The benthic shift of the Frisian Front (Southern North Sea) ecosystem : possible mechanisms

In the southern areas of the Frisian Front (southernNorth Sea), a drastic shift in the abundance of most of themacrobenthicfauna during 1992-1997 has also been revealed. Especially a shift in abundances from the brittle star Amphiura filiformis and the mud shrimpCallianassasubterranea was recorded. Amphiura filiformis had a main peak in densities of ~1330.individuals per m ² in 1982 and was at its maximum in 1992 with ~1750 individuals per m ² . At this time, the population was mainly composed of adults and few juveniles. After this 10-year period of high densities, the population decreased and nowadays it remains constant with 100 individuals per m ² . In contrast to this decrease, C. subterranea has been increasing in abundance since 1982, from ~40 to ~319 individuals per m ² in 2000. Nowadays, there are no signs of recovery towards the former situation in which A. filiformis dominated the community. This suggests a shift from one stable dominated state to another. In this thesis I investigate possible mechanisms that can be controlling the benthic ecosystem of an area located in the southernNorth Seato provide new and crucial insight in the functioning of marine ecosystems and to get a better understanding of how climate change may affect these benthic communities. This thesis highlights the importance of maintaining long term monitoring programmesof benthic fauna or even extend research.