ROLE OF MACROALGAL STRUCTURE IN THE DISTRIBUTION AND ABUNDANCE OF A TEMPERATE REEF FISH

Habitat structure can dramatically influence patterns of distribution and abundance of reef fishes. On temperate reefs, much of this structu re consists of macroalgae, especially large kelps. I explored the role of such algae, and in particular the structural features of the giant kelp Macrocystis pyrifera, in the distribution and abundance of the k elp perch Brachyistius frenatus. Several measures of the abundance of M. pyrifera were positively related to the density of kelp perch. An o ntogenetic shift in habitat use occurred within reefs in that young re sided initially within the floating surface kelp canopy, older juvenil es descended into the water column and became more loosely associated with bundles of fronds, and adults were distributed more uniformly amo ng several defined depth strata. The density of juveniles varied widel y both spatially and temporally, which was linked to variation in the percentage cover of the kelp canopy. Not surprisingly, the density of juvenile kelp perch among reefs was related to the density of adults, since young are born directly into the reef habitat. However, the dens ities of 1 yr old adults on reefs did not reflect the densities of tha t cohort as juvenile recruits the previous year, possibly due to tempo ral variation in the abundance of M. pyrifera. The hypothesis that mac roalgal structure may better predict recruitment strength for algal-as sociated reef fishes that are capable of only limited dispersal than f or those that are first subjected to a planktonic dispersive phase was not supported here. However, to make such comparisons between species , recruitment should be measured concurrently under the same environme ntal conditions and fluctuations in macroalgal abundance, and the part icular relationships between recruiting species and the structural fea tures of macroalgae must be considered.