Spatial patterning of coral reef benthic communities at landscape scales

Background/Question/Methods

Coral reefs are spatially complex ecological habitats, yet our understanding of their non-equilibrium dynamics is largely based upon data collected at relatively small (< 1 m²) spatial scales. This makes extrapolation to larger spatial scales challenging as we lack a highly taxonomically resolved appreciation of landscape-scale patterning in coral reef environments. Recent attempts to apply well-tested spatial hypotheses, such as the Janzen-Connell hypothesis of distance-dependent survivorship, to coral reef communities, while explicitly tested at small spatial scales, have only been theorized at a landscape level. Here we use large-scale (100s m²) photomosaic imagery collected at a remote coral reef atoll to test established hypotheses relating to spatial patterning among benthic species and competitors. Photomosaics, each covering 200 m²of benthic habitat, were collected from forereef habitats during 2012 and 2013 and all individual hard coral colonies were mapped and identified to the species level. Using point-pattern analysis and an array of spatial statistical techniques, we describe the spatial patterning of adult hard corals.

Results/Conclusions

We found strongly organized spatial distributions of coral colonies, but the spatial patterning was distinct for particular taxa. A number of coral taxa (e.g. Pocillopora spp., Stylophora spp.) exhibited patterns of over-dispersion, while several other species showed moderate to strong clustering (e.g. Acropora spp., Fungia spp.). The nature of these spatial patterns appeared to be stable through time. The observed patterns are likely due to differences in reproductive strategies and fragmentation/regrowth resulting from disturbance, suggesting that the spatial structure of a reef may reveal important biological processes. Taxa that are over-dispersed likely experience distance-related survivorship, a pattern that emerged from demographics at early life-history phases. In contrast, taxa that are spatially clustered (e.g., Fungia) are known to reproduce readily through clonal budding, leading directly to patchy distributions. Photomosaics provide us large-scale information allowing the investigation of spatial and temporal patterns on coral reefs in a mechanistic manner, by quantifying not only overall mean change but also the spatial arrangement of that change and relative species specific contributions. Our widened landscape-scale view of marine benthic communities allows for novel application of well tested terrestrial ecological principles in the marine realm.