Factors affecting fish diversity on a temperate reef

Synopsis

Subtidal studies of fish stocks conducted along a rock breakwater in Southern California reveal a rich and diverse fauna with elements from cool and warm temperate regions. More than 100 species have been observed with half of these resident. Only a single large, permanently territorial species occurs on the reef though many small, often cryptic species defend home and/or reproductive sites. Many of the larger, mobile species orient to temperature stratification and a portion of the diversity can be allied to the ecotonal effect of stable stratification. Both large predators and herbivores are rare; the majority of the species are micropredators, grazing on sedentary or benthic microinvertebrates.

Reproduction is keyed to spring-summer seasons, generally with pelagic eggs, embryos and larvae. The live-bearing resident embiotocids show the least fluctuation in numbers while many oviparous species have shown major changes in annual success during the study period. Although the success of individual species varies, the diversity and total abundance of fishes has remained relatively stable for the reef community as a whole. This stability cannot be considered to reflect an equilibrium community and in fact the structure of the community has changed significantly during the five year study.