Sedimentary Bottoms Research Articles

The molluscan fauna of Chella Bank and surroundings (Western Mediterranean Sea)

Molluscs of Chella Bank and its surroundings were studied from 21 samples collected with a van Veen grab in the depth range 95-729 m. A total of 299 taxa were identified (77 live-taken), thus increasing by more than 95% the species of molluscs reported in the recently declared site of community importance “Sur de Almería-Seco de los Olivos”. Two of the species are new records to Spanish waters and one to the Alboran Sea. The high species richness observed could be related to the location, the hydrological characteristics and the topographical heterogeneity of the area within the Alboran Sea. Four significant groups of samples were discriminated through multivariate analysis of quantitative data of live-taken molluscs: (I) bathyal muddy bottoms with buried rhodoliths; (II) bathyal muddy bottoms with coral rubble; (III) bathyal hemipelagic muddy bottoms and (IV) bathyal sandy bottoms. Molluscs were more diverse on coral framework bottoms than on sedimentary bottoms around Chella Bank. Most of the live-taken species are widely distributed along the Atlantic and Mediterranean Sea, and a few are strictly Mediterranean. The most striking feature was the occurrence of two species with planktotrophic larval development for which Chella Bank is the sole recorded locality in the Mediterranean (Episcomitra angelesae and Mitrella templadoi) and which elsewhere extremely rare (Mathilda spp.).

Life strategies and habitat preferences of Bythitidae and Zoarcidae, specialized fishes with particular life histories, in the Mediterranean deep sea

Deep-sea habitats are home for a variety of yet poorly known fish species, some of which display specialized life strategies, as is the case of Bythitidae and Zoarcidae. With the purpose of elucidating biological and ecological aspects of representatives of these families in NW Mediterranean waters, a large dataset based on 599 specimens of Cataetyx alleni, 30 C. laticeps and 284 Melanostigma atlanticum captured during the last 30 years within the framework of different research projects was used to address their geographical and bathymetric distribution, population structure, reproduction, trophic ecology, parasitism and enzymatic markers in the Balearic basin. Present outcomes revealed a patchy distribution mostly for M. atlanticum, possibly related to aggregation during reproduction and to the association with specific sediments. For the three species, higher densities occurred in the mainland vs. the insular margin, and a diminishing trend in estimated densities over the last decades was observed for C. alleni and M. atlanticum likely linked to climatic oscillations. Trophic data indicated that the two Cataetyx species inhabit the water-sediment interface and mainly feed on suprabenthic prey, while M. atlanticum inhabits the water column near the bottom preying on pelagic organisms and moving towards the seabed during reproduction. These results were supported by the parasitological assessment, which revealed that parasite communities were moderately diverse and abundant for Cataetyx spp. while being highly depauperate for M. atlanticum. Present outcomes from the Mediterranean Sea confirmed reproduction of C. alleni during autumn-winter and of M. atlanticum during autumn. Spawning of the former species may occur in winter-spring, as suggested by the finding, by the first time, of two females captured in March with fully-developed embryos inside. Levels of enzymatic markers quantified in muscle were provided for C. alleni and M. atlanticum for the first time. The special interactions found between the distribution and biology of Bythitidae and Zoarcidae and the sedimentary bottoms that they inhabit indicates that such conventional habitats are more heterogeneous than it is generally assumed and deserve higher attention for future protection.

