Macrofaunal community structure and distribution in a muddy coastal lagoon

Abstract

Macrofaunal communities and specific bulk properties of organically enriched sediments were investigated in the coastal lagoon of Cabras (Sardinia, western Mediterranean) on a grid of twenty-nine sampling stations, in spring 2001. Species composition and community structure indicated poor and heterogeneous macrofaunal communities, characterized by few predominant taxa typical of degraded environments, such as Polydora ciliata, Tubificidae nc and Neanthes succinea, distributed differently in some areas of the lagoon. Sediments were homogeneously muddy, with a mean silt + clay content of 93%. The analysis of specific grain size intervals within the mud fraction, however, highlighted a marked spatial variability of sediment particle distribution. Simple associations included a positive relationship of both Ficopomatus enigmaticus and Corophium sextonae, patchily distributed along the shores, with sediment sorting (σ), an index of sediment selection due to hydrodynamic energy. By contrast, inner areas, characterized by a major accumulation of finer particles (and organic matter), with a sediment mean size (Φ) up to 8.2 phi, were least populated. The results suggest the existence of an early stage of faunal succession which might be related to an excessive organic content of sediments and the tendency to dystrophic events in the Cabras lagoon.

Keywords:

• Benthic macrofauna
• Spatial distribution
• Sediment grain size
• Mediterranean Sea

Acknowledgements

We wish to thank Dr. B. Piergallini for his skillful assistance both in the laboratory and in the field, and Dr. S. Guerzoni for fruitful discussion. We extend our appreciation to the fishermen of Cabras (Consorzio Cooperative di Pontis) for logistic support during sampling campaigns. An anonymous reviewer and Dr. M. Chiantore are gratefully acknowledged for constructive criticisms that helped to improve an early version of this paper. This work was funded by the SIMBIOS project (‘Piano di Potenziamento della rete scientifica e tecnologica, Cluster Ambiente Marino’) of the Italian Ministry for Scientific Research.