers | New archaeological evidence for maritime trade in the Persian Gulf during the Late Protoliterate period[END_REF].

Without consideration of the main physical parameters, involving maritime navigation and port facilities, such as wind and surface current regimes, RSL history, climate changes and tectonic settings, it is not possible to fully grasp maritime trade and ancient harbours. Therefore, multidisciplinary geoarchaeological studies of ancient harbours and maritime structures help to understand the role of palaeoenvironmental changes in maritime trade activities and ancient civilisations (e.g., [START_REF] Benjamin | Late Quaternary sea-level changes and early human societies in the central and eastern Mediterranean Basin: An interdisciplinary review[END_REF][START_REF] Marriner | Tsunamis in the geological record: Making waves with a cautionary tale from the Mediterranean[END_REF][START_REF] Marriner | Geoscience of ancient Mediterranean harbours[END_REF]Marriner, Morhange, et al., 2017;[START_REF] Marriner | Coastal and ancient harbour geoarchaeology[END_REF][START_REF] Morhange | Changes of relative sea level during the past 5000 years in the ancient harbor of Marseilles, Southern France[END_REF][START_REF] Pourkerman | Geoarchaeology as a tool to understand ancient navigation in the northern Persian Gulf and the harbour history of Siraf[END_REF][START_REF] Vacchi | Millennial variability of rates of sea-level rise in the ancient harbour of Naples (Italy, western Mediterranean Sea)[END_REF]. The most important ancient harbours in the Persian Gulf were located on the Iranian coast until the 20th century AD [START_REF] Potter | The Persian Gulf in history[END_REF]. Coastal cabotage and the location of ancient harbours in the Persian Gulf were partly controlled by RSL changes, coastal morphology, the meteo-marine context (e.g., Shamal winds) and sea-surface currents [START_REF] Pourkerman | Geoarchaeology as a tool to understand ancient navigation in the northern Persian Gulf and the harbour history of Siraf[END_REF].

| MARITIME TRADE HISTORY IN THE PERSIAN GULF

The first evidence of maritime trade in the Persian Gulf dates back to the 3rd millennium BC. The archaeological remains attest to trade connections between both Mesopotamian and Indus civilisations [START_REF] Caspers | New archaeological evidence for maritime trade in the Persian Gulf during the Late Protoliterate period[END_REF]. Between 247 BC and 224 AD, the Parthian Empire ruled over local kingdoms in both the northern and southern Persian Gulf to exploit the Silk Road trade via maritime routes [START_REF] Daryaee | The Persian Gulf in late antiquity: the Sasanian era (200-700 CE)[END_REF].

Maritime trade continued under the Sassanid empires. The Sassanians sought to gain control of the Persian Gulf for both political and economic aspirations. [START_REF] Daryaee | The Persian Gulf in late antiquity: the Sasanian era (200-700 CE)[END_REF] believed that the Sasanians saw the Persian Gulf as their mare nostrum and part of Iranshahr, or the 'Domain of the Iranians'. A flourishing maritime trade between the Persians and the Romans reduced the amount of traffic on the Silk Road [START_REF] Potter | The Persian Gulf in history[END_REF]. The foundation of Najirum dates back to the Sassanid Empire [START_REF][END_REF]. It is classified as a sector of Siraf in the Ardeshir Khooreh ('Khooreh' means 'province' in Persian). The Ardeshir Khooreh was one of the largest provinces between the five main united provinces of Fars [START_REF][END_REF]. The southern part of the province was demarcated by the Persian Gulf coast. As it was adjacent to the central Sassanid Empire, and due to the importance of maritime trade activities at this time, Ardeshir Khooreh became one of the most important provinces.

The first acceleration in maritime trade in the Persian Gulf happened during late Antiquity when the connection between Fars and East Asia created conflicts between the Persians and the Romans [START_REF] Daryaee | The Persian Gulf trade in late antiquity[END_REF]. According to historical texts such as Tabari, Al-Istakhri, Ibn Hawqal and Al-Mas'udi (Al-Istakhri, 1870;[START_REF] Al-Mas'udi | Les prairies d'or[END_REF]Ibn, 1873;Tabari, 1987), maritime trade flourished again during the 9th and 10th centuries AD. Siraf (the main port) and Najirum (a subsidiary) played key roles in facilitating maritime

F I G U R E 1 (a)
The Persian Gulf bathymetry, coastal geomorphological classification and major structural elements of the Zagros fold-and-thrust belt (modified after [START_REF] Berberian | Master "blind" thrust faults hidden under the Zagros folds: Active basement tectonics and surface morphotectonics[END_REF][START_REF] Hassanpour | Salt tectonics in a double salt-source layer setting (Eastern Persian Gulf, Iran): Insights from interpretation of seismic profiles and sequential cross-section restoration[END_REF][START_REF] Jahani | Salt tectonics and tear faulting in the central part of the Zagros Fold-Thrust Belt, Iran[END_REF][START_REF] Jiménez-Munt | 3-D lithospheric structure and regional/residual Bouguer anomalies in the Arabia-Eurasia collision (Iran)[END_REF][START_REF] Pourkerman | Geoarchaeology as a tool to understand ancient navigation in the northern Persian Gulf and the harbour history of Siraf[END_REF] [START_REF] Priestman | The British museum Siraf project. The British Institute of Persian studies[END_REF]. The prosperity of Siraf during Sassanian and early Islamic times (apogee of the port) is confirmed by zooarchaeological studies [START_REF] Driesch | Animal exploitation in medieval Siraf. Iran, based on the faunal remains from the excavations at the Great Mosque (seasons 1966-1973)[END_REF]. Results suggest that the number of animal species decreased from 133 during flourishing stages to 72 when Siraf lost its importance. By the 13th to 16th centuries AD, a mere 39 species are recorded at Siraf.

After the decline of Siraf, the most important harbours shifted to the Persian Gulf Islands such as Kish (1000-1300 AD) and Hormuz (1300-1600 AD). Later, harbour activities returned to the coast at

Bandar-e Abbas from 1622 to the mid-18th century and at Khurramshahr after about 1900 [START_REF] Potter | The Persian Gulf in history[END_REF].

Although historical and archaeological studies shed light on the maritime trade history of the Persian Gulf, none of them can explain the reasons for important harbour displacements. In this study, we employ geoarchaeology to investigate the evolution of the ancient site of Bataneh (Najirum). The site was selected due to its location at the foothill of a salt diapiric fold to reconstruct RSL changes and the role of halokinesis in driving coastal changes.

| SALT TECTONICS

One of the most important features of the Zagros belt is the presence of several salt diapirs of Late Precambrian-Early Cambrian Hormuz salt that existed in the eastern part of the Zagros fault thrust belt and the Persian Gulf. Halokinesis started shortly after the deposition of the Hormuz salt in the early Paleozoic, and it has continued up to the present [START_REF] Jahani | The salt diapirs of the eastern Fars Province (Zagros, Iran): A brief outline of their past and present, Thrust Belts and Foreland Basins[END_REF]. The salt domes generally existed along/near the N-S and NE-SW fault system [START_REF] Jahani | Salt tectonics and tear faulting in the central part of the Zagros Fold-Thrust Belt, Iran[END_REF].

The central basin of the Persian Gulf is well known for several salt domes and diapiric folds along its coast (Kalat, Bostaneh, Mughu, Moallem, Homiran and Darang) and offshore islands (Great and small Tunb, Farur and Abu Musa) in Iran, the United Arab Emirates (Sir Abu Nuayer, Arzanah, Sir Bani Yas) and Qatar (Halul and Sharao) [START_REF] Beydoun | Arabian plate hydrocarbon geology and potential, a plate tectonic approach[END_REF][START_REF] Thomas | Salt domes of the UAE and Oman: Probing eastern Arabia[END_REF]. In the east of the central basin, salt tectonics is linked to the salt-bearing system of the Hormuz salt formation and late Oligocene-Early Miocene Fars salt (Figure 1) [START_REF] Hassanpour | Salt tectonics in a double salt-source layer setting (Eastern Persian Gulf, Iran): Insights from interpretation of seismic profiles and sequential cross-section restoration[END_REF]. In the early Miocene, after the beginning of the Zagros continental collision, the Hormuz salt extrusion started again. Consequently, Fars salt diapirism was triggered by gravitational loading produced by an overriding of the allochthonous Hormuz salt sheet. This process pushed the Fars salt outwards [START_REF] Snidero | Diapir kinematics in a multi-layer salt system from the eastern Persian Gulf[END_REF]. The salt diapir close to the present coast of the Persian Gulf emerged after the reactivation of salt domes during the final Zagros folding phase [START_REF] Jahani | The salt diapirs of the eastern Fars Province (Zagros, Iran): A brief outline of their past and present, Thrust Belts and Foreland Basins[END_REF]. The impacts of halokinesis on the coastal elevation of the United Arab Emirates has been discussed by [START_REF] Wood | Rapid late Pleistocene/Holocene uplift and coastal evolution of the southern Arabian (Persian) Gulf[END_REF] and [START_REF] Lidour | The prehistoric fisheries of Akab Island (United Arab Emirates): New insights into coastal subsistence during Neolithic in eastern Arabia[END_REF]. But its effects on RSL and coastal dynamics in the northern Persian Gulf are still unknown.

The ancient site of Bataneh is located in the foothills of the Darang Anticline (diapiric fold, Zone II) (Figure 1b). The Darang salt pillow is located along the southern end of the Dashti Fault system with a N-S orientation (Figure 1). The Darang salt pillow started to grow in the Paleozoic, and this growth continued through geological time [START_REF] Jahani | Salt tectonics and tear faulting in the central part of the Zagros Fold-Thrust Belt, Iran[END_REF]. The diapiric fold has exposed lithological units with evaporation minerals such as gypsum and gypsum marl.

