Fish functional diversity is modulated by small-scale habitat complexity in a temperate ecosystem

Rocky reefs and kelp forests form conspicuous habitats that promote species diversity and support livelihoods in coastal communities. However, taxonomic approaches often disregard biological identity and differences between species. In this study, we explore the relationship between functional diversity of fish communities and habitat complexity in temperate reefs and test if greater habitat complexity, such as rugosity or kelp three-dimensional structure, would result in higher functional diversity. We conducted fish surveys using SCUBA in four kelp forest sites and rocky reef sites. Although the rocky reef and kelp forest sites showed differences in habitat complexity, no significant differences in fish taxonomic or functional diversity were found between the two habitat types. However, we did find differences at smaller spatial scales for the kelp forest sites, where number of stipes, stipe bundle diameter, and kelp density influenced functional richness, but not species richness, highlighting the importance of functional approaches in certain ecosystems. The differences found among kelp forest sites may be linked with small-scale spatiotemporal oceanographic drivers of productivity such as upwelling exposure or nutrient availability. We recommend considering small-scale spatial drivers when aiming to understand how habitat characteristics link with functional diversity.