Beta and habitat diversity in marine systems: a new approach to measurement, scaling and interpretation

Habitat diversity is a widely used criterion for locating conservation acti vities such as protected areas. Most habitat diversity indices are measures of alpha diversity at the scale of habitats and are therefore insensitive to the underlying biological differences between habitats. To incorporate s uch inter-habitat differences, a new method is presented which calculates a measure of beta (beta) diversity from pixels within a window passed throug hout a habitat map. To avoid confusion with beta diversity indices, the new measure is called beta -dissimilarity. beta -Dissimiliarity is calculated from the mean Bray-Curtis dissimilarity, D-m, of field data which comprise each habitat class. The variance of D-m distinguishes discrete beta -dissim ilarity distributions from homogenous patterns. The method also attempts to remove some of the arbitrary aspects of habitat mapping, can be scaled to other levels of diversity or measures of community structure, is readily in terpretable and permits hypothesis testing. Its applications to ecosystem s cience and coastal management are discussed and illustrated.