Population dynamics, growth and production of the neozoon Marenzelleria cf. viridis (Verrill, 1873) (Polychaeta: Spionidae) in a coastal water of the southern Baltic Sea

The propagation of an immigrant from North America, viz. the spionid Marenzelleria cf. viridis in the Darss-Zingst Bodden (DZB) (southern Baltic Sea), was studied at three stations from March 1992 to December 1995. Highest mean abundances (over 28 000 ind. m^-2) and wet weights (400 g m^-2) were recorded at station 2 in 1994. The spionid also reached its highest dominances in terms of biomass (40 to 90%) at this station, which was selected for the population dynamics, growth and secondary production studies. The spionid has a life span of about 3 years, and many individuals achieved sexual maturity after one year. Their growth curve is steepest during the first year of life, during which the animals grow to a length of about 180 segments. However, growth depression was observed during the ripening of the gametes in April, May and June. Secondary production was in the region of 55 to 85 g AFDW m^-2 y^-1. Productivity (P/B) varied considerably from generation to generation, ranging between 0 and 4.8 with an average between 1.2 and 1.6.     

Benthic macrofauna associated to Thalassia testudinum in Bahía de Mochima, Sucre, Venezuela

Diversity and abundance of benthic macrofauna associated to Thalassia testudinum were studied at Ensenada de Reyes, Mochima Bay, in the northeastern coast of Venezuela. Samples were taken monthly in six stations, three at 1 m in depth and three at 6 m, between December 1992 and February 1994, using a quadrat of 0.25 m2 for collecting plants and sediment; each sample was washed with seawater through a 1 mm sieve. The specimens were fixed in 6% formaldehyde. A total of 1722 organisms (6 888 ind x m2) and 127 species of macroinvertebrates were collected. Mollusks dominated with 53 species, followed by polychaetes (40), crustaceans (18) and echinoderms (8). Remaining groups were represented by 1-2 species. The highest abundance was in October (214 specimens), and the lowest in December 1993 (79 specimens). Specific richness was between 47 species in October and 18 in May 1993. Mean species diversity was 2.79-1.36 bits/ind. There were differences (ANOVA p<0.01) in number of specimens at the two depths but not throughout the 15 month study period (p>0.05). There were more specimens and species at the lowest depth and in stations with higher Thalassia testudinum biomass.     

Observations of serotonin and FMRFamide-like immunoreactivity in palp sensory structures and the anterior nervous system of spionid polychaetes

Evidence suggests that ciliated sensory structures on the feeding palps of spionid polychaetes may function as chemoreceptors to modulate deposit-feeding activity. To investigate the probable sensory nature of these ciliated cells, we used immunohistochemistry, epi-fluorescence, and confocal laser scanning microscopy to label and image sensory cells, nerves, and their organization relative to the anterior central nervous system in several spionid polychaete species. Antibodies directed against acetylated alphatubulin were used to label the nervous system and detail the innervation of palp sensory cells in all species. In addition, the distribution of serotonin (5-HT) and FMRFamide-like immunoreactivity was compared in the spionid polychaetes Dipolydora quadrilobata and Pygospio elegans. The distribution of serotonin immunoreactivity was also examined in the palps of Polydora cornuta and Streblospio benedicti. Serotonin immunoreactivity was concentrated in cells underlying the food groove of the palps, in the palp nerves, and in the cerebral ganglion. FMRFamide-like immunoreactivity was associated with the cerebral ganglia, nuchal organs and palp nerves, and also with the perikarya of ciliated sensory cells on the palps.     

