Feeding of the Sparid Fish Sarpa salpa in a Seagrass Ecosystem: Diet and Carbon Flux

Abstract. In Revellata Bay Gulf of Calvi, Corsica, France, the sparid fish Sarpa salpa L. is the main macro-consumer of Posidonia oceanica L. D elile leaf. Stomach contents were analysed and ¹³C/¹²C isotopic ratios were measured in fish muscle and potential food sources algae, P. oceanica leaf and its epiphytes to determine their relative contribution to the fish diet. S. salpa has an age-related mixed diet: juveniles are plankton feeders, young, sub-adults and adults are herbivorous, and, the older the individuals, the higher the relative contribution of P. oceanica to the diet. Our results and former studies of carbon stocks and fluxes in the P. oceanica bed of Revellata Bay have enabled an estimation of the general impact of S. salpa grazing on infralittoral communities: the studied species consumes 24 g C.m^-2 -a^-1 from P. oceanica leaf, 4.8 from epiphytes and 13 from epilithic algae. The fish net production and biomass turnover in that zone have been estimated to be 1.2gC.m^-2.a^-1 and 1.5 a^-1, respectively.     

The Effects of Altering Seagrass Canopy Height on Small, Motile Invertebrates of Shallow Mediterranean Embayments

Abstract. The height of seagrass canopy was manipulated in experimental plots in meadows of the fine-leaves seagrass Cymodocea nodosa at two sites in the Mediterranean Sea, la Lagune du Brusc, Iles des Embiez near Toulon, and I'Etang de Diana on Corsica. Epifauna (small motile invertebrates associated with the seagrass canopy or sediment surface), was collected at night at both sites, and during the day at Diana only, from three treatments: full seagrass canopy, reduced canopy, and canopy removed entirely. Although epifaunal assemblages from the two sites were different, treatment modification had the same effect at both sites when analysed using multivariate ordinations. Abundance and biomass of total epifauna and of key taxa were all reduced in line with decreasing seagrass cover at both sites at night. The effects of treatment modification on epifauna during the day showed the same trend but were of greater magnitude, both for assemblages and for total abundance and biomass. At both sites and at both times, the fauna of plots from which seagrass had been cut tended to be dominated by animals of higher biomass than the fauna of plots with full canopy. Epifauna form the major dietary component of small fish inhabiting shallow, sheltered embayments. These results are therefore consistent with a model in which reduced abundance of fish associated with reduced seagrass canopy is explained by a reduction in food availability.     

Use of shallow water habitats by fish assemblages in a Mediterranean coastal lagoon

The present study investigates the different uses and the functional roles of shallow habitats for fish fauna in the Venice Lagoon, by applying the functional guilds approach. Temporal (seasons) and spatial (location) changes within the lagoon show different habitat uses by fish assemblages, not influenced by local factors. Unvegetated mud habitats (salt marsh creeks and sub-tidal mud flats) and sparsely vegetated (seagrass) habitats show a common nursery role, especially for marine migrant fishes; but, contrary to other similar areas elsewhere shallow seagrass beds in the Venice Lagoon do not have a primary nursery role. This latter habitat has a more important role as a spawning ground for a resident, highly specialized component of the fish community. The habitat uses and their role to fish fauna illustrate the balance between predation risk and foraging profitability, as major factors structuring the fish assemblages. Spatial effects at a larger scale also highlight general characteristics of the fish assemblages in the Venice Lagoon. These indicate differences between the Northern sub-basin and the other two lagoon sub-basins, due to differences in the hydrodynamic regime, habitats distribution, and contributions from land and sea.     

Effects of current exposure on habitat preference of mobile 0-group epibenthos for intertidal seagrass beds (Zostera noltii) in the northern Wadden Sea

In the northern Wadden Sea, the extent of intertidal seagrass beds, their plant biomass and shoot density highly depends on local current regimes. This study deals with the role of intertidal Zostera noltii beds as nursery for mobile epibenthic macrofauna and the impact of seagrass bed characteristics on their abundance and distribution patterns. According to their exposure to the main tidal gullies, sampling sites were separated into exposed, semi-exposed and sheltered. Dominant species of crustaceans and demersal fish were studied in respect of their abundances within seagrass beds and adjacent unvegetated areas. Quantitative sampling was performed at day and night high tide using a portable drop trap. In general, species composition varied little between seagrass beds and bare sand. However, the presence of vegetation had a quantitative effect increasing individual numbers of common epifaunal species. Abundances of 0-group shore crabs (Carcinus maenas), common gobies (Pomatoschistus microps) and brown shrimps (Crangon crangon) were highest within sheltered seagrass beds. With decreasing plant density habitat preference of epibenthos changed on species level. By regulating the habitat complexity the currents regime is profoundly influencing the nursery function of intertidal seagrass beds in the Wadden Sea.     