The concentration of deep rill erosion features in the upland areas

shows their high sensitivity to water erosion (Figure 1c). Bataneh has an open coastal morphology and a NW-SE longshore current responsible for coastal erosion and moving sandbars along the coast [START_REF] Pourkerman | Tracking shoreline erosion of "at risk" coastal archaeology (Persian Gulf: Sassanid-Islamic heritage relics in southeastern Bataneh, Iran). Final conference-What kind of environmental transition for the Mediterranean region? Marseille, France[END_REF].

| GEOMORPHOLOGICAL FEATURES AND ARCHAEOLOGICAL CONTEXT

According to field observations, the ancient site of Bataneh com- To the west of the city, two embankments have been erected

along either bank of the stream, for channel stability. A trace of dikes is observed at the end of the walls to prevent water runoff to the sea.

The eastern embankment is distinct, with the ancient canal that stretched along the ponds (Figure 3).

| METHODOLOGY

In this study, we integrated high-resolution CORONA, Google Earth and moderate-resolution Landsat 8 OLI images (overpass frequencies of 16 days) to map the ancient site and its geomorphological features [START_REF] Beck | Evaluation of Corona and Ikonos high resolution satellite imagery for archaeological prospection in western Syria[END_REF][START_REF] Myers | Field work in the age of digital reproduction: A review of the potentials and limitations of Google Earth for archaeologists[END_REF][START_REF] Saleem | On the possibility of using CORONA and Landsat data for evaluating and mapping long-term LULC: Case study of Iraqi Kurdistan[END_REF], in addition to updating the most recent anthropogenic constructions over the historical site. The satellite images were georeferenced using 1:100,000 topographic maps from the National Cartographic Center (NCC) with a root mean square error (RMSE) between 0.01 and 0.05 pixels.

A 3-m borehole was extracted from sector (iii) Zone B, an area in which human disturbance was negligible. The core was levelled using a theodolite (+4.5 m) in relation to the present mean sea level (MSL).

After core collection, nondestructive magnetic susceptibility (MS) was measured using a Bartington MS2C 100-mm diameter loop sensor with an MS2 metre at 2-cm resolution [START_REF] Delile | Geochemical investigation of a sediment core from the Trajan basin at Portus, the harbour of ancient Rome[END_REF]. Subsamples were obtained using the high-resolution sampling procedure described by [START_REF] Marriner | Geoscience of ancient Mediterranean harbours[END_REF]. Subsamples were oven-dried at 50°C for 12 h. Each sample was separated into three fractions for biostratigraphy, granulometry, organic matter (OM) and carbonate content. Wet sieving was performed using mesh sizes of 2 mm and 63 microns. After processing and oven-drying, the ostracods were picked from 10 g of >125-µm size fraction and placed on palaeontological slides to count and identify the species [START_REF] Marriner | Geoarchaeology of Tyre's ancient northern harbour, Phoenicia[END_REF]. Simultaneously, microscopic sedimentary properties and general minerals were noted.

Macrofossils (>2 mm) were identified using the Persian Gulf data set described by [START_REF] Sahafi | Persian Gulf Molluscs Atlas[END_REF].

A geomorphological map of the most morphological features in the hinterland and coastal zones was created. The map helped to interpret the interactions between marine (subtidal, sand bar and coastal) and terrestrial (alluvial fans, marshland and flooding plain) facies and palaeoenvironmental changes. Surface sampling of coastal zones was performed to identify sedimentological properties and ostracods species [START_REF] Marriner | Geoarchaeology of Tyre's ancient northern harbour, Phoenicia[END_REF]. The uncertain values for RSL were calculated according to the facies depth and species in relation to the present day. Uplift uncertainly was also evaluated according to the field elevation measurement errors and sediment compaction during drilling. Laser granulometry was performed using a Horiba La950E after treatment of sediments by peroxide hydrogen and HCL 0.1 to remove the effects of biological production on the sedimentary textures. The sediments were classified according to [START_REF] Folk | The distinction between grain size and mineral composition in sedimentary rock nomenclature[END_REF]. Ternary diagrams and statistical parameters were calculated by the method of moments [START_REF] Folk | Brazos River bar [Texas]; a study in the significance of grain size parameters[END_REF]. Organic matter (OM) and carbonate properties were calculated using loss on ignition at 550°C and 950°C [START_REF] Heiri | Loss on ignition as a method for estimating organic and carbonate content in sediments: Reproducibility and comparability of results[END_REF].

According to the main facies changes and anthropogenic horizons, three 14 C dates were undertaken at the Poznan Radiocarbon Laboratory, mainly on charcoal and juvenile bivalve shells due to the absence of organic matter. The data were calibrated using CALIB 8.1, with a marine delta reservoir specific to the Persian Gulf [START_REF] Southon | Marine reservoir corrections for the Indian Ocean and Southeast Asia[END_REF] (Table 2).

The glacial isostatic adjustment (GIA) simulations performed in this study are based on model ICE-6G (VM5a) of [START_REF] Peltier | Postglacial rebound and current ice loss estimates from space geodesy: The new ICE-6G (VM5a) global model[END_REF][START_REF] Peltier | Space geodesy constrains ice age terminal deglaciation: The global ICE-6G_C (VM5a) model[END_REF]. The Late-Pleistocene ice sheets chronology of model ICE-6G (VM5a) was implemented in the programme SELEN4 [START_REF] Spada | SELEN4 (SELEN version 4.0): A Fortran program for solving the gravitationally and topographically selfconsistent sea level equation in glacial isostatic adjustment modeling[END_REF]. SELEN4 solves the sea-level equation by taking into account the horizontal migration of shorelines, for the transition from grounded to floating ice and for the effects of rotational feedback on sea level. The sea-level equation was solved using a pseudo-spectral approach with a spatial resolution corresponding to The alluvial geomorphological features such as wadis, alluvial fans and flood plains underscore the high potential risk of flooding and debris flow by flash flooding events during winter and autumn on this specific lowland coast. One of the most important factors mediating runoff power discharge to downstream areas is soil permeability [START_REF] Sampson | The correlation between soil permeability and flooding in the northeast sector of the Dog River watershed[END_REF]. The upstream lithological units are made of low permeability gypsum marls with sandstone interlayers. The gypsum marl unit contains soluble evaporation minerals and fine-grained sediment (silt and clay). This leads to a decrease in permeability and soil strength against erosion [START_REF] Heshmati | Effects of soil and rock mineralogy on soil erosion features in the Merek watershed, Iran[END_REF]. As a result, a huge amount of sediment was reworked to downstream areas through the stream channels, leading to coastal progradation at the base level. Decreases in slope angles and sudden changes in watershed bedrock types from marl (soft bedrock) to sandstone (hard bedrock) mean that the runoff cannot be evacuated. Abrupt stream channel disruption has led to the formation of alluvial fans north of the ancient site at the base level (Figure 4b).

F I G U R E 3 (a)
To protect the city from flash floods, a cemented dike was erected at the end of the stream, with an aim to reduce runoff energy. The water was channelled in an artificial watercourse that was excavated into the bedrock (Figures 2 and4c,d). The watercourse directed runoff water to the city via a channel, which passed north of the city. During flooding events, muddy sediment passed through the artificial channel (Figure 4e). The runoff water, containing high amounts of dissolved salts, was channelled to the city for industrial purposes.

| Analysis of the urban area

We could not find any preserved ancient buildings to analyse the urban fabric, due to extensive erosion and destruction by industrial activities and also the absence of archaeological excavations. On the basis of the remains of building walls, it is possible to infer the widespread use of rubble and cooked gypsum for construction (Figure 3).

South of the zone, we identified 15 almost rectangular embankments, probably used as ponds (Figure 3).

| Litho-and biostratigraphy

The core station is +4.5 m above the current sea level. In the coastal stratigraphy, two main marine (A) and brackish (B) environments have been identified. The facies were differentiated according to the lithology, sediment properties (mineralogy and grain morphology), ostracod assemblages and grain size. The core was divided into four facies (Figure 6).

| Unit A: Marine facies and RSL fluctuations

The first marine facies is observed at 267-280 cm, where yellowish-brown silty sand changes to the dark brown sandy silt with negatively skewed, poorly sorted sediment and high OM content. The ostracod species Cytherella sericea, Chrysocythere An assemblage of euryhaline ostracods Cyprideis torosa and the marine lagoonal C. sericea and Venericythere papuensis species may indicate a minor oscillation of the RSL and the extension of shallow marine conditions (2-B). A marked increase in sediment grain size due to an increasing sand fraction (13.3%-71.75%), decreasing sorting, OM and MS suggest a higher energy environment at 250-267 cm between 50 BC and 354 AD (Table 3). An upward increase in sediment grain size continues to 235-250 cm, where the mean size is 2.2 φ with nearly symmetrical skewness. Improved sorting in the yellowish brown sand is consistent with stable environmental energy. A significant decrease in C. ). This facies represents the last evidence of marine species after isolation from the sea due to coastal uplift.

| Unit C: Anthropogenic zone

An anthropogenic facies is observed at 40-75 cm, where brownishblack sediment contains ceramics, charcoal and gypsum (crystals with charcoal inclusions, baked and amorphous) (Figure 7). Radiocarbon