Meiofauna and macrofauna communities in a mangrove from the Island of Santa Catarina, South Brazil

The composition and abundance of the meiofauna and macrofauna were studied in a survey carried out within 6 locations in a mangrove at the Island of Santa Catarina, South Brazil. Nine meiofaunal taxa were registered with densities ranging between 77 and 1589 inds.10 cm^?2. The nematodes, composed by 94 putative species (86 genera), largely dominated the meiofauna. The most abundant genera were Haliplectus (Haliplectidae), Anoplostoma (Anoplostomatidae) and Terschillingia (Linhomoidae). Contrary to the meiofauna, the macrofauna showed a low number of taxa (only 17 recorded) and abundance (up 7250 inds.m^?2). The macrofauna was mainly composed by deposit feeders, and numerically dominated by oligochaetes and capitellid polychaetes. For both components, differences in the composition and abundance along the sampling sites were significant but not primarily related to the typical variations along estuaries, such as salinity. The results of the stepwise multiple regression analyses showed that the detritus biomass (ash-free dry weight) was the most important predictor of faunal densities and diversity. The clear relationship between detritus and fauna, together with the contrasting community structure of the two component of the benthos suggest that the meiofauna showed a high efficiency in exploiting the micro-habitat created by the presence of the detritus. Yet the macrofauna, potentially the main consumer of the debris, is negatively affected by their low palatability and poor nutritive value.     

Diversity,Abundance and Community Structure of Benthic Macro- and Megafauna on the Beaufort Shelf and Slope

Diversity and community patterns of macro- and megafauna were compared on the Canadian Beaufort shelf and slope. Faunal sampling collected 247 taxa from 48 stations with box core and trawl gear over the summers of 2009–2011 between 50 and 1,000 m in depth. Of the 80 macrofaunal and 167 megafaunal taxa, 23% were uniques, present at only one station. Rare taxa were found to increase proportional to total taxa richness and differ between the shelf ( 100 m) where they tended to be sparse and the slope where they were relatively abundant. The macrofauna principally comprised polychaetes with nephtyid polychaetes dominant on the shelf and maldanid polychaetes (up to 92% in relative abundance/station) dominant on the slope. The megafauna principally comprised echinoderms with Ophiocten sp. (up to 90% in relative abundance/station) dominant on the shelf and Ophiopleura sp. dominant on the slope. Macro- and megafauna had divergent patterns of abundance, taxa richness ( diversity) and diversity. A greater degree of macrofaunal than megafaunal variation in abundance, richness and diversity was explained by confounding factors: location (east-west), sampling year and the timing of sampling with respect to sea-ice conditions. Change in megafaunal abundance, richness and diversity was greatest across the depth gradient, with total abundance and richness elevated on the shelf compared to the slope. We conclude that megafaunal slope taxa were differentiated from shelf taxa, as faunal replacement not nestedness appears to be the main driver of megafaunal diversity across the depth gradient.     

Differential Use of Nursery Areas Within the Tagus Estuary by Sympatric Soles, Solea solea and Solea senegalensis

The spatio-temporal pattern of estuarine use by both Solea solea and Solea senegalensis was investigated between April 1995 and November 1996 by beam trawl surveys. Spatial and seasonal distribution and abundance were different for each species. The highest densities of S. solea were recorded in deeper, warmer, low salinity areas and where the sediment consisted of a high proportion of fine sand and presented a high abundance of amphipods. The 0-group individuals of this species first occurred on the nursery ground in April. Numbers peaked in June and July, and from October to April abundance was low. S. senegalensis had a wider distribution and its abundance was related to food availability. The 0-group individuals of this species occurred in the nursery areas later than S. solea, from June to August.     

Macrofauna on flood delta shoals in the Wadden Sea with an underground association between the lugwormArenicola marina and the amphipodUrothoe poseidonis

