Ecological effects of ocean acidification and habitat complexity on reef-associated macroinvertebrate communities

Abstract

The ecological effects of ocean acidification (OA) fromrising atmospheric carbon dioxide (CO2) on benthic marine communities are largely unknown.We investigated in situ the consequences of long-term exposure to high CO2on coral-reefassociated macroinvertebrate communities around three shallow volcanic CO2seeps in Papua New Guinea. The densities of many groups and the number of taxa (classes and phyla) of macroinvertebrates were significantly reduced at elevated CO2(425-1100 matm) compared with control sites. However, sensitivities of some groups, including decapod crustaceans, ascidians and several echinoderms, contrasted with predictions of their physiological CO2tolerances derived from laboratory experiments. High CO2reduced the availability of structurally complex corals that are essential refugia for many reef-associated macroinvertebrates. This loss of habitat complexity was also associated with losses in many macroinvertebrate groups, especially predation-prone mobile taxa, including crustaceans and crinoids. The transition from living to dead coral as substratum and habitat further alteredmacroinvertebrate communities, with far more taxa losing than gaining in numbers. Our study shows that indirect ecological effects of OA (reduced habitat complexity) will complement its direct physiological effects and together with the loss of coral cover through climate change will severely affect macroinvertebrate communities in coral reefs. © 2013 The Authors.