Community structure and functional roles of meiofauna in the North Sea

Knowiedge on community structure of North Sea meiofauna has greatly increased recently. A quasisynoptic picture of meiofauna densities and copepod community structure from 171 stations of the southern North Sea, sampled in April–May 1986, has been obtained during the North Sea Benthos Survey. Latitudinal patterns in meiofauna abundance and copepod weight, abundance and diversity exist in an area between 51°30′N and 58°30′N. Using TWINSPAN-classification five major groups of copepod species can be recognized which are related to sediment type, latitude and depth. The part of the meiofauna in total benthic energy flow, their role in the benthic food web and in biogeochemical cycles is discussed based on existing literature. There are still considerable gaps in knowledge and the field is not progressing rapidly. Publication no. 599 Netherlands Institute of Ecology, Centre for Estuarine and Coastal Ecology, Yerseke, The Netherlands.     

Microscopic species make the diversity: a checklist of marine flora and fauna around the Island of Sylt in the North Sea

Based on the past 150 years of research and ongoing time-series observations we give a comprehensive overview of marine species composition around the island of Sylt in the eastern North Sea. A total of 2758 species is listed according to the categories microplankton (591 species), zooplankton (137), nekton (118), benthic microflora (158), benthic macroflora (125), benthic micro-and meiofauna (1204), benthic macrofauna (509), birds and mammals (91), and neobiota (39). Plants account for a third of the species, most (85%) of them are microscopic Chromista. Among animals, 60% of the species are micro- and meiofauna though this faunal component is still insufficiently known. These figures are similar to records from the southern North Sea and therefore may by typical for temperate climate sedimentary coastal areas. A comparison with the total of marine species suggests that the small benthic fauna may be severely understudied over most of the world. Analysis of global change depends on sound baseline data and species inventories like this can assist in the detection of biodiversity changes. They emphasise rare species and the full range of local habitats while time-series measurements usually rely on a few selected habitats and biotic components to generate a very general picture of the state of an ecosystem.     

Spatial variability of epifaunal communities in the North Sea in relation to sampling effort

Benthic epifauna was sampled in six areas from the German Bight towards the Norwegian Sea using a 2-m standard beam trawl. Nine replicates were taken in each area and year from 1999 to 2006. This data set (60–67 replicates per area) was used to describe the spatial variability in local species composition and to assess the effect of increasing sampling effort on species richness and community structure. Our results confirmed the importance of the 50-m depth contour for the separation of benthic fauna in the North Sea. Low species richness, sparse sessile fauna and high abundances of scavenging species such as Asterias rubens, Liocarcinus holsatus, Astropecten irregularis and Ophiura albida were characteristic of the low-water area south of the 50-m contour. Differences in community structure were less conspicuous in deeper waters north of the 50-m contour, but distribution patterns and abundances of single species such as Echinus elegans, Hyalinoecia tubicola, Ophiothrix fragilis, Scaphander lignarius as well as several hermit crabs resulted in well-defined epifaunal communities. One replicate caught 17–28% of the species found in 60–67 samples and was sufficient to separate the community in the German Bight from those in the central and northern North Sea by using multidimensional scaling. Nine replicates sampled a proportion of 53–60% and provided additional information on the spatial variability of community structure in the central and northern North Sea. Our study indicates that appropriate replication enhances the quality of the data and can partly overcome the constraints of sampling with a 2-m beam trawl. This might be helpful for future monitoring programmes.     

