Response of intertidal macrofauna to multiple disturbance types and intensities - an experimental approach.

Two of the best-supported theories which describe the effects of disturbance within marine benthic habitats are the organic enrichment 'Successional Model' and the 'Intermediate Disturbance Hypothesis'. Underlying these models, biological mechanisms thought to drive community change include competition, facilitation, inhibition, tolerance and random colonisation. To further examine the effects of disturbance an experimental test of the effects of different types (burial, raking and organic enrichment) and intensities of disturbance on infaunal intertidal communities at two different sites with similar suites of species was carried out. The same type and frequency of disturbance, applied to the two different sites, produced different responses at the species, community and trophic group level. In models that assume a linear relationship between disturbance intensity and effect, knowledge of the intensity of any novel disturbance, combined with the original disturbance regime experienced by a community (i.e. its 'starting point'), should be sufficient to predict final community characteristics. The current results do not conform to such a linear interpretation, as at both sites the intensity of treatments did not always predict the degree of disturbance. Therefore the response to disturbance may depend on site-specific factors such as the history of prior disturbance and the inherent ecological plasticity exhibited by many benthic species. Whilst current models perform well in predicting benthic responses to gross disturbance, detecting subtler effects requires a recognition that community response may depend on the site, the species and the sources of disturbance.