Benthic faunal responses to variations in patch density and patch size of a suspension-feeding bivalve

Responses of benthic macrofauna and epibenthic predators / sediment disturbers to controlled 22 2 density (0, 12, 120, 600 and 1200 individuals m ) and patch size (0.25, 1.0 and 9.0 m ) manipulations of the venerid bivalve Austrovenus stutchburyi (Gray) were examined on an 22 intertidal sandflat. Bivalve density manipulations greater than 600 m had a mixed influence on macrofauna colonisation; two species were reduced, three enhanced and three were unaffected. There was no clear functional group-related pattern as to which species were affected by Austrovenus. The most pronounced influence of high bivalve densities was the reduction in the abundance and alteration of the size-structure of post-set (ca. 250–360 mm) tellinid bivalves, Macomona liliana Iredale. Patch size manipulations of Austrovenus had no measurable effect on 22 macrofauna colonisation, probably because patch density (120 bivalve m ) was too low. While a variety of epibenthic predators were present at the study site, Austrovenus stutchburyi mortality 21 estimates in both experiments were relatively low (0.01–0.03% individuals lost day ) and were independent of both density and patch size. In contrast, the proportion of nipped bivalve siphons was relatively high (11–37%) in both experiments. While proportions of nipped siphons were similar across the range of manipulated densities, siphon browsing was more than 2 times higher 2 2 in 9.0 m plots than 0.25 m plots. Scale-dependent foraging of sub-lethal marine benthic predators is previously unreported and our results illustrate the necessity for conducting studies on predator–prey dynamics at ecologically meaningful spatial scales for both the predator and prey species.  1997 Elsevier Science B.V.