All shallow coastal habitats matter as nurseries for Mediterranean juvenile fish

Coastal zones are ecosystems of high economic value but exposed to numerous disturbances, while they represent nurseries for many fish species, raising the issue of the preservation of their functions and services. In this context, the juvenile fish assemblages of all types of habitats present in shallow coastal zones were studied on the south-east coast of France using underwater visual censuses in warm (June–July 2014) and cold (April 2015) periods. A total of fourteen habitat types were characterized, which could be grouped into three broad categories, rocky substrates (natural and artificial), sedimentary bottoms with all levels of granulometry, and seagrass beds including Cymodocea nodosa and Posidonia oceanica meadows; the ecotones or interfaces between the three broad habitat categories were individualized as particular habitat types. The abiotic and biotic descriptors of the 14 habitat types individualized did not vary with time, except for a higher cover percentage and canopy height of macrophytes in the warm period, which increased the three-dimensional structure of some habitats. The taxonomic composition and density of juvenile fish assemblages were analyzed using both multivariate and univariate descriptors, after grouping the 57 fish species recorded into 41 well-individualized taxa. Juvenile fishes were recorded in all habitat types, with higher mean species richness and abundance during the warm than the cold period. The richest habitats in terms of both fish species richness and abundance were the natural rocky substrates and the interfaces between Posidonia beds and the other habitats. Although juvenile fish assemblage composition differed among habitat types and between periods, the most abundant fish species were Atherina sp., Sarpa salpa, Gobiidae, Symphodus spp., Pagellus spp. and several Diplodus species, which colonized 7 up to 14 different habitat types (depending on taxa) during their juvenile life. Most species settled in one or a few specific habitats but rapidly colonized adjacent habitats when growing. This study provided evidence of the role of all types of shallow coastal habitats as fish nurseries and their varying pattern of occupation in space and time by the different juvenile stages. It highlighted the importance of the mosaic of habitats and interfaces for the complete development of all juvenile life stages of fishes, and for the preservation of a high diversity of coastal fish assemblages and fisheries resources in the Mediterranean Sea.

Free-living bryozoans (Cheilostomatida, Cupuladriidae) from northeastern and northern Brazil.

Free-living bryozoans, unlike most cheilostomes, live unattached from the substratum on or within soft sedimentary bottoms. Bryozoans of the family Cupuladriidae Lagaaij, 1952 are probably the best-studied free-living representatives. In Brazil, eight species of cupuladriids have been reported to date, including some regarded as species complexes. This paper documents cupuladriid taxa from northeastern and northern Brazil based on the examination of 1236 colonies. Three species previously reported from Brazil are described: Cupuladria monotrema (Busk, 1884), Discoporella gemmulifera Winston Vieira, 2013 and Discoporella salvadorensis Winston, Vieira Woollacott, 2014. A new species, Cupuladria minuta n. sp., is erected; it differs from its congeners in having small, flat discoid colonies, with the central area up to the fifth astogenetic generation composed of vicarious avicularia with an auriform opesia, and quadrangular to rectangular basal sectors with 1-6 small openings per sector. Our results suggest that four species previously recorded from Brazil are doubtful-Cupuladria canariensis (Busk, 1859), Cupuladria biporosa Canu Bassler, 1923, Discoporella umbellata (Defrance, 1923) and Discoporella depressa (Conrad, 1841). Some Brazilian specimens previously assigned to Discoporella umbellata var. conica are re-assigned to D. salvadorensis. The species studied here frequently co-occur on mainly sandy and muddy bottoms at 8-130 m depth, as it is typical of most living populations of cupuladriids. The sedimentation rate, and thus the bottom composition, likely influence the distribution of cupuladriids in Brazil, with Cupuladria species being more common in stabler and coarser sea bottoms than Discoporella species, which tend to be more broadly distributed.

Asteroids and Ophiuroids Associated With Sponge Aggregations as a Key to Marine Habitats. A Comparative Analysis Between Avilés Canyons System and El Cachucho, Marine Protected Area