Moderate predation on meiofauna by the macrobenthos of the Wadden Sea

The role of meiofauna in the trophic web of marine ecosystems is a controversial topic. During an experimental study on tidal flats in the eastern part of the North Sea, potential predators on meiofauna were kept in enclosures. A gobiid fish, shrimp, crabs, an amphipod, four polychaete worms and a nemertine were tested for their ability to decimate nematodes, turbellarians, ostracods and benthic copepods. Only few macrobenthic species preyed heavily on permanent meiofauna: juveniles of the shore crabCarcinus maenas, the hermit crabPagurus bernhardus with the colonial hydrozoanHydractinia echinata on its shells, and the rag wormNereis diversicolor. When benthic infauna was protected from these predators with exclosures, juvenile macrofauna responded with a marked increase in number, while the permanent meiofauna remained unaltered except for a limited increase in nematodes. It is concluded that in the Wadden Sea abundance of permanent meiofauna (Nematoda, Turbellaria, Ostracoda, Copepoda) is only locally or temporarily regulated by macrobenthic predators.I acknowledge a grant from the Deutsche Forschungsgemeinschaft (DFG).     

Diversity of larger consumers enhances interference competition effects on smaller competitors

Competition between large and small species for the same food is common in a number of ecosystems including aquatic ones. How diversity of larger consumers affects the access of smaller competitors to a limiting resource is not well understood. We tested experimentally how species richness (0–3 spp.) of benthic deposit-feeding macrofauna changes meiofaunal ostracods’ incorporation of fresh organic matter from a stable-isotope-labeled cyanobacterial bloom, using fauna from the species-poor Baltic Sea. Presence of macrofauna mostly decreased meiofaunal incorporation of bloom material, depending on the macrofauna species present. As expected, the species identity of macrofauna influenced the incorporation of organic matter by meiofauna. Interestingly, our results show that, in addition, species richness of the macrofauna significantly reduced meiofauna incorporation of freshly settled nitrogen and carbon. With more than one macrofauna species, the reduction was always greater than expected from the single-species treatments. Field data from the Baltic Sea showed a negative correlation between macrofauna diversity and meiofaunal ostracod abundance, as expected from the experimental results. We argue that this is caused by interference competition, due to spatial niche differentiation between macrofauna species reducing the sediment volume in which ostracods can feed undisturbed by larger competitors. Interference from macrofauna significantly reduces organic matter incorporation by meiofauna, indicating that diversity of larger consumers is an important factor controlling the access of smaller competitors to a limiting food resource.     

Cold winter effects on benthic macrofauna communities in near- and offshore regions of the North Sea

In order to investigate the effect of severe winters on the long-term variability of benthic macrofauna communities four stations from the inner German Bight towards the Dogger Bank (North Sea) were sampled in March 1990 and from May 1995 to 2002. The stations were chosen to reflect a gradient in the hydrographic regime, temperature and organic matter supply. We initially hypothesized that the effect of severe winters on benthic communities will be more pronounced in the offshore more stable environment than in the nearshore regions. Our results clearly showed the opposite pattern. The benthic communities at the nearshore stations in the German Bight changed dramatically in species abundance and community structure after the severe winter 1995/1996. But the community structure in the German Bight returned to the previous stage within 2 years. In contrast, the offshore stations in the Oyster Ground and at the Dogger Bank remained rather unaffected by the severe winter and changed gradually during the study period. The results are discussed concerning the ecological importance of severe winters for benthic communities and the utility of our results for interpreting long-term changes.     