T A B L E 3 RSL oscillation comparison between reconstructed sea level via GIA model and the obtained results from facies analysis at Siraf and Bataneh dating reveals that the first human traces occurred between 774 and 899 AD (Table 3). MS recorded maximum magnetic contents (3.8 and 4.48 × 10 -4 SI) and is positively correlated with OM. The anthropogenic facies begins with poorly sorted silty sand with positive skewness. It gradually changes to very poorly sorted sandy silt with nearly symmetric skewness. The grain size fines upwards, with a decreasing sorting index. MS and OM values continue to increase up to 40 cm, where the euryhaline species C. torosa attains 94.87%. A thin layer of amorphous white gypsum is deposited at the top of the unit and constitutes a marker for the termination of the anthropogenic facies.

| Unit D: Lagoon

The anthropogenic horizon is covered by aeolian sediments that contain yellowish-brown rounded to subrounded silty sand, gypsum crystals, plant remains, charcoal and a small fraction of ceramics with rounded edges (consistent with reworking by wind action from the exposed archaeological site). Sorting ranges from very poor to poor et al., 1999). The central basin hosts many active salt diapirs along deep N-S extensional faults and tear fault systems originating in the Hormuz salt formation [START_REF] Jahani | The salt diapirs of the eastern Fars Province (Zagros, Iran): A brief outline of their past and present, Thrust Belts and Foreland Basins[END_REF][START_REF] Jahani | Salt tectonics and tear faulting in the central part of the Zagros Fold-Thrust Belt, Iran[END_REF]. Correlations between growth of the Darang salt pillow and RSL fall suggest probable impacts of halokinesis in driving RSL oscillations. During the Persian Gulf highstand (3340-2620 BC), the lower Khuzestan plain experienced several RSL oscillations with short periods [START_REF] Heyvaert | Holocene sedimentary evolution and palaeocoastlines of the Lower Khuzestan plain (southwest Iran)[END_REF]. By contrast, a rapid RSL fall occurred in Abu Dhabi during a short period after a highstand [START_REF] Lokier | Late Quaternary sea-level changes of the Persian Gulf[END_REF] and reached below the current sea level by 510-780 AD. Therefore, disparate RSL histories in the north and south of the Persian Gulf appear to result from different tectonic settings and fault systems.

Halokinesis has a direct effect on RSL oscillations via the Persian Islam, the main harbours shifted from Apologus (Ubulla) to Siraf [START_REF] Wilson | The Persian Gulf[END_REF].

The first seawater column reduction was also concurrent with the foundation of a defensive outpost with a port at Siraf [START_REF] Whitehouse | Sasanian maritime trade[END_REF], but maritime trade flourished at Apologus. It could be related to maintaining sea level due to the Karun-Tigris-Euphrates delta subsidence and local uplift [START_REF] Uchupi | Late Quaternary stratigraphy, paleoclimate and neotectonism of the Persian (Arabian) Gulf region[END_REF]. Seawater intrusion to the river channel during high tide increased the water depth for ocean-going navigation. It was favourable to Apologus's maritime trade until the late Sassanid Empire (ca. 450-650 AD). During the Sassanid to early Islamic (50 BC-950 AD) periods, the settlement density reached its maximum in Mesopotamia [START_REF] Lawrence | Long term population, city size and climate trends in the Fertile Crescent: A first approximation[END_REF]).

An unconformity above subtidal facies could be a result of rapid seawater oscillation. The water column reduction is correlated with the first evidence of anthropogenic traces at Siraf. RSL rise and developing coastal facies were concurrent with the progradation of marine facies over the first Sassanid anthropogenic horizon at Siraf (50 BC-550 AD) (Figure 8).

The second RSL oscillation coincided with changes in sediment origin after an increase in summer northwest winds around 650 AD and a second phase of anthropogenic traces at Siraf (150-450 AD) [START_REF] Pourkerman | Geoarchaeology as a tool to understand ancient navigation in the northern Persian Gulf and the harbour history of Siraf[END_REF] (Figure 8). This period was concurrent with dune reactivation and a peak in the aeolian deposition in the southeast of the Persian Gulf [START_REF] Parker | Geomorphological and palaeoenvironmental investigations in the southeastern Arabian Gulf region and the implication for the archaeology of the region[END_REF][START_REF] Stokes | Optical dating as a tool for studying dune reactivation, accretion rates and desertification over decadal, centennial and millennial timescales[END_REF] and the development of marshland deposits over tidal channels in the southern part of the Khuzestan plain [START_REF] Heyvaert | Holocene sedimentary evolution and palaeocoastlines of the Lower Khuzestan plain (southwest Iran)[END_REF].

During the Umayyad to early Abbasid dynasties (650-750 AD), there was a decrease in maritime trade in the Gulf [START_REF] Potter | The Persian Gulf in history[END_REF]. This could be related to sudden changes in both RSL reduction and economic/political changes. A decreasing river water column at Shatt-al-Arab, following RSL fall and decreases in precipitation, led to accessibility problems at Apologus for ocean-going vessels (Al-Istakhri, 1870).

By contrast, risk of navigation in the western part of the Persian Gulf was accelerated during summer by the interaction of Persian Gulf water circulation and summer Shamal winds at Ras-e-Motaf [START_REF] Pourkerman | Geoarchaeology as a tool to understand ancient navigation in the northern Persian Gulf and the harbour history of Siraf[END_REF]. The Shamal wind generates the highest wave energy with an anticlockwise whirlpool (under storm conditions)

at Ras-e-Motaf. This area is famous as being Iran's 'Bermuda triangle' and has been a zone of numerous shipping accidents [START_REF] Kamranzad | Assessment of wave energy variation in the Persian Gulf[END_REF]. The environmental changes led to economic decline at the head of the Persian Gulf around the 10th century AD [START_REF] Adams | Land behind Baghdad: A history of settlement on the Diyala Plains[END_REF][START_REF] Wilkinson | Archaeological landscapes of the Near East[END_REF].

Bataneh is located in

  . HZF, High Zagros Fault; MFF, Mountain Front Flexure; MZF, Main Zagros Fault; NFS, Nezamabad Fault system. (b) Position of the ancient site at the Darang salt diapiric fold on a Landsat 8 image (RGB = 753), position of N-S Dashti and NE-SW Nezamabad fault systems. (c) Lithological units [Color figure can be viewed at wileyonlinelibrary.com] T A B L E 1 Geomorphological zonation and tidal levels at sites from the Strait of Hormuz to Shatt-al-Arab

  prises four sectors separated by natural geomorphological features such as rocks, bays and flood plains. All of the ancient sites lie on high ground, 7-11 m above the present sea level. Several streams and ephemeral rivers are sourced in the evaporation unit; the largest one passes north of site B. Alluvial fans, floodplains and wadis are the most important geomorphological features, with a high potential risk of flooding and debris flows for archaeological remains (Figure 2). Our knowledge about historic sites is limited to just two surveys conducted by Esmaeili Jelodar (2011) and Azarian (2013). Esmaeili Jelodar (2011) introduced three (A, B and C) ancient zones. He dated the sites to the late Sassanid-early Islamic period on the basis of a ceramics chronotypology. His study focused on Zone B due to the presence of features mentioned in historic texts, such as ancient mosques with staircases carved into the rock (Talle Ashrafi) to the north and an estuary to the west (Figure 3). A variety of ceramics and Chinese porcelains attest to a thriving city. The archaeological remains and spatial location of the ancient site (distance from Siraf) harbour have led archaeologists to identify the ancient site as the missing port town of Najirum. The site is elevated 8-10 m above present sea level to the north. To the south, the elevation decreases with a gentle slope. An ephemeral river channel passes between Zones B and C. Five alluvial fans are located 200 m north of the ancient site, along two ephemeral rivers (Figure 2). Although Zone B has been damaged by recent industrial constructions, Zones A and C contain three important types of artefacts. (i) The first artefact is an urban fabric containing several ancient walls and decorative gypsum objects. The building walls are made of rubble and baked gypsum. On the interior side, the walls are covered with plaster motifs. (ii) The second type of artefact is an artisanal area with remains of furnaces and (iii) the third one is an area of rectangular embankments (ponds) connected via an ancient canal (Figure 3).

F

  I G U R E 2 General geomorphological map of Bataneh and its ancient sites located on a Google Earth image (2011). Zones A, B and C are reported by Esmaeili Jelodar (2011) and Zone D is introduced in this study. The black dashed line denotes the location of a man-made dike and artificial watercourse for redirecting runoff water. The recent industrial constructions at site C have been updated using a Landsat 8 panchromatic band (2020) [Color figure can be viewed at wileyonlinelibrary.com]

  General geomorphological features of Zone B and sectors of the ancient city of Bataneh. The green point indicates the coring site. (b) Remnants of the ancient city wall, comprising rubble and baked gypsum. (c) Remains of an ancient furnace in the old industrial area (purple zone). (d) Several samples showing the use of baked gypsum for decorative elements and (e) plaster motifs [Color figure can be viewed at wileyonlinelibrary.com] T A B L E 2 Calibrated radiocarbon ages for the three studied facies

  The ponds were fed by an ancient canal. The canal lies on a gentle west-to-east slope and it has distribution canals between the ponds. The runoff water was stopped behind the dike to prevent outflow to the sea. The trapped water entered the canals and moved through them under gravity.Different elevations between each row of ponds (from north to south) facilitated this flow. Saturated water was collected in the wet seasons and gypsum was subsequently precipitated through evaporation processes during warm and arid seasons. The resulting gypsum crystals were collected for baking in the furnaces of the artisanal area.6.1.3 | Evaluation of site damageIn terms of archaeological erosion, the study site has been significantly damaged by anthropogenic processes during last 20 years.Satellite images and field observations demonstrated that anthropogenic activities have destroyed much of the ancient urban and artisanal areas. According to Esmaeili Jelodar's (2011) report, the destruction of the ancient site predates recent industrial developments. Unfortunately, the same trend is observed in the other ancient Zones A and C. But a newly discovered site (Site D) is almost void of recent human intervention (Figure5).

