Abstract
Polyp bailout is an established but understudied coral stress response that involves the detachment of individual polyps from the colonial form as a means of escaping unfavourable conditions. This may influence both the mortality and asexual recruitment of coral genotypes across a range of species. It has been observed in response to numerous stressors including high salinity and low pH. Polyp expulsion in association with thermal stress has once been described in a geographically restricted, temperate species. We therefore cannot reliably apply this observation to tropical coral reefs around the world, which are increasingly under threat from thermal stress events. We present the first qualitative observation of polyp bailout following acute temperature shock in a near-natural mesocosm experiment. Detached polyps show similar characteristics to those described in previous studies, including the retention of endosymbiotic zooxanthellae and the ability to disperse across short distances. This finding strongly suggests that polyp bailout occurs in tropical coral reef environments and warrants further detailed research into the implication of this response in terms of individual survival, rapid migration into cooler micro-habitats and local recruitment within the reef environment and its coral community.
Highlights
Coral reefs around the world are facing increasingly frequent acute thermal stress events (Ainsworth et al, 2016; Hughes et al, 2017)
Polyp bailout has been observed in at least six species of tropical scleractinian coral (Serrano et al, 2017) and involves the withdrawal of individual polyps from the coenosarc followed by their detachment from the skeleton (Sammarco, 1982)
Despite increasing temperatures being arguably the most significant threat to tropical coral reefs (Hughes et al, 2017), no tropical species have been observed to respond to thermal stress in this way
Summary
Coral reefs around the world are facing increasingly frequent acute thermal stress events (Ainsworth et al, 2016; Hughes et al, 2017). Polyp bailout has been observed in at least six species of tropical scleractinian coral (Serrano et al, 2017) and involves the withdrawal of individual polyps from the coenosarc followed by their detachment from the skeleton (Sammarco, 1982).
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