Variation in coral-associated cryptofaunal communities across spatial scales and environmental gradients

Abstract

Most of the diversity on coral reefs is in the cryptofauna, the hidden organisms that inhabit the interstitial spaces of corals and other habitat-forming benthos. However, little is known about the patterns and drivers of diversity in cryptofauna. We investigated how the cryptofaunal community associated with the branching coral Pocillopora meandrina varies across spatial scales and environmental gradients. We performed nondestructive visual surveys of the cryptofaunal community on 751 P. meandrina colonies around the island of O‘ahu (30–73 colonies per site, 3–6 sites per region, five regions). We identified 91 species, including 48 fishes and 43 invertebrates. Most of these species were observed rarely, with only 19 species occurring on greater than 5% of surveyed colonies. Variation in community abundance and species richness was greatest at the scale of the coral colony and lowest at the site scale. Abundance and species richness increased with increasing colony size and maximum wave height, and decreased with increasing surface chlorophyll-a. In an analysis of species-specific responses, colony size, wave height, and chlorophyll-a were significant drivers of occurrence. Depth and percent live coral tissue were also identified as important correlates for community composition with distinct responses across taxa. Analyzing species-specific responses to environmental gradients documented a unique pattern for the guard crab Trapezia intermedia, which had a higher probability of occurring on smaller colonies (in contrast to 18 other common taxa). The results of a principal coordinates analysis on community composition and a co-occurrence analysis further supported T. intermedia as having a unique distribution across colonies, even in comparison with four other Trapezia species. Overall, these patterns emphasize the importance of host coral characteristics (i.e., colony size and percent live tissue) and physical characteristics of the surrounding habitat (i.e., wave energy, chlorophyll-a, and depth) in structuring cryptofaunal communities and characterize species-specific responses to environmental gradients.