Regional patterns of macrofaunal diversity and abundance determined by antagonistic ecosystem engineers in soft-sediment intertidal habitats

Macrofaunal assemblages in soft-sediment environments frequently contain species, ecosystem engineers, that exert a disproportional influence on the structure and diversity of benthic communities. The present study examined the influence of co-occurring but antagonistic burrowing shrimps (Callianassidae) and intertidal seagrasses (Zosteracea) on the diversity of benthic assemblages in two temperate regions, south-eastern New Zealand and north-western United States. In each region, diversity and abundance patterns of intertidal macrofaunal assemblages were examined in relation to varying burrowing shrimp and seagrass densities across different-sized estuaries, in summer and winter.
Although the compositions of macrofaunal assemblages were distinctly different between sites dominated by burrowing shrimp and seagrass, differences in univariate assemblage indices were less distinct. While species diversity was generally similar at burrowing shrimp and seagrass sites, species abundance was frequently higher at the latter sites. These patterns were consistent across summer and winter, and across spatial scales, although there were some differences across regions. Even though population densities of burrowing shrimp and seagrass can vary over time, findings from this study highlight the relative influence of these antagonistic ecosystem engineers on the long-term structure and functioning of intertidal macrofaunal assemblages.