Jan Mees

Microplastic pollution in deep-sea sediments

Microplastics are small plastic particles (<1 mm) originating from the degradation of larger plastic debris. These microplastics have been accumulating in the marine environment for decades and have been detected throughout the water column and in sublittoral and beach sediments worldwide. However, up to now, it has never been established whether microplastic presence in sediments is limited to accumulation hot spots such as the continental shelf, or whether they are also present in deep-sea sediments. Here we show, for the first time ever, that microplastics have indeed reached the most remote of marine environments: the deep sea. We found plastic particles sized in the micrometre range in deep-sea sediments collected at four locations representing different deep-sea habitats ranging in depth from 1100 to 5000 m. Our results demonstrate that microplastic pollution has spread throughout the worlds seas and oceans, into the remote and largely unknown deep sea.

Feeding of the hyperbenthic mysid Neomysis integer in the maximum turbidity zone of the Elbe, Westerschelde and Gironde estuaries

The diet of the mysid Neomysis integer in the maximum turbidity zone (MTZ) of three European estuaries (Elbe, Westerschelde and Gironde) was investigated in spring 1993. The quality and quantity of the diet were assessed through measurement of the stomach fullness and microscopical analysis of the stomach content combined with image analyses. N. integer was found to be an omnivore which mainly utilizes mesozooplankton and detritus carbon pools. The quality of the diet did not differ between the sexes or between different developmental stages, although smaller individuals consumed fewer items. In all three estuaries the diet was dominated by Copepoda Calanoida (5–10 Eurytemora affinis ind−1 for adults; 2–5 ind−1 and 2–3 ind−1 for subadults and juveniles, respectively) and was supplemented with Rotifera and Cladocera. Phytoplankton and benthic organisms, though present in the stomachs, were negligible. Macrophytal detritus and amorphous material, the latter unidentifiable under the light microscope, were very abundant food items. The amorphous detritus was found to originate from the suspended sediment flocs which are characteristic for the MTZ and mainly consist of clay minerals. The energetic value of the flocs for N. integer remains unclear.

Comparative study of the hyperbenthos of three European estuaries

The hyperbenthic fauna of the subtidal channels of the Eems (N. Netherlands), Westerschelde (S.W. Netherlands), and Gironde (S.W. France) estuaries was sampled within a 15-day period in summer 1991. In each estuary, quantitative samples were taken at regularly spaced stations covering the entire salinity gradient from marine conditions at the mouth to nearly freshwater conditions upstream. The diversity of the samples and the distribution of the species along the main estuarine gradients were assessed. Hyperbenthic communities were identified using different multivariate statistical techniques. The species composition and the density and biomass of the dominant species of each community were compared among communities.

Assessment of marine debris on the Belgian Continental Shelf

A comprehensive assessment of marine litter in three environmental compartments of Belgian coastal waters was performed. Abundance, weight and composition of marine debris, including microplastics, was assessed by performing beach, sea surface and seafloor monitoring campaigns during two consecutive years. Plastic items were the dominant type of macrodebris recorded: over 95% of debris present in the three sampled marine compartments were plastic. In general, concentrations of macrodebris were quite high. Especially the number of beached debris reached very high levels: on average 6429±6767 items per 100 m were recorded. Microplastic concentrations were determined to assess overall abundance in the different marine compartments of the Belgian Continental Shelf. In terms of weight, macrodebris still dominates the pollution of beaches, but in the water column and in the seafloor microplastics appear to be of higher importance: here, microplastic weight is approximately 100 times and 400 times higher, respectively, than macrodebris weight.

Spatial community structure of the winter hyperbenthos of the Schelde estuary, the Netherlands, and the adjacent coastal waters

A first assessment of the ecological importance of the hyperbenthic fauna in coastal and estuarine systems was made in December 1988 in a pilot study (41 stations) covering the Westerschelde and Oosterschelde estuaries, and part of the neighbouring shallow coastal area, the Voordelta. Multivariate analysis revealed three major gradients which could be divided into seven spatially defined hyperbenthic communities. Canonical Correspondence Analysis was applied to correlate these species assemblages with a number of environmental variables measured at each station. Species distributions in the Westerschelde appear to be primarily determined by a gradient involving salinity, turbidity and dissolve oxygen. Hyperbenthic animals, mainly the mysid Neomysis integer, reached high densities in the brackish part (>12 ind·m−2), whereas the more seaward stations had lower densities but a higher number of species. In the benthic filter-feeder dominated Oosterschelde, the total density of the hyperbenthos was very low (<0.05 ind·m−2). The shallow coastal area had intermediate densities. There was a clear gradient from offshore to inshore but the environmental variables measured did not correlate well with this gradient. Though there were substantial overlaps between the clusters, as defined by the different multivariate techniques used, the Voordelta area can be divided into three main subareas.

Nursery function of an estuarine tidal marsh for the brown shrimp Crangon crangon

Abstract The brown shrimp Crangon crangon migrates into the brackish part of the Westerschelde estuary (southwest Netherlands) shortly after metamorphosis and uses the tidal marsh habitat as a nursery until reaching a total length of about 15 mm. The importance of the marsh as a nursery was evaluated by estimating foraging activity, predation mortality and residence time. In early postlarval stages, C. crangon utilised the intertidal creeks of an estuarine tidal marsh from early spring (March–April) until late autumn (October–November). Postlarval shrimp leaving the marsh with the ebb tide always had significantly more food in their stomachs than shrimp entering the marsh with the incoming flood water. Predation upon the shrimp population was relatively low during most months, but in increased between August and October when common gobies, Pomatoschistus microps , were present in high densities. There was also predation by the small seabass Dicentrarchus labrax . The marsh creeks function both as foraging areas and as predation refuge. Depending on temperature, postlarval shrimp stayed in the marsh for a period of two to three weeks. Quantitatively, the value of the marsh as a nursery area had changed drastically during a second year of sampling, illustrating high natural year-to-year variability. However, the seasonal pattern remained. Recruitment to the subtidal adult population represents an export of animals from the marsh to the estuary. This export is negligible in terms of biomass (as compared to the total biomass of the estuarine population) but it may be important in terms of numbers of individuals.

