In contrast to terrestrial biodiversity, marine biodiversity has a number of distinctive features that suggest that a broader strategy for its conservation might be more appropriate than a local reserve-based one. Traditional diversity measures based on species richness and evenness often have disadvantages in the assessment of biodiversity change on wide spatial scales and long timescales. Alternative measures based on the degree of relatedness of species overcome these problems to varying degrees. They fall into two categories. Taxonomic distinctiveness measures are used as a means of preferentially selecting species from an inventory for conservation purposes: species that diverge close to the base of a phylogenetic or taxonomic tree and have few close relatives will preserve more evolutionary history than those that diverge further up and have more congeners. Complementary subsets of species can also be selected to provide representativeness of the widest range of evolutionary characters. Taxonomic distinctness measures, on the other hand, are a means of comparing patterns of relatedness in community samples in the field, and monitoring changes in these patterns over space or time. They measure either the average distance apart of all pairs of individuals or species in a sample, traced through a taxonomic tree, or the variability in structure across the tree. These measures are beginning to find application in broad scale geographical comparisons of biodiversity, in environmental impact assessment and in evaluation of surrogates for biodiversity estimatio