Living conditions for macrofauna on flood delta shoals are determined by surf, strong currents and sediment mobility. Thus, a unique assemblage of invertebrate species colonize these far off-shore, low intertidal flats. We here describe the macrobenthic fauna of emerging shoals in the Wadden Sea between the islands of Römö and Sylt. Besides ubiquitous macroinvertebrates of the intertidal zone and species which attain their main distribution in the subtidal zone, the flood delta shoals are characterized by organisms adapted to live in these highly unstable sediments, like the polychaetesSpio martinensis, Streptosyllis websteri, Magelona mirabilis, Psammodrilus balanoglossoides, the pericarid crustaceansCumopsis goodsiri, Tanaissus lilljeborgi, Bathyporeia sarsi and a few others. Average abundance (1440 m^?2 of ind >1 mm) and biomass (12.9 g AFDW m^?2) were low compared to other intertidal habitats in the Wadden Sea. Biomass was dominated by largesized individuals of the lugwormArenicola marina. The U-shaped burrows of these polychaetes were inhabited by high numbers ofUrothoe poseidonis. Maximum densities of these amphipods occurred in the deepest parts of the burrows. Sampling at approximately montly intervals revealed no apparent seasonality ofU. poseidonis abundance. Together with smallCapitella capitata, these amphipods constitute a deep-dwelling component of the macrofauna associated with lugworms, which is separated from all other macrofauna living at the sediment surface. As a response to rising sea level and increasing tidal ranges, we expect the unstable sandy shoals, inhabited by numerousSpio martinensis andUrothoe poseidonis, to expand within the Wadden Sea at the cost of stable sandy flats with abundant macrofauna.     

Die Biomasse mariner Makrobenthos-Gesellschaften im Einflußbereich der Klärschlammverklappung vor der Elbemündung

The macrofauna of a dumping area in the eastern part of the German Bight (North Sea) was investigated in July, August and November, 1978 at five stations situated on a transect including central and peripheral areas of the dumping region. Abundance and biomass (ash free dry weight) of the macrofauna and its variation from July to November were analysed as well as the biomass of different taxa. Molluscs dominated over polychaetes, crustaceans and echinoderms. A positive correlation seemed to exist between mud content and biomass at the peripherally situated stations. In the central sewage sludge area, however, the biomass values were reduced. In late autumn the biomass decreased in the entire area due to the death ofDiastylis rathkei, Abra alba andPectinaria koreni. These species were replaced by the molluscNucula turgida and polychaeteNephtys hombergii. In autumn the biomass values also showed a distinct minimum at the central stations.     

Macrobenthic communities in a tropical lagoon (Tahiti, French Polynesia, central Pacific)

Soft bottom communities were sampled quantitatively in Tahiti lagoon (French Polynesia) at 18 stations in five zones around the island over 1 year. In addition, various environmental parameters (silt/clay fractions, organic content, chlorophyll and phaeopigment content) were sampled at the same stations over 2 years. The temporal and spatial variabilities of the macrobenthic communities are described and related to these environmental parameters. Each zone ran from the fringing reef to the inner flat of the barrier reef. The macrofauna exhibited a high richness (392 taxa) with an average mean biomass of 1.8 g AFDW m⁻² (grams ash-free dry weight per square metre). These communities exhibited temporal but not seasonal fluctuations. The biomass of the macrofauna increased from the fringing to the barrier reefs, and the density of individuals was significantly higher on the fringing reefs. Ordination techniques highlighted four groups of stations characterised by distinctive species composition, density and biomass. The first group included stations located on the inner flat of the barrier reef and in the shallow lagoon area and was characterised by highly diverse communities dominated by polychaetes. The second group primarily included stations from the industrial and hotel zones. This group had the lowest diversity and was also dominated by polychaetes, especially the capitellid Dasybranchus sp. 1. The third group was dominated by gastropods and bivalves. The final group of stations was represented only by station 51, in zone 5, which was characterised by mobile soft sediments and wave action and was dominated by the decapod Hippa cf. pacifica. Presumably, these mobile sediments facilitate the development of this benthic community, which does not occur elsewhere in the lagoon. The diversity and biomass of these benthic communities are low compared with most other areas in the South Pacific. Accepted: 10 May 2000     

Dinoflagellate resting cysts as factors in phytoplankton ecology of the North Sea

