Habitat fragmentation, patch size, and the recruitment and abundance of kelp forest fishes

Abstract

Studies of habitat fragmentation in marine ecosystems are few, despite a high potential for disturbance and the fragmentation of macrophytes that constitute important habitats. In this study, we investigated the relative importance of habitat fragmentation and loss on the recruitment and abundance of fishes associated with giant kelp Macrocystis pyrifera forests. We experimentally fragmented naturally occurring kelp forests at 3 sites along Santa Catalina Island, California, USA, into areas of 100 to 1600 m 2 . We also explored the relationship between kelp patch size and recruit- ment of fishes at smaller spatial scales by constructing kelp plots that were consistent in density but varied in area. The numerical and biomass densities of recruit, older juvenile, and adult fishes across fragment areas differed among species, resulting in linear, exponential, or asymptotic increases in numerical and biomass abundances with fragment size. Overall, fishes exhibited mostly linear rela- tionships between abundance and fragment area, suggesting that kelp-associated fishes are more affected by habitat loss than by fragmentation. When incorporating kelp forests of larger area, how- ever, formerly linear functions became non-linear, indicating that habitat fragmentation may become more important at larger spatial scales. At the scale of small kelp patches, the densities of Paralabrax clathratus and Oxyjulis californica were unrelated to patch size, and recruitment occurred in the smallest patches and was highly variable for both species. These results may provide resource man- agers with important information on the relative effects of habitat loss and fragmentation in the con- servation and management of coastal fishes.