Mesocosm investigation into the effects of bioturbation on the diversity and structure of a subtidal macrobenthic community

Benthic mesocosm experiments have highlighted the importance of bioturbatio n in maintaining levels of diversity and setting community structure in sub tidal macrobenthic assemblages. In the mesocosm facility of the Norwegian I nstitute for Water Research (NIVA) at Solbergstrand, Norway, partitioned bo xes of sediment were subjected to continuous disturbance through bioturbati on for a period of 20 wk. The effect of type and intensity of bioturbation on the macro-infauna was examined by exposing different partitioned areas t o different bioturbating species at different densities. The 3 test macrofa una species used were the bivalves Nuculoma tenuis (subsurface deposit feed er) and Abra alba (surface deposit/suspension feeder) at 3 different densit ies, and the heart urchin Brissopsis lyrifera (subsurface burrowing deposit feeder) at a single density. The presence of N. tenuis at low densities re sulted in significantly higher levels of alpha and beta diversity than were observed in the undisturbed or highly disturbed treatments. Previous exper iments have shown that B, lyrifera also elicits a response in the associate d fauna consistent with the 'intermediate disturbance hypothesis'. Such a r esponse was not observed in the A. alba treatments. Multivariate data analy sis demonstrated that the response of the associated fauna was influenced b y the identity of the organism causing the disturbance. It was also evident that different elements of the community responded differently to bioturba tion. This paper makes comparisons between the responses of macrofauna and meiofauna to bioturbation. Our experimental results suggest that the identi ty, density and distribution of large bioturbating organisms are important factors in the structuring of infaunal communities and in setting and maint aining levels of diversity in apparently homogeneous areas.