Spatial distribution of crustaceans associated with shallow soft‐bottom habitats in a coral reef lagoon

The ecology and diversity of the shallow soft‐bottom areas adjacent to coral reefs are still poorly known. To date, the few studies conducted in these habitats dealing with macroinvertebrate fauna have focused on their abundance spatial patterns at high taxonomic levels. Thus, some aspects important to evaluate the importance and vulnerability of these habitats, such as species diversity or the degree of habitat specialization, have often been overlooked. In this study we compared the crustacean assemblages present in four different habitats at Magoodhoo Island coral reef lagoon (Maldives): coral rubble, sandy areas and two different seagrass species (Thalassia hemprichii and Cymodocea sp.). Forty‐two different crustacean species belonging to 30 families and four orders were found. ‘Site’ was a significant factor in all of the statistical analyses, indicating that tropical soft‐bottom habitats can be highly heterogeneous, even at a spatial scale between tens and hundreds of meters. Although traditionally it has been considered that seagrass beds host greater species diversity and abundance of organisms than adjacent unvegetated habitats, no differences in the univariate measures of fauna (abundance of organisms, number of species and Shannon diversity) were observed among habitats. However, sandy areas, coral rubble and seagrass beds exhibited different species composition of crustacean communities. The percentage of taxa considered as potential habitat specialists was 27% and the number of species exclusively occurring in one habitat was especially high in seagrass beds. Thus, degradation of this vegetated habitat would result in a great loss of biodiversity in tropical shallow soft‐bottom habitats.     

Trawling or Visual Censuses? Methodological Bias in the Assessment of Fish Populations in Seagrass Beds

Abstract. Fishes associated with the seagrass Posidonia oceanica were censused both by skid trawl and visual counts around Ischia Island, Italy. Both sampling procedures were performed during the day in summer and in winter at two sites. Significant differences in the number of species, number of individuals, biomass, and trophic structure of the fish assemblage were observed between sampling methods. Fewer fish species were recorded by visual counts than by trawling. More individuals and a greater biomass, however, were recorded from visual counts. The population of macrocarnivores (Scorpaenidae, Serranidae) were better estimated by trawling, as were canopy-dwellers (Syngnathidae; Symphodus rostratus) and benthic species (Gobiidae; Blenniidae; Bothidae). Conversely, good swimmers ( Sparidae; Coris julis, Symphodus spp.), and planktivorous fishes (Centracanthidae, Pomacentridae) mostly escaped the trawl and were better assessed by visual counts. The importance of methodological biases differed from one season to the other and was higher in summer than in winter. Particular attention should be paid to the biases induced by sampling techniques when interpreting data, and different sampling methods should be used to accurately study the fish assemblages of seagrass meadows.     

Habitat characteristics and spatial arrangement affecting the diversity of fish and decapod assemblages of seagrass (Zostera marina) beds around the coast of Jersey (English Channel)

Recent research and management plans for seagrass habitats have called for landscape level approaches. The present study examines the spatial utilisation of subtidal seagrass beds by fish and decapods around the coast of Jersey (49°N 02° W). A hierarchical scale of landscape configuration and the plant characteristics of eight seagrass beds were measured and the contributions of these variables as predictors of the properties of the fish and decapod assemblages were evaluated using multiple linear regression models. The results indicated that total diversity had a negative relationship with transect heterogeneity and total species number had a weak negative association with increasing fragmentation. Both total diversity and total species number showed a positive relationship with depth. In fact, in all models of species number and densities, values were higher in deeper seagrass beds. Total decapod density increased with aggregation of seagrass patches within a landscape. In addition to landscape configuration, smaller-scale structural changes in both canopy height and epiphyte load appeared to influence densities of decapod crustaceans. At night, fewer patterns could be explained by the independent variables in the model.     

