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

Abstract

The impact of bioturbation by the burrowing ghost shrimp Callianassa filholi on benthic community composition was examined in relation to seasonal and small-scale spatial changes. Sites of naturally occurring low and high densities of C. filholi on an intertidal sandflat represented hfferences in bioturbation activity throughout the year. Univariate and multivariate analyses showed significant differences in community composition between high-and low-density sites. The total number of species and total number of individuals were lower at high-density sites. A corophiid amphipod, Paracorophium escavatum and a small bivalve, Perrierina turneri, appeared to have the greatest discriminating significance wlth lower abundances of both species at sites of high C. filholi density. Even though differences between sites of different dens~ty pers~sted throughout the year, the impact of bioturbation depended on season. Bioturbation had the highest maximum correlation to changes in macro-fauna1 community composition in winter, spring and, in association with seagrass blomass (Zostera novazelandica), in autumn. During summer, however, seagrass biomass contnbuted the most to observed differences and appeared to compensate for generally high bioturbation activity. The results imply that bioturbation impacted on macrofauna community composition over a small spatial scale and, although its impact varied seasonally, imposed patterns persisted throughout the year. As such, C. filholi can be considered a keystone species.