The occurrence and distribution of dinoflagellate resting cysts were investigated at 11 locations in the south-eastern part of the North Sea. Twenty-six known cyst species and 7 unknown cyst types, which may act as seed population for planktonic dinoflagellate blooms, have been recorded for the first time in the area. The most common cysts in recent sediments were those ofScrippsiella trochoidea, Zygabikodinium lenticulatum, Peridinium dalei, Scrippsiella lachrymosa, Protoceratium reticulatum, Protoperidinium denticulatum, andP. conicum. At all stations,S. trochoidea dominated the cyst assemblages with a maximal abundance of 1303 living cysts/cm³ in the uppermost half centimetre. Cysts of the potentially toxic dinoflagellatesAlexandrium cf.excavatum andA. cf.tamarense were scarce. In the upper 2-cm layer of sediment, dinoflagellate cysts were found in concentrations of 1.8 up to 682 living cysts/cm³. Empty cysts constituted 22–56% of total cyst abundance. The comparative distribution of the cysts showed a general increase in abundance from inshore sites to the offshore area, whereby sandy stations exhibited the lowest cyst abundance and diversity. The wide distribution of living and empty cysts ofScrippsiella lachrymosa suggests that its motile form, which has not been officially recorded in the area until now, is a common plankton organism in German coastal waters. The relatively high abundance of cysts in recent sediments demonstrates the potential importance of benthic resting stages for the initiation of dinoflagellate blooms in the study area.     

Roles of tidal and wind-generated currents in transporting white shrimp (Penaeus setiferus) postlarvae through a South Carolina (USA) inlet

The temporal and spatial abundance of postlarval Penaeus setiferuswas studied from plankton samples in oceanic and estuarine watersnear the North Edisto Inlet, South Carolina (USA), during threecruises in 1993 and 1994 (May 1993, August/September 1993 andJune 1994). Each covered a full cycle of neap-spring tides.On each cruise, bongo nets were towed at three stations acrossthe inlet throat on nightly flood tides. During the first twocruises, tows were made at surface and near-bottom depths inthe inlet, while sampling was confined to surface depths duringthe last cruise. Plankton tows were also made outside the inletalong transects extending in a cross-shelf direction and alongan arcuate transect around the inlet mouth. Stations along thearcuate transect were intensively sampled over a full tidalcycle during the last cruise. Extensive oceanographic and meteorologicalobservations were obtained from moored instrument arrays andshipboard sampling in order to relate fluctuations in tidal,lunar and wind phenomena to temporal changes in postlarval density.Densities of postlarvae were greater in the inlet throat thanat stations offshore. A significant interaction of postlarvaldensity among inlet stations and depth was noted in May. Forother cruises, no significant differences in density were notedamong stations across the inlet, but postlarvae were concentratedat the surface. The lack of a consistent horizontal salinitygradient and obvious pattern in water masses across the inletmay explain why postlarval densities did not consistently differlaterally in the inlet. Greater densities generally occurredduring the first quarter moon, although a clear relationshipof larval density to the spring-neap cycle was not observed.Highest mean densities of ingressing postlarvae in surface floodtide collections from the inlet were generally associated withdownwelling onshore winds which generate onshore flow near thesurface. The similarity between the time series curves of postlarvaldensity and the tidal component of currents just offshore ofthe inlet suggests that tidal transport may facilitate movementinto the estuary. Based on increased postlarval density at thesurface during early strong flood tides and a reduced densityat depth in the inlet, we hypothesize that postlarval P setiferusare utilizing selective tidal stream transport.     

Panicum maximum (Jacq.) density effect upon macrofauna structure in sediments of pilot-scale vertical flow constructed wetlands treating domestic wastewater

Plant density may have an impact on macrofauna structure in constructed wetlands (CW). In this study, Panicum maximum density effect on macrofauna structure in pilot-scale vertical flow CW treating domestic wastewater was estimated. Two beds were planted with P. maximum at 10 roots/m² (low density) and two others at 20 roots/m² (high density). Two unplanted beds were used as controls. After six months of wastewater treatment, macrofauna was collected by taking five cores of sediment samples at the corners and the centre of each bed following three layers in the vertical profile. Plant density seems not to impact significantly the CW performance. However, the plant density of 10 roots/m² (low density) provided higher wastewater treatment efficiency. Concerning macrofauna, 11 taxa belonging to 6 classes and 11 orders were collected. Macrofauna was significantly more diversified in the planted beds than in the control. But the two plant densities investigated do not show significant difference between macrofauna diversity of the planted beds. Macrofauna abundance was two- and three-fold higher, respectively, in the planted beds at high and low densities than in the controls. From the upper surface to the bottom of the beds, macrofauna diversity and abundance decreased, and were heavily dominated by Annelida.     

