Ocean warming and coral survival

Researchers find that aspects of climate change events can lead to more resilient coral offspring, able to acclimate to new environmental factors

KINGSTON, R.I. — June 24, 2021 — A two-year research project involving University of Rhode Island scientists demonstrated that offspring, coming from adult corals that had survived high-intensity environmental stresses such as bleaching events, are better suited to survive in new environments.

This means that parent corals that experience sub-lethal heat stressors may be able to “pre-condition” their offspring to survive in new environments in the following year.

Adult Porites astreoides colonies in the laboratory at BIOS where photosynthetic and respiration rates were measured.

The findings were published in the journal, Global Change Biology, with URI doctoral student Kevin Wong serving as first author. The team also included URI doctoral student Danielle Becker, URI Associate Professor Hollie Putnam and colleagues from Bermuda.  The article sheds some important light on how corals may respond to heat events, including both gradual surface temperature increases and more extreme, acute heat events. The team conducted its research at coral reef sites near Bermuda.

Such findings are important since coral reefs are the backbone of marine ecosystems. They serve a number of vitally important purposes including providing a complex habitat for fish, and also protecting shorelines from erosion. The impact that the health of coral systems has on local and global economies, whether relating to the fishing or tourism industries, is extremely significant.

Coral research, including that conducted by URI researchers, has been spurred on, in recent years, by climate change and, specifically, increased ocean surface temperatures, which could threaten the future viability of coral reefs.

This recent research project deepens scientists’ understanding of how long- and short-term parental environmental history can shape offspring characteristics, potentially leading to increased resiliency.  It was the first research project of its kind to apply longer term and shorter term thermal stress in multiple sequences to determine which type of stressor affected the corals the most. Through a complex and unique experimental design, the researchers suggest that  sub-lethal stressors could actually be beneficial to future coral offspring.

Putnam noted, “The coral used in this study is a notoriously resilient coral and these findings potentially demonstrate how this species is so persistent across the Caribbean.  Not all coral species are this robust to environmental stressors. This design of this experiment allowed us to unravel the mechanisms leading to coral acclimatization and resilience.”

The multi-year field and lab-based study, conducted by Wong, Becker, Putnam, and Bermuda Institute of Ocean Sciences marine ecologists Samantha de Putron and Gretchen Goodbody-Gringley and Alex Chequer, began in 2017 and involved collecting adult colonies of the notoriously resilient coral species, Porites astreoides, from two reef sites northwest of Bermuda. The two sites differ largely in environmental conditions, as Crescent Reef is a shallower lagoon environment, while, Hog Reef, is a barrier reef and more exposed to open ocean conditions.

Live corals were transplanted to a newly constructed mesocosm facility at the Bermuda institute, which was built with funds from Heising-Simons Foundation International, Ltd. The facility allowed researchers to control and adjust water temperatures in the tanks for the study. After collecting baseline data, “pulse” thermal stress events were simulated for 21 days over the coral’s reproductive period. Adult corals were halved and reciprocally transplanted to both reef sites. This means that half of the adult colony went to a new site, and the other half went to its originating site. The corals were collected again in the summer of 2018 so researchers could compare the physiologies of the adult coral and their offspring to their findings from the previous year.

The unique design of the experiment allowed the researchers to understand how the combinations of different thermal disturbances impact how adult corals function and their reproductive characteristics over prolonged time periods. This question is critical, as identifying the types of thermal events that impact corals the most (i.e. gradual sea surface temperature increase or marine heat waves) could aid in management decisions and improve the future of coral reefs.

The study showed that although adult corals were able to recover from the pulse thermal event one year later, this intense sub-lethal event altered their offspring, suggesting lasting carryover effects of this specific event one year later. This has important implications on how corals could rapidly respond to thermal stress events and prepare the next generation of corals for adverse conditions. 

“We know parental history influences the characteristics of offspring in corals, however, the experimental design used in this study provides us with a unique perspective on how multiple types of thermal events can accumulate over time and have lasting consequences across generations,” said Wong.

The abstract for the paper published in Global Change Biologycan be found here. This research study was supported by the Heising- Simons Foundation International Ltd., Bermuda Institute of Ocean Sciences (BIOS) Grant-In-Aid, Canadian Associates of BIOS Scholarship, BIOS University Programs Department, and a National Geographic Young Explorers grant.