The gulf of Bothnia: The northernmost part of the Baltic Sea

Summary The Baltic Sea, one of the largest brackish water areas in the world, can be characterized as a young, cold sea containing an impoverished ecosystem due to salinity stress. The present Baltic Sea was formed as late as 2000 to 2500 years ago when the Danish sounds became more narrow and shallow. The inflow of freshwater from the surrounding land areas caused the Baltic to gradually attain its brackish character. Today the Baltic covers an area of some 366,000 km² as a series of basins separated by shallower areas and filled with about 22,000 km³ of brackish water. These basins are, from north to south, the Gulf of Bothnia, the Gulf of Finland, the Gotland Sea and the Bornholm Sea. The climate gradient ranges from almost arctic conditions in the extreme north to a more maritime climate in the southern parts. The North Sea salt water is connected to the Baltic through the shallow Kattegat and the sills in the Danish sounds. The inflow of salt water occurs in two different ways,viz. as a continuous flow along the bottom due to the salinity gradient and as pulses of salt water generated by the distribution of air pressure and the direction of the wind. The freshwater input (500 km³) from mainly the large rivers equals roughly the net outflow and stresses the south-bound current along the Swedish coast that also compensates for the salt water inflow. Tidal movements can be seen in the southern Baltic, but are of minor importance for the system. The residence time of the total water mass is 25 years and the hydrographical conditions within the different basins are stable and dominated by a permanent halocline, and a thermocline developing every spring. The salinity ranges from about 1–2 per mille in the innermost part of the Gulf of Bothnia to 10–15 per mille in the Bornholm Sea. Total vertical mixing takes place during winter in at least the northern parts of the sea. Due to the climate-gradient, the ice condition differs from about four months of total ice-cover in the inner parts of the Gulf of Bothnia to one month or less of coastal ice in the southern part of the Baltic. Thus, the seasonal effect is more pronounced in the northern parts.The living systems of the Baltic are reduced and adapted to these varying conditions. When comparing the deeper soft bottoms of the Gulf of Bothnia to the rest of the Baltic, the following pattern can be seen. The pelagic primary productivity increases by a factor 6 from north to south. The southern parts of the sea show a pronounced spring peak, while in the north the spring development is delayed or replaced by a summer maximum. The total increase of the macrofauna biomass is striking, from about 1 g.m^–2 (w.wt) in the north to 100 g.m^–2 (w.wt) or more in the south. The meiofauna and the zooplankton biomasses show less variability. The meiofauna increases by a factor of 2–4, giving a biomass of about twice that of the macrofauna in the northernmost part. The extremely low salinity of this area causes the exclusion of bivalves (filter-feeders) from the fauna. Available data, pooled with the high metabolic rate of the meiofauna, roughly follow the changes in primary productivity within the Baltic Sea. The changing ratio of macro- to meiofauna, as well as results from intensive studies of the macrobenthic amphipodPontoporeia affinis (Lindström), suggest that the macrofauna is regulated mainly by food limitation and that the benthic and pelagic systems are closely coupled.     

Macrofauna communities of the Dogger Bank (central North Sea) in the late 1990s: spatial distribution,species composition and trophic structure

Macrofauna samples were taken in May 1996–1998 at 28 stations on the Dogger Bank (central North Sea) to describe species composition, spatial distribution and trophic structure of the macrofaunal communities. In general, five communities could be distinguished depending on the influence of different water masses, depth, type of sediment and food availability. Except for those species which feed in the sediment, macrofauna communities did not show any correlation to the measured sediment variables. In fact, macrofauna communities of the Dogger Bank were mainly structured by lateral food supply via frontal systems. This was indicated by the dominance of interface feeders foraging in the benthic boundary layer, which are able to switch from surface deposit to suspension feeding depending on flow conditions. The importance of sandlickers in the shallowest parts of the Dogger Bank hints at an important contribution of benthic primary production to the nutritional and energetic needs of the benthic community. Electronic Publication     

The biology of Roule's goby in the Kvarner area, northern Adriatic Sea

Roule's goby Gobius roulei in the Kvarner area of the northern Adriatic Sea attained ≥ 87.5 mm L _T and an age of 7 years. In both sexes gonad development began in their second year. All males were mature by 3 years, and females by 4 years. Fecundity was related to L _T and varied between 1200 and 8000 eggs. The breeding season lasted from April to August. Nests were built under empty shells of Pitaria chione or stones. Roule's goby was a predator and picker, feeding mostly on mobile benthic fauna, including bivalves, gastropods, polychaets, pagurids, mysids, gammarids and fishes. Larger specimens ate mainly macrofauna, while smaller specimens ate both meiofauna and macrofauna.     