  corralloides, Keijella karwarens, Asymmetricythere indoiranica, together with Hemicytheridea paiki and Keijella neaki, are consistent with a marine subtidal environment. The sandy portions have two different sources: (i) the first is quartz with bar-like shape with rounded edges, linked to an interbasin source, and (ii) the second comprises fine to very fine subrounded quartz, biotite sheets, imported by aeolian processes. The interbasin portions are generally aggregated by evaporitic minerals with rounded edges. The absence of euryhaline species and sudden changes in facies without a transitional facies show a marine transgression over a disconformity surface. This transition from playa (1-A) to marine (2-C) conditions was concurrent with increasing MS concurrent with imported iron (biotite) into the environment by wind and emerging Venericythere darwinii, H. paiki and K. neaki species. The finest sediment grain size, with the highest amounts of MS and OM in the marine environment, is observed at 278 cm.

  torosa and the high abundance of C. sericea, Cerallicythere adenensis, Cistacythereis sp., Alocopocythere reticulata, indoaustralica species, in addition to abundant joined juvenile bivalves, are consistent with a marine environment (2-C). At 225-235 cm, a decrease in mean grain size and a sandy texture was accompanied by improved sorting and positive skewness concomitant with a high-energy setting. These data testify to the onset of permanent longshore currents leading to the creation of sandbars. The abundance of C. torosa shows relative instability in the coastal environment. Nevertheless, other species such as C. sericea (marine lagoonal), Asymmetricythere whatleyi, Lankacythere elaborara, Corallicythere adenensis, Moosella striata, Chrysocythere keiji (coastal) and K. karwarens (subtidal) indicate the extension of the marine (2-C) setting. Also, high MS values indicate inputs of iron-rich minerals such as biotite to the environment through wind processes. This transgressive facies represents a lower shoreface facies with shoreface ridges. The ridges, comprising fine to coarse sands, are attributed to longshore transportation of tidal inlets, which are mainly active for cross-shore mobility during marine transgression (McBride & Moslow, 1991).

F

  I G U R E 4 (a) The red arrow represents an old ephemeral river direction that has led to erosion of the marl section of the rock. The cyan arrow and (b) show eroded sandstone rock from the outcrop. The yellow dashed line and (c) show the man-made dike used to reduce floodwater velocity and sluice water along a narrow artificial channel shown in purple. (d,e) Artificial channel over sandstone bedrock. Mud balls are formed due to the reworking of mud pieces over the hard bedrock [Color figure can be viewed at wileyonlinelibrary.com] OM enrichment in the silty sand sediment and a decline in sorting indices, positive skewness values and a significant reduction in single ostracod valves confirm a gradually decreasing energy setting. Marine lagoonal ostracod species (C. sericea and V. papuensis), together with C. torosa and coastal species (Paijenborchellina venosa, Paranesidea handel), indicate a shifting environment from 2-C to 2-A (212-225 cm). These data translate a backshore facies with oscillations in marine inundation and vegetation growth. A return to muddy deposition is identified within the sandy sediment of shore ridges or cheniers. F I G U R E 5 (a) View of part of the bulldozed ancient site of Bataneh (Zone B); (b) industrial construction in ancient Zone C. (c,d) Newly discovered ancient Zone D containing late Sassanid-early Islamic ceramics [Color figure can be viewed at wileyonlinelibrary.com] F I G U R E 6 Sediment stratigraphy, biostratigraphy, chronology and sedimentology of the studied core. Six main palaeoenvironments are defined [Color figure can be viewed at wileyonlinelibrary.com] The first brackish facies is between marine lagoonal facies (2-A) at 192-202 (1-B) and 181-192 (1-C). The ostracod assemblages and sediment textures in the two yellowish-brown sands are different from the other brackish facies. The main difference is the presence of a tiny crust of syn-sedimentary marine cement fractions (beachrock) in these facies. Mean sorting and skewness indices imply increasing environmental energy (increasing sediment grain size with increasing sorting index from the base to top). C. torosa is the main species in both facies, but its abundance increases from the base to top (57.17%-73.17%). The beachrock fractions generally contain fine to very fine sand portions resulting from wind influxes during cementation. The cementation occurred during increases in seawater injection within the sediments via increasing wave and tidal energy (increase wind events). Storm waves could be responsible for developing coarser sediment over marine lagoonal facies and creating chenier structures. At 181-192 cm, when hypersaline species abundances were high due to the RSL expansion, C. torosa is observed with marine lagoonal and coastal (2-C) species such as C. sericea, V. papuensis, Propontocypris bengalensis and Bishopina guhai. There is a mixture of rounded and angular sands with angular to subrounded beachrock fractions consistent with RSL expansion and increasing sediment transport with coastal processes. Marine lagoonal species (C. sericea and V. darwinii) and low abundances of C. torosa appear again at 171-181 cm (facies 2-A). An increase in sediment grain size, sorting index and skewness evokes an RSL expansion and developing backshore facies (2-C) at 144-162 cm. A variety of ostracod species are observed in this facies, including brackish (C. torosa), marine lagoonal (C. sericea and V. darwinii) and marine (Tanella gracilis, Cerallicythere adenensis) taxa. The RSL started to fall during 380-725 AD, and a marine lagoonal environment (2-A) with C. sericea and V. darwinii species was created at 123-144 cm (Table 3). Decreasing sediment grain size, together with increasing sorting index and positive skewness values, shows that deposition occurred in a confined environment without biotite sheets. The absence of biotite suggests a shift in wind directions and probably the onset of NW Shamal winds. RSL reduction led to the deposition of the second brackish facies at 123 cm. By this time, accessibility to the northwest ports had been restricted via Ras-e-Motaf and the unique morphological shape of Shatt-al-Arab palaeo-delta (Pourkerman et al., 2020). Navigation through Ras-e-Motaf became dangerous after the onset of summer time NW Shamal wind during ca. 650 AD. The highest wave energy, with an anticlockwise whirlpool under storm conditions, occurred in the Ras-e-Motaf. This part of the Persian Gulf is known as Iran's 'Bermuda triangle' and it has been an area of numerous shipping accidents (Kamranzad et al., 2013). 6.2.2 | Unit B: Open lagoon with freshwater flux The second brackish facies at 103-123 cm is characterised by a decrease in the marine lagoonal species C. sericea (15.63%) and an increase in the hypersaline species C. torosa, which represents 84% of total valves. Plant remains are also observed and they constitute the first evidence of freshwater flux in the open lagoon facies (1-C). The sediment changes to dark brown silty sand with light grey sandy silt lenses at 94-103 cm. The lenses contain charcoal and plant remains. The presence of the macrofossil Neogastropoda olividae points to the extension of an open lagoon (1-C) setting. Increasing mean sediment grain size, negative skewness, decreasing MS, increasing sorting index and the appearance of aggregated fine sand at 87-94 cm are consistent with changes in the environmental setting. C. torosa attains relative abundances of 94%, and the percentage of single valves and joined valves is 30.4% and 69.5%, respectively. This facies represents a hypersaline playa environment (1-A) with aeolian influxes. Dark brown silty sand with a rounded sand fraction, nearly symmetrical skewness and extremely poor sorting (4.3 φ) is observed at 80-87 cm. The presence of the marine lagoonal species C. sericea (14.06%), together with C. torosa (85.9%) and gravels, suggests limited access to the sea. C. sericea attains relative abundances of up to 20% with Urocythereis margaritifera and C. torosa at 75-80 cm, suggesting an open lagoon environment (1-C

  (3.46-1.24 φ). The sediment sorting improves from the base to top.The sedimentology suggests environmental oscillation changes between playa (1-A) and playa lagoon (1-B) in the man-made evaporation ponds. Lagoonal species such as U. margaritifera and Penthesilenula olivencae, together with C. torosa, are consistent with variable salinities, typical of playa lagoon environments (1-B). The abundance of ostracod shells decreases from the base to the top. A maximum shell abundance is observed at 5-7 cm (1-A), where C. torosa is the single species. At 35-37 and 15-17 cm (1-B), the percentage of C. torosa decreases and U. margaritifera comprises a quarter of the shells. MS varies between 3.32 and 4.66 × 10 -4 SI, with a maximum value logged at 15-17 cm, where carbonate content and mean sediment size decrease. 7 | DISCUSSION RSL changes in the Persian Gulf are controlled by eustatic sea-level rise, basin subsidence and local uplifts. During the Holocene, the axial zone of the Persian Gulf experienced twofold subsidence, followed by a rapid sea-level rise, especially in the central basin (Uchupi

