The sublittoral macrobenthic community structure of an Irish sea-lough: Effect of decomposing accumulations of seaweed

Abstract

The deposition and decay of seaweed has been identified as producing localized changes in sublittoral macrobenthic community structure on the basin floor of a small sea-lough. Surveys of the abundance of seaweed accumulations revealed ≈7 accumulations · 100 m −2, of which many were of sufficient size and stability to cause anoxic patches. A manipulative field experiment was conducted to assess changes in sediment conditions and community structure in areas covered with seaweed, adjacent areas, and clear areas. Sediment pH and Eh were reduced in smothered areas. Differences in the macrobenthic community between the three treatments indicated a rapid increase in the abundance of two polychaetes, Capitella spp. and Malacoceros fudiginosus (Claparède), and a loss of rare species in disturbed areas. Sixty nine days after the initiation of the experiment a similar number of species were found in each treatment, although areas under seaweed were still numerically dominated by Capitella spp. These results indicate that patches of decomposing seaweed have an important rôle in determining the pattern of species distribution and benthic community structure.