Ecological studies of the kelp,Laminaria hyperborea, and its associated fauna in South-West Ireland

Abstract

Populations of the kelp, Laminaria hyperborea (Gunn.) Foslie, in Bantry Bay, south-west Ireland and in neighbouring Dunmanus Bay and Kenmare River were examined. In addition, trophic component analysis of the fauna of kelp holdfasts at sites in these bays was carried out. The lower limit of the kelp decreases away from the open sea, from about 30 m at the bay mouth to 9 m near the head of Bantry Bay. This decrease is correlated with a gradienr of increasing turbidity into the bays. Both the density and mean fresh mass of kelp plants are reduced with increasing depth and the rate of decrease in these parameters with depth is greater at sites further from the open sea. The species diversity of holdfast communities is reduced at more turbid sites where the holdfast fauna is dominated by suspension feeders, notably Pomatoceros triqueter (L.). It has been suggested previously that kelp holdfast communities dominated by suspension feeders may be indicative of pollution. The present findings are discussed in this context and it is concluded that naturally increased turbidity may also lead to a suspension feeder dominated community.