  Gulf axial zone subsidence and localised uplift through the fault systems. As a result, our reconstructed RSL is not correlated with the ICE-6G (VM5a) model for the study sites. Although the model shows a continuous fall, the studied facies record three RSL oscillations. The duration between each oscillation was correlated with the modelled sea-level position. An increasing water column in the central basin floor can lead to increasing crustal mobility in coastal areas. F I G U R E 7 (a) Anthropogenic section of the studied core with evaporation minerals of different crystal morphologies. This section ends with gypsum crystals at 38-40 cm. (b) Needle aragonite; (c-e) different crystal shapes of gypsum with black organic matter inclusions [Color figure can be viewed at wileyonlinelibrary.com] Meanwhile, the time interval between the lowstand and the ensuing highstand decreased. The Darang salt anticlinal recorded 3.7 ± 0.4 m uplift by the second lowstand. RSL in the Persian Gulf is an important factor for ancient harbour location. Rishar (Rev Ardeshir) and Apologus were two important Sassanid harbours in the northwest of the Persian Gulf (Le Strange, 1905; Whitehouse & Williamson, 1973). Apologus was a riverine harbour located at Shatt-al-Arab, and Rishar is situated on the Bushehr coastal peninsula. The archaeological evidence shows that the port of Bushehr was connected to Kazirun and Shiraz via a road used for the export of commodities to other regions. It was the nearest port to Fars and it made Rishar an important port (Boucharlat & Salles, 1981). The first water column reduction had negative impacts on the Rishar harbour operation due to its coastal morphology (Figure 1). The same trend is observed in other Zone I ancient harbours (Mahroyan, Ceniz, Jenaba). This problem of harbour accessibility provided an opportunity for Apologus to replace them. Apologus maintained its importance in maritime trade until the early Abbasid Caliphate (750-1260 AD), which coincided with the second RSL reduction. Then, in the first century of

  Zone II where halokinesis has had direct effects on the coastal zone and its hinterland. Darang salt diapiric fold and the geomorphological changes in the hinterland were concurrent with a second RSL fall. The rapid transition from open lagoon to brackish facies translates to a rapid uplift of ca. 3.7 ± 0.4 m in the coastal zone due to the Darang salt pillow growth. The uplift changed local watershed geomorphology and fluvial directions. These changes caused the abrupt cessation of the stream channel and extending alluvial fans. The stream sourced in the sensitive gypsum marl unit was a great risk for the ancient city. The city was protected by embankment walls and a dam with an artificial canal over hard bedrock that safely channelled floodwater through the city. One of the reasons that Bataneh port failed was probably coastal uplift. The expansion of Siraf brought rapid urbanisation of the city and local towns. This rapid expansion necessitated new building materials. At this time, cooked gypsum was widely used as cement, in plaster motifs and in decorative objects. Therefore, gypsum very soon became a noteworthy commercial good. Several ancient gypsum mines existed around Siraf. Traditional mining necessitated time and labour for the extraction and transfer of raw gypsum. As a result, gypsum became expensive. New gypsum extraction methods via evaporation pools at Bataneh led to cheaper F I G U R E 8 Age-depth model of the Bataneh facies changes, Siraf anthropogenic traces (Pourkerman et al., 2020) and ICE-6G (VM5a) model. This figure shows the impacts of relative sea-level changes and coastal uplift on Siraf's ancient harbour and Bataneh [Color figure can be viewed at wileyonlinelibrary.com] gypsum. The method took advantage of Bataneh's geomorphological traits and gypsum units present in the local geology. 8 | CONCLUSIONS Two RSL falls have been recorded. The first event (510-780 AD) had negative impacts on harbours in the western basin such as Rishar. There were only minor impacts on Apologus due to crustal mobility between 150 and 650 AD. The second RSL fall event at 770-900 AD and the onset of summer time Shamal wind since 650 AD were coincident with important harbours shifted to the central part of the Persian Gulf. Both Bataneh and Siraf were suitable locations. Siraf was surpassed by Bataneh due to its stable rocky coast. Uplift at Bataneh led to changes in geomorphological features in the hinterland and the city was exposed to flooding risk. The runoff water that originated from marl gypsum units was harnessed by a dam and an artificial canal and sluiced to the city through safe channels. The runoff water was collected in evaporation ponds and left to precipitate as gypsum during the warm and arid summers. The gypsum trade brought prosperity to the city. Coastal uplift was a key factor in reducing port accessibility and therefore activity at Bataneh. The location of Najirum's harbour is still unclear. Recent oil and gas infrastructure has destroyed large parts of the ancient sites. These structures are also at risk from natural hazards such as coastal uplift and flooding. South Pars offshore oil and gas field has led to the expansion of several petrochemical companies along the coastal. They have had direct and indirect impacts on the destruction of ancient sites. Further geoarchaeological studies are required at waterfront sites of the Persian Gulf, because many sites are being destroyed by modern developments, present RSL rise and coastal erosion[START_REF] Pourkerman | Tracking shoreline erosion of "at risk" coastal archaeology: The example of ancient Siraf (Iran, Persian Gulf)[END_REF].

  navigation for ocean-going vessels. For the first time in history, regular trade between merchants from the Persian Gulf and India, Southern Asia, South Arabia and East Africa was initiated. In fact,

	Siraf was a redistribution centre linked to Basra (Abbasid caliphate
	capital). At this time, Siraf became the wealthiest settlements in the
	region

ACKNOWLEDGMENTS

This study was supported by the Center of International Scientific Studies and Collaborations (CISSC), the Iran National Science Foundation (INSF Grant Number: 94-44915), the French Embassy in Iran, Campus France (PHC GUNDISHAPUR 2016-2017, Project Number: 35630QH) and Labex OT-Med (ANR-11-LABX-0061). Radiocarbon datings were funded through the project 'LIA HAOMA' supported by the Centre National de Recherche Scientifique (CNRS, France). The study was also supported by Iran National Elite's Foundation and National Science Foundation Grant 94-44915. Giorgio Spada is funded by an FFABR (Finanziamento delle Attività Base di Ricerca) grant of the MIUR (Ministero dell'Istruzione, dell'Università e della Ricerca) and by a DiSPeA (Dipartimento di Scienze Pure e Applicate of the Urbino University) research grant.


Frédéric Médail
email: frederic.medail@imbe.fr

Katia Diadema
email: k.diadema@cbnmed.fr

Marine Pouget

Alex Baumel
email: alex.baumel@imbe.fr

Identification of plant micro-reserves using conservation units and population vulnerability: The case of an endangered endemic Snowflake (Acis nicaeensis) in the Mediterranean Basin hotspot

Erosion of natural habitats due to urban sprawl constitutes a major threat to biodiversity. The development of the Plant Micro-Reserve (PMR) is an efficient concept for the in situ conservation of rare plants with narrow ecological niche and threatened by human impacts. We provide a framework for initiating site selection of PMRs, including evolutionary and ecological uniqueness. The proposed cross-analysis is based on (i) the estimate of population vulnerability, (ii) the contribution of each population to the evolutionary originality of the species by designating conservation units, and (iii) the gap analysis of the current protection status of the populations. As a case study, we apply this framework to the Nice Snowflake Acis nicaeensis, a narrow Mediterranean endemic plant of the French-Italian Riviera which, being caught in the turmoil of urban sprawl, is threatened by tremendous anthropogenic pressures. On the basis of historical data (past land-use and herbarium data) we show that over the last 150 years, the impact of urbanization has been severe for 70 % of the populations and has caused the disappearance of at least 11 of them, i.e. 20 % of the known populations. Similar levels of urban sprawl are observed between the most vulnerable and already extinct populations. In this context of biodiversity decline, our cross-analysis highlights that two of the five conservation units call for a rapid setting up of PMRs because of their high originality and their great risk of extinction: one unit including the populations of the Principality of Monaco and one unit that includes the populations of Nice and its surroundings. This study demonstrates the importance of integrating population vulnerability and conservation units. In a context of huge urbanization our approach makes a clear case for the design of PMRs.

Introduction

In the context of the severe biodiversity crisis of the Anthropocene, urbanization and habitat destruction or degradation of natural ecosystems are the primary drivers of plant extinctions worldwide, notably in biodiversity hotspots where they represent 39 % of the deleterious drivers vs 25 % for the coldspots [START_REF] Le Roux | Recent anthropogenic plant extinctions differ in biodiversity hotspots and coldspots[END_REF]. Urban expansion is occurring at an unprecedented scale, and today more than 50 % of the global human population live in urban environments (United Nations, 2018). The urban ecological footprint extends beyond city boundaries and drives severe environmental and biological changes (e.g. [START_REF] Grimm | Global change and the ecology of cities[END_REF][START_REF] Hahs | A global synthesis of plant extinction rates in urban areas[END_REF][START_REF] Wenzel | How urbanization is driving pollinator diversity and pollination -A systematic review[END_REF]. Indeed, urban areas threaten ecosystems as a result of direct habitat conversion [START_REF] Mckinney | Urbanization, biodiversity, and conservation[END_REF] and through various indirect effects, e.g. land-use changes, fragmentation by linear infrastructures such as roads, waste generation disturbances associated with recreational activities and diverse pollution (e.g. [START_REF] Defries | Land use change around protected areas: management to balance human needs and ecological function[END_REF][START_REF] Mcdonald | The implications of current and future urbanization for global protected areas and biodiversity conservation[END_REF]. Urbanization changes the biological integrity of habitats and the nature of food webs between species. High levels of urban densification (above 50 %) has largely led to pollinator declines and loss of pollination services [START_REF] Wenzel | How urbanization is driving pollinator diversity and pollination -A systematic review[END_REF]. Another impact is related to the frequent invasion by exotic species in natural areas adjacent to urbanized sectors, since habitat invasiveness is associated with disturbed landscapes (With, 2002).

