Ostracods and environmental variability in lagoons and deltas along the north-western Mediterranean coast (Gulf of Lions, France and Ebro delta, Spain)

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Original article

Ostracods and environmental variability in lagoons and deltas along the north-western Mediterranean coast (Gulf of Lions, France and Ebro delta, Spain) Ostracodes et variabilité environnementale dans les lagunes et deltas du nord-ouest de la Méditerranée (Golfe du Lion, France et delta de l’Ebre, Espagne) Tiphaine Salel a,∗ , Hélène Bruneton b,∗ , David Lefèvre a a

CNRS, MCC, UMR 5140 Archéologie des Sociétés Méditerranéennes, Campus de Saint-Charles, Université Paul-Valéry Montpellier 3, 34199 Montpellier cedex 05, France b UMR-CNRS 6635 CEREGE, Europole Méditerranéen de l’Arbois, Université Aix-Marseille, BP 80, 13545 Aix-en-Provence cedex 04, France

Abstract The aim of this paper is to characterize various lagoon and delta environments through the analysis of ostracod fauna. Various aquatic environments from the Mediterranean coastline of the Gulf of Lions (Languedoc-Roussillon, France) and Ebro delta (Catalonia, Spain) were studied. The sample sites (60) are different in terms of marine and fluvial influence. Environmental parameters (salinity, water depth, sedimentary texture, plant cover) were measured and compiled from available data in order to characterize the biotopes. We interpreted the species distribution as related to the degree of isolation from the sea, the hydrological internal currents and the proximity of river mouths. Moreover, the assemblage composition seems influenced by the lagoon vegetation growth. These data can be used for the palaeoenvironmental reconstructions, particularly in Holocene deltaic context where the mobility of river mouths and the forming and evolution of sand bars and lagoons are recurring issues. © 2016 Elsevier Masson SAS. All rights reserved. Keywords: Bioindicator; Brackish water; Marginal marine environments; Confinement gradient; River mouths influence

Résumé L’objectif de ce travail est de caractériser différents environnements lagunaires et deltaïques par leur faune d’ostracodes. Plusieurs milieux aquatiques des côtes basses du Golfe du Lion (Languedoc-Roussillon, France) et du delta de l’Ebre (Catalogne, Espagne) ont été étudiés. Les sites de prélèvement (60) sont variés en termes d’influence marine et fluviale. Les paramètres environnementaux mesurés ou disponibles (salinité, hauteur d’eau, texture des sédiments, recouvrement végétal) ont été utilisés pour caractériser les biotopes. Nous interprétons la répartition des espèces en fonction du degré de fermeture morphologique par rapport à la mer, des circulations hydrologiques internes, et de la proximité des embouchures fluviales. De plus, le développement de la végétation dans les lagunes semble influencer la composition des assemblages. Ces données peuvent être utiles pour reconstituer des milieux anciens, en particulier en contexte deltaïque Holocène, où les questions relatives à la mobilité des embouchures fluviales, à la formation et à l’évolution des barrières littorales et des lagunes, se posent souvent. © 2016 Elsevier Masson SAS. Tous droits r´eserv´es. Mots clés : Bioindicateurs ; Eaux saumâtres ; Environnements marins littoraux ; Gradient de confinement ; Influence des embouchures fluviales

1. Introduction ∗

Corresponding authors. E-mail addresses: [email protected] (T. Salel), [email protected] (H. Bruneton).

The study of ostracods in coastal environments has been ongoing for quite some time (Carbonel, 1980). Research into present-day ecology shows that the composition, density and

http://dx.doi.org/10.1016/j.revmic.2016.09.001 0035-1598/© 2016 Elsevier Masson SAS. All rights reserved.

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Fig. 1. Location of the study zones and others works concerning recent ostracods (1. Reys, 1961a, 1961b, 1963, 1964, 1965a, 1965b, 2. Kruit, 1955, 3. Steger, 1972, 4. Bodergat, 1983, 5. Hartmann, 1958 et Kurc, 1961, 6. Hartmann, 1953, 1960).

diversity of assemblages are controlled by natural environmental parameters (salinity, temperature, pH, oxygen, hydrodynamic conditions, nature of substratum) and/or linked to anthropogenic pollution (nutrient and heavy metal contents) (Frenzel and Boomer, 2005). More recently, ostracods have been frequently used in coastal geomorphology/geoarchaeology as bioindicators of past hydrologic and geomorphologic conditions (Mazzini et al., 2015). In the Mediterranean, ecological studies have focused extensively on stenohaline marine environments (bibliography summarized by Lachenal, 1989). A collection of detailed ecological data for brackish water ostracods in northern Europe can be found in Frenzel et al. (2010), but no compilation of this kind of study is available for the Mediterranean area. The need for more ecological data in lagoonal and deltaic environments remains in spite of a growing body of local studies such as the Venice lagoon (Ruiz et al., 1999, 2000b), the Moroccan Nador lagoon (Ruiz et al., 2006a), the Tunisian El Melah lagoon (Ruiz et al., 2006b), and the estuarine brackish environments of the adjacent Atlantic coast in southern Spain (Ruiz et al., 1997, 2000a) and northern Morocco (Nachite et al., 2010). The aim of this paper is to enhance knowledge of the ostracod ecology in North-western Mediterranean brackish environments by the analysis of a main area located on the coast

of the Gulf of Lions (Languedoc-Roussillon, France; Fig. 1) and an additional area of the Ebro delta (Catalonia, Spain). The resulting database was also conceived as an aid for the reconstruction of late Quaternary coastal environments, especially in our main research area. As such, it aims to characterize the largest possible panel of brackish-water environments. The main French study area is composed of several lagoons, some of them connected to rivers (such as the Aude, Berre, Lez, Vidourle river), while the Spanish site allows us to investigate a deltaic environment. Some lagoons in this general area have been studied (Kruit, 1955; Hartmann, 1953, 1958, 1960; Kurc, 1961; Steger, 1972; Bodergat, 1983) but results are sometimes ambiguous regarding species determinations, and imprecise regarding the environmental characterization of sites. Lagoon and delta ostracods typically belong to the “coastal brackish-marine” and “continental brackish” ecological groups, according to the four classification groups of Anadon et al. (2002). For example, these are certain species of the Cyprideis, Loxoconcha, Leptocythere, Xestoleberis and Heterocypris genus. They are euryhaline and eurythermal, tolerating important seasonal salinity and temperature variations. On account of this high tolerance and the lack of references on modern ecology, these ostracods are often used in Holocene coastal

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geomorphology studies to establish a stage of hydromorphological separation from the sea (“confinement” according to Guelorget and Perthuisot, 1983). Any brackish environment then appears as lagoonal, a term which does not take into account the diversity of environments with variable salinity. The morphological diversity of the study areas allows us to offer a more complex model, aiming to include the influence of fluvial hydrological inputs and to demonstrate the internal complexity of a given lagoonal system. An in-depth study of the present-day distribution of faunal assemblages was thus necessary to test the response of ostracods to this diversity of hydro-geomorphological conditions, and provide a better quality collection reference for palaeoenvironmental studies. We focus on how ostracod assemblages describe the different types of brackish environments by introducing different parameters such as euryhalinity, water depth, sedimentary texture and plant cover. Finally, we also aim to illustrate how assemblages reveal exchanges between the different compartments of aquatic environments from both rivers and freshwater bodies to the sea, while reflecting local environmental conditions.

