Validation of qualitative habitat descriptors commonly used to classify subtidal reef assemblages in north-eastern New Zealand

On shallow temperate subtidal reefs, habitat types are usually defined subjectively by the dominance or presence of major macroalgal species. Many of these habitat types (e.g., urchin barrens, kelp forest) are frequently used in the literature but little attempt has been made to quantitatively define these habitats. A survey of shallow subtidal reefs in north-eastern New Zealand identified a number of commonly occurring habitat types. In this paper the abundances of habitat-forming species within each of these habitats are quantified and the validity of the subjective classification system is tested. In addition to previously-described reef habitats from north-eastern New Zealand a number of other habitat types were encountered and described in this study (e.g., mixed algae, red foliose algae, and Caulerpa mats). The algal communities within each habitat were biologically distinct and there was strong concordance between the grouping of samples from cluster analysis and the subjective habitat type assigned to each. The habitat classification system was reliable and canonical analysis of principal coordinates revealed an overall classification success of 81%. This provides strong evidence that the habitat classifications used in this study are biologically meaningful based on the abundances of habitat-forming algal groups. Furthermore, this demonstrates that these habitat types can be reliably categorised visually, which has important applications in classification and mapping of the marine environment.