Impact of an exotic clam, Corbula gibba, on the commercial scallop Pecten fumatus in Port Phillip Bay, south-east Australia: Evidence of resource-restricted growth in a subtidal environment

Abstract

Corbula gibba (Olivi, 1792) a small exotic bivalve from the eastern Atlantic and the Mediterranean has been present in Port Phillip Bay, Victoria, Australia, from as early as 1987. C. gibba is widespread, abundant, and possesses characteristics such as fast growth which may confer a competitive advantage over endemic species like the commercial scallop Pecten fumstus Reeve, 1855. Experimental manipulations in the field showed that ambient densities of C. gibbs significantly affected the size and growth of juvenile P. fumatus. This effect was greater than the effect of an equivalent number of conspecific scallops. C. gibbs did not, however, affect scallop condition or survival in the short term, although the power of the test to detect a 50 % decrease in survival was low. The percentage of experimental scallops lost to different sources of mortality was also unaffected by the presence of C. gibbs, as was the density of predators found in experimental enclosures. This study is the first to experimentally demonstrate the impact of an introduced marine mollusc on an endemic species in Australia. A possible mechanism underlying this impact is competition for food, as both species are suspension feeders which live in an environment where resource limitation may occur.