MEPS 340:41-53 (2007)  -  doi:10.3354/meps340041

ABSTRACT: In the past decade there has been a rapid increase in the study of the ecological consequences of marine invasions, but we still have data for only a small proportion of established marine invaders. This is exemplified by Port Phillip Bay, Australia, for which we have quantitative data on the impacts of only a handful of the >160 introduced and cryptogenic species present. Some of the most conspicuous of these invaders are the large epibenthic suspension feeders living on soft sediments. In this study, we examined the impact of 2 of the most common epibenthic suspension feeders in Port Phillip Bay, the introduced polychaete Sabella spallanzanii and an introduced solitary ascidian, Styela clava, by manipulating their densities in the field across the range of naturally occurring densities. Because of their physical presence at the sediment–water interface and suspension feeding activities, we predicted varying impacts across different macrofaunal groups (suspension feeders, deposit feeders, recruits and mobile species). These predictions were not supported for either introduced species despite good power. For individual taxa, there was a significant negative relationship between Sabella density and the abundance of lumbrinerid polychaetes and gammarid amphipods, and between Styela density and the abundance of lumbrinerids, tanaids, crustaceans as a group, and the bivalve Laternula rostrata. Nonetheless, these taxa only represent a small proportion of those present, and importantly, the effects generally emerged at Sabella and Styela densities (>1 to 2 ind. m^–2) greater than those typically recorded on Port Phillip Bay sediments. Therefore, we suggest that the effects of Sabella and Styela on soft sediment assemblages in Port Phillip Bay are likely to benegligible.

KEY WORDS: Introduced species · Suspension feeders · Density manipulation · Soft sediments · Epibenthic