The Influence of Sedimentary Heterogeneity on Within Maerl Bed Differences in Infaunal Crustacean Community

A study was undertaken of the crustacean community associated with maerl habitats in Mannin Bay, Ireland. Based on a visual classification of sedimentary fractions, eight sedimentary facies could be distinguished. These ranged from live maerl banks and seagrass-covered live maerl banks in the shallow, low energy parts of the inner bay to maerl debris facies, mixed with varying proportions of sand, mud and shell gravel in the more exposed, high energy, parts of the bay. Amphipoda dominated the crustacean fauna, accounting for more than 95% of total numerical abundance. Overall, the crustacean fauna occurring in the studied maerl habitats is similar to the fauna occurring in subtidal gravel habitats, with little evidence of elective species. Only the mud-maerl debris facies and the seagrass-covered live maerl banks appear to harbour a relatively different crustacean fauna from the remainder of the sedimentary facies. These differences were mainly changes in the numerical abundance of dominant species, rather than species displacements.