Distribution of benthic diatom assemblages in the Westerschelde (Zeeland, The Netherlands)

The benthic diatom assemblages of the Westerschelde-estuary were studied by means of multivariate analysis. Two main groups and eight subgroups were distinguished. The relation with salinity and sediment composition was investigated. A clear relation between grain size and the distribution of the assemblages was found

Diversity, ecology and the role of protist communities in the Schelde estuary: research by the "Protistology & Aquatic Ecology" group, University Gent (poster)

The section ‘Protistology & Aquatic Ecology’ has been studying the diversity and ecology of planktonic and benthic communities of unicellular eukaryotes (or protists) in the Schelde estuary. The study area involves the entire estuarine gradient, going from the freshwater tidal reaches in the Belgian part of the estuary to the estuary mouth in The Netherlands. Large research efforts were invested in the diversity of protistan communities (diatoms and other micro-algae, heterotrophic flagellates and ciliates) and the biotic and abiotic factors that regulate their structure and composition. In addition, several studies dealt with the role of microbial plankton and benthos in the functioning of estuarine food webs. In these studies, attention was paid to the importance of diversity of microbial communities for fluxes of matter and energy through the estuarine microbial ecosystem. This poster aims at illustrating certain aspects of this research

Ciliate predation by nematodes in tidal flat sediments

The present study investigates the possibility of a trophic link between ciliates and nematodes in fine sandy sediments of the Molenplaat intertidal flat (Schelde estuary, SW Netherlands). Grazing experiments were conducted under controlled laboratory conditions, with ciliate species isolated from enrichment cultures and nematodes directly collected from the field. Significant reductions in ciliate numbers were found in the presence of the predatory nematode Enoploides longispiculosus, a prominent species (and genus) in fine to medium sandy sediments of the North Sea and adjacent estuaries. No such effects were found when ciliates were inoculated with a mix of mainly deposit-feeding nematodes from the same sampling site. Based on these results, ciliate predation by E. longispiculosus was tested for several benthic ciliate species and abundances, at a range of predator abundances and temperatures, and in the presence of alternative prey (in casu nematodes). E. longispiculosus was capable of significantly reducing densities of 5 out of 6 ciliate species offered as prey. Depending on the experimental conditions and the prey species, predation rates ranged from 0.19 to 10.8 ciliates predator-1 hour-1, corresponding to a biomass consumption of 0.001-0.33 µg C predator-1 day-1. An overall positive relation between available ciliate biomass and predation rate was found. Comparison of experimental data with field conditions suggests that a considerable part of the ciliate production in fine sandy sediments of the Molenplaat is likely to be consumed by E. longispiculosus, which largely dominates meiofaunal biomass there. Estimated carbon requirements for the predator and production estimates of ciliate and nematode prey at the study site, strongly suggest that ciliates are probably a far more important carbon source for E. longispiculosus than nematode prey, at least between late spring and autumn. This implies that carbon transfer from primary producers and bacteria to predatory nematodes may to a large extent be mediated through the microbial food web. In view of the generally high densities/biomasses of ciliates as well as predacious nematodes in fine sandy sediments, similar patterns are to be expected in many other estuarine and marine sediments

Trophic interactions between ciliates and nematodes from an intertidal flat

The present study investigated the possibility of a trophic link between ciliates and nematodes in fine sandy sediments of the Molenplaat intertidal flat (Schelde estuary, SW Netherlands). Grazing experiments were conducted under controlled laboratory conditions, with ciliate species isolated from enrichment cultures and nematodes collected directly from the field. Significant reductions in ciliate numbers were found in the presence of the predatory nematode Enoploides longispiculosus, a prominent species (and genus) in fine to medium sandy sediments of the North Sea and adjacent estuaries. No such effects were found when ciliates were inoculated with a mix of mainly deposit-feeding nematodes from the same sampling site. On the basis of these results, ciliate predation by E. longispiculosus was tested for several benthic ciliate species and abundances, at a range of predator abundances and temperatures, and in the presence of alternative prey (in casu nematodes). E. longispiculosus significantly reduced the densities of 5 out of 6 ciliate species offered as prey. Depending on the experimental conditions and the prey species, predation rates ranged from 0.19 to 10.8 ciliates predator-1 h-1, corresponding to a biomass consumption of 0.001 to 0.33 µg C predator-1 d-1. An overall positive relation between available ciliate biomass and predation rate was found. Comparison of experimental data with field conditions suggests that a considerable part of the ciliate production in fine sandy sediments of the Molenplaat is likely to be consumed by E. longispiculosus, which largely dominates meiofaunal biomass there. Estimated carbon requirements for the predator and production estimates of ciliate and nematode prey at the study site strongly suggest that ciliates are probably a far more important carbon source for E. longispiculosus than nematode prey, at least between late spring and autumn. This implies that carbon transfer from primary producers and bacteria to predatory nematodes may to a large extent be mediated through the microbial food web. In view of the generally high densities and biomasses of ciliates as well as predacious nematodes in fine sandy sediments, similar patterns are to be expected in many other estuarine and marine sediments

Ecological implications of life-forms in intertidal benthic diatoms in macrotidal estuaries

Diatom communities inhabiting intertidal estuarine sediments are composed of different life-forms, ranging from adnate epipsammic to free-living epipelic and tychoplanktonic forms. A detailed study of the spatial and temporal distribution patterns of various life-forms in the macro-tidal Westerschelde estuary (South-West Netherlands) revealed that the specific life-form composition of a community has an important influence on its temporal dynamics and might also have major implications for the transfer of diatom-fixed carbon to higher trophic levels. The importance of substrate structure and availability, stochastic (e.g. climate-induced and anthropogenic) hydrodynamic events and the nature and rate of sediment development in regulating the dynamics of these communities are evaluated

Late quaternary climate history of Heart Lake and Pup Lagoon (Larsemann Hills, East Antarctica)

Information on East-Antarctic coastal environments during the Holocene is relatively sparse. This is surprising as sedimentary records from the interface between land and sea can provide chronologies of climate change, isostatic uplift, relative sea level and the colonisation of newly formed biomes. Here we examine a sediment core from Pup Lagoon and Heart Lake (Larsemann Hills, East Antarctica). Sediment stratigraphy, fossil pigments and diatoms were used to infer the sequence of Holocene environmental and climate change. Results show that between 5800 and 4785 corr. yr BP the marine coast of Prydz bay was characterized by stratified, open water conditions during spring and summer and seasonally warm conditions. From 4785 to 2615 corr. yr BP sea ice duration in Prydz Bay increased with the coast being ice-free for 2-3 months each year, conditions which are similar to the present day. A return to stratified, open water conditions and a reduction in winter sea ice extent between 2615 corr. yr BP - 2200 uncorr. yr BP is signaled by enhanced biogenic production and more open water diatom taxa