Changes in benthic community structure following construction of a harbour impoundment scheme

Long-term monitoring (May 1990 – November 1994) of benthic macrofauna and sediment composition was undertaken to examine changes in community structure following the construction of a tidal barrage at the entrance to Sutton Harbour, Plymouth (South West England). The harbour has permanently anoxic sediments, below a depth of 3 cm, consisting mainly of silt with relatively high total metal concentrations in the m<63 m fraction for Cu (96 – 222 g g^–1), Hg (0.7 – 2.0 g g^–1), Pb (93 – 297 g g^–1) and Zn (114 – 460 g g^–1). Polychaete worms, particularly of the family Cirratulidae, dominated the 93 taxa that form the macrofauna of the fine sediments. Multi-dimensional scaling (MDS) identified significant changes, surpassing all seasonal variability, in benthic community structure between pre-construction and construction phases and the similarities percentages procedure (SIMPER) isolated the species differentiating pre- and post-construction samples. Principal components analysis (PCA) revealed changes in heavy metal concentrations and sediment size distribution, primarily between surveys encompassing the start of construction. Rank correlations between the biotic and abiotic similarity matrices (BIOENV) were highest for sediment Pb and Zn concentrations, indicating that these variables offered a potential explanation of the changes in community structure. The results demonstrate the sensitivity of the benthic community to man-induced change and the need for ecological factors to be accounted for in harbour development at other locations.