Zoobenthic diversity-gradients in the Baltic Sea: Continuous post-glacial succession in a stressed ecosystem

The Baltic Sea, formed after the latest glaciation, is an enclosed, low-saline, non-tidal ecosystem and has steep latitudinal and vertical gradients from sub-arctic conditions in the north to temperate in the south. The sea has undergone rapid changes since the glaciation, and the “ecological age” of the present ecosystem is only about 8000 years. Primary successional processes are still ongoing, and numerous ecological niches (e.g. large-bodied sediment bioturbators) remain available for immigration. The system is species-poor and vulnerable to the threat of exotic invasive species, and to date about 50 zoobenthic species have established populations in the Baltic Sea. The present biota is a mixture of species of different ecological and zoogeographical origin (marine to limnic; northern Arctic marine and limnic, to North Sea and Atlantic marine). The current distribution patterns of zoobenthos are illustrated, using marine, limnic and non-indigenous examples of structure and ecosystem functions. The species richness decreases from over 1600 marine benthic species in the open Skagerrak to about 500 in the western parts of the Baltic Sea, approximately 80 in the southern regions, to less than 20 in the northern regions. On the other hand, limnic species increase diversity in the inner reaches of the Gulf of Finland and the Gulf of Bothnia. Polychaetes, molluscs and echinoderms are dramatically reduced in numbers from the south to the north.     

Salinity drives meiofaunal community structure dynamics across the Baltic ecosystem

Coastal benthic biodiversity is under increased pressure from climate change, eutrophication, hypoxia, and changes in salinity due to increase in river runoff. The Baltic Sea is a large brackish system characterized by steep environmental gradients that experiences all of the mentioned stressors. As such it provides an ideal model system for studying the impact of on‐going and future climate change on biodiversity and function of benthic ecosystems. Meiofauna (animals < 1 mm) are abundant in sediment and are still largely unexplored even though they are known to regulate organic matter degradation and nutrient cycling. In this study, benthic meiofaunal community structure was analysed along a salinity gradient in the Baltic Sea proper using high‐throughput sequencing. Our results demonstrate that areas with higher salinity have a higher biodiversity, and salinity is probably the main driver influencing meiofauna diversity and community composition. Furthermore, in the more diverse and saline environments a larger amount of nematode genera classified as predators prevailed, and meiofauna‐macrofauna associations were more prominent. These findings show that in the Baltic Sea, a decrease in salinity resulting from accelerated climate change will probably lead to decreased benthic biodiversity, and cause profound changes in benthic communities, with potential consequences for ecosystem stability, functions and services.     

Meiofaunal prominence and benthic seasonality in a coastal marine ecosystem

Summary The muds of a shallow (7 m) site in Narragansett Bay, Rhode Island contained higher abundances of meiofauna (averaging 17×10⁶ individuals per m² and ash free dry weight of 2.9 g/m² during a 3 year period) than have been found in any other sediment. The majority of sublittoral muds, worldwide, have been reported to contain about 10⁶ individuals per m². This difference is attributed primarily to differences in sampling techniques and laboratory processing.Extremely high meiofaunal abundances may have also occurred because Narragansett Bay sediments were a foodrich environment. While the quantity of organic deposition in the bay is not unusually high for coastal waters, this input, primarily composed of diatom detritus, may contain an unusually high proportion of labile organics. Furthermore, meiofauna could have thrived because of spatial segregation of meiofauna and macrofauna. While meiofauna were concentrated at the sediment-water interface, most macrofauna were subsurface deposit feeders. Macrofaunal competition with, and ingestion of meiofauna may thus have been minimized.The seasonal cycles of meiofauna and macrofauna were similar. Highest abundances and biomass were observed in May and June and lowest values in the late summer and fall. Springtime increases of meiofaunal abundance were observed in all depth horizons, to 10 cm. We hypothesize that phytoplankton detritus accumulated in the sediment during the winter and early spring, and that the benthos responded to this store of food when temperatures rose rapidly in the late spring. By late summer, the stored detritus was exhausted and the benthos declined.     

