Does increased habitat complexity reduce predation and competition in coral reef fish assemblages?

Abstract

Greater habitat complexity is often associated with a greater abundance and diversity of organisms. High complexity habitats may reduce predation and competition, thereby allowing more individuals to occupy a given area. Using 16 spatially isolated reefs in the Bahamas, I tested whether increased habitat complexity reduced the negative effects of resident predators and competitors on recruitment and survival of a common damselfish. Two levels of habitat complexity were cross-factored with the presence or absence of two guilds of resident fishes: predators (sea basses and moray eels) and interference competitors (large territorial damselfishes). I monitored subsequent recruitment and recruit mortality for 60 days. Residents had strong negative effects on recruitment regardless of habitat complexity. In the presence of residents, recruits suffered high mortality immediately after settlement that was similar on low and high complexity reefs, although high complexity reduced mortality of recruits that survived this early postsettlement period. Comparisons between shelter hole diameters and the sizes of residents suggest that territorial damselfishes and small resident predators could access most shelter holes, whereas large resident predators were excluded from many shelter holes. This study demonstrates that whether habitat complexity reduces predation and competition may depend on several key factors, such as the availability of appropriate shelter, behavioral attributes of interactors, and developmental stage of prey/inferior competitors.