Temporal variability in southern North Sea epifauna communities after the cold winter of 1995/1996

Epifauna communities in the southeastern North Sea were studied from 1998 to 2008 to evaluate the effect of hydroclimatic change in community structure. The spatial analysis revealed four communities along the West and North Frisian coasts, on the Oyster Ground, and on the Dogger Bank. The variability between communities was caused mainly by differing abundance of widespread species such as Asterias rubens, probably reflecting differences in environmental conditions, e.g. temperature variation and food supply. Community structure varied between 1998–2000 and 2003–2008 at the shallow West and North Frisian coasts. The hypothesis is that epibenthic communities in these areas were severely affected by the cold winter of 1995/1996, resulting in the outbreak of the opportunistic brittlestar Ophiura albida and followed by characteristic post-disturbance succession stages from 1998 to 2000. The period between 2003 and 2008 was characterized by a continuous decrease in O. albida and by an increase in other species and diversity in the coastal areas. In contrast, secondary production increased in all four areas after 2003, probably because of an increase in sea surface temperature (SST) and in the length of the warming season. We conclude that the cold winter affected epifauna mainly in shallow areas and that the increasing SST influenced the epifauna in the entire southeastern North Sea mainly through an increased food supply.