 The rate and efficiency of any processes that marine organisms mediate, as well as the range of goods and services that they provide, are determined by interactions between organisms and interactions between organisms and their environment; and therefore by biodiversity (Gaston 1996, Gaston and Spicer 1998).These relationships have not yet been quantified, and we are at present unable to predict the consequences of loss of biodiversity resulting from environmental change in ecological, economic or social terms (Walker, 1992, Lawton and Brown, 1994, Ehrlich and Ehrlich, 1981, Lawton, 1994, Vitousek and Hooper 1994).The influence of species diversity on the productivity of marine ecosystems on a large scale is still unclear (Cardinale et al.