What Do Natural Reefs Tell Us about Designing Artificial Reefs in Southern California?

We investigated the relationship between fish abundances and easily-measured environmental variables on shallow subtidal shoals in Southern California. Our object was to develop a method for large-scale prediction of the fish fauna of natural and artificial shoals. In a 2-year period, 337 samples were taken at 85 survey sites located between Pt. Conception and the Mexican border. Substrate variables and cryptic, demersal fish were counted with transects. Other fish were counted with a visibility-proportioned free swim. Fish abundance and species number were usually saturating functions of environmental variables, i.e., fish abundances changed with environmental variable values when the values of these variables were low, but were constant at the maximum when environmental variable values were high. On hard substrates, the abundances of about half of the fish species were saturating functions of bottom relief; the abundances of most of the rest appeared unrelated to bottom relief. Species number and total fish abundance were saturating functions of bottom relief. Species number and total fish abundance were not clearly related to kelp density, algal turf density and rock area per square meter of sea surface on high relief, but were saturating functions of these variables on low relief. Since invertebrate prey are probably more abundant on sites with high relief, dense turf, dense kelp and much rock surface area, these results suggest that fish abundance is not always limited by food. These results also suggest that fish abundance is not always limited by shelter availability because the number of shelter interstices probably increases with relief and rock area, and because most fish were not significantly more abundant on breakwaters, which have many large interstices, than on high natural reefs. These data suggest that a high, complex artificial reef enriched with algal plantings might produce no more fish than a smaller, simpler, cheaper reef.