Local human impacts interact with geography to drive benthic community depth zonation on contemporary coral reefs

Changes in biophysical conditions and energetic resource supply across depths are predicted to promote or limit the abundance of different coral reef benthic groups. However, the degree to which regional differences in biophysical processes govern and local human activities might alter naturally occurring depth zonation patterns remains unclear. Here, we used 2239 reef surveys conducted between 0 and 30 m depth around 33 islands (18 unpopulated and 15 populated) across the Pacific Ocean to quantify the percentage cover change of seven broad benthic groups. We tested whether natural depth zonation patterns differed across geographies (using six ecoregions) and whether and how local human impacts might disrupt these natural zonation patterns. We found benthic community depth zonation did not always occur. At the three ecoregions where depth zonation existed, there was no universal 'natural' zonation pattern and the benthic groups most responsible for driving patterns of depth zonation differed across geographies. We also found evidence of human-disrupted changes to benthic community depth zonation; patterns were inversed across depths and less distinct at populated compared to unpopulated islands within two ecoregions. We show coral reef communities are naturally highly variable and that human activities can disrupt natural patterns of ecological organization in contemporary ecosystems.