Sediment-associated cues for larval settlement of the infaunal spionid polychaetes Polydora cornuta and Streblospio benedicti

Do patchy distribution patterns of infaunal polychaetes result from active site selection of larvae influenced by sediment-associated microbial cues? This hypothesis was tested with still-water laboratory settlement assays revealing the acceptance or rejection of polychaete larvae to qualitatively different sediments. Laboratory brood cultures of the spionid polychaetes Polydora cornuta and Streblospio benedicti yielded a sufficient number of larvae with planktotrophic development for bioassays. High settlement rates (75-95%) of test larvae were observed in response to natural sediment. Sterilization of natural sediment significantly decreased settlement of P. cornuta (25-55%) while combustion of sediment significantly decreased the settlement rate in both species (5-50%). Differences in settlement responses to sediments treated by sterilization or combustion most likely resulted from a variety of factors such as modified sediment fabric, grain size distribution and quantity of adsorbed organic matter. To experimentally address the potential role of microorganisms and microbial metabolites as mediators of larval settlement, ashed sediment was inoculated with viable microorganisms obtained from natural sediment. In both polychaete species, this treatment significantly increased larval settlement in comparison to the control of ashed sediment indicating that larval settlement was at least partially mediated by the presence of microorganisms associated with sediment.     

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.     

Marenzelleria cf. viridis (Polychaeta: Spionidae) – ecophysiological adaptations to a life in the coastal waters of the Baltic Sea

Since its introduction into the Baltic Sea about ten years ago, the polychaete species Marenzelleria cf. viridis has spread rapidly. Meanwhile, this spionid settled in remarkable numbers predominantly in the coastal waters which provide some of the more variable and unstable habitats in terms of abiotic conditions. In the present paper, some of the underlying biochemical and physiological processes were experimentally examined which enables this polychaete to deal with several kinds of environmental stress such as variations in salinities, low oxygen concentrations and occurrence of hydrogen sulphide. The results obtained reveal that in the process of acclimation to different salinities free amino acids are involved, mainly alanine and glycine. The content of these amino acids were increased in worms acclimated to a higher salinity. When exposed to low ambient oxygen concentrations (severe hypoxia) M. cf. viridis started to produce energy anaerobically via pathways known from several other marine organisms. The presence of hydrogen sulphide in higher concentrations (1 mmol l^-1) results in a more rapid production of succinate (indicator for anaerobic energy production via the succinate-propionate pathway) as compared to hypoxia alone, indicating a higher energy demand. Nevertheless, when exposed to enhanced ambient hydrogen sulphide concentrations (3 mmol l^-1), M. cf. viridis is less affected by this toxic compound than other marine species, such as the related species Marenzelleria cf. wireni (North Sea). The field data indicate that the metabolic response obtained under experimental conditions is also important in the worm's natural habitat. Although the extent of anaerobic metabolites produced as well as the amount of thiosulphate (main sulphide detoxification product) was lower in the field as compared to the experiments, M. cf. viridis very likely has to face hypoxia and hydrogen sulphide in higher concentrations in its natural habitat.     

Distribution and diversity of Gallionella-like neutrophilic iron oxidizers in a tidal freshwater marsh

Microbial iron oxidation is an integral part of the iron redox cycle in wetlands. Nonetheless, relatively little is known about the composition and ecology of iron-oxidizing communities in the soils and sediments of wetlands. In this study, sediment cores were collected across a freshwater tidal marsh in order to characterize the iron-oxidizing bacteria (FeOB) and to link their distributions to the geochemical properties of the sediments. We applied recently designed 16S rRNA primers targeting Gallionella-related FeOB by using a nested PCR-denaturing gradient gel electrophoresis (DGGE) approach combined with a novel quantitative PCR (qPCR) assay. Gallionella-related FeOB were detected in most of the samples. The diversity and abundance of the putative FeOB were generally higher in the upper 5 to 12 cm of sediment than in deeper sediment and higher in samples collected in April than in those collected in July and October. Oxygen supply by macrofauna appears to be a major force in controlling the spatial and temporal variations in FeOB communities. The higher abundance of Gallionella-related FeOB in April coincided with elevated concentrations of extractable Fe(III) in the sediments. Despite this coincidence, the distributions of FeOB did not exhibit a simple relationship to the redox zonation inferred from the geochemical depth profiles.     

