Testing a depth-based Habitat Classification System against reef fish assemblage patterns in a subtropical marine park

1. The Solitary Islands Marine Park (SIMP) in New South Wales (NSW), Australia, has strong cross-shelf patterns of reef fish assemblages on shallow reefs (< 25 m). While the SIMP also contains reef at depths of up to 75 m, marine communities below 25m are poorly described. The Habitat Classification System (HCS) used for planning the arrangement of zones in this marine park included three depth categories for reef: shallow (< 25 m); intermediate (25-60 m); and deep (> 60 m). However, these had not been tested to determine if they adequately reflect biotic patterns. 2. Using baited remote underwater video (BRUV), fish assemblages were surveyed at 56 sites spread across shallow, intermediate, and deep reefs within the SIMP to examine spatial variation between depth categories. Relationships between assemblage patterns, depth, and four additional factors considered likely to affect assemblage patterns (distance from shore, reef type, dominant benthos, and latitude), were subsequently explored using multivariate statistical methods. 3. Reef fish assemblages differed significantly among the depth categories. Assemblage patterns for fish were strongly correlated with depth and moderately correlated with the dominant benthic assemblage. Correlations with the other factors were generally weak. Three distinct assemblages occurred on reefs < 25 m, 25-50m and > 50 m. Shallow (< 25 m) reefs also displayed strong cross-shelf patterns, supporting the results from other studies. Weaker cross-shelf patterns were evident at intermediate depths (25-50 m). 4. Depth-based and cross-shelf categories are clearly fundamental components for a HCS that will adequately represent reef fish assemblages for conservation planning in the SIMP. Further refining the depth criteria for the intermediate/deep boundary (to 50 m) improves this representation. Further research is required to determine the wider application of the refined HCS to other marine parks in NSW and to determine how well it represents other components of biodiversity. Copyright (C) 2011 John Wiley & Sons, Ltd.