2. Materials and methods 2.1. Study area The North-western Mediterranean coastline consists of depositional coasts, alternating with rocky areas. The river mouths supply high sediment input that support the development of barrier-lagoon systems and deltas, in a wave-influenced microtidal context (Anthony et al., 2014) (Fig. 1). Between the Rhone delta and the north-eastward Pyrenees border, the LanguedocRoussillon coast of the Gulf of Lions (France) is made up of slightly concave sandy beach barriers, anchored by a sequence of rocky promontories. This barrier system encloses a series of lagoons. The early Holocene coast was more irregular, with rias, shallow marine bays and low continental plains located in the present-day lagoonal areas. From ca. 7000 years BP onwards, the decreasing rate of relative sea-level rise (Aloïsi et al., 1978) allowed for the progressive building of the sandy barriers and the regularization of the coastline. The shoreline dynamics are under the influence of longshore drift cells, which rework river sediments originating mainly from the Rhone to the north of the study zone and secondarily from the Herault, Orb and Aude rivers (Certain et al., 2005; Brunel, 2010). The lagoonal environments closest to the sedimentary sources were isolated first, such as the Palavas complex (Raynal et al., 2010; Sabatier et al., 2010). Their most inland-lying areas, filled in by river deposits, were turned into shallow marshes landlocked in the coastal plain (Aloïsi and Gadel, 1992). The distant basins were closed later (Ferrer, 2010; Dolez et al., 2015) and still keep permanent natural inlets. On the adjacent Catalan coast (Spain), the Ebro delta forms one of the largest Mediterranean open-coast deltaic plains. It is shaped by the sea swell which spreads fluvial sediments on both sides of the river mouth, creating two sandy spits which protect two marine bays (Somoza and Rodriguez-Santalla, 2014).

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The confinement relative to the open sea and the continental water input are different from one site to the other, and partially control physico-chemical parameters such as salinity. The local hydrodynamic and hydrological conditions are also influenced by the Mediterranean climate, characterized by a usual three months summer drought. Annual rainfall amounts may range between 400 and 600 mm, with a primary and a secondary peak in autumn and spring, respectively. The prevailing N–NW winds blow from the continent and limit the build-up of sand dunes on the shores. They contrast with episodic E–SE winds associated with sea storms (Durand, 1999). Finally, this large array of geomorphological and hydrological conditions is influenced further by human activities such as salt marsh exploitations, artificial inlet opening through the lidos, river damming or diking. 2.2. Fieldwork and sample processing The samples were collected during the summer season (between June and September 2013 and 2014). Altogether 60 samples were put together: 25 from lagoons, 17 from river mouths and downstream ends of artificial canals, 12 from marine bays, 1 from a salina, and 5 additional samples were taken from coastal plains (landlocked marshes MAT1, CAP1, CAP2 and rice fields RIZ1, RIZ2). Environmental parameters recorded were conductivity, pH, water depth, plant species and vegetation cover ratio over 1 m2 . Oxygen content could not be measured. In addition, sediment samples were extracted manually in order to estimate deposit textures by sieving. The sediments were dried, weighed then separated on 50 and 2000 ␮m mesh with water. Ostracods were collected from the upper 2 millimeters of the substrate with a plankton net (63 ␮m mesh) (Meisch, 2000). If aquatic plants were developed around the sampling site, the vegetation was gathered with the sieve in order to collect the phytal ostracods. Each sample was dried, weighed, diluted with water then washed on sieves with a 125 and 500 ␮m mesh. The valves were extracted under a stereomicroscope (magnification × 100). When faunal density was high, each fraction was divided into equal sub-samples in order to limit counts to about 300/350 valves. These values correspond to the number of individuals required for the statistical analysis of ostracod assemblages (Ruiz et al., 1997). 2.3. Determinations Carapaces were determined under stereomicroscope observations and Scanning Electron Microscope (SEM) pictures, using the Bonaduce et al. (1975), Oertli (1985), Athersuch et al. (1989), Meisch (2000) and Fuhrmann (2013) atlases. As often as possible determinations of the species level were made, apart from some rare taxa or juvenile specimens which are limited to the genus (Plates 1–4). Spinileberis sp. is not described in the mentioned atlases. The valves attributed to this genus are characterized by a reticulated carapace with smoother posterior and anterior margins (Plate 1, nos. 11–12). Two strong ridges ending in a

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Plate 1. 1. Bairdia sp. M’Coy, 1844. External view, right valve (Lez river mouth); 2. Propontocypris cf. pirifera Müller, 1894. External view, left valve (Lez river mouth); 3. Propontocypris sp. Sylvester-Bradley, 1947. External view, right valve (Fangar bay). 4–5. Leptocythere type lacertosa Hirschmann, 1912: 4. External view, right valve; 5. Internal view, right valve (Bages-Sigean lagoon); 6. Leptocythere fabaeformis Müller, 1894. External view, left valve (Fangar bay); 7–8. Callistocythere littoralis Müller, 1894: 7. External view, left valve; 8. Internal view, left valve (Ayrolle lagoon); 9. Callistocythere sp. Müller, 1894. External view, left valve (Fangar bay); 10. Cyprideis torosa Jones, 1850. External view, right valve (Castelou marsh); 11–12. Spinileberis sp. Brady, 1880: 11. External view, left valve; 12. Dorsal view, complete carapace (Fangar bay); 13. Neocytherideis cf. subulata Puri, 1952. External view, left valve (Aude river mouth); 14. Neocytherideis cf. complicata. Puri, 1952. External view, left valve (Fangar bay); 15. Pontocythere turbida Müller, 1894. External view, right valve (Ayrolle lagoon); 16. Carinocythereis carinata Roemer, 1838. External view, left valve (Lez river mouth); 17. Carinocythereis whitei Baird, 1850. External view, left valve (Fangar bay); 18. Costa sp. Neviani, 1928. External view, right valve (Lez river mouth).

