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A Looming Threat in The Great Barrier Reef: Coral Bleaching

Hi all! Gabby here again. This fall, I’m taking a community college course on environmental science at De Anza. Every week I learn something new, so I decided to write up something that caught my eye—coral bleaching. This is a topic barely talked about and needs more attention, so I hope you all find this eye-opening!

Known as one of the seven wonders of the world, the Great Barrier Reef is home to over 9,000 known species. Despite stretching over 1,429 miles along Australia’s coast, the Great Barrier Reef suffers from a serious ongoing issue: coral bleaching. Coral bleaching is a stress response under which corals expel the symbiotic zooxanthellae living within their tissues, algae that removes waste and utilizes it to produce food with photosynthesis. Zooxanthealle is the source of the corals’ bright color; without this source of food and color, corals are left with their white skeletons after starvation (Great Barrier Reef Foundation). The primary cause of coral bleaching is the increase in marine heat waves and UV radiation from climate change–even a one degree Celsius increase can initiate this. Bleached corals can recover from this stress, but the frequency of these events cause the natural recovery proces unable to keep up. The changes in water quality from rising temperatures have caused mass coral bleaching in 2016, 2017, and 2020, resulting in over half of the corals dying (Sommer). This unfolding crisis not only impacts the abundant sea life, but also local communities that rely on the reef for living via tourism and fishing. Coral bleaching is one of the many examples of climate change’s effects, emphasizing the connection between human actions and the planet’s health. This threat calls for increased global focus to preserve the Great Barrier Reef and the myriad of ecosystems and species within.

Currently, there is new research in something called assisted evolution that has potential to be a solution for coral bleaching. This involves scientists engineering heat-tolerant variants in corals for them to be resistant to the rising sea temperatures. In depth, coral samples are collected and are exposed to heat stress in laboratory environments that allow the identification of genes activated to stress. The heat-tolerant genes are identified and are selected to be in newly grown corals; these selected corals are then transplanted back into the reef. Although this mechanism needs more research, it could increase coral population size with the resistant coral genotypes among the species and accelerate coral adaptation to climate change. This strategy was experimented in 2022 through a simulation that modeled corals’ performance under increasing climate conditions with this genetic variance. DeFilippo, McManus, and others found from their experiment that in scenarios without any supplement in the reef, genetic diversity contributed the most to the corals’ resilience to the marine heat waves. The study highlighted how supplementation was the most beneficial when genetic variation was low; given these two conclusions, balancing and combining both supplementation and heat-tolerant corals can provide the most improvement in coral restoration. Corals also recover over time, so moderate levels of both factors will be highly effective (DeFilippo et al.). Another study was done at the Palau International Coral Reef Center that supported the incorporation of restoration techniques in assisted evolution methods; Humanes, Beauchamp, and others involved in the study specifically observed coral larval propagation (CLP) for effectiveness. CLP is a method that produces high numbers of corals; the experimental process began with a parent colony selection, CLP, collection of gametes for CLP, larval hatching, settling onto growing substrate colonies, and lastly coral outplant to the reef and monitoring growth. This technique resulted in a success since larvae seeded onto substrates, improving the overall coral reef survival rates (Humanes et al.). With this conclusion, a reliable and well-researched plan to rehabilitate the bleached coral in the Great Barrier Reef would be assisted evolution balanced with a supplement of coral larval propagation!


“Coral Bleaching.” Great Barrier Reef Foundation, reef/threats/coral-bleaching.

DeFilippo, Lukas B., et al. “Assessing the Potential for Demographic Restoration and Assisted Evolution to Build Climate Resilience in Coral Reefs.” Ecological Society of America, The Nature Conservancy; Gordon and Betty Moore Foundation, 10 May 2022,

Humanes, Adriana, et al. “An Experimental Framework for Selectively Breeding Corals for Assisted Evolution.” Frontiers, Frontiers Marine Science, 4 May 2021,

Sommer, Lauren. “Australia’s Great Barrier Reef Is Hit with Mass Coral Bleaching yet Again.” NPR, NPR, 26 Mar. 2022,

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