scanned and georeferenced maps. Fernandez et al. (2006) made accurate maps of Urbino lagoon for 1990, 1994, 1996 and 1999. These maps distinguished four main bottom types: (1) clear sand bottom, (2) pebble bottom and coarse shell, (3) seagrassmeadows (essentially Cymodocea nodosa), and (4) silt bottom. Image pro- cessing was made from aerial photographs using MULTISCOPE software (version 2.4, Matra Cap System and Information Ò ), and according to the method described in Pasqualini et al. (1997) . This technique combines a high level of precision and rapid processing ( Pasqualini et al., 1997, 2001; Fernandez et al., 2006 ). Brie ﬂy, three images, corresponding to three different layers (i.e., red, green and blue), were obtained from aerial photographs. The terrestrial domain was eliminated on the raw image by delimiting the shoreline with closed polygons. The dynamics of each layer was adjusted by enhancing image contrast (linear contrast enhance- ment) to improve precision and clarity. Principal Component Analysis (PCA) was run on the green and blue layers. A supervised classi ﬁcation (by generalized hypercube) was applied to the col- oured composition using both the 0e2 and 2e5 m depth layers in order to avoid any depth-related confusion between classes. The polygons were then positioned based on in situ ﬁeld observations. Occasional corrections were made to the ﬁnal images on the basis of ﬁeld data, especially when the meadows were down to 5 m depth. For the present study, all four of Fernandez et al. ’s (2006) maps were georeferenced with Lambert 93 coordinates and con- verted to a vector format in a GIS database.
II. Application of the SIAR mixing model
Using only δ 13 C data and experimentally measured TEF (Δ 13 C = 0.2 ± 0.6 ‰). Source were lumped in 3 groups.
Trophic tracers reveal considerable diversity among diets of
dominant amphipods from Posidonia oceanica seagrassmeadows
A B S T R A C T
Seagrassmeadows constitute marine habitats in shallow water temperate and tropical coastal areas worldwide that have a high ecological and economic importance. Amongst the 60 or so seagrass species, the endemic Mediterranean species Posidonia oceanica forms meadows that are arguably the most important shallow water coastal habitat in the region but which are subjected to high anthropogenic pressures. Because of the relatively large size of the plant, the meadows formed by this seagrass have high architectural and morphological com- plexity, which results in di ﬀerent morphotypes or seascapes. While numerous studies of P. oceanica architectural characteristics for continuous meadows of the seagrass are available, few works have addressed seascape eco- logical features and the inﬂuence of environmental factors (natural and anthropogenic) thereon. In the present review, we give an overview of P. oceanica meadow architectural and morphological characteristics and how these contribute to Mediterranean landscapes and seascapes. Studies addressing the in ﬂuence of natural and anthropogenic factors on morphometric features of diﬀerent meadow types and landscape ecological char- acteristics of P. oceanica habitat are also reviewed, as well as their in ﬂuence on ecosystem processes. Finally, by considering the available data and tools for seascape studies, we present a discussion on methods to assess seagrass seascapes within the framework of coastal management. Our review highlights several gaps in P. oceanica seascape ecology knowledge such as the lack of data on the spatial distribution of this engineer species, and the possibility to use modern techniques and procedures for analysing structural and ecosystemic data.
not occur, as these were totally absent in all species. This supports the view that most primary consumers from P. oceanica meadows do not feed on their seagrass host (Dauby 1989; Lepoint et al. 2000; Vizzini et al. 2002). Although herbivory can have a substantial impact on leaf biomass (Prado et al. 2007), Neptune grass seems to be grazed by only a few consumers. These include the fish Sarpa salpa, the urchin Paracentrotus lividus and isopods from the genus Idotea (Mazzella et al. 1992). This is probably explained by the low palatability (hard tissues containing a lot of structural carbohydrates) and nutri- tional quality (high C/N ratios) of seagrass leaves. More- over, living P. oceanica leaves contain high amounts of phenolic compounds that could act as herbivore repel- lents (Gobert et al. 2006; Vizzini 2009). The situation is quite different in other temperate seagrassmeadows. In Californian Zostera marina meadows, diet of mixed Capr- ellidae and Ampithoidae are composed of about 50% and 60% of seagrass material, respectively (Farlin et al. 2010). One key difference could be the abundance of epiphytic organisms, typically greater in P. oceanica meadows than in other seagrass systems (Mazzella et al. 1989). As epiphytes are more easily digestible and have better nutri- tional quality, amphipods may preferentially graze on
4.3. Stabilizing eﬀects of seagrassmeadows on food web structure The species-speci ﬁc and community isotope niche approach appli- cation revealed the patterns of seasonal and between-habitat variability in coastal benthic food webs in Puck Bay. Overall, the comparison of community isotopic niches indicated that seagrass cover for the benthic food web is more critical in winter, which is a season with lower re- source availability. The presence of seagrass is important not as a po- tential food source itself but because the presence of seagrassmeadows increases ecological stability (in terms of the range of food sources utilized by consumers) in the faunal assemblage associated with un- derwater vegetation, while invertebrates from unvegetated areas had to shift their diet to adapt to winter conditions. In contrast to our ex- pectations, the diﬀerences in trophic diversity between the habitats were greater in winter, even if abundance and diversity of the vegeta- tion decreased in that season. The contrast between the habitats in winter was produced by the strong dietary shift of bare sands fauna. However, the stronger similarity between the two studied habitats in summer may resulted from the meadows in ﬂuence on sandy sediments via the export of phytodetritus. It would be useful to assess the mag- nitude and spatial range of this export and to compare the seasonal variability of faunal communities along the gradient of the meadow inﬂuence in future studies.