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Plate 2. 1. Semicytherura sulcata, Müller, 1894. External view, right valve (Lez river mouth); 2. Semicytherura cf. sella. Sars, 1866. External view, right valve (Ayrolle lagoon); 3. Semicytherura incongruens, Müller, 1894. External view, right valve (Fangar bay); 4. Heterocythereis albomaculata Baird, 1838. External view, left valve (Lez river mouth); 5. Aurila woodwardi Brady, 1868. External view, right valve (Ayrolle lagoon); 6. Aurila convexa Baird, 1850. External view, left valve (Fangar bay); 7. Loxoconcha rhomboidea Fischer, 1855. External view, right valve (Bages-Sigean lagoon); 8–9. Loxoconcha elliptica Brady, 1868: 8. External view, right valve; 9. External view, left valve (Palazy lagoon); 10. Palmoconcha cf. turbida Müller, 1894. External view, right valve (Fangar bay); 11. Cytheromorpha fuscata Brady, 1869. External view, right valve (Aude river mouth); 12. Xestoleberis communis Müller, 1894. External view, left valve (Bages-Sigean lagoon); 13–14. Xestoleberis cf. nitida Liljeborg, 1853: 13. External view, right valve; 14. Internal view, right valve (Palazy lagoon); 15. Paradoxostoma simile Müller, 1894. Internal view, left valve (Ayrolle lagoon); 16. Cytherois cf. fischeri Sars, 1866. External view, left valve (Alfacs bay); 17. Cytheretta adriatica Müller, 1894. External view, left valve (Ponant inlet); 18. Basslerites sp. Teichert, 1937. External view, right valve (Alfacs bay).

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Plate 3. 1–3 Candona cf. neglecta Sars, 1887: 1. External view, right valve; 2. External view, left valve, immature; 3. Internal view, right valve, immature (Vendres lagoon). 4–6. Candona angulata Müller, 1900: 4. External view, left valve; 5. External view, right valve, immature; 6. Internal view, left valve, immature (Vidourle river mouth); 7–8. Pseudocandona cf. albicans Brady, 1864: 7. External view, right valve; 8. External view, left valve, immature (Vendres lagoon); 9. Candonopsis cf. scourfieldi Brady, 1910. Internal view, left valve, immature (Aude river mouth). 10–11. Cypria ophtalmica Jurine, 1820; 10. External view, left valve; 11. Internal view, right valve (Capestang marsh); 12. Cypria ophtalmica Jurine, 1820. Dorsal view, complete carapace (Capestang marsh); 13–15. Cyclocypris sp. Brady & Normann, 1889: 13. External view, right valve; 14. Internal view, right valve; 15. Dorsal view, complete carapace (field rice, Ebro delta); 16. Darwinula stevensoni Brady & Robertson, 1870. External view, left valve (Ebro river mouth); 17–18. Ilyocypris braddy/gibba Brady & Norman, 1889; 17. External view, left valve; 18. Internal view, right valve (Vendres lagoon).

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Plate 4. 1–2. Cypris bispinosa Lucas, 1849; 1. External view, left valve; 2. External view, left valve, immature (La Matte marsh); 3. Eucypris virens Jurine, 1820. External view, right valve (Capestang marsh); 4–6. Heterocypris salina Brady, 1868: 4. External view, right valve; 5. Dorsal view, complete carapace; 6. Internal view, right valve, immature (Vendres lagoon); 7–9. Herpetocypris cf. reptans Brady & Norman 1889: 7. External view, left valve; 8. Internal view, right valve; 9. Dorsal view, complete carapace (Capestang marsh). 10–12. Herpetocypris cf. helenae Müller, 1908: 10. External view, left valve; 11. Internal view, left valve; 12. Dorsal view, complete carapace (field rice, Ebro delta); 13–14. Cypridopsis vidua Müller, 1776: 13. External view, left valve; 14. Internal view, right valve (Vidourle river mouth); 15. Sarscypridopsis aculeata Costa, 1847. External view, left valve (Castelou marsh); 16. Potamocypris cf. variegata Brady & Norman, 1889. External view, left valve (Capestang marsh); 17. Limnocythere inopinata Baird, 1843. External view, left valve (Aude river mouth); 18. Paralimnocythere cf. psammophila Flössner, 1965. External view, right valve (Vendres lagoon).

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posterior spine are visible in ventral and central positions. These ostracods are similar to the invasive Indo-Pacific species Spinileberis quadriaculeata BRADY, 1880. This species is common in Japan, China, Korea and Hawaï (Tanaka et al., 2011).

are sufficient to distinguish the main hydro-geomorphological features of the sites, although other parameters such as the depth of the inlets or the river discharges affect the water inputs. 3.2. Density

2.4. Data analysis Faunistic density was defined by the total number of individuals for an average sediment weight of 10 g (Supplementary data,Table S2). The species assemblages were analyzed by hierarchical clustering using paired group algorithm (UPGMA) based on the chord distance (Legendre and Legendre, 1998). Correspondence analysis (CA) was then used to study similarities between sites. Both analyses were performed on relative abundances with the XLSTAT software, excluding poor samples (a limit to 300 counted valves has been used), and species present in a single sample (Supplementary data,Tables S3 and S2). Environmental parameters were integrated as supplementary variables in the CA, in order to position them on the factorial planes without including them in the inertia calculations. Water depth, grain size (% sands, % silts + clays), and vegetation (plant cover index) were integrated, as well as the available data for the annual range of salinity variations (Supplementary data,Table S1). In the Languedoc-Roussillon, a pluriannual (15 years) archive for salinity measurements is available and provided by IFREMER and “Parc naturel regional de la Narbonnaise en Méditerranée”. When this information was not available, the range of salinity variations was estimated by two summer/winter measurements. The pH variations proved not very significant (pH 7–8, except in the salina pH 4–5), which led us to discard this parameter. The relationship between salinity, calculated after conductivity at the time of sampling, and the presence of living species, was presented. Specimens considered alive at the time of sampling bear remains of organs between two valves still attached (Ruiz et al., 1997). 3. Results 3.1. Classification of samples The selected sites are located near Narbonne, Vendres and Palavas (Languedoc-Roussillon), Deltebre and Port-Vendres (Catalonia) (Fig. 1). The aim was to gather the most varied environments possible in terms of water body morphology, opening onto the sea and contribution of fluvial supplies. We chose to express this diversity through a personal classification system based on three metric ratios: isolation 1/(a + 1), marine influence a/b, influence of fluvial water distributors 1/(c + 1) (where a = width of the inlet, b = distance to the open sea, c = distance to the fluvial mouth) (Supplementary data,Table S1). a, b, c parameters were measured in meters on satellite images (Google Earth). The ratios were converted to percentage and form the axes of a ternary diagram presenting the sites (Fig. 2). They

