After the Earth Summit in Rio, 1992 and the adoption of the Convention on Biological Diversity, the term biodiversity has become a component of research policy in many countries and international bodies and initiatives. Biodiversity however, is not a concept but an umbrella term (Haila and Kouki 1994); the content of which is quite diverse as can be inferred by definitions provided in many different texts (Wilson 1988, Reid and Miller 1989, CBD 1992, Margalef 1997). The distinction between diversity and biodiversity is also fairly unclear in many studies in biology. As with most other issues in Ecology and Evolution, paradigms dominating the study of biodiversity on both global and regional scales come mainly from the terrestrial environment despite the marked distinctive features of marine biodiversity and the fact that the aquatic (freshwater & marine) environment occupies more than two thirds of the Earth’s surface (Vanaverbeke et al. 1997, Gessner et al. 2004). Marine organisms play crucial roles in many bio-geochemical processes that sustain the biosphere, and provide a variety of products and functions which are essential to mankind’s well-being, including the production of food and natural substances, the assimilation of waste and regulation of the world’s climate. 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