As important biodiversity hotspots, Mediterranean-type ecosystems are particularly threatened by the increase of population density and urban areas [START_REF] Garci ́a-Nieto | Impacts of urbanization around Mediterranean cities: Changes in ecosystem service supply[END_REF][START_REF] Egidi | Towards local forms of sprawl: A brief reflection on Mediterranean urbanization[END_REF]; UNEP/MAP & Plan [START_REF] Bleu | State of the environment and development in the[END_REF]. In the Mediterranean region, the severe distortion between the loss of natural environments and their protection [START_REF] Hoekstra | Confronting a biome crisis: Global disparities of habitat loss and protection[END_REF][START_REF] Cuttelod | The Mediterranean: A biodiversity hotspot under threat[END_REF][START_REF] Doxa | Prioritizing conservation areas for coastal plant diversity under increasing urbanization[END_REF] implies a need to develop integrative policies of preservation through the strengthening of the network of protected areas [START_REF] Underwood | Threats and biodiversity in the mediterranean biome[END_REF]. But the high biodiversity, environmental heterogeneity and vulnerability of the Mediterranean Basin hotspot [START_REF] Médail | Hot-Spots analysis for conservation of plant biodiversity in the Mediterranean Basin[END_REF][START_REF] Blondel | Biodiversity and conservation[END_REF], combined with various political or administrative organizational schemes, preclude large scale conservation efforts that are often ineffective. It is therefore often necessary to build a more local and smaller-scale approach to preserve rare species. Despite the importance of the urbanization phenomenon for the alteration of Mediterranean biodiversity and ecosystem service supply [START_REF] Garci ́a-Nieto | Impacts of urbanization around Mediterranean cities: Changes in ecosystem service supply[END_REF], very few studies examine the consequences of these impacts and the possibilities of mitigating the induced effects on rare plants (e.g., [START_REF] Lhotte | Are there contrasted impacts of urbanization and land uses on population persistence? The case of Teucrium pseudochamaepitys, an endangered species in Southern France[END_REF][START_REF] Sulis | Assessing the global conservation status of the rock rose Helianthemum caput-felis[END_REF][START_REF] Samad | New insights on the conservation status of the endangered coastal endemic plant Astragalus berytheus (Fabaceae) in Lebanon[END_REF].

An efficient tool for the in situ protection of the threatened Mediterranean plants was the development of the Plant Micro-Reserve (PMR) network, a concept that was successfully developed 30 years ago first in Spain and then in other European and Mediterranean countries [START_REF] Laguna | The role of small reserves in plant conservation in a region of high diversity in eastern Spain[END_REF]Kadis et al., 2013). Although no fixed limit exists for the size of a PMR, this kind of small protected area is generally comprised between 0 and 100 ha. However, the definition of PMR remains quite empirical and based on the presence of one or more very rare and highly threatened plant species, mostly endemic, without clearly taking into account their evolutionary and functional components [START_REF] Laguna | PMR site selection and boundaries procedures[END_REF]. These shortcomings represent crucial shortfalls for conservation policies [START_REF] Hoban | Genetic diversity targets and indicators in the CBD post-2020 global biodiversity framework must be improved[END_REF]. They prevent the integration of the evolutionary history and the adaptive potential of the populations which are decisive for rare plant conservation in heterogeneous Mediterranean environments [START_REF] Médail | Using phylogeography to define conservation priorities: The case of narrow endemic plants in the Mediterranean Basin hotspot[END_REF][START_REF] Thompson | Plant evolution in the Mediterranean. Insights for conservation[END_REF]. This could also preclude the efficient conservation of unique populations in terms of evolutionary and ecological originality, and therefore the preservation of the global evolutionary heritage of the species. To better define relevant PMRs for a focus species, we propose to include a more complete assessment of its evolutionary and ecological patterns. Our approach is based on a spatial comparison of conservation units and population vulnerability with regards to the current conservation network. When genetic evidence is not available to delineate conservation units (e.g. [START_REF] Baumel | Population genetic structure and management perspectives for Armeria belgenciensis, a narrow endemic plant from Provence (France)[END_REF], environmental and floristic data can be used to account for ecological distinctiveness which is an important component of the adaptive potential at the species level [START_REF] Crandall | Considering evolutionary processes in conservation biology[END_REF].

To assess the relevance of this new PMR approach, we chose to study a highly urbanized area: the coastal region of the Maritime and Ligurian Alps (i.e. the French-Italian Riviera), one of the then regional biodiversity hotspots of the Mediterranean region [START_REF] Médail | Hot-Spots analysis for conservation of plant biodiversity in the Mediterranean Basin[END_REF][START_REF] Médail | Biodiversité végétale méditerranéenne et anthropisation : Approches macro et micro-régionales[END_REF] which is severely threatened by urban sprawl [START_REF] Vimal | Detecting threatened biodiversity by urbanization at regional and local scales using an urban sprawl simulation approach: Application on the French Mediterranean region[END_REF]. Our case study is focused on a narrow endemic plant: the Nice Snowflake Acis nicaeensis, a species directly impacted by land-use changes such as urbanization and tourist resort development (Diadema et al., 2007a, b;[START_REF] Pouget | Conservation unit allows assessing vulnerability and setting conservation priorities for a Mediterranean endemic plant within the context of extreme urbanization[END_REF]. An ecological and genetic delineation was previously performed in order to identify the conservation units for this species (see [START_REF] Pouget | Conservation unit allows assessing vulnerability and setting conservation priorities for a Mediterranean endemic plant within the context of extreme urbanization[END_REF]. Historical records from herbaria tend to indicate a reduction of Snowflake populations Diadema et al., 2007b) but no detailed analysis has been carried out to quantify this process and the vulnerability of this rare species, and a global conservation program is missing.

The main objectives of this study are (i) to propose a better distinction of Plant Micro-reserves (PMRs) by spatially integrating population vulnerability and conservation units, ii) to apply this method for a better distinction of original, highly threatened and not yet protected populations of a narrow endemic plant located in a highly urbanized area, (iii) to examine the appropriateness of the use of the PMRs in these patchy and heterogeneous Mediterranean landscapes.

Materials and methods

Study site and species

The Nice Snowflake (Acis nicaeensis (Ardoino) Lledo, A.P.Davis & M. B.Crespo, Amaryllidaceae) is a narrow endemic plant from the Maritime Alps, characterized by a patchy distribution on calcareous rocky grasslands. The distribution of A. nicaeensis covers approximately 420 km 2 , between the Pre-Alps of Grasse (col de Vence) to the West, and the only Italian population near the French-Italian border (Grimaldi, near Ventimiglia) to the East, including the five populations (two extinct) of the Principality of de Monaco (Fig. 1). The highest population density is found between Nice and Menton [START_REF] Diadema | Apport de la phylogéographie, de la dynamique et de la structure des populations pour la conservation des végétaux endémiques méditerranéens[END_REF][START_REF] Pouget | Conservation unit allows assessing vulnerability and setting conservation priorities for a Mediterranean endemic plant within the context of extreme urbanization[END_REF]. This Snowflake is characterized by a large ecological amplitude and it occurs between 5 and 1000 m a.s.l., i.e. from the thermo-Mediterranean to the upper meso-Mediterranean vegetation levels (Diadema et al., 2007a, b).

The species has only several thousand individuals scattered to form a highly fragmented and heterogeneous distribution range. It is registered in the annexes II and IV of the European Habitats Directive, and is included in the IUCN Red list of threatened vascular plants as an endangered taxa (EN) both in France (UICN et al., 2018) and in Italy [START_REF] Orsenigo | Red Listing plants under full national responsibility: Extinction risk and threats in the vascular flora endemic to Italy[END_REF]. Several factors threaten this species, and during the XIXth and early XXth centuries some populations were severely damaged by massive sampling for herbarium collections [START_REF] Diadema | Apport de la phylogéographie, de la dynamique et de la structure des populations pour la conservation des végétaux endémiques méditerranéens[END_REF]. Nowadays, the major threats are the huge development of urbanization along the coast of the Maritime Alps, the increase of the tourism activities and the impact of invasive plants [START_REF] Diadema | Apport de la phylogéographie, de la dynamique et de la structure des populations pour la conservation des végétaux endémiques méditerranéens[END_REF]Diadema et al., 2007b).

Population structure and conservation units

The data collection consists of 804 geolocated occurrence data of A. nicaeensis (http://flore.silene.eu), for a total of 53 populations (42 current and 11 extinct) whose delimitation is based on a geographical discontinuity of more than 500 m between two populations (Fig. 2). The area of each population was calculated as the size of a polygon representing the area of the population in two dimensions (elevation wasn't taken into account) using SIG software QGIS 3.10 (QGIS Development Team, 2020). Surface areas of populations vary between 4 and 170 ha and they were classified into three classes: small (I) = population area inferior to 20 ha; medium (II): population area between 20 and 50 ha; large (III) = population area superior to 50 ha.

The assessment of historical localities was performed using the 195 specimens contained in diverse herbaria: Aix-en-Provence (AIX), Firenze (FI), Geneva (GE), Genova (G), Grenoble (GR), Lyon (LY), Marseille (MARS), Paris-MNHN (P), Montpellier (MPU), Nice (NICE) and Torino (TO). This made it possible to precisely locate 78 historical occurrences (see [START_REF] Diadema | Apport de la phylogéographie, de la dynamique et de la structure des populations pour la conservation des végétaux endémiques méditerranéens[END_REF] for more detail). The disappearance of several historical localities was attested by visiting these areas several consecutive years.

The ecological and evolutionary divergences between the populations of Acis nicaeensis has allowed us to define five conservation units. Phylogeographical structure (three groups according to plastid haplotypes revealed) was considered as a proxy for evolutionary legacy, and ecological differentiation (three groups defined by multivariate analysis of habitat) was used as a proxy for ecological distinctiveness. Two populations were assigned to the same conservation unit if bearing the same haplotype and living in the same ecological group (see [START_REF] Pouget | Conservation unit allows assessing vulnerability and setting conservation priorities for a Mediterranean endemic plant within the context of extreme urbanization[END_REF] for more details, and Fig. 2b). The shape of each conservation unit depends on the area and the actual geographic configuration of each population that composes it.