Ostracods are present in 54 out of a total of 60 studied samples. Faunal density is generally higher than 100 individuals/10 g (max. 3712 individuals/10 g) (Supplementary data,Table S2). However, this is not the case for inlets (AY1, PON1) (1–11 individuals/10 g), sandy shorelines of bays (FAN2, FAN7, ALF1, ALF4, POR1, POR2) (0–2 individuals/10 g), certain estuary sites (AUD1, EBR1, EBR6) (3–10 individuals/10 g), the salina (SAL1) (0 individual/10 g), rice fields (RIZ1, RIZ2) (1–36 individuals/10 g), and one of the seasonally dried lagoons (PI1, PI2, PI3) (0–48 individuals/10 g) (Supplementary data,Table S2). 3.3. Assemblages A total of 52 species were identified (Supplementary data,Table S2). The taxa were classified into four main assemblages by hierarchical cluster analysis (Fig. 3). Assemblage 1 This assemblage encompasses a blending of marinebrackish (Cyprideis torosa smooth form, Loxoconcha elliptica, Xestoleberis cf. nitida, Cytheromorpha fuscata) and continental ostracods (Heterocypris salina, Darwinula stevensoni, Pseudocandona cf. albicans, Candona angulata, Limnocythere inopinata). Assemblages 2 and 3 Both are composed of marine and marine-brackish ostracods (Loxoconcha cf. rhomboidea, some with more or less punctuated carapaces, Leptocythere fabaeformis, Aurila woodwardi, Semicytherura cf. sella, Paradoxostoma simile, Xestoleberis communis, Callistocythere littoralis, Cytheretta adriatica, Hiltermannicythere turbida, Pontocythere turbida and Neocytherideis cf. subulata in the assemblage 2; Cytherois fisPropontocypris sp., Carinocythereis whitei, cheri, Basslerites sp., Semicytherura incongruens, Spinileberis sp., Carinocythereis carinata, Palmoconcha turbida and Aurila convexa in the assemblage 3). The case of Leptocythere type lacertosa This ostracod is characterized by its small size and a smooth carapace (Plate 1) ornamented by more or less clear dots, depending on the individuals. It is similar to L. lacertosa photographed by Oertli (1985). However, as Athersuch et al. (1989) exclude it from the Mediterranean, we have left the determination open (type lacertosa). It occupies an isolated position in the dendrogram, between the assemblages 1, 2 and 3. It is a secondary species, which rarely dominates sandy

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ISOLATION OUL1 SAL1 CAS1,2 VE1,2,3 ARN1 PI2,3 PI1

closed lagoon

open lagoons

& isolated compartment (confinement stage 3)

DOU1 CAM1 MAR2 MAR1

(confinement stage 2) BS2 BS3 BS4 AY4

open lagoons

BS1 BS5

(confinement stage 1)

1/(a+1) 50

BS6 AY3

MAU1 50

1/(c+1)

AY2

AY1

river/canal FAN1,2,3,5,7 ALF1,2,3,4 POR1,2

BER1 CAN1,2

PON1 FAN4

FAN6

marine bays MARINE INFLUENCE

LEZ1

AUD1,2 EBR5 EBR4 EBR2,1 EBR3,6

mouths

VID1,2,3

50

a/b

FLUVIAL INFLUENCE

color groups: see correspondence analysis (Fig. 4-5) gray samples: no statistical analysis lagoon Ponant inlet (PON1), Ayrolle inlet (AY1), Ayrolle lagoon (AY2, AY3, AY4), Bages-Sigean lagoon (BS1, BS2, BS3, BS4, BS5, BS6), Palazy lagoon (MAR1, MAR2), Campignol lagoon (CAM1), Doul lagoon (DOU1), Pissevache lagoon (PI1, PI2, PI3), Arnel lagoon (ARN1), Mauguio lagoon (MAU1), Vendres lagoon (VE1, VE2, VE3), Oulous marsh (OUL1), Castelou marsh (CAS1, CAS2) mouth of fluvial distributary Ebro river (EBR1, EBR2, EBR3, EBR4, EBR5, EBR6), Lez river (LEZ1), Aude river (AUD1, AUD2), Berre river (BER1), Vidourle river (VID1, VID2, VID3), Canelou channel (CAN1, CAN2) marine bay Fangar bay (FAN1, FAN2, FAN3, FAN4, FAN5, FAN6, FAN7), Alfacs bay (ALF1, ALF2, ALF3, ALF4), Port-Vendres bay (POR1, POR2) salina (SAL1) (landloacked marshes MAT1, CAP1, CAP2 are not represented on the triangular diagram, see Table 1 and Table 2)

Fig. 2. Classification of the studied coastal environments, based on the isolation and the relative influence of the sea and fluvial water suppliers. The distances a, b and c represent respectively the width of the inlet, the distance between the sample site and the open sea, and the distance between the sample site and the freshwater mouth. The groups of samples identified by the correspondence analysis (Figs. 4 and 5) are represented in color.

substrata with little or no vegetation (BS4, EBR3) (Supplementary data,Table S1). Assemblage 4 This assemblage is comprised only of continental ostracods (Ilyocypris bradyi/gibba, Candona cf. neglecta, Cypridopsis vidua, Potamocypris cf. variegata, Sarscypridopsis aculeata, Cypria ophtalmica, Eucypris virens, Herpetocypris cf. reptans).

3.4. Spatial distribution Correspondence analysis (CA) CA 1 (Fig. 4) relates to all of the 46 statistically significant samples (Supplementary data,Table S3 and Appendix). Axis 1 (inertia: 16.7%) separates coastal from landlocked environments (CAP1, CAP2, MAT1). Axis 2 (inertia: 15.2%) separates marine bays from euryhaline environments (lagoons and mouths). The

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Species associations

Similarity (chord distance) 1.44 1.28 1.12 0.96 0.80 0.64 0.48 0.32 0.16

0 Dast Psal Caan Liin Cyfu Hesa Cyto Loel Xeni Lefa Lorh Auwo Sese Pasi Xeco Cali Cyad Hitu Potu Nesu Lela Cyfi Prop Cawh Bass Sein Spin Caca Patu Auco Cyop Pova Saac Ilyo Euvi Cane Here Cyvi