Effects of the severe winter 1995/96 on the benthic macrofauna of the Wadden Sea and the coastal North Sea near the island of Sylt

The development of benthic macrofauna in the Wadden Sea and in the coastal North Sea after the severe winter of 1995/96 is compared with the preceding years with mild to moderate winters. In the intertidal of the Wadden Sea, ice-drift and low temperature caused the expected changes in species composition by increasing winter mortality in sensitive species, and by exceptionally high recruitment of some species during the succeeding summer. In the shallow subtidal (10–20 m depth), similar winter effects were observed. However, recovery of many subtidal populations was still incomplete until the summer of 1997. It is suggested that this was due to hydrographic conditions that carried many larvae or drifting juveniles into more distant offshore areas. This may have limited larval supply and may have delayed recovery at the onshore sites. Since in the eastern North Sea severe winters are accompanied by frequent easterly winds, it is not clear whether decreasing winter abundances in some species were due to increased mortality, or to a seaward dislocation of organisms. Received in revised form: 7 May 2001 Electronic Publication     

Interrelationships of bacteria,meiofauna and macrofauna in a Mediterranean sedimentary beach (Maremma Park,NW Italy)

Collelungo beach (Maremma Park, NW Italy), was sampled quantitatively for macrofauna, meiofauna and bacteria in May 2003; several physicochemical variables and variables associated with food availability and sediment structure were also measured. Replicated samples were collected from three sites representing natural conditions, an erosion regime, and the influence of the Ombrone River, respectively, as well as from four stations each located in the surf and sublittoral zones. Both uni- and multivariate techniques were used to assess the benthic community structure and the associated environmental variables. Different diversity indices revealed no pattern; in contrast, multivariate techniques applied on the macrobenthic fauna and the polychaete taxocommunity distinguished between the sites located in natural and eroding conditions from the one located nearby the discharges of the Ombrone river. Τhe community patterns deriving from meio- and macrofauna are clearly divergent. The overall benthic faunal community appears to be influenced by both groups of organisms. The patterns of the meio- and macrofaunal communities seem to be affected synergistically by a number of environmental variables, in accordance with the multicausal environmental severity hypothesis. Meiofaunal patterns are more often correlated with bacteria and the protein concentration than are macrofaunal patterns, indicating a potential utilization of bacteria as a food source by the meiofaunal organisms. Total bacterial numbers are associated with the macrofaunal pattern under the erosion regime, probably as a consequence of competition for food between macrofauna and meiofauna.     

The benthic infauna and benthic respiration off the Banc d'Arguin (Mauritania,Northwest Africa)

In May 1988, a study was made of the benthic community structure and benthic respiratory activity along two transects across the Mauritanian shelf off Banc d'Arguin. The main emphasis of the present paper is put on the macrobenthos, but results of a gross analysis of the meibenthos are discussed as well. Macrofaunal and meiofaunal density showed no consistent decrease with distance from the shore. The composition of the macrofauna taxa appeared to be closely correlated with sediment parameters and less so with depth. The highest macrofaunal biomass was found at the northern edge of the Banc d'Arguin, and the lowest biomass along the outer shelf. The biomass levels on the shelf match the ones reported for the northern Cap Blanc area where, in contrast to the seasonal upwelling in the investigated area, upwelling takes place all year round.Benthic respiration rates on the offshore shelf were relatively high at the nearshore stations and low near the shelf break. Experimental evidence suggests that the low O₂ levels in the upwelling water covering part of shelf, inhibited benthic respiration. The high respiratory activity at some northern inshore stations coincided with the presence of oxygen-rich coastal water. In this area benthic respiration surpassed the level previously reported for the enriched Cap Blanc area. On the basis of our respiration data, an estimate is made of the total carbon demand of the benthic community on the shelf in May and this quantity is compared with the measurements of daily primary production.     

