Abstract
Polyp bailout is an established but understudied coral stress response that involves the detachment of individual polyps from the colonial form as means of escaping unfavourable conditions. This may influence both the mortality and asexual recruitment of coral genotypes across a range of species. It was first described by Goreau & Goreau (1959) and has been observed in response to numerous stressors including high salinity and low pH. However, polyp bailout has not previously been described in association with thermal stress and the coral bleaching response, which is becoming increasingly common around the world. We present the first qualitative observation of polyp bailout following thermal stress in a 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. As the frequency of thermal stress increases globally, we suggest further detailed research into the prevalence of this response in situ and its implications for the survival of individual corals, as well as the potential for migration into cooler micro-habitats within the coral reef environment.
Highlights
Coral reefs around the world are facing increasingly frequent acute thermal stress events (Ainsworth et al, 2016; Hughes et al, 2017)
Implications and future research In past observations of polyp bailout, corals have been subjected to extreme aquarium conditions such as high salinity, low pH (7.2; Kvitt et al, 2015) or little to no water replacement resulting in anoxic and low nutrient conditions (Serrano et al, 2017; Sin et al, 2012)
The peak daily temperature of 34°C was sustained over several days, reflecting severe thermal stress
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 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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