Comparison of the fish assemblages associated with Posidonia oceanica after the partial loss and consequent fragmentation of the meadow

An extensive Posidonia oceanica meadow was partially destroyed by excavation, resulting in areas of seagrass habitat of equal complexity (shoot density) but different heterogeneity (degree of fragmentation). The fish assemblages associated with differently fragmented beds were compared from a landscape perspective. Differences in the fish assemblages were detected, with several species showing different patterns: (1) species that increased their abundance along with the degree of bed fragmentation, (2) species that were more abundant in fragmented beds, but did not show differences between more or less fragmented beds, and (3) species that were mostly abundant in large seagrass patches or in the continuous meadow. The fish assemblages were also affected by depth, but further research is needed to determine properly this effect. Some ecological mechanisms are suggested to operate in the interaction between P. oceanica and the held fish assemblage.     

Meiobenthic communities of seagrass beds (Zostera capricorni) and unvegetated sediments along the coast of New South Wales,Australia

Seagrass beds have higher biomass, abundance, diversity and productivity of benthic organisms than unvegetated sediments. However, to date most studies have analysed only the macrofaunal component and ignored the abundant meiofauna present in seagrass meadows. This study was designed to test if meiobenthic communities, especially the free-living nematodes, differed between seagrass beds and unvegetated sediments. Sediment samples from beds of the eelgrass Zostera capricorni and nearby unvegetated sediments were collected in three estuaries along the coast of New South Wales, Australia. Results showed that sediments below the seagrass were finer, with a higher content of organic material and were less oxygenated than sediments without seagrass. Univariate measures of the fauna (i.e. abundance, diversity and taxa richness of total meiofauna and nematode assemblages) did not differ between vegetated and unvegetated sediments. However multivariate analysis of meiofaunal higher taxa showed significant differences between the two habitats, largely due to the presence and absence of certain taxa. Amphipods, tanaidacea, ostracods, hydrozoans and isopods occurred mainly in unvegetated sediments, while kinorhyncs, polychaetes, gastrotrichs and turbellarians were more abundant in vegetated sediments. Regarding the nematode assemblages, 32.4% of the species were restricted to Z. capricorni and 25% only occurred in unvegetated sediments, this suggests that each habitat is characterized by a particular suite of species. Epistrate feeding nematodes were more abundant in seagrass beds, and it is suggested that they graze on the microphytobenthos which accumulates underneath the seagrass. Most of the genera that characterized these estuarine unvegetated sediments are also commonly found on exposed sandy beaches. This may be explained by the fact that Australian estuaries have very little input of freshwater and experience marine conditions for most of the year. This study demonstrates that the seagrass and unvegetated sediments have discrete meiofaunal communities, with little overlap in species composition.     

Consistency of temporal and habitat-related differences among assemblages of fish in coastal lagoons

The consistency of habitat-related differences in coastal lagoon fish assemblages was assessed across different spatial and temporal scales. Multimesh gillnets were used to sample assemblages of fish on a monthly basis for 1-year in three habitats (shallow seagrass, shallow bare and deep substrata) at two locations (>1 km apart), in each of two coastal lagoons (approximately 500 km apart), in southeastern Australia. A total of 48 species was sampled with 34 species occurring in both lagoons and in all three habitats; species caught in only one lagoon or habitat occurred in low numbers. Ten species dominated assemblages and accounted for more than 83% of all individuals sampled. In both lagoons, assemblages in the deep habitat consistently differed to those in the shallow strata (regardless of habitat). Several species were caught more frequently or in larger numbers in the deep habitat. Assemblages in the two shallow habitats did not differ consistently and were dominated by the same species and sizes of fish, possibly due to habitat heterogeneity and the scale and method of sampling. Within each lagoon, very few between location differences in assemblages within each habitat were observed. Consistent differences in assemblages were detected between lagoons for the shallow bare and deep habitats, indicating there were some intrinsic differences in ichthyofauna between lagoons. Assemblages in spring differed to those in summer, which differed to those in winter for the shallow bare habitat in both lagoons, and the deep habitat in only one lagoon. Fish-habitat relationships are complex and differences in the fish fauna between habitats were often temporally inconsistent. This study highlights the need for greater testing of habitat relationships in space and time to assess the generality of observations and to identify the processes responsible for structuring assemblages.     