Purpose: AxIOM is a sample-based dataset (n = 187 samples) documenting occurrences of amphipod crustaceans associated to Posidonia oceanica seagrassmeadows from Mediterranean Islands (Corsica, Sardinia). In total, it contains 1775 records, documenting occurrence and abundance of 10720 amphipod specimens belonging to 72 species spanning 29 families. Samples were collected over diﬀerent periods 3 consecutive years, both during the day and during the night. A nested hierarchical sampling design was set up, and multiple sampling methods were combined to ensure a holistic view of the taxocenosis. The dataset package is composed of two data ﬁles: one describing sampling events, and the other reporting occurrence data of amphipod crustaceans.
P. oceanica meadows (F rancour 1990; m ezali 2004). The micro-distribution of the species studied
during the present work was different from that observed by m ezali (2004) on the same holothurian
species in Sidi Fredj site (central region of Algeria). This author found that H. tubulosa and H. poli preferred P. oceanica “intermattes”, whereas H. forskali and H. sanctori were situated at the level of the eroded vertical edge and between P. oceanica rhizomes. It is possible that this difference in the micro-distributions of holothurians is due to the nature of P. oceanica meadows. Indeed, the meadows of Stidia and Salamandre are installed on rocky substratum, while the meadow of Sidi Fredj is installed on Posidonia “matte”. This indicates that the micro-niche of these species could be, to some extent, variable and plastic according to local environmental conditions.
§ Differences in foraging ecology of these two hermit crabs è could limit interspecific competition
and facilitate coexistence of D. scutellatus and C. tricolor in Malagasy seagrass beds
§ Analysis of food items sampled at the same time and location will enable use of a mixing model and ultimately reveal which producers actually support hermit crabs populations
§ These ecosystems undergo multiple anthropogenic threats (eutrophication,
overfishing, invertebrate overharvesting)
§ Data about functional ecology of meadows and structure of the associated
food webs are needed to understand how they could react to human impacts
Accumulations of macrophytodetritus are ubiquitous features of marine ecosystems and are found from littoral zones to deepest can- yons, and from high latitudes to tropical zones. These accumulations shelter speci ﬁc and very abundant animal assemblages (e.g. Crawley and Hyndes, 2007 ; Gallmetzer et al., 2005 ; Vetter, 1995 ), acting as a faunal magnet ( Duggins et al., 2016 ). They are commonly found asso- ciated to seagrassmeadows. Seagrassmeadows are net autotrophic ecosystems and key components of the carbon cycle in coastal areas ( Champenois and Borges, 2012 ). They are now recognised for their importance in the burial of organic carbon in marine sediment and, consequently, in the mitigation of atmospheric CO 2 increase (i.e. blue
other known blue and green carbon stocks, as most of the values used for comparison in this study were measured from the top 1-m section.
2.7. Predictors of Among-Site Variation in Carbon Stocks
To explain the among-site variation in carbon stocks, we statistically assessed the relative importance of environmental variables (latitude, water depth, salinity, and water temperature), sediment variables (sedi- ment density, sediment mud content, degree of sediment sorting, and 15 N content of sediment) and charac- teristics of seagrassmeadows ( 15 N content of Z. marina eelgrass leaves, PON content of Z. marina leaves, Z. marina shoot density, aboveground Z. marina biomass, belowground Z. marina biomass, root: shoot ratio, and Z. marina contribution to the sediment surface C org pool). We used partial least squares (PLS) regression in SIMCA 13.0.3 software (UMETRICS, Malmö, Sweden) to model projections to latent structures (Wold et al., 2001) on untransformed data. PLS is a developed generalization of multiple linear regression, where latent structures (i.e., variables with the best predictive power) are constructed based on linear associations between a set of predictor variables (x) and the response variable (y). PLS regression modeling was used since this technique can handle multicollinearity and large numbers of predictor variables (Carrascal et al., 2009). This regression technique is applicable in analyses of various types of ecological data (e.g., Asplund et al., 2011; Carrascal et al., 2009; Staveley et al., 2017) and has recently been used to address the in ﬂuence of dif- ferent types of predictors on carbon stocks (Dahl et al., 2016; Gullström et al., 2018). We also used principal component analysis (PCA) to visualize general relationships between ocean margins or seas and environmen- tal predictors (i.e., the ﬁve predictors having a major contribution to the PLS model) and the C org stock (g C/
This work is foundational in describing a ubiquitous Mediterranean coastal fish sound that meets the proposed criteria relevant for PAM of P. oceanica seagrassmeadows. It sets the bases for future studies aiming at revealing if the /kwa/ can be used as an environmental proxy for habitat monitoring. Fish sounds are used in communica- tion; they reflect an organism’s activity and play a role in the species survival (Ladich 2015). Across taxa, there is evidence that environmental disturbance and habitat quality are reflected in the acoustic behaviour and varia- tion in animal communities and populations (Riede 1998; van Oort et al. 2006; Pillsbury and Miller 2008; Laiolo 2010; Rosenthal and Stuart-Fox 2012). The next step to further evaluate if the /kwa/ is valuable for PAM of P. oceanica meadows would be to test /kwa/ diversity, chorus output and calling activity in relation to environmental variables and the status of P. oceanica seagrassmeadows, characterized by different quality index values (e.g. BiPo, PREI, EBQI). Besides identifying a possible environmental proxy of a key habitat, this work also describes a sound with unique features compared to other known Mediter- ranean fish vocalizations that is potentially significant in the study of fish communication. Future studies need to be designed to further elucidate the source of the sound, the communicative role of the /kwa/ and its diversity.