1

oligohaline / mesohaline to very euryhaline

2

polyhalineeuhaline

3

polyhalineeuhaline

4

freshwater to oligohaline / mesohaline

Fig. 3. Dendrogram obtained by ascendant hierarchical classification of frequent species (more than 1 occurrence). Significance of abbreviations: Dast Darwinula stevensoni, Psal Pseudocandona cf. albicans, Caan Candona angulata, Liin Limnocythere inopinata, Cyfu Cytheromorpha fuscata, Hesa Heterocypris salina, Cyto Cyprideis torosa, Loel Loxoconcha elliptica, Xeni Xestoleberis cf. nitida, Lefa Leptocythere fabaeformis, Lorh Loxoconcha cf. rhomboidea, Auwo Aurila woodwardi, Sese Semicytherura cf. sella, Pasi Paradoxostoma simile, Xeco Xestoleberis communis, Cali Callistocythere littoralis, Cyad Cytheretta adriatica, Hitu Hiltermannicythere turbida, Potu Pontocythere turbida, Nesu Neocythereis cf. subulata, Lela Leptocythere type lacertosa, Cyfi Cytherois fischeri, Prop Propontocypris sp., Cawh Carinocythereis whitei, Bass Basslerites sp., Sein Semicytherura incongruens, Spin Spinileberis sp., Caca Carinocythereis carinata, Patu Palmoconcha turbida, Auco Aurila convexa, Cyop Cypria ophtalmica, Pova Potamocypris cf. variegata, Saac Sarscypridopsis aculeata, Ilyo Ilyocypris brady/gibba, Euvi Eucypris virens, Cane Candona cf. neglecta, Here Herpetocypris cf. reptans, Cyvi Cypridopsis vidua.

distribution of species on the same factorial plane shows the assemblage 4 isolated along axis 1. Axis 2 opposes the species from assemblage 3 to those of assemblages 1 and 2. The environmental parameters integrated as supplementary variables are negatively grouped on axis 1, except for the percentage of silts and clays which are positive. The depth and the annual range of salinity variations are separated on axis 2.

CA 2 (Fig. 5) focuses on the 37 negatively isolated samples on CA 1 (Supplementary data,Table S4 and Appendix) that characterize euryhaline environments, hence excluding data from sites where salinity is more stable (marine bays, inland marshes). The first axis (inertia: 27.7%) isolates open lagoon sites (AY3, BS6, AY2, AY4, BS5). The second axis (inertia 17.1%) opposes the very confined lagoons (VE1, CAS2, VE2, CAS1, ARN1, VE3, OUL1, DOU1) to the freshwater mouths and other lagoons (MAR2, MAR1, BS1, BER1, BS4, CAN1, BS3, VID3, AUD2, CAN2, BS2). We observed that the LEZ1 sample occupies an intermediary position between these different groups of points. On the same factorial plane, axis 1 isolates the main species of the assemblage 2 (X. communis, L. cf. rhomboidea). Axis 2 opposes species of the assemblage 1 (on the one hand C. torosa, on the other hand X. cf. nitida and L. elliptica). The degree of euryhalinity is opposed to vegetation on axis 1, and to the vegetation, percentage of sands and depth on axis 2. Distribution maps Cyprideis torosa dominates in the isolated lagoons (VE1, VE2, VE3, PI2, CAS1, CAS2, OUL1, DOU1, ARN1) (Figs. 6–8). However, two lagoon sites represent an exception to this observation (PI1, CAM1). The first (Fig. 7) is characterized by a marked development of macrophytes (Supplementary data,Table S1), associated with the dominant species Xestoleberis cf. nitida. The second (Fig. 6), situated near the mouth of one of the canals branching from the Aude river, is dominated by Loxoconcha elliptica. Loxoconcha elliptica dominates near fluvial water suppliers (0 m < c < 422 m) (CAM1, BS1, BER1, CAN1, CAN2, AUD2, VID1, VID2, VID3, MAU1, EBR1, EBR2, EBR4, EBR5, FAN4, FAN6) (Figs. 6–9), apart from two river mouth sites (EBR3, LEZ1). The first (Fig. 9) is exceptionally dominated by Leptocythere type lacertosa. The second (Fig. 8) is dominated by Cyprideis torosa, which are represented by immature specimens differentiated by the black color of their valves, and which appear to have been reworked. Only the living Bairdia sp. specimens are confidently considered to be autochthonous in this sample. They are representative of the marine conditions that prevailed during sampling in a fluvial low water period. The mixing with allochthonous valves explains the isolation of the sample LEZ1 on the CA 2. Xestoleberis communis (AY3, AY4, BS5, BS6), Xestoleberis cf. nitida (BS3, MAR1, MAR2), Loxoconcha cf. rhomboidea (BS2, AY2) and Leptocythere type lacertosa (BS4) dominate alternately in the less isolated lagoons (Figs. 6–7). The distribution of Xestoleberis communis is limited to the southern part of the Narbonne lagoon complex (Fig. 6), under marine influence. Palmoconcha turbida (ALF2, ALF3, FAN3, FAN5) or Spinileberis sp. (FAN1) are predominant in the marine delta bays of the Ebro (Fig. 9). In all these environments opening onto the sea, Cyprideis torosa is present, but systematically secondary. Loxoconcha elliptica is also secondary, except near river mouths, as described above.

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CA 1

11

4,2

a

4,0 3,8 3,6 3,4

Marine bays

3,2 3,0

ALF3 ALF2

2,8

FAN3

2,6 2,4 2,2

FAN1

F2 (15,18 %)

2,0 1,8 1,6

FAN5

1,4 1,2

FAN6 BER1 EBR4 MAR2 LEZ1CAN2 VID3 AUD2 MAR1 EBR1 VID1 VID2 BS1 EBR2 PI1 PI2 CAN1 BS4 BS3 EBR3 CAM1 MAU1 OUL1 BS2 DOU1VE3 VE2 ARN1 CAS1

1,0 0,8 0,6 0,4 0,2

Inland marshes CAP1 CAP2

CAS2 MAT1 FAN4

0 -0,2 -0,4 -0,6

EBR5 VE1

AY2 BS5 AY3 AY4 BS6

lagoons and river mouths

-0,8 -0,8 -0,6 -0,4 -0,2

0

0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 2,8 3,0 3,2 3,4 3,6 3,8 4,0 4,2

F1 (16,66 %)

4,2

b

4,0 0,8

DEP

3,8

c

3,6 3,4 3,2 3,0 2,8 2,6

Association 3 Bass Cawh

VEG 0

Prop

SC

SAN

Cyfi Patu Sein

VAR

2,4 2,2

F2 (15,18 %)

2,0

Spin Auco

-0,8 0

-0,8

0,8

1,8 Potu

1,6

Dast Loel Xeni Lela Caan Psal Cyad Liin Cyfu Nesu Hitu Hesa Cyto Cali Lorh Sese Auwo

1,4 1,2 1,0

Caca

0,8 0,6

Association 4

Xeco

0,4 0,2

Saac

Pasi Lefa

Cyvi

Cane

Cyop Euvi Pova Ilgi

Here

0 -0,2

Association 1

-0,4 -0,6

Association 2 -0,8 -0,8 -0,6 -0,4 -0,2

0

0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6 2,8 3,0 3,2 3,4 3,6 3,8 4,0 4,2

F1 (16,66 %)

Fig. 4. Distribution of sites (a), species (b) and environmental factors (c) on the first factorial plan of CA 1. Significance of abbreviations: VAR annual range of salinity variations (max-min), DEP depth, VEG vegetal cover, SAN % sands, SC % silts and clays (abbreviations of species in the legend for Fig. 3).