This study analyzes the fauna composition of the community of brittle and sea stars associated with sponge aggregations located in Avilés Canyons System and El Cachucho, Marine Protected Area (MPA). Diverse sampling methods were used depending on bottom morphology, such as rock dredges and specific samplers for sedimentary bottoms, mainly beam trawl models. These banks are made up of sponge and coral species that build a very appropriate substrate for the proliferation of benthic species, which together create Vulnerable Marine Ecosystems that are highly relevant for management and conservation. Among these benthic species, echinoderms are of great interest due to their value as indicators of good habitat. In total, 1261 specimens were collected (934 brittle stars and 327 starfishes), belonging to 42 species (28 ophiuroids and 14 asteroids) from INDEMARES AVILÉS, ECOMARG, and SponGES project surveys. Specimens were distributed among four sponge aggregations (F: fields) that were considered according to the sponge records obtained in the same stations (36). These fields were defined and named based on the five most common sponge species:Aphrocallistes beatrixandRegadrella phoenix(F1: Avilés Canyon);Pheronema carpenteri(F2: Intraslope basin of Le Danois Bank);Asconema setubalense(F3: Le Danois Bank); andNeoschrammeniellaaff.bowerbankii(F4: Corbiro Canyon). Faunistic results show thatOphiactis abyssicola(55.55% occurrence),Brisinga endecacnemos, Ophiolycus purpureus, andPeltaster placenta(33.33%) were the most frequently found species in F1;Psilaster andromeda(80%),Pseudarchaster parelii(60%), andNymphaster arenatus(46.67%) in F2;Ophiura carnea(71.43%) andOphiacantha smitti(42.86%) in F3; andOphiacantha densa, andHenricia caudani(100%) in F4. The asteroid and ophiuroid species collected seem to be composed of four different communities that fit to areas with particular morphological and biological features, related to the presence of species specialized in the use of the resources they can find there. In general, the abiotic factor controlling this structure is depth. This assemblage structure, which favors the dissimilarity between the canyons and the bank, is not so clear, since the deepest stations are located on the intraslope basin of El Cachucho, Marine Protected Area (MPA), therefore, using ita prioricould lead to misunderstandings. Once the structure of the echinoderm community was known, we compared the expected and obtained results to analyze evidence which should prove the existence of any association between echinoderms and sponges, which enabled us to refute the incongruous hypothesis.

The positive effect of coexisting ecosystem engineers: a unique seaweed-mussel association provides refuge for native mud crabs against a non-indigenous predator.

In marine sedimentary bottoms, mussels and macroalgae have long been recognized as important autogenic engineers that create habitat and modify abiotic conditions. The structural complexity added by bivalves and macroalgae may also mediate intraguild predation amongst marine decapod crustaceans. While spatial distributions of these ecosystem engineers frequently overlap, there is limited understanding of compounded effects when more than one engineer is present. Here we demonstrate that the coexistence of two ecosystem engineers may create habitat valuable for the survival of a small native species, the Atlantic mud crab (Panopeus herbstii), in the presence of the invasive green crab (Carcinus maenas). Using laboratory and field habitat mimics, we measured mud crab survival rates as a proxy for refuge quality. We compared the refuge provided by a unique association between shells of blue mussels (Mytilus edulis) and the giant strain of Irish moss (Chondrus crispus) to that provided by bare substrate, and by each engineer alone. These experiments revealed that the association of giant Irish moss with blue mussel shells positively and non-additively increased mud crab survival compared to the other less complex habitat mimics. In contrast, parallel experiments revealed that high habitat complexity was less important for young green crabs to survive predation from large conspecifics. These results suggest that the impact of ecosystem engineers on trophic dynamics should be considered in a broader, whole-community context encompassing multiple habitat-forming species present.

