Spatial variation in the effects of predator exclusion on epifaunal community development in seagrass beds

Biotic interactions have critical effects on the structure of ecological communities, and the variation in the strength of these interactions over space and time contributes to biogeographic variation in communities. Predation shapes community composition in a variety of habitats, although there have been comparatively few experimental studies of these effects across latitudinal scales. We tested the impact of predator exclusion on the development of epifaunal communities across 3 sites (Florida [USA], Belize, and Panama) in seagrass habitats dominated by Thalassia testudinum using caged and uncaged settlement panels. We found that predators altered composition and slowed development of epifaunal communities. The nature and magnitude of these effects, however, were complex, site-dependent, and tightly coupled to community development. Fast-growing, soft-bodied species dominated space when predators were excluded, while more resistant calcifying species were dominant in communities exposed to predators. In Panama, non-native ascidians dominated communities in cages, while ascidians were consumed when exposed to predators, indicating the importance of biotic resistance at that site. Predators also reduced the abundance of associated small mobile fauna, and the positive correlation between mobile faunal abundances and sessile biomass in our study suggests a potential indirect effect of predator-mediated habitat modification. Overall, prey characteristics were important in explaining the site-specific effects of predators on communities, indicating that taxonomic resolution can influence the results of multi-regional studies examining the mechanisms affecting community structure.

Epifaunal invertebrate assemblages associated with branching Pocilloporids in Moorea, French Polynesia

Reef-building corals can harbour high abundances of diverse invertebrate epifauna. Coral characteristics and environmental conditions are important drivers of community structure of coral-associated invertebrates; however, our current understanding of drivers of epifaunal distributions is still unclear. This study tests the relative importance of the physical environment (current flow speed) and host quality (e.g., colony height, surface area, distance between branches, penetration depth among branches, and background partial mortality) in structuring epifaunal communities living within branching Pocillopora colonies on a back reef in Moorea, French Polynesia. A total of 470 individuals belonging to four phyla, 16 families and 39 genera were extracted from 36 Pocillopora spp. colonies. Decapods were the most abundant epifaunal organisms (accounting for 84% of individuals) found living in Pocillopora spp. While coral host characteristics and flow regime are very important, these parameters were not correlated with epifaunal assemblages at the time of the study. Epifaunal assemblages associated with Pocillopora spp. were consistent and minimally affected by differences in host characteristics and flow regime. The consistency in abundance and taxon richness among colonies (regardless of habitat characteristics) highlighted the importance of total habitat availability. With escalating effects of climate change and other localized disturbances, it is critical to preserve branching corals to support epifaunal communities.