Urbanization level and population vulnerability

Urbanization level and urban sprawl were estimated per population of A. nicaeensis using two maps: (i) the "Carte d' État-Major" (EM) map, drawn in 1866 to estimate "past urbanization" (Fig. A1a) and (ii) the IGN (National Institute of Geography, France) map of 2006 to estimate "current urbanization" (Fig. A1b). The EM map is the oldest available with sufficient details to document and quantify roads or buildings, and the IGN map presents similar spatial features thus allowing the best diachronic comparison. The term "urbanization" included all the possible artificialization features such as buildings of all types, sport centers and fields, roads, staircases, parkings, water tanks etc.

A class value of urbanization was given for a 100 × 100 m grid for each period. We used mesh to easily assess artificialization pooled in 5 classes: 0 = no urbanization; 1 = urbanization for less than 25 % of surface; 2 = urbanization between 25 and 50 % of surface; 3 = urbanization between 50 and 75 % of surface; 4 = urbanization for more than 75 % of surface. The final urbanization percentage is the average of all mesh values present within an Acis' population polygon. The difference between the current urbanization and the past urbanization (IGN value minus -EM value) was used to estimate the urban sprawl rate. The value were converted in % to be more explicit (Fig. 2a). A permutation test based on absolute differences between medians was performed in R (R core team, 2020) to evaluate if the level of urban sprawl of the extinct populations is significantly higher than the level of those extinct (R code available in supplementary material: Table A3).

To assess population vulnerability, we used a simple vulnerability index combining three classes of populations superficies (small, medium, large: see above) and four classes of urbanization. This vulnerability index was assigned to each population, including five classes (Table 1): V0 = populations of any surface area with no urbanization (I) or low urbanization (II) in large populations; V1 = populations with low urbanization (II) and small or medium populations; V2 and V3 = average (III) or high urbanization (IV) according to the surface area of the populations; V4 = small or medium and highly urbanized (IV) populations. A vulnerable population (classes V2, V3 and V4) will be even more vulnerable if the number of individuals is low. The high number of individuals per population (>500 individuals) are found in less vulnerable populations (V0).

Current protected area network

The cartographic data of the protected areas where the Snowflake occurs were compiled both for France (Région Sud-Provence-Alpes-Côte d'Azur) and for Italy (Regione Liguria), as no protected area currently exists in the Principality of Monaco. It was necessary to standardize the various existing statuses of protected areas according to the IUCN classification [START_REF] Dudley | Guidelines for applying protected area management categories. Gland, Switzerland: IUCN[END_REF][START_REF] Lefebvre | Les espaces protégés français : Une pluralité d'outils au service de la conservation de la biodiversité[END_REF]. Two types of protected area networks were considered, depending on the level of protection and the management implemented therein: (i) the global protection network which groups IUCN categories I to 4, i.e. protected areas exclusively dedicated to the conservation of biodiversity (e.g. core area of national park, national natural reserve, sites of the Conservatoire du littoral in France) or aimed at reconciling the conservation of nature and the sustainable use of resources (e.g. regional biological reserve, forest reserve); (ii) the European Natura 2000 network.

The geographic outlines of the two networks were obtained for France from the INPN (National Inventory of Natural Heritage: http ://inpn.mnhn.fr), the DREAL-PACA and the Conservatoire du littoral, while for Italy the data was provided by the Liguria region. The different protected areas of IUCN (levels I-IV) were merged (QGis 3.10 software: QGIS Development Team, 2020) to form a single cartographic layer. Degrees of spatial overlap between the general population distribution envelope of each Snowflake population and the related protected areas were calculated. Then, to find populations that should be included in Plant Micro-Reserves (PMRs) we looked for unprotected populations with high vulnerability and high conservation values. Thus for each population, we examined their spatial overlap with current protected areas, their conservation units already defined by [START_REF] Pouget | Conservation unit allows assessing vulnerability and setting conservation priorities for a Mediterranean endemic plant within the context of extreme urbanization[END_REF] and their vulnerability (Table 1). This approach refers to the gap analysis methodology, performed for example in the conservation of threatened flora of some Mediterranean countries [START_REF] Christodoulou | Using threatened plant species to identify conservation gaps and opportunities on the island of Cyprus[END_REF][START_REF] Laguna | Role of micro-reserves in conservation of endemic, rare and endangered plants of the Valencian region (Eastern Spain)[END_REF].

Results

Influence of urban sprawl on the persistence of Acis nicaeensis populations

The distribution of urbanization in the French-Italian Riviera around the populations of A. nicaeensis presents a very distinctive gradient, from very high urbanization (>75 %) near the coast (even near 100 % for MRO population in Monaco) to near absence (e.g. CMO) or low urbanization level (<25 %) for most of the populations located in the upper altitudinal range (Fig. 2a). The percentage of urbanization was already high in 1866 near the coast (more than 25 %, Fig. A1) and higher in 2006 (more than 50 %, Fig. A2). The urban sprawl is still highly active on the coast, as represented by the high value of urbanization increase (Fig. A3), and 70 % of the A. nicaeensis population areas suffer from this alteration of natural habitat. A low urbanization level characterizes some isolated populations (e.g. CVE, BSJ or PSL) in the far east and west of the Snowflake's distribution (Fig. 2a). Low urbanization between 1866 and 2006 is observed for the central inland populations (e.g. CAR, GCO, EZE).

Among the 53 known populations occurring at the beginning of the XIXth century, eleven cannot be found nowadays and are considered extinct, i.e. 20 % of all populations (Table A2). There is a very significant correlation between the disappearance of these populations and the urban sprawl. The statistical analysis shows that the median value for urban sprawl is significantly higher for extinct populations (Table A4) and the permutation test confirmed this difference (p < 5%). Among the extinct populations, three of them (BEA, MJE and MMO) were impacted by a very high level of urban sprawl (Table A2); three populations (LAZ, PVE and ROQ) were subjected to medium or low levels of urban sprawl between 1866 and 2006 but a high level of urbanization already in 1866, and their last mentions occurred before the beginning of the XXth century; in contrast, two populations (CMO and MGO) are currently subject to a low urbanization level and their disappearance in the 2000s is due to site layout for recreation or outdoor activities. The median urban sprawl rate of the most vulnerable populations (V4) is close to those of already extinct populations (Table A4).

Vulnerability of Acis nicaeensis populations

The majority of A. nicaeensis populations occur in the center of the distribution, whereas few have a high geographical isolation (e.g. CVE and CAS). 45 % of the inventoried populations (i.e. n = 14,) present less than one hundred individuals and are mainly situated in the south-west of the area (e.g. MAL or MVI). The vulnerability of populations ranges according to the urban pressure and the superficies of each population (Table A1). The most vulnerable ones (classes V2, V3, V4) are found especially along the coast and in the eastern part of the range (Fig. 2c).

The less common conservation units (CB and BB) are assigned to the vulnerable classes V2 and V4. We must underline the lack of genetic information for two of the most vulnerable (V4 class) populations (MSD and TDA). Populations included in the conservation units AA, AC and BA, are less vulnerable, belonging to V0 class in majority and never reaching the V3 class.

Current protected areas and identification of gaps for a PMR network

From the 42 current populations of the Snowflake, 16 are included in the global network of protected areas (categories I to IV sensu IUCN) (Fig. A2a) and 24 are partially or totally included in the Natura 2000 network (Fig. A2b). If we consider the spatial congruence of the two networks, 21 populations are more or less protected or managed whereas 13 populations with low vulnerability are located outside of these two networks and, more worryingly, 7 populations with high vulnerability (≈20 %) are not included into a protected area (Fig. 2d). The latter concerns four populations with high vulnerability and ecoevolutionary originality: the three current populations of the Principality of Monaco (MRO, MRE: BB unit, MSD), and one of the three populations of the CB unit (CFE). It also concerns also three populations (TDA, CRO, MMU) of the south-eastern part of the range. These seven populations have priority to be included into a PMR network.

Discussion

Urban sprawl as the main threat to Acis nicaeensis populations

During the last decades the Mediterranean Basin underwent a dramatic increase of urban expansion with a rate of 17 % between 1990 and 2000 [START_REF] Underwood | Threats and biodiversity in the mediterranean biome[END_REF]. In the Mediterranean French region, a land-use change model predicts that 35 % of the sites of high biodiversity interest can potentially be impacted by urbanization over a 20 year period [START_REF] Vimal | Detecting threatened biodiversity by urbanization at regional and local scales using an urban sprawl simulation approach: Application on the French Mediterranean region[END_REF]. The complex process of urban sprawl [START_REF] Egidi | Towards local forms of sprawl: A brief reflection on Mediterranean urbanization[END_REF] represents the main threat for the biodiversity and for the persistence of Mediterranean rare species including narrow endemic plants that often possess distinct conservation units [START_REF] Médail | Using phylogeography to define conservation priorities: The case of narrow endemic plants in the Mediterranean Basin hotspot[END_REF]. However, very few studies have so far quantified this phenomenon for conservation planning (e.g. [START_REF] Doxa | Prioritizing conservation areas for coastal plant diversity under increasing urbanization[END_REF].