Aporte de las Áreas Marinas Protegidas del Sistema de Parques Nacionales Naturales a la representatividad de ecosistemas en Colombia

Se llevó a cabo un análisis de representatividad de ecosistemas marinos y costeros en las 18 Áreas Marinas Protegidas (AMP) administradas por el Sistema de Parques Nacionales Naturales de Colombia (SPNN) y sus cambios a 2020 con respecto a 2010. Para el Caribe, aumentó la representatividad de manglares, pastos marinos, fondos sedimentarios y playones salinos, mientras para el Pacífico, aumentó la representatividad de estuarios, fondos sedimentarios, manglares, planos intermareales de lodo, playas arenosas y montañas submarinas. Se incluyeron los corales de profundidad como un nuevo ecosistema para el SPNN. A partir de clases de representatividad determinados para este análisis, se encontró que el único ecosistema sin representatividad (0 %) (corales de profundidad) pasó a ser sobrerrepresentado (≥ 60 %). El número de ecosistemas en representatividad baja disminuyó de 8 a 7 (< 10 %) mientras los ecosistemas en representatividad media aumentaron de 9 a 10 (10-29 %). En la última década, ecosistemas de importancia ecológica como los estuarios (0,55 %) en el Caribe y los bosques mixtos de guandal (0,22 %) para el Pacífico no presentaron ningún cambio en su representatividad. Se evidencia la necesidad de incrementar la investigación y conocimiento de los hábitats bentónicos profundos para incluirlos dentro del sistema, y aprovechar el escenario de diálogo internacional para contribuir y comprometerse con metas ambiciosas de conservación en marco pos-2020 del Convenio de Diversidad Biológica.

Community disruption in small biogenic habitats: A coastal invader overcomes habitat complexity to alter community structure.

Non-indigenous species are often identified as threats to native species and communities. Yet, the mechanisms that enable many of these invaders to thrive and alter their newly invaded habitats are still not fully understood. This applies to habitats such as widespread sedimentary shorelines characterized by the presence of scattered biogenic clumps of blue mussels (Mytilus edulis) structurally more complex than bare sediments. In Atlantic Canada, some of these shorelines are numerically dominated by native mud crabs (Dyspanopeus sayi) but have been gradually invaded by the European green crab (Carcinus maenas). This study describes between-habitat (mussel clump vs. bare sediment) differences in density and diversity of invertebrates. It also tests the impact of juvenile green crabs in comparison to native mud crabs using two approaches: First, measuring habitat-related differences in these crabs’ feeding rates on a common prey (soft-shell clams, Mya arenaria). Second, measuring their influence on invertebrate communities associated with mussel clumps. The results show that mussel clumps hold higher invertebrate density and diversity than surrounding sedimentary bottoms. In the laboratory, the feeding rates of native mud crabs were dependent on the type of habitat (sand flat > mussel clump), whereas those of green crabs were significantly higher and unrelated to the habitat in which predation occurred. In field experiments, juvenile green crabs were also the only predators that changed community structure in the mussel clump habitat. These results indicate that green crabs can cause a significant impact on native species and communities. Moreover, they suggest that the ability of this species to overcome the refuge provided by complex biogenic habitats for prey may represent an unexplored mechanism to explain this invader’s expansion here and elsewhere.

Diversity, distribution, and habitat associations of deep-water echinoderms in the Central Mediterranean

Limited research effort in the Central Mediterranean deep sea has reported a lower species diversity in this area than in adjacent regions. With the recent advent of remotely operated underwater vehicles (ROVs), the deep sea has become more accessible to surveys, especially rocky benthic areas such as canyons and escarpments. The aim of the present study was to assess diversity, spatial and bathymetric distribution, density, habitat, and microhabitat associations of echinoderms in deep waters around the Maltese Islands. Video data were acquired through ROV surveys as part of the LIFE BaĦAR for N2K project, at depths of 216 to 1031 m. In total, 25 echinoderm taxa were recorded, including the first Central Mediterranean records of the sea stars Marginaster capreensis (Gasco, 1876) and Sclerasterias neglecta (Perrier, 1891), and the first record of the holothuroid Mesothuria intestinalis (Ascanius, 1805) from Maltese waters. Six species were observed deeper than their currently accepted depth range in the Mediterranean. The most abundant species were the crinoids Antedon mediterranea (Lamarck, 1816) and Leptometra phalangium (Muller, 1841), which formed very dense aggregations of up to 2900 individuals/1000 m2 in a small area to the south of Malta. This area also supports the only known Mediterranean population of the Atlantic sea star Coronaster briareus (Verrill, 1882). Bathymetric distribution varied for each species, and the overall echinoderm diversity seemed stable across the surveyed depths. Since previous deep-sea studies in the area were based on trawling surveys, many deep-sea echinoderm species are reported in the literature as occurring on sedimentary bottoms. However, the present study revealed that several occur more often on rocky substrata, corals, or anthropogenic objects than on sediments. Our study based on video footage also provided insights into the microhabitat of many deep-sea species, yielding information that is not obtainable through remote sampling.

