Observing change in a North Sea benthic system: A 33 year time series

Abstract

Since 1972 the macro-benthic infauna at station M1, 10.5 km off the Northumberland coast (central western North Sea), have been sampled by grabbing each March and September. The data series now includes over 500 taxa from 327 genera. During the 1970s the system showed a regular alternation of high and low abundance years and this was interpreted as evidence of density dependence, when this broke down in the 1980s winter temperature appeared to be involved. After 20 years of data collection analysis of the time series, showed that variability had increased and that there was a very strong link to phytoplankton production in the overlying water. The latest analyses show that this relationship has now also disappeared. The number of genera represented in the system has increased over time while total productivity has not altered significantly. Multivariate ordinations also show changes through time with breakpoints occurring in the early 1980s and early 1990s. The coastal benthos of this region shows decadal scale and longer term changes in biological composition and ecological function. The system is certainly influenced by climatic variation, environmental conditions (winter temperature) and carbon flux to the benthos. Over the 33 year time series none of these appears to have a dominant effect, rather different factors seem to dominate at different times. The extent to which this is due to a biological ‘system memory’ imposed by good recruitments of long lived taxa would warrant further study.