Temporal and spatial variation in macrofauna community composition imposedby ghost shrimp Callianassa filholi bioturbation

The impact of bioturbation by the burrowing ghost shrimp Callianassa filhol i on benthic community composition was examined in relation to seasonal and small-scale spatial changes. Sites of naturally occurring low and high den sities of C, filholi on an intertidal sandflat represented differences in b ioturbation activity throughout the year. Univariate and multivariate analy ses showed significant differences in community composition between high- a nd low-density sites. The total number of species and total number of indiv iduals were lower at high-density sites. A corophiid amphipod, Paracorophiu m excavatum and a small bivalve, Perrierina turneri, appeared to have the g reatest discriminating significance with lower abundances of both species a t sites of high C. filholi density. Even though differences between sites o f different density persisted throughout the year, the impact of bioturbati on depended on season. Bioturbation had the highest maximum correlation to changes in macrofaunal community composition in winter, spring and, in asso ciation with seagrass biomass (Zostera novazelandica), in autumn. During su mmer, however, seagrass biomass contributed the most to observed difference s and appeared to compensate for generally high bioturbation activity. The results imply that bioturbation impacted on macrofauna community compositio n over a small spatial scale and, although its impact varied seasonally, im posed patterns persisted throughout the year. As such, C, filholi can be co nsidered a keystone species.