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The Depths of the Ocean: Coral Reef Restoration

By: Anushya Nedunuri

Photo by Francesco Ungaro on Pexels

Did you know that the Great Barrier Reef is the largest living coral reef on the planet? Coral reefs are one of the most diverse ecosystems in the world and support around a quarter of the earth’s marine species. They are essential to the biological balance of our oceans, protect our shorelines, and serve as a home for many marine organisms. Coral reef structures form when coral organisms, also known as polyps, attach to substrate and secrete calcium carbonate skeletons. Coral reefs are natural ecosystems; they can degrade over time, and recover by regrowing on their own. Unfortunately, corals face increasing pressure as environmental conditions worsen due to climate change. 30 to 50% of coral reefs are already lost in the world. Reef ecosystems are increasingly struggling to repair themselves in response to environmental stressors.

Many environmental factors affect the health of coral reefs in our oceans. Most corals have a symbiotic relationship with plant-like organisms known as Zooxanthellae algae. Zooxanthellae algae live within coral tissue and benefit by making use of the coral's metabolic waste products and calcium carbonate structure protection. In return, the algae produce food for the corals through a process known as photosynthesis.

There are several ways in which changes in the ocean's physical, chemical, and biological characteristics affect the health of coral reefs. Climate change is causing an increase in ocean temperatures, leading to coral bleaching. The bleaching process occurs when the polyps expel their zooxanthellae algae in response to stress, causing the corals to lose color. Ocean acidification comes with rising ocean temperatures, causing the calcium carbonate structures secreted by corals to dissolve. Additionally, the rise in CO2 and decline in pH leads to reduced calcification rates. Invasive species may contribute to declining reefs by outcompeting native species, reducing biodiversity, and causing habitat loss. Sedimentation may also contribute to the damage of coral reefs. Prolonged sediment exposure through erosion can lead to the accumulation of sediments on corals and smothering, which may inhibit growth and lead to mortality. Sedimentation also causes turbidity, which inhibits light, a necessity for coral growth. Eutrophication, which also limits light, occurs when there is an excessive amount of nutrients in the ecosystem. In most cases, nitrogen and phosphorus are the nutrients in excess, which cause anoxic conditions (areas depleted of oxygen) and stimulate algal growth.

Human activity also plays a part in ongoing coral reef damage. The overexploitation of fisheries has led to the loss of important fish species and an increase in the dominance of macroalgae (seaweed). Pesticides and fertilizers used in farming sometimes make it into the ocean. Chemicals in these substances may become trapped in the water as pollutants threatening reef ecosystems. Oil spills and microplastics are harmful pollutants that alter coral behavior, growth, and reproduction. Mangroves are also affected by human-induced environmental problems. Mangroves help ensure that coral reef ecosystems stay healthy because they remove pollutants, help stabilize water quality, and provide food and shelter for organisms within the reef community.

Coral reefs provide many irreplaceable ecosystem services and play a major role in the health of the ocean. Coral reefs have generated about $10 trillion a year globally and more than $3 billion a year domestically to our economy. A significant amount of the income from coral reefs comes from tourism, recreation, and fisheries that depend on these ecosystems. Coral reefs also protect coastlines, properties, and businesses from storm events. Not only are coral reefs beneficial for us, but they also are the foundation of food chains in the ocean, providing stability to other marine species.

There are so many threats that corals are facing, making coral restoration more crucial than ever. Recovering and restoring coral reefs is done through many methods, each one unique. The National Oceanic and Atmospheric Administration (NOAA) has created a Coral Reef Conservation Program, with a strategic plan highlighting four main strategies to lead the agency's efforts:

  • Improving habitat quality for corals

  • Preventing the loss of corals and their habitat

  • Enhancing coral population resilience

  • Improving coral health and survival

NOAA scientists use multiple forms of coral restoration to implement these strategies. To help foster the growth of detached corals found in the environment, NOAA operates over 20 active nurseries throughout the Caribbean. Once grown, coral pieces are attached to existing reefs. NOAA has also removed harmful invasive species from reefs in Florida, Puerto Rico, and Hawaii. Increasing coral resilience is also essential to coral restoration by determining a community's ability to recover from environmental disturbances. A method to increase coral resilience is through the introduction of heat-tolerant species.

What we do matters. We can do a lot to help save our coral reefs. Pollution and climate change are two of the most significant threats that coral reefs face, and as humans, we can do our part to mitigate these consequences. If you are looking for places to start, consider recycling, limiting the use of fertilizers, educating the public, snorkeling responsibly, practicing sustainable seafood consumption, and using reef-safe sunscreen. You can continue making a significant impact by advocating for the regulation of fishing and shipping industries and ensuring local and coastal communities are doing their part.


Works Cited

El-Naggar, H. A. (2020). Human Impacts on Coral Reef Ecosystem. In IntechOpen.

Great Barrier Reef Foundation. (2023, February 20). What is reef restoration?. Great Barrier Reef Foundation.

Hoegh-Guldberg, O., Pendleton, L., & Kaup, A. (2019). People and the changing nature of coral reefs. Regional Studies in Marine Science, 30(30), 100699.

National Geographic Society. (n.d.). Coral reefs. Education.

NOAA Fisheries. (2021, September 27). Restoring coral reefs.

Rogers CS and Ramos-Scharrón CE (2022) Assessing Effects of Sediment Delivery to Coral Reefs: A Caribbean Watershed Perspective. Front. Mar. Sci. 8:773968. doi: 10.3389/fmars.2021.773968


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