Are Some Photosymbiotic Bioeroding Sponges More Bleaching-Tolerant than Hard Corals?

Are Some Photosymbiotic Bioeroding Sponges More Bleaching-Tolerant than Hard Corals?

Some bioeroding sponges of the Cliona viridis species complex are aggressive space competitors on coral reefs, which can often kill hard corals. Like hard corals, C. viridis complex spp. are symbiotic with the dinoflagellates Symbiodinium spp., which provide vital energy for the hosts’ survival. In this study, C. viridis complex spp. and hard corals were observed on a Caribbean reef over a year. Many hard corals were found bleached (tissue whitening due to the loss of Symbiodinium spp.) at elevated temperatures. However, C. viridis complex spp. appeared to be unaffected and remained dark brown at all times, indicating abundant Symbiodinium within the sponges. Our observations suggest a higher tolerance of some C. viridis complex spp. to bleaching compared to hard corals. This finding also implies a competitive advantage of these bioeroding sponges over hard corals during increasingly frequent and severe mass bleaching events under climate change, potentially leading to net reef erosion.