New data of Tetractinellida (Porifera) in Aviles Canyon system and Le Danois Bank (Cantabrian Sea). Results of the SponGES Project

New data of Tetractinellida (Porifera) in Aviles Canyon system and Le Danois Bank (Cantabrian Sea). Results of the SponGES Project

Spatial and temporal characterization (2006-2012) of the trawling activity in the Site of Community Importance "Volcanes de fango del golfo de Cádiz" (southwestern Iberian Peninsula).

Spatial and temporal characterization (2006-2012) of the trawling activity in the Site of Community Importance "Volcanes de fango del golfo de Cádiz" (southwestern Iberian Peninsula).

Temporal variation of polychaete assemblages and their bioturbation potential in subtidal sedimentary bottoms

Temporal variation patterns and bioturbatory activity of polychaete assemblages have been insufficiently studied. Two subtidal fine-sediment sites have been sampled in order to describe and compare polychaete temporal variation patterns. In order to estimate bioturbation potential (BP), a new approach is proposed that aims maximum versatility for comparative studies. Both assemblages differed significantly in terms of temporal variation of sedimentary and faunal attributes. The most exposed site was dominated by species characteristic of muddy-fine sand and presented a seasonal pattern with higher densities and BP values from mid-summer to early winter. The most sheltered and muddy site was dominated by Paradoneis lyra and presented an irregular temporal variation. Signs of moderate organic enrichment were found, particularly in the less exposed site. Spatial and temporal variations appear to be related to sediment features and hydrodynamic stress, which also affect BP of each assemblage. Our results suggest that the bioturbatory activity of polychaetes is more extensive and relevant in finer sediments.

Landscape configuration modulates carbon storage in seagrass sediments

Climate change has increased interest in seagrass systems as natural carbon sinks and recent studies have estimated the carbon stocks associated with seagrass meadows. However, the factors that affect their variability remain poorly understood. This paper assesses how landscape-level attributes (patch size and matrix composition) influence carbon storage in seagrass sediments. We quantified the organic carbon (Corg) content and other geochemical properties (δ13C and particle size) in surface sediments of continuous Posidonia oceanica meadows, patchy meadows interspersed with rocky-algal reefs and patchy meadows on sedimentary bottoms. We also took samples of potential carbon sources for isotopic composition determination. Our results indicate that the continuous meadows accumulated larger amounts of Corg than patchy meadows, whether embedded in a rock or sand matrix. The Corg from continuous meadows was also more 13C enriched, which suggests that a high proportion of the carbon was derived from plant material (autochthonous sources); in contrast in patchy meadows (especially in a sand matrix), lower δ13C values indicated a higher contribution from allochthonous sources (mainly suspended particulate organic matter, SPOM). These findings suggest that the sediment of continuous meadows stores more Corg in than that of patchy meadows. This is probably due to the increased contribution from seagrass leaves, which are much more refractory than SPOM. In general, certain landscape configurations, and especially patchiness, appear to reduce the carbon storage capacity of seagrasses. Since the current decline of seagrass is leading to habitat fragmentation, our results increase the argument for the promotion of effective measures to preserve the integrity of these natural carbon sinks.

