Gribben, P.E., Wright, J.T., O’Connor, W.A. and Steinberg, P., 2009. Larval settlement preference of a native bivalve: the influence of an invasive alga versus native substrata. Aquatic Biology, 7: 217-227.

Summary

Settlement of bivalves such as clams and cockles is strongly influenced by the habitat preference of their larvae, and larvae can choose to settle or not in response to many cues. Large numbers of the Sydney cockles, Anadara trapezia, have been found in the invasive alga Caulerpa taxifolia compared to other native habitats. This could be due to larvae preferentially settling on C. taxifolia or to other factors such as C. taxifolia ultimately providing a refuge from predation.  In laboratory experiments, we investigated the general habitat preference of A. trapezia larvae exposed to various potential settlement substrates, both natural (adult A. trapezia, the native seagrass Zostera capricorni, and sediment from unvegetated areas) and invasive (C. taxifolia and sediments from C. taxifolia) that occur in estuaries in New South Wales. When exposed to all substrata simultaneously, more larvae settled on adult shells compared to all other substrata except seagrass, although settlement to C. taxifolia did occur. Manipulations of shells of adults indicated that larvae may be responding positively to biofilms on the surface of shells. This study indicated that while A. trapezia larvae do not preferentially recruit to C. taxifolia, they do not reject it as a settlement surface. We suggest that C. taxifolia may serve as a ‘sink’ habitat for A. trapezia. That is a habitat that may not be ideal, but because it is common in areas containing adult A. trapezia populations, it ends up with significant larval settlement.