Bioturbation as a mechanism for setting and maintaining levels of diversity in subtidal macrobenthic communities

Over 2 years, experiments were conducted to compare the effects of sediment disturbance by different bioturbating, macrofaunal organisms on the divers ity and structure of the associated infaunal community. The four species in vestigated were the bivalves Nuculoma tenuis (Montagu, 1808) and Abra alba (Wood, 1802), the heart urchin Brissopsis lyrifera (Forbes, 1841), and the burrowing decapod Calocaris macandreae (Bell, 1846). These organisms were c hosen to allow assessment of the effects of contrasting feeding activities and body sizes of the bioturbating species on the diversity of the macroben thic communities. Bioturbation by the sub-surface deposit feeders N. tenuis and B. lyrifera promoted higher levels of alpha and beta diversity in trea tments exposed to intermediate levels of disturbance. Whilst no such interm ediate response' was demonstrated for A. alba or C. macandreae, it was evid ent that changes in the associated fauna were influenced by the feeding typ e of the bioturbating organism responsible. It was also shown that differen t elements of the associated community responded differently to biotic dist urbance. The results indicate that the variability in density and distribut ion of such bioturbators are important factors in structuring infaunal comm unities, and in setting and maintaining levels of diversity in apparently h omogeneous areas.