中国文昌红树林-海草床-珊瑚礁连续生境的鱼类连通性

Understanding the connectivity of fish among different typical habitats is important for conducting ecosystembased management, particularly when designing marine protected areas(MPA) or setting MPA networks. To clarify of connectivity among mangrove, seagrass beds, and coral reef habitats in Wenchang, Hainan Province,China, the fish community structure was studied in wet and dry seasons of 2018. Gill nets were placed across the three habitat types, and the number of species, individuals, and body size of individual fish were recorded. In total, 3 815 individuals belonging to 154 species of 57 families were collected. The highest number of individuals and species was documented in mangroves(117 species, 2 623 individuals), followed by coral reefs(61 species,438 individuals) and seagrass beds(46 species, 754 individuals). The similarity tests revealed highly significant differences among the three habitats. Approximately 23.4% species used two habitats and 11.0% species used three habitats. A significant difference(p0.05) in habitat use among eight species(Mugil cephalus, Gerres oblongus, Siganus fuscescens, Terapon jarbua, Sillago maculata, Upeneus tragula, Lutjanus russellii, and Monacanthus chinensis) was detected, with a clear ontogenetic shift in habitat use from mangrove or seagrass beds to coral reefs. The similarity indices suggested that fish assemblages can be divided into three large groups namely coral, seagrass, and mangrove habitat types. This study demonstrated that connectivity exists between mangrove–seagrass–coral reef continuum in Wenchang area; therefore, we recommend that fish connectivity should be considered when designing MPAs or MPA network where possible.     

Polychaete Fauna of Seagrass Beds (Halodule wrightii Ascherson) Along the Coast of Rio de Janeiro (Southeast Brazil)

Abstract.  The polychaete community structure from six Halodule wrightii seagrass beds along the Rio de Janeiro coast (Southeast Brazil) was investigated. Variations in species diversity, overall density and species composition in relation to sediment grain size, seagrass biomass and selected plant structural features such as root and shoot length from the study sites were analysed. Ten core samples (0.02 m²) were randomly collected from each site. Three additional samples were taken for grain size analysis of sediment. Sixty-eight species of polychaetes belonging to 24 families were found. The dominant species as well as species composition varied greatly among sites, showing that a typical polychaete community does not exist. The number of species was positively correlated with the silt-clay percent and sorting coefficient of the sediment. A positive correlation between polychaete density and plant biomass was also obtained. Multivariate analysis indicated that polychaete communities were influenced greatly by seagrass plant features: plants with longer shoots harbour mainly surface-deposit feeders such as Magelona papillicornis , whereas plants with a higher root-shoot length relation sheltered mainly suspension or interface feeders like Fabricia filamentosa . This study demonstrates that granulometric properties as well as plant architecture play an important role in structuring the polychaete community. As the community-level response can reflect changes in local seagrass beds, the structure of the polychaete community can be an important indicator for management plans and the restoration of seagrass ecosystems.     

To what extent are the characteristics of nematode assemblages in nearshore sediments on the west Australian coast related to habitat type, season and zone?

This study has determined the ways in which the characteristics of the nematode assemblages in nearshore marine waters along the microtidal lower west coast of Australia are influenced by habitat type, time of year and shore-perpendicular zones. The habitat types (1, 2 and 6), which had previously been identified on the basis of a suite of enduring environmental characteristics, could be broadly described as highly sheltered from wave activity and containing dense seagrass (1), moderately sheltered from wave activity with sparse seagrass (2) and relatively exposed to wave activity with no seagrass (6). Sampling in five consecutive seasons yielded 15 751 nematodes representing 75 species, of which, at present, only three can be referred to described species. The number of species and densities in habitat type 1, and particularly those in its subtidal zone (C), were far greater than those in the other two habitat types. Both of these biotic variables underwent marked seasonal changes, declining to low levels during winter. The compositions of the assemblages differed significantly among the three habitat types, with the differences between habitat types 1 and 6 being particularly marked. Species of Paracomesoma, Dichromadora, Marylynnia, and Pomponema, which are assumed to feed primarily on benthic diatoms, were particularly abundant at the most sheltered habitat type, whereas those of Gonionchus, Theristus and Bathylaimus, which are assumed to be deposit feeders, were relatively abundant at the most highly exposed habitat type. The compositions of the assemblages differed among seasons and were most discrete in spring, due to marked increases in the densities of certain species. However, differences in the compositions in the different zones of each habitat type were relatively small, presumably reflecting the presence of only a small tide in the region.     

