Climate effects and benthic-pelagic coupling in the North Sea

The North Sea is one of the most biologically productive ecosystems in the world and supports important fisheries. Climate-induced changes occurred in the pelagic ecosystems of the North Sea during the 1980s. These changes, which have been observed from phytoplankton to fish and among permanent (holoplankton) and temporary (meroplankton) plankton species, have resulted in alterations in plankton community composition and seasonality. Until now, the effects of climate-driven changes on biological linkages between pelagic and benthic ecosystems have not been examined. The present study indicates that changes in benthic organisms could have a profound effect on the trophodynamics of the pelagos. We demonstrate this by analyses of a long-term time series of North Sea plankton and sea surface temperature data. We discover that pronounced changes in the North Sea meroplankton, mainly related to an increased abundance and spatial distribution of the larvae of a benthic echinoderm, Echinocardium cordatum, result primarily from a stepwise increase in sea temperature after 1987 that has caused warmer conditions to occur earlier in the year than previously. Key stages of reproduction in E. cordatum, gametogenesis and spawning, appear to be influenced by winter and spring sea temperature and their larval development is affected by the quantity and quality of their phytoplankton food. Our analyses suggest that a new thermal regime in the North Sea in winter and spring may have benefited reproduction and survival in this benthic species. As a result, E. cordatum may be altering the trophodynamics of the summer pelagic ecosystem through competition between its larvae and holozooplankton taxa.

Distribution Of Sublittoral Macrofauna Communities In Bristol Channel In Relation To Substrate

Grab and dredge samples have been collected on a grid of 155 sublittoral stations in the Bristol Channel. The faunal data have been analysed using a hierarchical sorting technique to cluster stations with similar species compositions. At a similarity level of 18%, groups of stations with a species composition similar to the classical Petersen communities were defined. Three of Petersen's communities were recognized in the outer part of the Channel, the Venus, Abra and Modiolus communities. The fauna of the inner part of the Channel is reduced and does not correspond with any previously recognized community type. Possible causes for this faunal reduction are discussed. The substrate distribution and the macrofaunal community distribution are mapped. Side-scan sonograms are shown to be a useful adjunct to the interpretation of faunal distributions.