Habitat selection is an important behavioral process by which animals disproportionately use or avoid habitat characteristics at multiple spatial scales. For example, some large mobile animals avoid predators at landscape scales, but select for resources at smaller scales. Unlike mobile animals that can continuously make habitat selections, sessile organisms have only one opportunity to select their habitat during settlement and are bound to those selections for life. Therefore, these one-time decisions must simultaneously integrate avoidance and selection for different habitat characteristics. Scleractinian corals begin life as small (microns to millimeters), mobile larvae that display strong attraction and avoidance of benthic taxa during settlement. However, coral habitat selection has been studied almost exclusively in monocultures and we know little about the hierarchy of attraction and avoidance of different taxa. Here we investigate the habitat selection of an ecologically-important and endangered coral, Orbicella faveolata, over a gradient of benthic community composition. We used experimental coral settlement assays that exposed larvae to settlement substrate with benthic communities that varied in abundance of benthic spaceholders. We then mapped the settlement location onto digital images of the substrate and carried out a compositional analysis of habitat use across several biologically-relevant spatial scales (millimeters to centimeters).
Results/Conclusions
O. faveolata larvae showed significant habitat selection at the centimeter and millimeter scales which likely reflects both avoidance of competitors and selection for open space. At the centimeter scale O. faveolata larvae strongly avoided sediment, which is known to smother and kill newly settled corals. Larvae also avoided crustose coralline algae, which can overgrow and compete with coral recruits. Therefore, selection against these substrate types likely reflects avoidance of sources of mortality for young corals. At smaller spatial scales (millimeters) larvae preferred settling in areas that were low in turf algal abundance, and high in abundance of bare space and green fine filamentous algae. Selection for these substrates may allow larvae to simultaneously avoid competitors and select for areas with space to grow. These different spatial patterns of settlement suggest that coral larvae may hierarchically select for settlement habitats. Understanding how coral larvae select settlement locations is a critical step to furthering our understanding of how benthic community composition influences patterns in coral abundance.