Effects of physical disturbance on an estuarine intertidal community: field and mesocosm results compared

The response of an estuarine macrobenthic community to different intensitie s of physical disturbance was examined using comparable field and mesocosm experiments. In the field study, areas of sediment (2500 cm(2)) were distur bed by surface-raking at a range of disturbance intensities: no disturbance , once every 2 mo, once every month, once every 2 wk, once or three times e very week. These disturbance regimes were also imposed on buckets of sedime nt (855 cm(2)) collected from the field study site and maintained within a mesocosm system. In the univariate data analysis, neither field nor mesocos m communities displayed any trends in relation to the frequency of disturba nce. Diversity indices were generally reduced in the mesocosm communities c ompared with the field communities. Multivariate analysis indicated signifi cant differences between the field communities subjected to the most intens e disturbance and those communities disturbed every +/-2 wk or less. These differences were attributed to reductions in the five numerically dominant species in the high-disturbance treatments. More statistically significant differences were observed between the different disturbance intensities in the mesocosm experiment than in the field study. The implications of differ ences between field and mesocosm experiments results are discussed.