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CA 2

2,0

a 1,8 1,6

closed lagoon 1,4

&

VE1 CAS1

1,2

isolated compartment

VE2

(confinement stage 3)

CAS2

ARN1 1,0 VE3

OUL1

0,8

F2 (17,11 %)

0,6

open lagoons

DOU1

AY3

(confinement stage 1)

LEZ1

PI2

0,4

BS6 AY2

EBR1

0,2

MAU1 0 EBR3

VID2

AY4 BS5

CAM1 EBR4 EBR5 VID1 PI1 EBR2 FAN6

-0,2 -0,4

CAN2 VID3

-0,6

BS2

AUD2 BS3

CAN1

BS4

BER1

-0,8

BS1

river mouths

open lagoons

-1,0 MAR2 MAR1

-1,2 -0,8

-0,6

-0,4

-0,2

(confinement stage 2) 0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

2,2

2,4

2,6

2,8

F1 (27,73 %)

2,0

b

Cane 0,8

1,8

c 1,6 SC

1,4

VAR 0

1,2

Association 1

DEP

1,0 Cyto

0,8

-0,8 -0,8

0,6

F2 (17,11 %)

VEG

SAN

0

0,8

Cyad

Hesa

Cali

Hitu 0,4

Ilgi

Prop

Potu

Pasi Auwo

Xeco

Psal

0,2

Cyfi Sese 0 Caan -0,2

Nesu

Patu Lorh

Lela

Dast

Association 2

-0,4 Auco Cyvi

-0,6

Loel Cyfu

Lefa

Liin -0,8 Xeni

-1,0 -1,2 -0,8

-0,6

-0,4

-0,2

0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0

2,2

2,4

2,6

2,8

F1 (27,73 %)

Fig. 5. Distribution of sites (a), species (b) and environmental factors (c) on the first factorial plan of CA 2. Significance of abbreviations: VAR annual range of salinity variations, DEP depth, VEG vegetal cover, SAN % sands, SC % silts and clays (significance of abbreviations in the legend for Fig. 3).

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NARBONNE LAGOONAL COMPLEX

BS1

BS2

13

BS3

CAS1/2 CAN1/2

CAM1 BS4 DOU1

AY4 BS5 BER1

beach barrier

OUL1 AY3 AY2 (AY1)

BS6

Berre river inlets

LAGOON

MEDITERRANEAN SEA

3 km river canal

VENDRES

Aude river

Continental:

Marine-brackish:

Marine:

Ilyocypris bradyi/gibba Heterocypris salina Candona cf. neglecta

Leptocythere type lacertosa Cyprideis torosa Xestoleberis cf. nitida Loxoconcha elliptica

Loxoconcha rhomboidea Leptocythere fabaeformis Xestoleberis communis Aurila woodwardi Callistocythere littoralis Rare species: Propontocypris sp., Paradoxostoma simile, Semicytherura sella, Cytheretta adriatica, Hiltermannicythere turbida, Pontocythere turbida, Neocytherideis cf. subulata

NARBONNE

N

(Samples in brackets refer to absence or very low density)

Proportion per sample:

100 %

50

0

Fig. 6. Distribution of ostracods from the Narbonne lagoon complex (Languedoc-Roussillon).

Continental ostracods were collected in small quantities in coastal environments (Figs. 6–9). Candona angulata and Cypridopsis vidua (VID1, VID2, VID3), Candona cf. neglecta, Pseudocandona cf. albicans, Ilyocypris bradyi/gibba and Paralimnocythere psammophila (VE1), Heterocypris salina (VE1, CAS1, EBR4), Darwinula stevensoni (EBR5) are represented by adult and immature individuals which characterize an in situ fauna. The other samples contain small immature individuals, pointing towards the grain-size sorting of the valves linked to transport.

4. Discussion 4.1. Environmental conditions inferred by ostracods 4.1.1. Ecological significance of assemblages The assemblage 1 is a mix of slightly brackish and very euryhaline ostracods (Fig. 3, Fig. 10). Cyprideis torosa, Loxoconcha elliptica and Xestoleberis cf. nitida tolerate large variation of salinity. They are adapted to salinities ranging from low values (oligohaline or mesohaline) to euhaline, and even

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VENDRES LAGOONAL COMPLEX

VE1 VE2 VE3

Aude river

beach barrier

MAR1/2 AUD2/(AUD1)

PI1

PI2 LAGOON

MEDITERRANEAN SEA

(PI3)

1 km

temporary inlet

anti-salt dam canal

VENDRES

Aude river

NARBONNE

N

Continental:

Marine-brackish:

Limnocythere inopinata Darwinula stevensoni Pseudocandona cf. albicans Candona cf. neglecta Paralimnocythere psammophila Ilyocypris brady/gibba Heterocypris salina

Leptocythere type lacertosa Cyprideis torosa Xestoleberis cf. nitida Loxoconcha elliptica Cytherois fischeri

Brackish: Cytheromorpha fuscata

Marine:

Leptocythere fabaeformis Palmoconcha turbida Loxoconcha rhomboidea, Xestoleberis communis, Neocytherideis cf. subulata, Cytheridea adriatica, Semicytherura cf. sella

Proportion per sample: 100 %

50

0

(Samples in brackets refer to absence or very low density)

Fig. 7. Distribution of ostracods from the Vendres lagoon complex (Languedoc-Roussillon).

hyperhaline for C. torosa (Athersuch et al., 1989). Cytheromorpha fuscata and the associated continental species tolerate a mesohaline maximum (Fuhrmann, 2013, Meisch, 2000, Neale, 1988, Steger, 1972). The assemblages 2 and 3 are composed of species adapted to polyhaline and euhaline waters (Bonaduce et al., 1975, Guernet et al., 2003, Lachenal, 1989, Ruiz et al., 1997, 2000a). Some are relatively stenohaline in this range of salinity, for example Carinocythereis whitei (Fig. 10). Cytherois fischeri

is euryhaline; however this species prefers polyhaline waters (Ruiz et al., 2000a). Both assemblages suggest coastal marine-brackish environments with low salinity gradients. Previously unrecorded in the Mediterranean, Spinileberis appears to have adapted to these conditions. It was found living in the Ebro delta in salinities approaching 25 ‰ (Fig. 10). It is mentioned in marine bays with normal salinity, but tolerates mesohaline dilutions (Bodergat and Ikeya, 1988).

