Reach Out to Bleached Reefs

Grace Huang and Anjali Pagidi Thomas Jefferson High School for Science and Technology

Imagine yourself deep sea diving. You’re immersed in an amazing underwater world full of wildlife and vibrant, colorful corals. Now imagine that same world, completely devoid of color and scattered with white coral skeletons. Unfortunately, if we don’t manage the progression of global warming and take care of our aquatic environments, the second world could be our future.

Coral reefs can lose their color through a process called coral bleaching, which occurs when corals expel the symbiotic algae (zooxanthellae) that live within their tissues [6]. Coral bleaching occurs when corals are placed under stressful conditions such as sharp changes in ocean temperature, runoff and pollution, overexposure to sunlight, and extreme low tides. For example, a massive bleaching event that took place in 2005 caused the U.S. to lose over half of its corals in the Caribbean. The warm waters that flow near Puerto Rico and the Virgin Islands expanded southward, resulting in more thermal stress than in the past 20 years combined. Conversely, another bleaching event that took place in Florida in 2010 was actually caused by cold temperatures; the water temperature dropped 12.06 ℉ below normal [6]. The notable increase in frequency of coral bleaching events has led scientists to investigate their effect on the environment.

Why does coral bleaching matter? Corals not only affect our tropical vacations, but also play a vital role in their ecosystem. They support about a third of marine life, which is more species per unit area than any other marine ecosystem [2]. They aid other organisms by providing them with habitats and essential nutrients [8]. Additionally, corals benefit their environment by converting carbon and nitrogen from a less usable to a more usable form for other organisms, a crucial part of the nutrient-recycling process known as carbon and nitrogen fixation. Finally, they protect coastlines from tropical storms and waves and give us information about the state of the climate [8].

The aftermath of a bleaching event can severely impact the corals’ habitat. When corals bleach, they suffer several hardships such as elevated mortality rates, a reduced ability to reproduce, an increased susceptibility to diseases, and a slower growth rate [9]. This negatively impacts the fish and invertebrates that depend on corals for food or shelter and decreases the number of species and genetic diversity. A study conducted in Papua New Guinea revealed that a decline in coral communities was followed by a decline in fish communities; similar patterns were observed in Tanzania, the Seychelles, and the Great Barrier Reef. The study also showed that juvenile fish are more likely to reside in areas with high coral concentration [9].

A mass bleaching event not only harms the underwater ecosystem, but also undermines the local economy. Over 100 million people around the world depend on coral reefs for survival [9]. When corals lose their color, reef tourism loses some of its appeal, which affects the livelihood of nearby communities. The loss of coral may affect fish communities, causing difficulties in the fishing industry. Furthermore, some coral reefs provide pharmaceuticals, which would also be lost after bleaching. Moderate degradation of reefs can cost around 20 billion dollars while severe degradation can cost around 84 billion dollars. Tourism can face 10 to 40 billion dollar losses, and the fishing industry can face 7 to 23 billion dollar losses [9].

The extensive costs of coral bleaching soon caught the attention of researchers, so they began to analyze the recent history of bleaching events. The Great Barrier Reef is currently undergoing one of the most widespread coral bleaching events ever recorded [7]. Out of its 1,036 reefs, 25% were severely affected. In total, 60% of reefs experienced some type of bleaching. Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University in Townsville, said, “This is the second most severe event we have seen, but it is by far the most widespread.” The first large bleaching that occurred in the Great Barrier Reef was in 1988, followed by another in 2002. Recently, there have been episodes in 2016, 2017, and 2020. With less gaps between the events, scientists are concerned about how the reefs will recover in so little time [7].

Many corals have a difficult time surviving after bleaching. However, some corals are able to regain their vivacious hues [11]. Elena Bollati, a marine biologist at the National University of Singapore, reported that certain wavelengths of light can trigger a coral’s pigment production. This acts like a sunscreen, which protects the returning algae. Daniel Wangpraseurt, a coral reef scientist at the University of Cambridge, stated that the research “shows that some of these corals are trying to protect themselves with really spectacular side effects.” To demonstrate these effects, scientists simulated a bleaching event by slowly increasing the temperature. As the heat increased, the amount of algae in the corals decreased. Surprisingly, a few weeks afterwards, they observed an increase in the production of a fluorescent compound that gives corals their color. Corals usually rely on its algae’s pigments to absorb some sunlight. The scientists found that a decrease in algae allowed the corals to absorb more blue light from the sun. The reflection of these blue wavelengths caused the algae to pump out more protective pigments. In this manner, corals can help themselves recover from bleaching [11].

As people’s actions have been negatively affecting our environment, the frequency of bleaching events has increased rapidly. Although some corals have the ability to recover from bleaching, most others struggle to recover in time before the next wave of bleaching events. To assist these corals in their battle against bleaching, marine biologists have been implementing coral transplants [10]. The authorities managing the coral reefs in the Great Barrier Reef have traditionally refused to interfere with coral growth. However, two back-to-back marine heat waves in 2016 and 2017 caused mass bleaching events that killed almost a third of the corals, forcing the managers to intervene to save these reefs. A team of researchers in the Future Reefs Program at the University of Technology Sydney contributed to the rescue by choosing a wide variety of corals that survived the bleaching event and artificially growing them on mesh platforms in a sandy lagoon adjacent to the reef. After the corals grew and stabilized, they transplanted them back onto the reefs using a clip that allows quick and convenient attachment between corals. This traditional transplant method can help expand the coral population after a high-mortality bleaching event. However, since the growth and stabilization of coral fragments take a few months to complete, researchers still wish to test novel methods to fight coral bleaching [10].