Since the last 150 years, the magnitude of the urbanization increase

Table 1

Assessment on vulnerability indexes based on urbanization levels and surface areas of Acis nicaeensis populations. V0: population of any size with no urbanization; V1: population with low urbanization; V2 and V3: medium size or high urbanization according to population size; V4: small or medium size and highly urbanized population.

is severe for 70 % of the A. nicaeensis populations, and this urban extension is mainly observed along the coast, i.e. along the French-Italian Riviera [START_REF] Médail | Biodiversité végétale méditerranéenne et anthropisation : Approches macro et micro-régionales[END_REF][START_REF] Pouget | Conservation unit allows assessing vulnerability and setting conservation priorities for a Mediterranean endemic plant within the context of extreme urbanization[END_REF]. The extinction of eleven populations has been attested by herbaria records but this is a minimum value since several populations unrecorded in the past may have disappeared (cryptic extinction). Comparisons of land use maps of 1886 and 2006 shown that urban sprawl was significantly higher for extinct populations than for current ones. There is no doubt as to the cause of the disappearance of certain populations (MMO: near Monaco and BEA: Beaulieu-sur-Mer) that are currently in the heart of a massive urban area and for which a complete habitat destruction has been attested. For the others, we found a high and significant correlation between urbanization level and disappearance, especially for LAZ (Lazaret) and ROQ (Roquebrune-Cap-Martin).

Thus our study shows with confidence that urbanization caused the disappearance of most of the extinct A. nicaeensis populations. Moreover, our analyses indicate that some situated along the coast (e.g. MRO, MRE, MSD: Monaco or TDA: La Turbie, "Trophée des Alpes") are characterized today by the same level of urbanization and urban sprawl than those characterizing extinct populations. As indicated above, a large part of these populations, embedded in a strong urban environment, have less than one hundred individuals, well below short and long term persistence thresholds [START_REF] Frankham | Genetics in conservation management: Revised recommendations for the 50/500 rules, Red List criteria and population viability analyses[END_REF]. So we estimate that there is a high probability of extinction in the short-term due to their very low size and the deleterious effects of urbanization. The extinction of a population is an irreplaceable loss for genetic and ecological attributes, notably in narrow endemic plants with highly diverse genetic structures induced by heterogeneous environments and various historical biogeography as in the Mediterranean Basin hotspot (e.g. [START_REF] Médail | Using phylogeography to define conservation priorities: The case of narrow endemic plants in the Mediterranean Basin hotspot[END_REF][START_REF] Thompson | Plant evolution in the Mediterranean. Insights for conservation[END_REF].

Integration of conservation units and vulnerability to discriminate PMRs

The use of conservation units is a relevant toolstill too neglectedto better assess the originality of the populations of a species. It relies on the neutral and adaptive components of genetic variation at an intraspecific level [START_REF] Fraser | Adaptive evolutionary conservation: Towards a unified concept for defining conservation units[END_REF] and includes the ecological characterization of each considered population [START_REF] Crandall | Considering evolutionary processes in conservation biology[END_REF]. For A. nicaeensis, the presence of significant variations at the intraspecific level brings to light the imperative need for a more precise conservation policy. Five conservation units were delineated based on genetic and ecological data [START_REF] Pouget | Conservation unit allows assessing vulnerability and setting conservation priorities for a Mediterranean endemic plant within the context of extreme urbanization[END_REF]. Two units present unique evolutionary and ecological properties: the very few populations that compose the CB unit (Nice and St-Jean-Cap-Ferrat) and especially the one of the Principality de Monaco (BB unit) (Fig. 2b).

Once conservation units have been designated, it is necessary to assess the population's vulnerability. We have considered the degree of urbanization affecting both A. nicaeensis population and its surface area (Fig. 2a). Among the five conservation units, two (CB and BB) are in imminent danger because of their restricted range, the few populations they contain and the low number of individuals per population. These two units are threatened by a very high level of urbanization (more than 75 %), but also a high competition pressure induced by exotic plants. Because of its location in the outskirt of two big cities (Nice and Monaco), certain populations (e.g. CRO, MMU) of the AC unit are very vulnerable and a regular monitoring is necessary. But urbanization is not the only risk. In the northern part of the distribution, one population is already extinct at Peille (CSS: Chapelle Saint Siméon) probably because of the collapse of traditional agro-pastoral land-uses (Diadema et al., 2007b), and so are two others (CMO and MGO) due to the recent development of recreation activities for the public.

The positive correlation between the significant originality and the high vulnerability of V3 and V4 population groups deserves to be considered in a conservation plan. So it's important to examine the relevance of the current conservation network for the Nice Snowflake in France, Italy and the Principality of Monaco. Among the 42 current populations, 21 are more or less protected or managed but at least 7 populations with high vulnerability are not protected to date (Fig. 2d). The Natura 2000 protection network represents an important tool for the conservation of the habitats of the Nice Snowflake since it integrates 57 % of the populations. The spatial congruence is also poor with the global protection network (i.e. nature reserve, national park…) and real major gaps appear, mainly for the most coastal populations (Fig. 2d). The areas where the populations of the two highly threatened conservation units occur (CB and BB) are not included in a high level protection area sensu IUCN [START_REF] Dudley | Guidelines for applying protected area management categories. Gland, Switzerland: IUCN[END_REF]. The conservation unit BB presents the most vulnerable populations (V4), including the three current populations of Monaco (MRO, MRE and MSD). Due to its very small range size and the strong urbanization of the Principality of Monacoone of the highest human densities of the world -, the BB unit is the most at risk of extinction and if nothing is done, these populations are likely to go extinct in the near future.

Remnants of intact vegetation within highly urbanized landscapes can still retain endemic or rare species [START_REF] Aronson | A global analysis of the impacts of urbanization on bird and plant diversity reveals key anthropogenic drivers[END_REF]. This is the case for the Principality of Monaco, both for endemic plants such as Limonium cordatum (L.) Mill. or Campanula rotundifolia L. subsp. macrorhiza (DC.) Bonnier & Layens [START_REF] Médail | Inventaire de la flore terrestre spontanée de la Principauté de Monaco[END_REF] and invertebrates such as the Coleoptera Otiorhynchus monoecirupis Lemaire et al. present in only one known locality on the Rocher de Monaco [START_REF] Lemaire | Les Curculionides cavernicoles de la région niçoise, France. III. Description d'Otiorhynchus (Lixorrhynchus) monoecirupis n. sp. de Monaco (Coleoptera, Curculionidae, entiminae)[END_REF]. The designation of PMRs in this small country which does not yet have a protected terrestrial network would be thus a clear priority. It would also be important to define a PMR for the population of the CB unit localized at St-Jean-Cap-Ferrat (CFE), and for some populations of the south-eastern part of the distribution (e.g. CRO, MMU, TDA) even if their assignment to a specific conservation unit could not be carried out to date. Land owners and stakeholders analysis is now ongoing to best develop a land acquisition strategy or a regular management of the PMRs.

Conclusions

The present approach provides a more precise and operational framework for site selection of PMRs [START_REF] Laguna | PMR site selection and boundaries procedures[END_REF]. We demonstrate the relevance of developing a cross-analysis for threatened species in highly urbanized and heterogeneous landscapes, including (i) the clear estimate of population vulnerability, (ii) the contribution of each population to the evolutionary potential of the species by designating conservation units, and (iii) the gap analysis of the current protection status for each site. This approach allows a good selection of the priority conservation issues at the species scale.

This study shows the clear impacts of ancient, strong and ongoing urbanization on the populations of a narrow endemic plant, Acis nicaeensis, in the French-Italian Riviera. Despite its status as a protected species at European and national levels, this Snowflake is still very threatened and its future remains uncertain. The conservation status for A. nicaeensis according to the standardized evaluation of the European Union is thus "unfavorable inadequate (U1)" with a tendency towards a deterioration of the state of conservation of the species between the two reports (2013 vs. 2019). Our gap analysis shows that two conservation units are in imminent danger and seven populations with high vulnerability are not protected to date.

The application of the PMRs to these patchy and heterogeneous Mediterranean landscapes is very appropriate, especially to improve the conservation status of the Snowflake in the Principality of Monaco. That country is not concerned by the European Directive 92/43/EEC on the conservation of nature and of wild fauna and flora and there is currently no legal protection status there for this species. The creation of plant microreserves would be probably the best solution to preserve the last remnants of semi-natural habitats where the Snowflake persists and to get a real conservation status for this emblematic plant.

Fig. 1 .

 1 Fig. 1. Total distribution area of Acis nicaeensis populations located between Vence (France) and Grimaldi (Ventimiglia, Italy); empty circles correspond to recent populations (>2000) and full circles correspond to ancient populations (<2000).

Fig. 2 .

 2 Fig. 2. a: Urban sprawl rate, expressed as the % of surface affected by urbanization between 1886 and 2006, impacting Acis nicaeensis populations in the French-Italian Riviera; b: The five defined conservation units and the other current populations; c: The different classes of vulnerability (V0-V4) of the current populations and the 11 extinct populations; d: The conservation priority of each A. nicaeensis population, including the 7 populations in orange proposed as Plant-Micro-Reserves (PMRs).

Acknowledgments

Field and molecular works were partly funded by the Prince's Government of the Principauté de Monaco, Department of the Environment (project n • 389.2018.14: Plan local d'actions pour la nivéole de Nice-Acis nicaeensis, 2018-2020), the Prince Albert II of Monaco Foundation (project MONACOBIODIV) and the DREAL-PACA. This research was part of the PhD thesis of Marine Pouget supported by the Région Sud / Provence-Alpes-Côte d'Azur (Bourse doctorale régionale 2011-2014) and performed at Aix-Marseille University / IMBE. Molecular analyses benefited from equipment and services from the molecular biology facility (SCBM) at IMBE. The current protected area network and the identification of conservation gaps by GIS were performed by Guilhem De Barros (Mediterranean National Botanical Conservatory of Porquerolles). We thank Julien Baret (BIODIV) and Jérôme Volant (ECOMED) for their contribution in the census of the populations, and Adeline Almero, Julie Grondin and Camille Laval for their contribution to this work.

Declaration of Competing Interest

The authors declare that there is no conflict of interest.

Appendix A. Supplementary data

Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jnc.2021.125980.