This report presents data on the macrozoobenthos of 8 permanent stations in the Oosterschelde, during 1983-89. Data on abiotic characteristics of the different stations are included.
Based on the 11 biomass-dominant species, the situation in the period before the construction of the storm-surge barrier (1983-84) is described. The Cockle (Cerastoderma edule) was dominant in biomass, comprising 21-83 % of the total biomass per station (21-83 %), except for the high and muddy station 27. The Mudsnail (Hydrobia ulvae dominated in density (48-99 %). Total biomass is nearly completely divided over two trophic groups: filter feeders and deposit feeders. A multivariate analysis distinguished two categories of stations, sandy and muddy ones. The former are characterised by Nephtvs hombergii and Lanice conchilega and a dominance of C. edule the latter include Mya arenaria and Scrobicularia plana and very high numbers of H. ulvae
Seasonal variation is important over the whole study period and more obvious in deposit feeders than in filter feeders. No overall positive or negative trend in total biomass and biomasses of trophic groups was found. At species level however, some effects of the engineering works can be demonstrated. In 1983-84 H. ulvae was numerically dominant in 6 out of 8 stations with more than 10 % of total biomass, while in 1989 this was only true for 3 stations. Scoloplos armiger became as important in relative density as H. ulvae. This polychaete have probably benefited from the decrease of its predator, the frost-sensitive Nephtvs hombergji, a situation which has maintained after the three successive severe winters 1984-85, 1985-86 and 1986-87.
Considering not only the 11 biomass-dominating species, effects of the engineering works become more clearly. Tha~ marioni, a species known trom organically enriched, muddy sediments, drastically declined at the sandy stations. Species, characteristic tor dynamic, sandy places like Spio filicornis, Bathyporeia en Urothoe poseidonis increased. This corresponds with the tact that the Roggenplaat and Galgenplaat have lost some of their fine sediment, while wave-action has increased. On the stations with finer sediments, there are no obvious changes except for station 27. which is situated high in the intertidal area. Here, a conspicuous synchronity was found between the increase of opportunistic species/taxa and the decrease in inundation time and temporal silt- enrichment during 1985-87. These organisms (Corophium sp., Oligochaeta sp. and Capitella capitata) are characteristic for organically enriched areas and although in terms of biomass unimportant, they seem to be valuable indicators to demonstrate change-effect relationships.
|Uitgeverij||University of Gent, Laboratory of oecology for animals, zoogeography and nature conservation: Gent|