Trophodynamics and functional feeding groups of North Sea fauna: a combined stable isotope and fatty acid approach

The trophodynamics of pelagic and benthic animals of the North Sea, North Atlantic shelf, were assessed using stable isotope analysis (SIA) of natural abundance carbon and nitrogen isotopes, lipid fingerprinting and compound-specific SIA (CSIA) of phospholipid-derived fatty acids (PLFAs). Zooplankton (z), epi- and supra-benthic macrofauna were collected in the Southern Bight, at the Oyster Grounds and at North Dogger, 111 km north of the Dogger Bank. The study included 22 taxonomic groups with particular reference to Mollusca (Bivalvia and Gastropoda) and Crustacea. Primary consumers (Bivalvia) were overall most ¹⁵N enriched in the southern North Sea (6.1‰) and more depleted in the Oyster Grounds (5.5‰) and at North Dogger (2.8‰) demonstrating differences in isotopic baselines for bivalve fauna between the study sites. Higher trophic levels also followed this trend. Over an annual cycle, consumers tended to exhibit ¹⁵N depletion during spring followed by ¹⁵N enriched signatures in autumn and winter. The observed seasonal changes of δ ¹⁵N were more pronounced for suspension feeders and deposit feeders (dfs) than for filter feeders (ffs). The position of animals in plots of δ ¹³C and δ ¹⁵N largely concurred with the expected position according to literature-based functional feeding groups. PLFA fingerprints of groups such as z were distinct from benthic groups, e.g. benthic ffs and dfs, and predatory macrobenthos. δ ¹³C_PLFA signatures indicated similarities in ¹³C moiety sources that constituted δ ¹³C_PLFA. Although functional groups of pelagic zooplankton and (supra-) benthic animals represented phylogenetically distinct consumer groups, δ ¹³C_PLFA demonstrated that both groups were supported by pelagic primary production and relied on the same macronutrients such as PLFAs. Errors related to the static categorization of small invertebrates into fixed trophic positions defined by phylogenetic groupings rather than by functional feeding groups, and information on seasonal trophodynamic variability, may have implications for the reliability of numerical marine ecosystem models.     

Species size distributions in marine benthic communities

Summary Species body size distributions from eight temperate benthic communities show a highly conservative pattern with two separate lognormal distributions, corresponding to the traditional categories of meiofauna and macrofauna. The meiofaunal mode occurs at a dry body weight of 0.64 g and the macrofaunal mode at 3.2 mg, with a trough between them at 45 g. It is suggested that there is a particular body size at which meiofaunal life-history and feeding traits can be optimised, and another for macrofaunal traits. As size departs in either direction (larger or smaller) from these optima, fewer species of the same size are able to co-exist. The split occurs at 45 g because many life history and feeding characteristics switch more or less abruptly at about this body size, compromise traits being either non-viable or disadvantageous. Meiofauna and macrofauna therefore comprise two separate evolutionary units each with an internally coherent set of biological characteristics.The expression of this conservative pattern is modified by water depth: the proportion of macrofauna species increases from intertidal situations to deeper water, and it is suggested that mechanisms of resource partitioning and diversity maintainence in the meiofauna and macrofauna are affected differentially by sediment disturbance. Salinity does not affect this proportionality, and so does not differentially affect mechanisms for maintaining species diversity in any particular size category of animals. Meiofauna species size distributions may be modified in sandy sediments because of physical impositions on interstitial or burrowing lifestyles.Brief discussion of some implications of these observations includes speculations on the larval ecology of macrofauna, on gigantism in Antarctic invertebrates, and on the benthic Sheldon spectrum.     

Regional patterns in prevalence of principal external diseases of dab Limanda limanda in the North Sea and adjacent areas 1992-1997