Polychaete Depth Distribution in a Posidonia oceanica Bed (Rhizome and Matte Strata) and Neighbouring Soft and Hard Bottoms

Abstract. The study was carried out in a Posidonia oceanica bed and in the neighbouring sandy and rocky bottoms, at Ponza Island (Central Tyrrhenian Sea), in order to investigate the distributional pattern of the polychaete community at different depths. A total of 15232 individuals of polychaetes belonging to 218 species was collected and three new species of Syllidae were found. The polychaete community of the matte can be clearly distinguished from the neighbouring communities; this is due to the high species richness in Posidonia , which is related to the heterogeneity of the biotope. In the Posidonia bed the shallow stations (1 m and 5 m depth) were the richest in terms of species numbers and individuals due to the high shoot density of the seagrass bed. In the shallow waters polychaete community structure changed according to the different exposure to water movement. Rocky bottom species, which preferentially inhabit crevices, were more abundant in the matte exposed to water movement (5–10 m depth). In contrast, soft-bottom species were more abundant in the sheltered zone (1 m depth) as well as in the deeper zone due to the reduction of the Posidonia bed.     

Spatial distribution of surgeonfish and parrotfish in the north sector of the Mesoamerican Barrier Reef System

Surgeonfish and parrotfish play an important role in structuring the benthic communities of coral reefs. However, despite their importance, little is known about their distribution patterns in the north sector of the Mesoamerican Reef System. This study evaluated the distribution of these fish in 34 sites in four habitats (lagoon, front, slopes and terrace) along a depth gradient (c 0.5–20 m). These herbivorous fish were assessed by visual censuses. Species dominance was evaluated for each habitat using SIMPER analysis. Habitat characteristics data were collected to determine the relationship between habitat conditions and spatial variations in herbivorous fish (using abundance and biomass as a proxy) via redundancy analysis. The herbivorous fish assemblage had a low density (fish per 100 m²) and biomass (g·100 m^?2) in comparison with assemblages in similar studies. In contrast, species richness was high compared with other studies in the Caribbean. Spatial variation of the abundance, biomass and size of herbivorous fish was strongly related to coral and seagrass cover, as well as to depth and rugosity. These four variables were critical in controlling the distribution patterns of the herbivorous fish assemblages. No associations were found between fish and macroalgae or any other benthic group. The present study indicates that the species richness of surgeonfish and parrotfish was not regionally affected by the dominance of macroalgae in the habitats studied. Seagrass beds and the coral reef matrix need to be preserved for the herbivorous fish assemblages to remain healthy and capable of controlling excess macroalgae growth.     

Spartina anglica eradication experiment and in situ monitoring assess structuring strength of habitat complexity on marine macrofauna at high tidal level

The cordgrass Spartina anglica is an introduced species that tends to invade sheltered sand and mudflats, at the upper low marsh level. In Arcachon Bay, a lagoon in South West of France, the cordgrass can also replace Zostera noltii beds. The consequence of cordgrass presence on macrobenthic fauna was estimated and compared to adjacent habitats (bare sands, Z. noltii sea grass beds) during one year. The communities of the three habitats were characterised by low species richness, low abundance and biomass (when Hydrobia ulvae, 90% of abundance, is not considered) and high seasonal stability. The infaunal assemblages were particularly homogeneous between habitats without any characteristic species.Cordgrass eradication experiments were performed and zoobenthic recolonisation was observed the following year. Modifications in benthic fauna were observed on epifauna only.These results highlight the limited structuring effect of habitat heterogeneity at high tidal levels and in soft-bottom sediments where desiccation becomes the dominant factor determining infauna community structure.     

华南沿海海草床分布区大型底栖动物群落特征初探

为探究华南沿海海草床大型底栖动物群落特征、地区差异及其与海草群落间的关系,2020年在华南沿海12个海草床区域开展了大型底栖动物调查。共布设33个调查断面99个站位,在主要群落参数的基础上,运用相关性分析和聚类分析、nMDS排序、相似性百分比分析等群落生态学统计方法分析了底栖动物群落特征及其与海草群落的关系。共鉴定出大型底栖动物9大门类199种,其中,软体动物种类最多,占总种类数的39.7%。各区域底栖动物的平均栖息密度为155.7 ind/m²,青葛—龙湾(琼海)的平均栖息密度最低,珍珠湾(防城港)的平均栖息密度最高;平均生物量为118.36 g/m²,最低值出现在义丰溪(汕头),最高值出现在珍珠湾。各区域底栖动物的优势种以潮间带泥沙滩常见腹足类、双壳类和多毛类为主;底栖动物的种类多样性指数(H′)平均值为1.12,最低值出现在唐家湾(珠海),最高值出现在铁山港(北海);各调查区域底栖动物主要群落参数大致呈现“北部湾>海南沿岸>珠江口及粤东”的规律。华南沿海海草床分布区大型底栖动物群落的区域性特征较为明显,地理位置相近的海草床底...     