Seafloor characterization and benthic megafaunal distribution of an active submarine canyon and surrounding sectors: The case of Gioia Canyon (Southern Tyrrhenian Sea)

In this paper, we used multibeam bathymetry and backscatter, high-resolution seismic profiles, ROV video images and sediment samples to identify the principal morpho-sedimentary features and related megabenthic communities along the upper reach of the Gioia Canyon (depth<600m) and the surrounding shelf and slope areas. Interpretation of the multidisciplinary dataset was undertaken to evaluate the relationships between seafloor characteristics and faunal distribution along a submarine canyon in an active tectonic setting. The results from this study indicate that physical disturbance on the seafloor at the canyon head and surrounding shelf, related to high sedimentation rates and occasional turbidite flows, may limit the variability of megabenthic communities. Evidence of diffuse trawl marks over soft sedimentary bottoms indicates anthropogenic impact due to fishing activities, which could explain low abundances of megabenthic species observed locally. The canyon margins and flanks along the continental slope host octocorals Funiculina quadrangularis and Isidella elongata, species that are indicative of vulnerable marine ecosystems (VMEs) and relevant in terms of sustainable management priorities. At the Palmi Ridge, the occurrence of outcropping rocks and bottom currents related to the presence of Levantine Intermediate Waters, provide conditions for the development of hard-bottom assemblages, including the black coral Antipathella subpinnata and deep-sea sponges fields.

Temporal variation of the free-living Isopoda (Crustacea: Peracarida) in two subtidal muddy bottoms of the Ría de Aldán (Galicia, NW Iberian Peninsula)

Temporal variation of the free-living Isopoda (Crustacea: Peracarida) in two subtidal muddy bottoms of the Ría de Aldán (Galicia, NW Iberian Peninsula)

First record of genus Orbiniella Day, 1954 (Polychaeta: Orbiniidae) in North Atlantic Ocean with the description of a new species.

A new species of the genus Orbiniella Day, 1954 (Polychaeta: Orbiniidae), collected during the BIOICE programme on sedimentary bottoms off Iceland, is described. Orbiniella petersenae sp. nov. is a shelf and slope species (107 to 1,915 m) chiefly characterized by having notopodial postchaetal papilla from first chaetiger, long crenulated capillary chaetae and several acicular chaetae on each parapodial rami, and pygidium with four lobes. External micromorphology and gross internal anatomy were studied using, respectively, SEM and micro-CT; this is the first time these techniques are used for any species in this genus. A key to all species of this genus worldwide is provided.

Dynamics and morpho-sedimentary interactions in the lower mesotidal estuary of Villaviciosa (NW Spain): A management proposal

The accumulation of sediment in the mouth of Villaviciosa estuary (NW Spain) is becoming an obstaclefor the safe navigation in this estuary. One sector of its outer inlet is characterised by a broad shoal linkedwith a longshore bar of a beach, whose erosion is causing the silting of this area. On this basis, this paperaims to describe the processes that occurred in the lower part of the estuary due to the anthropogenicactivities in the channel and inlet. For this purpose, several measurements were made in the watercolumn and in the sedimentary bottoms to characterise the processes that occur in this area. Based onthese results, a dynamic and morpho-sedimentary model was developed to examine the interactionsbetween the lower estuary and the exposed part of the confining barrier beach, which allows to establishthe evolutionary trends of sedimentary bottoms linked to the marina of El Puntal. Different managementmeasures are carried out to reduce the impact of the sediment accumulation on the navigability, such asperiodically dredging in the inlet of the estuary, and the subsequent dumping of the sediments in areasnear to the closure depth. Consequently, future retreat of narrow inlet and sandy shoal can be avoided,maintaining the sedimentary volume in the system.