The prevalence and spatial distribution of major diseases of dab Limanda limanda in the North Sea and adjacent areas were studied in the summers 1992 to 1997. Areas covered were the North Sea, Irish Sea, northern and northeastern British Waters and the English Channel. The diseases studied were lymphocystis, epidermal hyperplasia/papilloma and skin ulceration. To standardise data, results were analysed for females >15 cm (>3 yr old). Data were subjected to median polish, and additive, extended and additive plus multiplicative models were applied to best account for effects of region and year. Annual differences in disease prevalence were low whilst differences between areas were pronounced. For lymphocystis higher prevalence was observed in the northwestern sector of the North Sea, at the northern tip of Scotland and in an area south of Iceland. Prevalence was low in the Irish Sea, the English Channel and the southern North Sea, and intermediate in the German Bight. For epidermal hyperplasia/papilloma, levels were low at Icelandic stations, in the northern Irish Sea, in the southern North Sea and the English Channel, whilst levels were high in the northwestern part of the North Sea and the German Bight. Elevated levels of skin ulceration were found on the Dogger, at 1 station in the Irish Sea (off Sellafield) and at 1 station to the south of Iceland. Lower levels were detected west of Iceland. Prevalence in all other areas was intermediate. It is concluded that a detailed analysis of available data on disease prevalence and putative causative factors is desirable and, given the good availability of data, would be a promising step forward toward elucidating possible cause and effect relationships between diseases and anthropogenic factors.     

Spatial variability in structural and functional aspects of macrofauna communities and their environmental parameters in the Jade Bay (Wadden Sea Lower Saxony, southern North Sea)

Spatial distribution and functional structure of intertidal benthic macrofauna in relation to environmental variables in the Jade Bay (southern North Sea) were studied and compared with other intertidal areas of the Wadden Sea. A total of 128 stations covering the whole Jade Bay were sampled in summer 2009. A total of 114 taxa were found. Highest species numbers occurred in the subtidal areas, whereas highest mean abundances were found in the upper intertidal areas. Based on species abundance data, six significantly distinct macrofauna communities in the Jade Bay were identified and evaluated with multivariate statistics, univariate correlations and canonical correspondence analysis. Differences in these community patterns were caused by the response of the dominant species (Hydrobia ulvae, Tubificoides benedii, Pygospio elegans, Caulleriella killariensis, Scoloplos armiger, Urothoe poseidonis, Microprotopus maculatus) to prevailing environmental conditions along the gradient from the lower and exposed sandy intertidal areas via intermediate mixed sediments to the upper mudflat areas. Distribution patterns in relation to tidal zonation were best explained by variability in submergence time, Chlorophyll a (chl a) content and sediment composition (mud content), which are proxies for hydrodynamic conditions and food availability. Species inventory and species richness were comparable with other intertidal areas of the Wadden Sea, but the Jade Bay differs from these areas regarding dominant species. Differences in sediment composition and morphological characteristics (macrotidal versus mesotidal Wadden Sea areas) are discussed for comparison of regional differences.     

Metazoan meiofauna dynamics and pelagic–benthic coupling in the Southeastern Beaufort Sea,Arctic Ocean

Pelagic–benthic coupling is relatively well studied in the marginal seas of the Arctic Ocean. Responses of meiofauna with regard to seasonal pulses of particulate organic matter are, however, rarely investigated. We examined the dynamics of metazoan meiofauna and assessed the strength of pelagic–benthic coupling in the Southeastern Beaufort Sea, during autumn 2003 and spring–summer 2004. Meiofauna abundance varied largely (range: 2.3 × 10⁵ to 5 × 10⁶ ind m⁻²), both spatially and temporally, and decreased with increasing depth (range: 24–549 m). Total meiofauna biomass exhibited similar temporal as well as spatial patterns as abundance and varied from 25 to 914 mg C m⁻². Significant relationships between sediment photopigments and various representatives of meiofauna in summer and autumn likely indicate the use of sediment phytodetritus as food source for meiofauna. A carbon-based grazing model provided estimates of potential daily ingestion rates ranging from 32 to 723 mg C m⁻². Estimated potential ingestion rates showed that meiofauna consumed from 11 to 477% of the sediment phytodetritus and that meiofauna were likely not food-restricted during spring and autumn. These results show that factors governing the distribution and abundance of metazoan meiofauna need to be better elucidated if we are to estimate the benthic carbon fluxes in marginal seas of the Arctic Ocean. This paper is dedicated to the memory of our dear friend and colleague Gaston Desrosiers who contributed so much to benthic ecology. We will continue in his spirit.