Environmental disturbances such as bleaching events can have lasting consequences across generations of corals
Adult corals that survive severe environmental stresses such as bleaching can produce offspring that are better suited to surviving in new environments. These results from a series of experiments conducted at the Bermuda Institute of Ocean Sciences (BIOS) in 2017 and 2018 deepen scientists’ knowledge of how gradual increases in sea surface temperatures and other environmental disturbances may affect future generations of corals.
Researchers on the project included BIOS marine ecologists Samantha de Putron and Gretchen Goodbody-Gringley (now at the Central Caribbean Marine Institute), ecophysiologist Hollie Putnam from the University of Rhode Island (URI), and Kevin Wong, then a first-year PhD student URI. Primary funding came from Heising-Simons Foundation International, Ltd. with additional funding from the National Geographic Society and the Canadian Associates of BIOS (CABIOS).
The team spent last year processing the data into a manuscript that was published in the journal this month Biology of global change and listed Wong as the lead author. Wong, now nearing the end of his fourth year at URI, led by Putnam, plans to graduate in May 2022.
“We know that parental history affects the properties of the offspring in corals, but the experimental design used in this study gives us a unique perspective on how multiple types of thermal events can accumulate over time and have lasting effects over generations “Said Wong.
Coral collection and study
The multi-year field and laboratory study began in the summer of 2017. Starting from BIOS on a small boat with diving equipment, the team gathered 40 adults Porites astreoides (Mustard Hill) corals from two different reef locations northwest of Bermuda: a patch reef (Crescent Reef), which is in a shallower lagoon environment, and a marginal reef (Hog Reef), a barrier reef that is more exposed to the conditions of the open ocean.
Next, they placed the living corals in the then newly built BIOS mesocosm facility, where large seawater systems for outdoor aquariums allowed researchers to control and adjust the water temperature in the tanks for the completion of the study.
Various basic data were collected on the corals in each colony, such as the metabolic rate and the density of Symbiodinaceae, the symbiotic algae that live in the coral tissue. To simulate a thermal stress event, the adult corals were exposed to two different temperature treatments – ambient temperature (84 ° F or 29 ° C) or heated (88 ° F or 31 ° C)) over a period of 21 days during their reproductive period. . The team then assessed the physiology of the adult corals and looked at key functions such as breathing and the rate of photosynthesis. They also monitored the release of coral larvae and assessed their physiology by, among other things, measuring the larval size and density of Symbiodinaceae within each larva.
Upon completion of the experiment, the adult corals were cut in half and transplanted into each other, with half of the fragments being positioned in the new environment and the other half being returned to their original environment. All fragments remained in place until the summer of 2018, when they were collected again and the physiology of both adult corals and coral larvae was assessed in the same way as in 2017.
A stronger generation of corals
The results of this two-year investigation showed that adult corals exposed to the thermal stress event produced offspring that were better able to thrive in their current environment. This means that stressed parent corals may “precondition” their offspring to survive in new environments for the following year. The results also suggest that high-intensity environmental stress events such as bleaching can have lasting effects on adult colonies and the way they produce their offspring.
“The coral used in this study is a notoriously resilient coral and these results may show how persistent this species is throughout the Caribbean,” Putnam said. “Not all coral species are so robust against environmental stressors. However, this system enables us to decipher the mechanisms that lead to resilience and identify which corals are most sensitive to climate change. “
Longstanding member of the BIOS community
Wong, 27, is a familiar face at BIOS. He first arrived on campus as a CABIOS intern in the summer of 2014 when he worked with de Putron for 12 weeks on a research project examining the role of temperature and light on the growth and survival of young mustard hill corals from two different reef zones. The following year he received CABIOS funding to work with then faculty member Gretchen Goodbody-Gringley on a project that focused on the reproductive ecology of corals from mesophotic reef ecosystems, deeper reefs typically stretching from 30 to 500 feet 150 meters ) into the deep.
While presenting the results of his research at the 2016 International Coral Reef Symposium in Hawaii, he had the opportunity to speak with Putnam for URI’s PhD program in Life and Environmental Sciences. Wong then returned to BIOS to work for six months as a teaching assistant on several summer and fall courses in 2016. He also received BIOS Grants-in-Aid funding for a research project with Goodbody-Gringley and de Putron that focused on the reproductive ecology of mustard hill corals from various reef sites around Bermuda, which resulted in a publication in Coral Reefs magazine.
“It’s wonderful to see an intern grow into a successful PhD student publishing manuscripts,” said de Putron. “Many years of hard work and many strenuous but entertaining days in the field and in the laboratory culminated in interesting and critically relevant discoveries that further our understanding of the resilience of corals.”
Now, a year after graduation, Wong is delving deeper into the mechanisms that drive environmental memory within and between generations of corals at the molecular level. Using approaches such as metabolomics (identification and quantification of metabolic by-products), transcriptomics (quantification of gene expression), and epigenetics (traits that regulate gene expression), Wong aims to elucidate the key relationships between metabolism and coral bleaching phenotypes on a cellular level.
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