A decline in the abundance and condition of a native bivalve associated with Caulerpa taxifolia invasion

Abstract

Caulpera taxifolia is a fast-spreading invasive seaweed that threatens biodiversity in temprate Australian estuaries. To date, little is known about its effects on infauna. In the present study, we describe variation in demographic and life-history traits of the abundant infaunal bivalve, Anadara trapezia, in C. taxifolia and uninvaded habitats (seagrass and unvegetated sediments) at multiple sites across three estuaries in south-eastern New South Wales. Densities of A.trapezia werw always lower in C. taxifolia than on unvegetated sediment, and lower in C. taxifolia than in seagrass at three out of four sites where they were compared. Dry tissue weight of a. trapezia was also lower in C. taxifolia than on unvegetated sediment at most sites, but was onlylower in C. taxifolia than in seagrass at one of four sites. Populations were dominated by larger individuals (>45 mm length), but smaller individuals (35-45 mm length) wwere more common in C. taxifolia and seagrass. A. trapezia shell weight and morphology was variable and appeared weakly affected by invasion. Generally our findings are consistent with the hypothesis that A. trapezia is negatively affected by C. taxifolia. However, C. taxifolia invasion appears complex and, at some places, its effects may not differ from those of native seagrass. There is a need for manipulative studies to understand the mechanisms underlying the effects of C. taxifolia on infauna.