Patterns of polychaete communities in tropical sedimentary habitats: a case study in south-western Thailand

ABSTRACT. – Few studies have compared macrofaunal assemblages (organisms retained on a 0.5 mm sieve) between different tropical sedimentary habitats. The present study aims to address this issue, investigating vegetated (seagrass), non-vegetated organic mud and exposed beach habitats. Polychaetes were the dominant taxonomic group at all sampling sites, followed by crustaceans and molluscs. Thirty-six polychaete families were recorded, 31 % of which were present in all three habitats. All families were represented in non-vegetated habitats. Polychaete family and functional group assemblages did not differ greatly between vegetated and non-vegetated habitats despite varying densities. Differences in polychaete assemblage structure were most pronounced between exposed beach and non-vegetated habitats. Polychaete assemblages were also negatively affected by the onset of the wet monsoon season. Overall, macrofaunal density (29- 2,629 ind. m-2) fell within the range of that reported by other authors in the region. Small-scale physical and environmental factors are thought to be responsible for the large variation in polychaete assemblage structure within habitats. Identification of polychaetes to species, together with further analysis of small-scale physical data should provide a deeper understanding of the spatial and temporal changes reported in this study. A call is made for the standardisation of future sampling efforts and techniques to allow meaningful comparisons amongst sedimentary habitats across large spatial scales. KEY WORDS. – seagrass, polychaete, macrofaunal density, inter-habitat