Long-term changes in the diversity and faunal structure of benthic communities in the northern North Sea: natural variability or induced instability?

Changes in benthic sedimentary communities in many areas of the northern North Sea in the vicinity of oil and gas fields have been monitored intermittently over the past three decades, in most cases triennially but in some areas annually for short periods. Accumulating evidence from these; surveys suggests that large scale temporal variability occurs in both the diversity and structure of these communities on time scales varying from years to decades. A recent change to regional, rather than field based, surveys in the Norwegian sector of the North Sea has provided evidence that spatially such changes occur on broad scales and are not local responses to field based environmental disturbance. The possible factors inducing such changes are reviewed and the relative temporal and spatial stability of benthic infaunal communities in response to fluctuating pelagic conditions and levels of sedimentary disturbance are discussed. It is suggested that broad scale temporal and spatial variability in these benthic communities is driven by climatic forces influencing the overlying water masses but that there may have been some increase in pelagic productivity and/or in benthic pelagic coupling in the area in recent years.