Diel Changes in Assemblages of Fishes Associated with Shallow Seagrass and Bare Sand

The evaluation and management of fisheries resources requires knowledge of spatial and temporal changes in the habitat-associations of fishes. However, most studies concerning habitat associations of small fishes in the shallow regions of estuaries have been limited to daytime sampling strategies. Diel changes were investigated in assemblages of fishes associated with shallow seagrass (Zostera capricorni) and bare sand in two estuaries in south-eastern Australia. Habitat-related differences in assemblages were strong day and night, and were greater than diel changes in assemblages. The seagrass-associated assemblages remained similar day and night and consistently differed from those associated with bare sand. In contrast, the assemblages over sand varied on a diel basis as larger individuals of several species (e.g.Gerres subfasciatus,Platycephalus fuscus) that resided over other (deeper) habitats during the day were caught over shallow sand at night. Further, some species (e.g.Ambassis jacksoniensis) that resided in seagrass during the day occurred over sand at night. Both habitats were utilized by newly recruited juveniles of economically important species and the habitat-associations of these species generally did not differ on a diel basis. Therefore, both habitats are considered important to the fisheries resources of south-eastern Australia. Inclusion of night-time sampling provided a greater understanding and appreciation of the use of the unvegetated habitat by fishes than has previously been acknowledged from studies based solely on daytime sampling. This study indicates that greater consideration of temporal changes in habitat associations of fishes is required in other geographic regions.     

印尼混合海草床大型底栖生物丰度和多样性生态研究

海草床是海岸带最富生产力的生态系统之一,支撑着各种各样的伴生生物。热带的印度和太平洋地区被认为拥有海草植物种类多样性最高,且分布面积最广,然而,这个区域的海草床大型底栖生物我们知之甚少。为了填补认知的空白,我们在该区域开展了一项生态调查,旨在描述该区热带海草床大型底栖生物的丰度和多样性,以及确定大型底栖生物丰度、物种丰富度和群落结构是否明显存在断面内的站间变化和样地间变化。2014年5月和2015年10月我们分别在北苏拉威西省东海岸和西海岸开展野外工作,使用柱状取样器采集海草床大型底栖生物样品。所得样品共计鉴定14大类149种底栖生物,种类最为丰富的类别为多毛类（56种,占26%的总个体数）,十足类（20种,占9%的总个体数）和端足类（18种,占35%的总个体数）。东、西海岸海草床大型底栖生物表现出不同的空间分布模式。在东海岸,同一断面的大型底栖生物和端足类的丰度存在显著的站间差异;而在西海岸,大型底栖生物和多毛类的种类丰富度和丰度都表现出明显的站间变化,这可能归结于同一断面底质不均所造成。单因素ANOSIM以及MDS排序表明了北苏拉威西省东海岸和西海岸海草床大型底栖生物群落结构存在显著不同,正好对应于将海草床分成两大类型的栖息地,即西海岸的红树林-海草床-珊瑚连续体和东海岸的海草床-珊瑚连续体。与在热带海区开展的其他研究相比,本研究的大型底栖生物丰度和多样性处于中等水平。东、西海岸海草床大型底栖生物群落存在显著区别,其原因可能源于多方面,包括了沉积物模式,海草床结构和时间变化。     

Use of different intertidal habitats by faunal communities in a temperate coastal lagoon

The faunal communities of four intertidal habitats namely sand, mud, seagrass (Zostera noltii) and seagrass patches (mixSM) of a temperate coastal lagoon, Ria Formosa (southern Portugal), were sampled. A total of 47 species were taken in 428 bottomless drop sampler samples, with the highest number of species and the more commonly occurring species belonging to the Mollusca phylum. The dominance of these gastropod species underlines the importance of the grazing food chain in these habitats. Bittium reticulatum was the most abundant species, being especially abundant in the seagrass habitat. The most frequent and highest biomass species in the community was Carcinus maenas, a predator that makes use of the available resources and that is adapted to the highly variable intertidal environment. Pomatoschistus microps was the most abundant fish species, with highest densities in the mud habitat, which demonstrates an ability to occupy a low depth area. The seagrass habitat had the highest diversity, abundance and biomass, followed by the mixSM habitat and was different from all the others. Assemblages were highly influenced by the presence of vegetation, providing forage and refuge from predation. A well defined summer group was identified in all habitats. These results highlight the importance of seagrass beds and the idea that their decrease implies the decrease of lagoon production through the impoverishment of the trophic structure of the lagoon.