Following the footsteps of early marine biologists, a group of researchers in Australia explored whether reintroducing heat-evolved microalgal symbionts into corals could increase their bleaching tolerance [1]. These researchers spent four years exposing ten microalgal symbiont strains to elevated temperatures (31℃) in the laboratory. After four years, all ten strains exhibited improved heat tolerance in comparison to two wild-type strains, as the heat-evolved strains experienced a 66% increase in cell densities in response to a three-week testing exposure to elevated temperatures while the wild-type strains suffered a 79% decrease. The researchers hypothesized that reintroducing these heat-tolerant algal strains into coral larvae would also improve the corals’ heat tolerance, therefore improving their bleaching tolerance. When they tested their hypothesis under similar conditions (prolonged heat exposure), they found that three of the ten lab strains had a 26% cell density increase on average, but all other lab and wild-type strains experienced a decrease. In addition to maintaining growth, these three strains also preserved their photosynthesis capacity, which further indicates the researchers’ success. Although this novel method efficiently enhances the coral’s heat and bleaching tolerance by evolving their microalgal symbionts, the research team expressed concerns about whether the corals will be able to maintain their ability to fight high heat and effectively battle the increasing frequency of bleaching events [1].

This issue is not only relevant to the global scientific community, but also concerns politicians and citizens. The Environmental Protection Agency (EPA) has imposed several regulations and acts to help protect coral reefs. For example, the Clean Water Act ensures a reduction in the amount of pollution that enters the water from land [4], which helps preserve the health of coastal waters and the reefs that reside there. To do this, the EPA provides funding to monitor coastal health and water quality improvement programs. They also work with the U.S. Army Corps of Engineers to minimize the impacts of pollution. The U.S. Coral Reef Task Force develops tools to aid and monitor reefs and their environments. One such tool was the Corals and Climate Adaptation Design Tool, which is used to include climate-smart designs into programs and projects. Finally, the International Coral Reef Initiative, an organization involving several nations, works as a global effort to support the conservation, protection, and research of reefs and related ecosystems [4].

While there are government regulations in place to protect coral reefs, there are things you can do to help too. Be a safe snorkeler and diver [3]. Make sure not to touch coral reefs or anchor your boat on the reef. Try to find a sandy moor when anchoring. Use sunscreen with coral-friendly ingredients or wear long sleeves instead. In general, you can practice good habits that limit the waste and ocean pollution you create when diving [3].

While many people are working on protecting coral reefs from mass bleaching events, other researchers strive to warn people of the severity of the issue by creating models to predict the future of coral reefs. According to their model, unless humans can control the average global warming rate to be under 1.5 ℃, the corals will face severe damages [5]. In the more likely occasion that humans put in very limited effort to control greenhouse gas emissions, the model predicts that approximately 50% of the world’s corals will suffer annual bleaching in 2040. Even worse, this percentage approaches a tragic 99% by 2100 if we keep ignoring this environmental issue. These researchers hope that by slowing the rate of greenhouse gas emissions and therefore delaying global warming, corals will gain more time to gradually adapt to bleaching events [5].

Coral reefs not only paint the underwater world with rainbow-like colors, but play a key role in demonstrating a classic mutualistic relationship with their algal symbionts. However, over the past decades, global warming has caused mass bleaching events, killing these vital algae, ridding corals of their beautiful colors, and continuously weakening these corals. Although some corals “have this capacity to fight back”, as marine biologists said, they also warned us how crucial people’s actions to control global warming is to the long-term survival of corals around the world [11]. If we do not take the appropriate actions, at some point, corals will reach their tolerance capacity and suffer catastrophic deaths, permanently losing their ability to fight back. Please do not realize the value of corals after we lose them. The earlier we act, the less we will regret in the future.

References

[1] Buerger, P., Alvarez-Roa, C., Coppin, C. W., Pearce, S. L., Chakravarti, L. J., Oakeshott, J.G., Edwards, O. R., & van Oppen, M. (2020). Heat-evolved microalgal symbionts increase coral bleaching tolerance. Science Advances, 6(20). https://doi.org/10.1126/sciadv.aba2498

[2] Climate Foundation. (n.d.). Reversing coral bleaching. https://www.climatefoundation.org/reversing-coral-bleaching.html

[3] Environmental Protection Agency. (2018, September 26). What you can do to help protect coral reefs. https://www.epa.gov/coral-reefs/what-you-can-do-help-protect-coral-reefs

[4] Environmental Protection Agency. (n.d.). What EPA is doing to protect coral reefs. https://www.epa.gov/coral-reefs/what-epa-doing-protect-coral-reefs

[5] Heron, S. F., & Eakin, M. C. (2020, February). Coral bleaching. Access Science. https://www.accessscience.com/content/coral-bleaching/161530

[6] NOAA. (2020, January 7). What is coral bleaching? https://oceanservice.noaa.gov/facts/coral_bleach.html

[7] Pickrell, J. (2020, April 7). The Great Barrier Reef is suffering its most widespread bleaching ever recorded. https://www.sciencenews.org/article/great-barrier-reef-suffering-most-widespread-bleaching-ever-recorded

[8] Queensland Museum. (n.d.). Importance of coral reefs. https://www.qm.qld.gov.au/microsites/biodiscovery/05human-impact/importance-of-coral-reefs.html

[9] Reef Resilience Network. (n.d.). Bleaching impacts. https://reefresilience.org/stressors/bleaching/bleaching-impacts/

[10] Warne, K. (2018, November 29). Can new science save dying coral reefs? https://www.nationalgeographic.com/environment/2018/11/great-barrier-reef-restoration-transplanting-corals/

[11] Wilke, C. (2020, May 29). Neon colors may help some corals stage a comeback from bleaching. https://www.sciencenews.org/article/corals-algae-neon-colors-bleaching-recovery-oceans