Note: this article is an abridgement of a full (open source) research article by Keri L. O’Neil, Rachel M. Serafin, Joshua T. Patterson, and Jamie R. K. Craggs.

Global and local anthropogenic impacts have led to severe declines in the abundance of coral species worldwide. If stressors such as high water temperatures and increased acidification due to climate change are not improved, declines are predicted to continue. In Florida, United States, coral reefs have undergone a consistent loss of live coral cover over the past four decades that can be attributed to repeated thermal events, land-based pollution, sedimentation, and disease outbreaks. A recent devastating disease outbreak, termed stony coral tissue loss disease (SCTLD) originated in southeast Florida and has spread to the Florida Keys and other areas in the Caribbean. SCTLD has affected at least 24 coral species and resulted in very high levels of mortality between initial onset in 2014 and the present.

The family Meandrinidae consists of four extant coral genera limited to the Atlantic Ocean and Caribbean. Corals in this family are considered highly susceptible to SCTLD and “are the first to become affected at a site” according to the case definition for the disease and studies on the spatial progression of the disease. Maze coral Meandrina meandrites and Atlantic pillar coral Dendrogyra cylindrus are both particularly susceptible and populations of these species have been severely affected.

In the face of ongoing threats from climate change, and in direct response to the precipitous declines observed following the SCTLD outbreak, multi-agency, and -institution partnerships in Florida have executed coral “rescue” projects and placed extracted colonies into ex situ holding facilities. The immediate objective of these efforts was to protect susceptible species from exposure to the disease, and in the case of D. cylindrus, to treat and stabilize actively infected individuals. Coral rescue goals were to preserve genetic diversity in the Florida population before it was lost to SCTLD and to establish land-based gene banks for future repopulation efforts through translocation of fragments or sexually produced offspring from ex situ facilities to in situ coral nurseries or directly onto reefs.

This study aimed to address these challenges and build upon novel technologies by inducing gametogenesis and synchronized broadcast spawning in two coral species in the family Meandrinidae, whose populations in Florida and elsewhere have been severely impacted by SCTLD. This work represents the first successful induced gametogenesis and spawning of Atlantic coral species in land-based systems. Corals used were removed from the ocean as part of SCTLD rescue work and thus this research represents an opportunistic augmentation of genetic preservation efforts rather than an extractive exercise conducted solely for the purposes of experimentation. Repeated and predictable sexual reproduction in coral colonies held long-term ex situ under fully controlled conditions represents the first step toward a managed breeding program for threatened species that will be able to produce genetically diverse offspring for future population restoration under improved environmental conditions.

Over two consecutive years we documented synchronized ex situ broadcast spawning in two highly SCTLD susceptible coral species in the family Meandrinidae. This work represents an opportunistic study on corals removed from the reef to preserve the diversity of the local population before it was lost to the disease. Here we have shown that at-risk corals can be protected ex situ, gametogenesis and spawning can be maintained using entirely artificial cues, and ex situ spawning occurs at similar times to wild observations. We also present novel information on the spawning time of M. meandrites, and the first documentation of hermaphroditism in this species. Although we do not yet know when it will be safe to return highly disease-susceptible species to the reef post-SCTLD, nor the best methods for incorporating these offspring into the surviving populations, the methods presented here will serve to produce larvae and sexual recruits for further research into these questions for years to come.

This study made numerous modifications to the methods of Craggs et al. (2017), most notably the lack of trace element dosing, less heterotrophic feeding, and a modified means of replicating annual solar irradiance cycles. However, spawning occurred in all aquaria with only relatively minor variations in gamete release time. This indicates that the general method of inducing gametogenesis and spawning is tractable under minor modifications and that these techniques can be successful when all methods and procedures are not replicated with precision. The method was originally developed to induce spawning in Indo-Pacific coral species, but has here proven viable for western Atlantic species when programmed with appropriate local data. In addition to the species in this study, the authors have successfully spawned three additional species of western Atlantic stony corals in the same systems, suggesting that this method can be successful with a wide range of species and life histories.

The full article, as well as a link to the supplementary material that has most of the programming info, can be found HERE

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