Two new species of Sphaerodoropsis Hartman & Fauchald, 1971 (Polychaeta: Sphaerodoridae) from Iceland (BIOICE programme)

Two new species of Sphaerodoropsis Hartman & Fauchald, 1971 (Polychaeta: Sphaerodoridae), collected during the BIOICE programme on sedimentary bottoms off Iceland, are described. Sphaerodoropsis gudmunduri sp. nov. is a shelf species (<400 m) chiefly characterized by having one transverse row of up to 10–12 dorsal macrotubercles per chaetiger (‘Sphaerodoropsis group 2’) and body papillae present only on the prostomium, peristomium, parapodia and ventral surface. It also has up to 7–9 ventral papillae per chaetiger arranged following a non-random pattern and parapodia which bear one digitiform prechaetal lobe, 1–4 papillae and compound unidentate chaetae with blades with thin spinulation along their cutting edge. Sphaerodoropsis halldori sp. nov. has been found in deeper waters (>1000 m) and may be distinguished mostly by having up to 13 dorsal macrotubercles arranged in two transverse rows (6–7 macrotubercles, respectively) defining a zig-zag pattern (‘group 3’) and 7 dorsal papillae per chaetiger, up to 8–10 ventral papillae per chaetiger arranged in a non-random pattern and parapodia which bear one digitiform prechaetal lobe, one antero-lateral papilla and compound unidentate chaetae with blades with thin spinulation along their cutting edge. Both species show sexual dimorphism characterized by different arrangements of modified ventral cirri and/or special ventral structures in some mid-body chaetigers; a brief discussion about the presence of these structures on sphaerodorids and their possible importance on the systematics of the family is provided.

Patterns of juvenile habitat use by the spider crab &lt;i&gt;Maja brachydactyla&lt;/i&gt; as revealed by stable isotope analyses

Patterns of habitat use by spider crab juveniles, Maja brachydactyla, from two geographic areas on the NW coast of the Iberian Peninsula were studied through the analysis of carbon and nitrogen stable isotope relations in muscle and hepatopancreas. Main potential preys of spider crab juveniles in rocky and sandy habitats and different organic matter sources in coastal food webs were also analysed. Isotopic ratios showed no difference between rocky and sandy habitats. The use of carapace colour and epibiosis as an indicator of habitat use was not supported by our data. These results suggest that movements between the two habitats are much more frequent than suggested in previous studies. In the coastal food web, two main trophic compartments were identified according to their organic matter source: one based on plankton and seaweeds (rocky habitats), and one based on sedimentary particulate organic matter (sandy bottoms). By means of the model of Phillips and Gregg (2003), it was found that juveniles of Maja brachydactyla from both habitats consumed approximately two thirds of the preys in rocky habitats and one third in sedimentary habitats. The results indicate that in exposed environments large juveniles spend most of the time on sedimentary bottoms, where they find more refuge, moving frequently to nearby rocky substrates to feed.

Interactive effects of global and regional change on a coastal ecosystem

Shallow waters and lowland meet at the same level in the Wadden Sea, but are separated by walls of coastal defense. What are the prospects of this coastal ecosystem in a warmer world? We focus on tidal waters and inshore sedimentary bottoms, expect nutrient supply from land to decline and species introductions, temperature and sea level to rise. The effects are interrelated and will have an increasing likelihood of abrupt and irreversible developments. The biotic interactions are hardly predictable but we anticipate the following changes to be more likely than others: blooms of phytoplankton will be weak mainly because of increasing pelagic and benthic grazing pressure, both facilitated by warming. Possibly birds feeding on mollusks will encounter decreasing resource availability while fish-eaters benefit. Extensive reefs of Pacific oysters could facilitate aquatic macrophytes. Sea level rise and concomitant hydrodynamics above tidal flats favor well-anchored suspension feeders as well as burrowing fauna adapted to dynamic permeable sand. With high shares of immigrants from overseas and the south, species richness will increase; yet the ecosystem stability may become lower. We suggest that for the next decades invasions of introduced species followed by warming and declining nutrient supply will be the most pressing factor on the changes in the Wadden Sea ecosystem, and the effects of sea level rise to be the key issue on the scale of the whole century and beyond.