The history, biological relevance, and potential applications for polyp bailout in corals

Abstract

Corals have evolved a variety of stress responses to changing conditions, many of which have been the subject of scientific research. However, polyp bailout has not received widespread scientific attention, despite being described more than 80 years ago. Polyp bailout is a drastic response to acute stress in which coral colonies break down, with individual and patches of polyps detaching from the colony and the calcareous skeleton Polyps retain their symbiotic partners, have dispersal ability, and may undergo secondary settlement and calcification. Polyp bailout has been described worldwide in a variety of anthozoan species, especially in Scleractinia. It can be induced by multiple natural stressors, but also artificially. Little is known about the evolutionary and ecological potential and consequences of breaking down modularity, the dispersal ability, and reattachment of polyps resulting from polyp bailout. It has been shown that polyp bailout can be used as a model system, with promise for implementation in various research topics. To date, there has been no compilation of knowledge on polyp bailout, which prompted us to review this interesting stress response and provide a basis to discuss research topics and priorities for the future.

Coral recruits are highly sensitive to heavy fuel oil exposure both in the presence and absence of UV light

“…In the present study, none of the bailed-out polyps that were transferred to uncontaminated FSW reattached. There is evidence that coenosarc apoptosis and the separation of soft tissues from the skeleton may represent key steps in successful polyp bail-out for reef-building corals (Schweinsberg et al, 2021). This, combined with the observations of the present study, raises the question as to whether some of the previously reported polyp retraction, tissue swelling, lesions, tissue rupture and rapid tissue loss in adult corals exposed to oil pollutants (e.g.…”

“…This 'reverse metamorphosis', where stressed polyps revert to a planktonic state is proposed as a survival or risk-spreading strategy. However, the reattachment rate appears to generally be low (Schweinsberg et al, 2021).…”

“…Polyp bail-out is a stress response where coral recruits reverse initial metamorphosis, or adult polyps detach from the colony, and leave the skeleton due to adverse environmental conditions (Negri et al, 2005;Sammarco, 1982;Schweinsberg et al, 2021). During exposure, polyp bail-out was observed on 7 different occasions in the low-to mid-range treatment concentrations (2.8-45.8 μg TAH L -1 ; Fig.…”

“…Polyp bail-out was observed in 1.4% of 1-wo recruits during exposure to HFO WAF containing 2.8-45.8 μg TAH L -1 , but not for any of the 2-mo recruits. Polyp bail-out is a recognised stress response to detrimental environmental conditions and has been observed in recently settled recruits and established adult colonies across several anthozoan groupings (as reviewed by Schweinsberg et al (2021)). This 'reverse metamorphosis', where stressed polyps revert to a planktonic state is proposed as a survival or risk-spreading strategy.…”

Inducing Polyp Bail-out in Coral Colonies to Obtain Individualized Micropropagates for Laboratory Experimental Use

“…These include investigating different aspects associated with the coral holobiont physiology 44 and host-microbiome interactions 45 , the molecular mechanisms involved in coral bleaching 5 , 25 , and the health, resilience, and protection of the coral holobiont 12 , 13 , 46 , 47 . Moreover, released coral polyps can be used for applications outside the realm of research and have been suggested to be useful for creating propagules that can attach to a substrate and grow, potentially creating multiple coral individuals that can be used for restoration purposes once standardized protocols for bailout become widespread 28 . Overall, although more in-depth experiments using bailed-out polyps should be performed to standardize the methodology, it has been shown that polyp bail-out is a reproducible approach that can be applied as a tool in coral research for several purposes.…”