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PALAVAS LAGOONAL COMPLEX

Vidourle river

Lez river Rhône-Sète canal LAGOON

MAU1

VID1 (PON1)

VID2 VID3

inlet beach barrier

ARN1 LEZ1

1 km

MEDITERRANEAN SEA N

Continental:

Marine-brackish:

Marine:

Limnocythere inopinata Darwinula stevensoni Candona angulata Cypridopsis vidua Ilyocypris brady/gibba

Loxoconcha elliptica Cyprideis torosa Xestoleberis cf. nitida Leptocythere type lacertosa

Loxoconcha rhomboidea Xestoleberis communis Pontocythere turbida Cytheretta adriatica Bairdia sp. Semicytherura sulcata, Paradoxostoma simile, Aurila woodwardi, Neocytherideis cf. subulata, Carinocythereis carinata, Costa sp., Paracytheridea sp., Propontocypris sp., Heterocythereis albomaculata, Hiltermannicythere turbida

Proportion per sample 100 %

(Samples in brackets refer to absence or very low density)

50

0

Fig. 8. Distribution of ostracods from the Palavas lagoon complex (Languedoc-Roussillon).

The assemblage 4 consists only of continental species adapted to freshwater, oligohaline or mesohaline water (Meisch, 2000, Neale, 1988). 4.1.2. Types of environments The correspondence analysis (CA1 and CA2) and the distribution maps lead to distinguish coherent sets of sites. The first separation is made between coastal (bays, lagoons, fluvial mouths) and landlocked environments (marshes, rice fields). The low and stable salt content (1.2 to 2.2 ‰) allows the establishment of continental species belonging to the assemblage 4 (Fig. 4, Supplementary data,Table S1). Other studies (Bodergat, 1983, Nachite et al., 2010) indicate similar assemblages in marshes from deltaic and estuarine areas. The marine and marine-brackish ostracods appear in the more saline coastal waters. Nonetheless, the assemblage of ostracods in the bays is different from those of lagoons and river mouths. This group of species corresponds to the polyhaline-euhaline assemblage 3 (Fig. 4), which is well adapted to the marine context of this area. Note that the main taxa Palmoconcha, Propontocypris and Carinocythereis also live in open lagoons (Kurc,

1961, Ruiz et al., 2006a) where the salinity is euhaline and more stable than in the studied Narbonne lagoonal complex. Otherwise, it is interesting to see that euryhaline species from the assemblage 1 (particularly Loxoconcha elliptica) dominate in the most coastal area of the Fangar marine bay (Fig. 9), which is probably due to the strong influence of continental inputs from irrigation canals. The samples from open lagoons are divided into two groups (Fig. 5). The polyhaline-euhaline assemblage 2 characterizes samples close to the inlets (confinement stage 1 according the Fig. 2). More euryhaline species dominate in the samples located further inland in the lagoon (confinement stage 2). More particularly, the plotting of the ostracod assemblages on map (Fig. 6) illustrates this spatial distribution and shows that different assemblages can cohabitate in the same lagoonal complex. It hints at the complexity of hydrological circulation in the compartmented Narbonne lagoon, with rapid sea/lagoon exchanges in the southernmost basins compared to the northern part (Ifremer, 2005). Oxygen concentrations were not measured during this study, but it is known that they can locally influence the ostracod distribution in the lagoons and bays. In the Baltic

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EBRO DELTA

1 km

MEDITERRANEAN SEA

A sand spit Ebro river

B

(FAN2) (FAN7)

FAN1

C

FAN3

FAN6

N

FAN5 FAN4

FANGAR BAY

canal

B

1 km

MEDITERRANEAN SEA

EBR5

EBR4 EBR3 EBR2 EBR1

(EBRE6)

Ebro river

C

(ALF1) (ALF4) ALF3 ALF2 AFLAFCS BAY (SAL1)

sand spit

1 km

MEDITERRANEAN SEA

Proportion per sample Continental:

Marine-brackish:

Marine:

Darwinula stevensoni Pseudocandona sp. Candona angulata Heterocypris salina

Loxoconcha elliptica Cyprideis torosa Xestoleberis cf. nitida Leptocythere type lacertosa Cytherois fischeri

Leptocythere fabaeformis Palmoconcha turbida Bassleristes sp. Aurila convexa Propontocypris sp. Semicytherura incongruens Spinileberis sp. Carinocythereis whitei, Carinocythereis carinata Callistocythere littoralis, Neocytherideis cf. complicata, Paradoxostoma simile, Pontocythere turbida, Xestoleberis communis

(Samples in brackets refer to absence or very low density)

100 %

50

0

Fig. 9. Distribution of ostracods from the Ebro delta (Catalonia).

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Loxoconcha elliptica. Other studies (Creuzé des Châtelliers and Marmonier, 1993, Marmonier et al., 1994) show that upstream fluvial environments are colonized by ubiquitous ostracods from flood plains and channels, or specific to the interstitial waters of channels, likely to be transported with sediments towards river mouths. In the studied deltaic sediments, these displaced freshwater individuals are absent or rare (some Darwinula stevensoni, Heterocypris salina, I. braddy/gibba, Limnocythere inopinata, Candona cf. neglecta, Pseudocandona sp.). In comparison, sediments from Holocene deltas contain more allochthonous continental microfauna, as is the case for the past deltaic channel of the Rhône (Muller et al., 2008) or the former Aude river mouth (Dolez et al., 2015). This change could be explained by the anthropogenic influence on the fluvial network (channeling, dams), which currently limits the diversification of running water habitats upstream, and creates a barrier which obstruct the sediment transfer. Fanget et al. (2013) highlight another explanation, the frequency of the ostracod-carrying floods. The tiny, fragile ostracods do not usually colonize the main fluvial channel because of the fast-moving, heavy and coarse sediment load, but the shells coming from secondary channels or marshlands can float in the water column during floods and reach the delta and prodelta depositional environments. The occurrence of these events is nonetheless rare enough that only a few specimens can be found mingled with the abundant local ostracods in prodelta deposits, even for high flood frequency periods. Thus, for detecting this type of reworking, we need to study sediments deposited within a longer timeframe. 4.2. Comparisons with other Mediterranean coastal environments

Fig. 10. Relationship between the main ostracod species and salinity (tolerated range) (explanation of the abbreviations in the legend for Fig. 3) (Venice System, 1959).

area, the identified brackish species are associated with different oxygen tolerance values, which appear to be a major driving factor (Frenzel et al., 2010). Closed lagoons, confined compartments (confinement stages 2 and 3 according to Fig. 2) and fluvial water distributors are characterized by the brackish to euryhaline assemblage 1 (Fig. 5). We can identify the lagoonal sites with abundant vegetation (algae or phanerogams, index 3–4) where Xestoleberis cf. nitida is dominant (BS3, PI1, MAR1, MAR2) (Supplementary data,Table S1). River and canals mouths are dominated by

