A field test of the intermediate disturbance hypothesis in the soft-bottomintertidal

The intermediate disturbance hypothesis has had success in explaining chang es in local diversity in many habitats. Recent laboratory work has shown th at disturbance may act to increase diversity in soft-bottom marine communit ies as predicted by the hypothesis. In this paper, we present the results o f a field experiment which tested the impacts of physical disturbance on so ft-bottom, intertidal macrobenthic communities. Five disturbance treatments were used, differing in the frequency of applied disturbance events: the h ighest frequency treatments were dug every week, lowest every eight weeks. The experiment was run for a total of 25 weeks over the winter of 1997/98. Our experiment controlled for differences in recovery time after disturbanc es. Abundances of Pygospio elegans, Macoma balthica, Hydrobia ulvae and Str eblospio benedicti were all significantly reduced in high disturbance treat ments, as was the total number of species. No species showed significant in creases in abundance in disturbed treatments, and there was no evidence of an increase in diversity in any treatments. These results are discussed in the context of the intermediate disturbance hypothesis. Our results suggest that the interspecific competitive effects postulated by the hypothesis ar e not important in structuring this low diversity, intertidal community. Ho wever. unequivocally rejecting the hypothesis is difficult because it conta ins many ambiguities, and acts more as a conceptual model than as a falsifi able hypothesis.