Meiofaunal bivalves in maerl and other substrata; Their diversity and community structure

The abundance and diversity of meiofaunal bivalve species from four substrata (live maerl, dead maerl, gravel and sand) were investigated to assess the effects of habitat heterogeneity. Maerl grounds are unusual coastal habitats derived of non-geniculate coralline algae (Corallmaceae, Rhodophyta) and typically exhibit high benthic biodiversity, including a large number of molluscan species. In total 38 species of bivalves were recorded, with the greatest number found in dead maerl (29). These results were contrary to the findings of other authors who have shown dead maerl grounds to have a poorer fauna than live maerl beds. Significant differences were observed in the community structure of the substrata examined, with assemblages on sand being easily distinguishable from those on other substrata. Mysella bidentata was found to be an important species in dead maerl and gravel. In sand the tellinids Moerella pygmaea and Angulus tenuis were the most discriminatory species observed. Number of species, species richness and species diversity observed in dead maerl were considerably greater than in all other substrata. There were no apparent r- or K-selected species associations with particular substratum types. Differences observed may have been linked to habitat heterogeneity affecting differential survival (e.g. predator-prey interactions) both during settlement and post-settlement phases.