Environmental disturbances, such as bleaching events, can have lasting consequences for generations of corals – sciencedaily


Adult corals that survive high-intensity environmental stresses, such as bleaching events, may produce offspring better suited to survive 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’ understanding of how the gradual increase in sea surface temperatures and other environmental disturbances can influence future generations of corals.

Project researchers included BIOS marine ecologists Samantha de Putron and Gretchen Goodbody-Gringley (now with the Central Caribbean Marine Institute), ecophysiologist Hollie Putnam at the University of Rhode Island (URI), and Kevin Wong, then a student in first year of doctorate. to the URI. The main funding came from the Heising-Simons Foundation International, Ltd. with additional funding from the National Geographic Society and the Canadian Associates of BIOS (CABIOS).

The team spent the last year working the data into a manuscript, which was published this month in the journal Biology of global change and cited Wong as the first author. Wong, who is now nearing the end of his fourth year of study at URI under Putnam’s mentorship, plans to graduate in May 2022.

“We know that parental history influences the characteristics of coral offspring, but the experimental design used in this study offers us a unique perspective on how several types of thermal events can accumulate over time and have lasting consequences over several generations, ”said Wong.

Collection and study of corals

The multi-year field and laboratory study began in the summer of 2017. Starting from the BIOS on a small boat with diving equipment, the team collected 40 adults Porites astreoides (mustard hill) corals from two different reef sites in northwest Bermuda: a patch reef (Crescent Reef), which is located in a shallower lagoon environment, and an edge reef (Hog Reef) which is a barrier reef more exposed to open ocean conditions.

They then placed the live corals in the then-newly constructed BIOS mesocosm facility, where large “flow-through” seawater systems from outdoor aquariums allowed researchers to monitor and adjust the temperature of the sea. water in reservoirs to complete the study.

Various baseline data was collected on the corals of each colony, such as metabolic rates and density of Symbiodinaceae, the symbiotic algae that live in coral tissue. To simulate a heat stress event, adult corals were exposed to two different heat treatments – ambient (84 ° F or 29 ° C) or heated (88 ° F or 31 ° C) – for a period of 21 days during of their breeding season. Subsequently, the team assessed the physiology of adult corals, examining key functions such as respiration and rates of photosynthesis. They also monitored the release of coral larvae and assessed their physiology, measuring, among other factors, the size and density of Symbiodinaceae larvae within each larva.

At the end of the experiment, the adult corals were split in half and transplanted reciprocally, with half of the fragments positioned in the new environments and the other half returned to their original environments. All the fragments remained in place until the summer of 2018, when they were collected again, and the physiologies of adult corals and coral larvae were assessed in the same way as in 2017.

A stronger coral generation

The results of this two-year investigation showed that adult corals that underwent the heat stress event produced offspring more capable of thriving in their current environment. This means that parent corals that experience stressors may be able to “precondition” their offspring to survive in new environments the following year. The results also indicate that high-intensity environmental stress events, such as bleaching, can have lasting impacts on adult colonies and the way they produce their offspring.

“The coral used in this study is a notoriously hardy coral and these results potentially demonstrate just how persistent this species is in the Caribbean,” Putnam said. “Not all coral species are equally resistant to environmental stressors. However, this system allows us to unravel the mechanisms leading to resilience and identify the corals most sensitive to climate change.”

Long-time member of the BIOS community

Wong, 27, is a familiar face to BIOS, having first arrived on campus in the summer of 2014 as a CABIOS intern when he spent 12 weeks working with de Putron on a research project studying the role of temperature and light on growth and survival. juvenile mustard corals from two different reef areas. The following year he received funding from CABIOS to work with then faculty member Gretchen Goodbody-Gringley on a project focusing on the reproductive ecology of corals in mesophotic reef ecosystems, deeper water that generally extends from 100 to almost 500 feet (30 to 150 meters) in depth.

While presenting his research results at the 2016 International Coral Reef Symposium in Hawaii, he had the opportunity to interview Putnam for the URI Biological and Environmental Sciences PhD program. Wong then returned to BIOS to spend six months in 2016 as a teaching assistant for several summer and fall courses. He also received BIOS Grants-in-Aid funding for a research project with Goodbody-Gringley and Putron focused on the reproductive ecology of mustard hill corals from various reef sites around Bermuda, which resulted in to a publication in the journal Coral Reefs.

“It’s wonderful to see an undergraduate intern evolve into a successful graduate student who publishes manuscripts,” said de Putron. “Many years of hard work and many exhausting, but fun, days in the field and in the lab have all resulted in interesting and critically important discoveries that improve our understanding of coral resilience.”

Now, a year after graduation, Wong is digging deeper into the mechanisms that govern environmental memory within and between generations of corals at the molecular level. Using approaches such as metabolomics (the identification and quantification of metabolic byproducts), transcriptomics (quantification of gene expression) and epigenetics (characteristics that regulate gene expression), Wong aims to determine the key links between metabolism and coral bleaching phenotypes at a cellular level.

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