Physical habitat structure in marine ecosystems: the meaning of complexity and heterogeneity

Habitat structure (HS) corresponds to the presence of physical structures in a system and is one of the most important ecological features that influences patterns and processes of biological communities. In this study, the use of complexity and heterogeneity in marine empirical studies in the context of HS was investigated. Empirical publications that discussed the role of physical structure on marine communities were surveyed and the use of different HS-related terms were analyzed and classified as: (i) complexity; (ii) heterogeneity; (iii) both as synonymous; and (iv) both as non-synonymous. A cluster analysis showed different patterns of use on different habitats. A conceptual clarification, through studies that presented definitions, was performed and a conceptual scheme was built considering two applications: (i) multidimensional or unidimensional measures; and (ii) quantitative, qualitative, or quali-quantitative measures. There was no agreement in the use and application of HS related terms in different marine habitats, and the analyses performed here indicated that (i) complexity corresponds to a multidimensional measurement with parts that interact and (ii) heterogeneity is one dimension of the habitat complexity. The present study provided the starting point for closer communication within different areas of ecology and contributes to future robust generalizations regarding HS.