Seasonal composition and spatial distribution of hyperbenthic communities along estuarine gradients in the Westerschelde

The hyperbenthic fauna of the Westerschelde estuary was sampled in spring, summer and winter of 1990 at 14 stations along the salinity gradient. Mysids dominated the hyperbenthos in each season. Other important species, either permanently (e.g. amphipods and isopods) or temporarily (e.g. fish larvae and decapod larvae) hyperbenthic, belong to a variety of faunistic groups. Spatial structure was stable through time: the estuary could be divided in the same geographically defined zones in each season. Each zone had a characteristic fauna. Gradients in salinity, dissolved oxygen and turbidity correlated strongly with the observed variation in community structure. The spatial patterns dominated over the temporal patterns, especially in the brackish part of the estuary. In the marine part, seasonal differences in the communities were more pronounced due to the occurrence of a series of temporary hyperbenthic species in spring and summer. In each season, the upstream (brackish) communities were characterized by few species occurring in very high numbers, whereas the downstream (marine) communities were composed of many species but at lower densities.

Mysid crustaceans as potential test organisms for the evaluation of environmental endocrine disruption: a review

Anthropogenic chemicals that disrupt the hormonal systems (endocrine disruptors) of wildlife species recently have become a widely investigated and politically charged issue. Invertebrates account for roughly 95% of all animals, yet surprisingly little effort has been made to understand their value in signaling potential environmental endocrine disruption. This omission largely can be attributed to the high diversity of invertebrates and the shortage of fundamental knowledge of their endocrine systems. Insects and crustaceans are exceptions and, as such, appear to be excellent candidates for evaluating the environmental consequences of chemically induced endocrine disruption. Mysid shrimp (Crustacea: Mysidacea) may serve as a viable surrogate for many crustaceans and have been put forward as suitable test organisms for the evaluation of endocrine disruption by several researchers and regulatory bodies (e.g., the U.S. Environmental Protection Agency). Despite the long-standing use of mysids in toxicity testing, little information exists on their endocrinology, and few studies have focused on the potential of these animals for evaluating the effects of hormone-disrupting compounds. Therefore, the question remains as to whether the current standardized mysid endpoints can be used or adapted to detect endocrine disruption, or if new procedures must be developed, specifically directed at evaluating hormone-regulated endpoints in these animals. This review summarizes the ecological importance of mysids in estuarine and marine ecosystems, their use in toxicity testing and environmental monitoring, and their endocrinology and important hormone-regulated processes to highlight their potential use in assessing environmental endocrine disruption.

The mobile epibenthic fauna of soft bottoms in the Dutch Delta (south-west Netherlands): spatial structure

During 1989 monthly beam trawl samples were collected at 48 stations in the Dutch Delta. The annual mean densities of the demersal fishes and mobile epibenthic invertebrates at these stations were calculated. These data were then subjected to multivariate statistical techniques for an analysis of the spatial structure of the communities found and to study the relationship between these communities and their environment. The present study confirms the results of HENDERSON (1989) that, given a fairly limited number of environmental variables, mainly salinity and exposure/substratum type, quite accurate predictions of the type of community expected at a certain site can be made. The explicit inclusion of epibenthic invertebrates, a dominant group in most assemblages, in studies mainly targeted at demersal fishes, is strongly recommended. In the Dutch Delta rich and varied communities exist in the Voordelta. A number of groups, such as salmonids, anadromous species and starfish, expected in the westerschelde are absent or extremely rare probably as a consequence of pollution stress. The Oosterschelde is relatively poor in density terms but has a highly diverse epibenthic fauna dominated by fishes.

Spatial patterns of the hyperbenthos of subtidal sandbanks in the southern North Sea

Abstract The hyperbenthos of the Belgian continental shelf, the Dutch continental shelf off Zeeland and the Westerschelde estuary was sampled. Seven biotic communities were identified and the distribution was correlated with the presence of isolated sandbanks. A community in the Westerschelde estuary was different from the shelf hyperbenthos and was characterised by the highest density and biomass and lowest diversity. Two gradients in community structure were detected on the continental shelf: the principal onshore-offshore gradient perpendicular to the coastline and a less pronounced east-west gradient parallel to the coastline. The first gradient mainly indicated differences in density and biomass, while the second reflected species richness and diversity. The holohyperbenthos reached highest densities onshore and consisted nearly exclusively of mysids; Schistomysis spiritus and S. kervillei were the most common species. The high levels of suspended matter and mud in this area probably advantage this motile fauna in terms of food. Community composition altered with distance from the shore and planktonic species increased in abundance. Estuarine influence may have caused a decline of species richness eastward. The merohyperbenthos was most abundant at a certain distance from the coast and was mainly composed of a variety of larval decapods. Biomass peaked onshore with a dominance of postlarval gobies. A strong diversity gradient was found for the merohyperbenthos with a richer fauna off the Belgian coast than in the waters off Zeeland. Current direction and habitat heterogeneity are believed to be the most important structuring factors.