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 activities 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 such inter-habitat differences, a new method is presented which calculates a measure of beta (β) diversity from pixels within a window passed throughout a habitat map. To avoid confusion with β diversity indices, the new measure is called β-dissimilarity. β-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 β-dissimilarity 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 interpretable and permits hypothesis testing. Its applications to ecosystem science and coastal management are discussed and illustrated.