Relative importance of habitat attributes to predation risk in a temperate reef fish

Abstract

Complex habitats serve as a refuge by impeding predator movement and the detection and capture of prey. The attributes that make up these habitats often covary and are difficult to evaluate. The purpose of our study was to understand how attributes of habitat structure contribute to the survival of a temperate rocky reef fish, the bluebanded goby, Lythrypnus dalli. We first used natural substrata (rock) and then artificial standardized habitat units (SHUs) to explore attributes that likely reduce predation of L. dalli. Survival was positively related to the size of rock, but multiple attributes covaried, including rugosity, interstitial space between rocks, total surface area, rock height, and the number of rocks per plot. Using SHUs, we manipulated gap distance (to limit predator access) and potential refuge volume (interstitial space) orthogonally between artificial ‘rocks’ while controlling other habitat attributes. Degree of predator access (PA) was more influential on survival of individuals when combined with low interstitial space (IS) than high, but a combination of low IS and low PA was necessary for consistently high survival. We also conducted a behavioral laboratory experiment to ascertain whether the distribution of L. dalli among configurations of habitat differed in the presence and absence of an important predator, the kelp bass, Paralabrax clathratus. Individuals selected habitat configurations with low spacing between structures, consistent with survival patterns observed in the field. Our study indicates that habitat attributes vary in their importance to survival, but their combined effects may be greater than those of any single attribute.