Patterns in pelagic and benthic nanoflagellate densities in the coastal upwelling system along the Banc d'Arguin,Mauritania

We studied spatial variation in abundance of marine benthic and pelagic heterotrophic nanoflagellates in relation to abundances of autotrophic flagellates, bacteria and cyanobacteria in an upwelling area off the Banc d'Arguin, Mauritania.There was enormous spatial variation in densities. In the sediments these ranged from 8–219 × 10³ cm^–3 for heterotrophic flagellates. Maximum values are in the range of those for temperate shallow marine bottoms. Low densities (< 20 × 10³) were confined to the deep stations (> 1000 m). Over the shelf (10–100 m depth) densities were high but related to grain size rather than to concurrent upwelling phenomena or to the abundance of benthic macrofauna.Pelagic flagellate abundance appeared to be more indicative of contemporary hydrographic conditions, most obvious by an increase in the ratio heterotrophic/autotrophic nanoflagellates away from the area of most intense upwelling.     

Spatial structure of a subtidal macrobenthic community in the Bay of Veys (western Bay of Seine, English Channel)

The spatial distribution of the muddy fine sand community from the Bay of Veys (western English Channel) were investigated during spring and autumn 1997. A grid of 55 and 54 sites was sampled in March and October, respectively, using two replicates per site of a Hamon grab (0.25 m²) for macrofauna collection and an additional one for sediment analysis. A total of 172 species were sampled with a dominance of polychaetes, followed by crustaceans and bivalves. The species richness and abundance show low temporal changes despite higher values in October than in March. In March, the mean abundance was 165 ind. 0.5 m⁻²; in October, the mean abundance was 212 ind. 0.5 m⁻². Four assemblages from the Abra alba-Pectinaria koreni community were identified corresponding to a bathymetric and sedimentary gradient from muddy fine sands with high levels of fine particles in shallow water to fine sands in deeper water. The discussion focuses on factors prevailing on the spatial structure of sandy communities in the English Channel.     

Nereidid polychaetes as the major diet of migratory shorebirds on the estuarine tidal flats at Fujimae-higata in Japan

The dietary items of five migratory shorebirds, Dunlin (Calidris alpina), Red-necked Stint (C. ruficollis), Grey Plover (Pluvialis squatarola), Whimbrel (Numenius phaeopus) and Black-headed Gull (Larus ridibundus), were examined by analyses of fecal droppings during the birds' migration or wintering and by surveys of macrobenthic fauna around their foraging sites on the tidal flats of Fujimae-higata, Nagoya, central Japan. Body parts of nereidid, capitellid, and spionid polychaetes and crustaceans were found in fecal droppings from all of these shorebirds. Two nereidid species (Hediste diadroma and Neanthes succinea) with relatively large body sizes seemed to be the majority dietary items. At one site, H. diadroma was dominant in terms of biomass (40-370 g/m(2)) throughout year except, for less than 1 g/m(2) in March and May (within or just after reproduction of this species). Monthly changes in the occurrence of food items in fecal droppings of C. alpina were examined in 1999 and 2000. Most (85-100%) of the fecal droppings contained nereidid body parts, including Hediste-specific simple chaetae from November to April, whereas only 23% of the droppings contained them in May. Chaetae of capitellid or spionid polychaetes were frequently found from January to April (38-86% of droppings). Crustacean body parts, including amphipod appendages, were frequently found from March to May (86-100% of droppings). The relationship between foraging habits of the shorebirds and the life history of their major prey nereidid species is discussed.     

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.