Assessing sponge resilience to ocean acidification in natural reef environments

Sponges are key components of coral reefs globally providing a range of important functional roles. While sponges are under threat from the impacts of global climate change, there is an emerging picture of sponge tolerance to ocean acidification (OA). However, to date all physiological studies on sponge tolerance to OA have been under ex-situ experimental conditions and only for a limited number of sponge species. Instead, here we used in situ incubation chambers to measure chlorophyll concentrations and oxygen fluxes for two common Indo-Pacific sponge species ( Melophlus sarasinorum and Neopetrosia chaliniformis ) at a natural CO 2 vent (pH T 7.6–7.7) and control site in Papua New Guinea. We also explored differences between the sponge microbial community composition between control and vent locations for N. chaliniformis . We found very low concentrations of chlorophyll in both species, compared to other sponges, suggesting these species are largely heterotrophic. We also found little evidence for any physiological differences between vent and control sponges, and no differences in the overall microbial communities, except some specific microbes. Overall, our results support the emerging evidence that heterotrophic sponges will likely be resilient to future ocean acidification.