4.2.1. Density The density of ostracods is relatively low in inlets and sandy shorelines; and also irregular in the fluvial mouths of the Ebro and the Aude. Carbonel (1980) and Ruiz et al. (2004, 2006a) observed similar values in other lagoon inlets and estuarine mouths. Unfavourable currents in these environments sweep away the ostracods which are living at the surface of the sediment (Carbonel, 1988). The absence of ostracods in the salina could be attributed to a low pH (4–5). Ruiz et al. (2000a) note that ostracods are absent from acidic environments, whereas other micro-crustaceans live there. The low population density in the Pissevache lagoon and rice fields is attributed to seasonal drying. Similarly, Carbonel (1980) observed the variability in the number of individuals during prolonged emersions. The highest values in Languedoc-Roussillon (> 3,000 individuals/10 g) are frequent in other Mediterranean lagoons with numerous Cyprideis torosa (for example Ruiz et al., 2006b). 4.2.2. Dominant species and their significance The results obtained on the Narbonne lagoons (Fig. 6) are surprising due to the relative underrepresentation of C. torosa. In comparison, present-day studies carried out on other Mediterranean lagoons frequently identify this species as overwhelmingly dominant. The lagoons of Nador (Morocco) and Venice (Italy) are examples of lagoons opening onto the

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sea (width of the Nador inlet: 300 m, width of the Venice inlets: 400 to 900 m) studied by Ruiz et al. (2000b, 2000c, 2006a). In the Nador lagoon, C. torosa is dominant at the confined ends of the basin, but also in the deepest central area. Elsewhere, the marine Loxoconchidae (L. cf. rhomboidea and/or P. turbida) have a predominant presence. In the Venice lagoon, C. torosa is dominant, associated with L. elliptica near the fluvial mouths or with Xestoleberis in sectors rich in macrophytes. The El Melah lagoon (Tunisia) is an example of a lagoon opening onto the sea by a temporary inlet (inlet width is about 8 m), studied by Ruiz et al. (2006b). C. torosa dominates in confined areas, as well as in the marine channel linked to the inlet; while L. elliptica dominates around the water treatment plant where fresh water discharge leads to lower salinity. The distribution of C. torosa in the Languedoc-Roussillon lagoons is unusual since this species dominates only in very confined zones, while it is secondary in abundance in the open basins of Narbonne (this paper) or Thau (Kurc, 1961). Those zones are relatively unaffected by the agricultural, industrial and urban development compared to most of the Mediterranean lagoons (Nevers and Becerra, 2003). Moreover, since 2000, regular water quality controls have shown the beneficial impact of the decrease in nutrient discharge from the water treatment plant, resulting in less eutrophication (Ifremer, 2012). The dominance of X. communis in the south of the lagoon complex is probably linked to low anthropogenic impact (Triantaphyllou et al., 2005). In comparison, the Nador, Venice and El Melah open lagoons are contaminated by polluted water (Ruiz et al., 2000b, 2000c, 2006a, 2006b) inducing bottom water eutrophication. These conditions might explain the dominance of Loxoconchidae, which can tolerate the hypoxia of eutrophic waters (Alvarez Zarikian et al., 2000, Ruiz et al., 2006a). They could also explain the dominance of C. torosa, which does not seem to be very affected by contamination (Ruiz et al., 2000b, Barut et al., 2015) in comparison to the less euryplastic marine species (Dimiza et al., 2009). On the other hand, the distribution of L. elliptica in environments with varied salinity in Languedoc-Roussillon and Catalonia is similar to that observed in the aforementioned Mediterranean lagoons. This species is only dominant in or near the outlet of freshwater suppliers, regardless of the degree of confinement. These environments display marked salinity oscillations (about 25–35‰), with dilution in the mesohaline or even oligohaline range, and a substratum containing variable proportions of sands (Supplementary data,Table S1). Pascual and Carbonel (1992) observed the same relationship in the Gernika estuary (Spain). According to them, the presence of sands at the surface of the sediments could favor the nutritive elements/oxygen exchanges.

• in the highly confined lagoons characterized by an extreme euryhalinity, Cyprideis torosa dominates. The development of Xestoleberis cf. nitida is observed in sectors rich in macrophytes; • in the open lagoons, C. torosa is a secondary species. Different taxa may dominate depending on the inlet proximity and internal hydrological circulation, in possible relation with the residence time of water bodies in paralic basins. Xestoleberis communis is limited to undisturbed areas with the lowest confinement; • the proximity of fluvial channels influences the assemblage composition in lagoonal and marine environments. Loxoconcha elliptica is dominant in or near continental suppliers (rivers or canals) regardless of the confinement degree. These environments display marked salinity oscillations with high dilution, and a substratum containing variable proportions of sands. The ecological descriptions of sites (Supplementary data,Table S1) provide useful information for palaeoenvironmental models, supplementing the existent data in the Mediterranean area. Furthermore, this study brings into focus the richness of ostracod assemblages in lagoonal environments, with faunas that are less dominated by Cyprideis torosa than in other Mediterranean lagoons. In order to further our understanding of this variability, it will be necessary to continue this work by improving the spatial resolution of samples, and the environmental parameters including testing for pollution and oxygen content. Other diversified littoral sites should be integrated in future studies. Disclosure of interest The authors declare that they have no competing interest. Acknowledgements This work has been carried out thanks to the support of the Paul-Valéry University Doctoral School “Territoires, Temps, Sociétés et Développement”, the UMR-CNRS 5140 “Archéologie des sociétés méditerranéennes”, the LabEx ARCHIMEDE (PIA ANR-11-LABX-0032-01), and the ECCOREV federation. We thank Olivier Grauby for the SEM photographs taken at the CINAM laboratory, Serge Muller for his advice on quantitative ecology, Doriane Delanghe for her help and warm welcome in the CEREGE laboratory, and the reviewers Maria-Angela Bassetti and Peter Frenzel for their encouragements and the valuable comments that helped us to improve the original version of this paper.

5. Conclusion Appendix A. Supplementary data Our aim was to correlate environmental conditions to specific assemblages. The spatial distribution of assemblages has been studied by CA and by maps. The following conclusions can be highlighted:

Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/ j.revmic.2016.09.001.

Please cite this article in press as: Salel, T., et al., Ostracods and environmental variability in lagoons and deltas along the north-western Mediterranean coast (Gulf of Lions, France and Ebro delta, Spain). Revue de micropaléontologie (2016), http://dx.doi.org/10.1016/j.revmic.2016.09.001

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