Endemic to the Mediterranean Sea, the seagrass Posidonia oceanica (L.) Delile forms widespread meadows which exert crucial roles in the coastal waters (see Gobert et al., in press). These meadows cover a surface area of 25,000 to 50,000km 2 representing 1 to 2% of the Mediterranean Sea surface (Pasqualini et al. 1998). Despite their ecological and economical importance, since the sixties, an increasing number of reports documents their ongoing loss or regression in all countries (e.g.Boudouresque et Meinesz 1982). The decline in seagrassmeadows and associated communities of plants and animals coverage is generally attributed to anthropic activities (Cambridge et al. 1986, Short and Wyllie-Echeverria 1996). In the damaged areas, healthy meadows have been replaced with deserts of dead matte, sand or mud.
The POC enhancement in the seagrass beds was not accompanied by a change in the mean δ 13 C signatures (as indicated by no signi ﬁcant effects detected by the PERMANOVA tests). This discrepancy between the clear effect on POC and the absence of response in the mean δ 13 C values in the vegetated sediments was noted in other studies [Simenstad and Wissmar, 1985; Boeschker et al., 2000; Hemminga et al., 1994; Kennedy et al., 2010]. The clear difference between different habitats was only noted for δ 15 N (as for TN), with higher values recorded in the vegetated bottom. The variation in δ 15 N values among the vegetated and unvegetated habi- tats remains poorly understood but is usually correlated to inorganic nitrogen incorporation by seagrass and sediments [Lepoint et al., 2004]. The ﬁxation of nitrogen by sulfate reducers in seagrass bed rhizospheres has been previously detected [Welsh, 2000]. This microbial ﬁxation is an additional source of organic nitrogen for seagrass bed sediments, pore waters, and living plants [Sacks and Repeta, 1999]. Papadimitriou et al.  stated that δ 15 N changes within the sediments of Western Mediterranean Posidonia meadows, which may be a result of the mixing of 15 N-enriched nitrogen from primary sources with 15 N-depleted nitrogen ﬁxed in the sediments. Indeed, signi ﬁcantly higher bacteria abundance and biomass were detected in the Puck Bay sedi- ments within the seagrassmeadows compared to the bare bottoms in the studied area [Jankowska et al., 2015] and other coastal locations [Pollard and Moriarty, 1989; Danovaro, 1996]. The increased numbers of bacteria in the vegetated bottoms may also more ef ﬁciently decay organic matter, resulting in higher δ 15 N signatures. Despite the nearby location of the Gda ńsk-Sopot agglomeration, no effects of sewage disposal (i.e., sewage-derived NH 4 + , which can be the source of 15 N-enriched particulate matter, [Cifuentes et al., 1988]) could be detected at the GS site, which did not differ in its δ 15 N signature from other sites.
ABSTRACT: Marine protected areas (MPAs) are a key tool for conservation purposes, but few studies have assessed the responses of small macrozoobenthic assemblages to different protection levels in the Mediterranean Sea. In this study, we used a hierarchical sampling design spanning 3 orders of magnitude (1, 10 and 100 m) to investigate whether a MPA exerts an effect on amphi- pod assemblages associated with Posidonia oceanica meadows. We report spatial and temporal variability patterns of amphipod assemblages in 4 different protection levels and discuss potential confounding effects, such as habitat features. The structure of amphipod assemblages based on density data was patchy at all spatial scales investigated, but differed markedly among protection levels. Among outstanding points, multiscale analyses showed that lower densities and/or bio- masses of several taxa occurred within fully protected and external areas, in comparison with par- tially protected areas (PPAs). Furthermore, P. oceanica meadow features (shoot density, leaf and epiphyte biomasses, coefficient A and litter biomass) accounted for only a low proportion of the total variability. We consequently infer that the observed patchiness is likely to occur for multiple and interconnected reasons, ranging from the ecological and behavioural traits of amphipod spe- cies to protection-dependent processes (e.g. fish predation). Long-term multiscale spatial and temporal monitoring, as well as experimental manipulations, are needed to fully understand the effects of protection on macrozoobenthic assemblages.