Saving Coral Reefs

Although coral reefs cover an extremely small amount of the Earth’s surface, less than 1 percent, they support 25 percent of all marine life. People worldwide rely on coral reefs for food resources, protection from the damaging properties of waves, and economic benefits including recreation and tourism. Coral reefs also act like the proverbial canary in the cold-mine when it comes to insight into the health of the ocean. Coral reefs are negatively impacted by changes in water chemistry (e.g., ocean acidification) and increases in water temperature and sediment levels. Because heatwaves are becoming increasingly frequent across the globe and ocean temperatures are rising, it is important to understand how reefs are impacted and promote their survival.

What is coral?

There are many types of coral. There are soft corals, deep water corals that live in cold waters far below the surface, and probably the more iconic hard structure, colorful formations found in warm tropical ocean water. Most all corals can be described as colonial. This means that what  appears to be a single structure is actually made up of many individuals. But there is one universal trait for all corals – they all are animals. Unlike humans, however, coral has a single opening that serves both as the mouth and the rear end of their digestive system. This means that food enters and waste products are expelled through the same opening. This opening is surrounded by tentacles. The tentacles have stinging cells or nematocysts that help protect the coral as well as aid in the capture of food. The tentacles also act in a sanitary disposal capacity expelling waste products generated from the digestion of food.

Most reef-building corals have evolved a mutually beneficial relationship with algae as a result the relationship is beneficial to both the coral and the algae. Algae are plant-like organisms that contain chlorophyll. Algae use sunlight to produce nutrients through a process known as photosynthesis. The coral uses the nutrients to make proteins, fats, carbohydrates and produce calcium carbonate, the material that makes up the coral’s hard structure. The algae is also responsible for the color typically associated with coral. “Corals that host algae can deposit calcium carbonate, the hard skeleton that forms the reefs, up to 10 times faster than non-symbiotic corals.” The algae sheltered within the tissues of the coral receives nutritional benefit from the ammonium which is a waste produced by the coral.

Coral in trouble

According to the International Union for the Conservation of Nature (IUCN), coral reefs are one of the most threatened ecosystems on Earth. Those who study coral have warned that reefs are experiencing a dramatic decline. Dr. Elizabeth McLeod, Global Reef Systems Lead for The Nature Conservancy, estimates that 50% of coral reefs have already been lost and says that “Some scientists predict that we could lose up to 90% by 2050 unless bold actions are taken to reduce climate change impacts and improve marine management.” 

Many factors have contributed to the loss of coral reefs. Some factors are local and catastrophic like the dynamiting of coral reefs to make it easier for commercial fishers to harvest fish that live in the reefs. Another local problem is pollution.  Land development and deforestation results in sedimentation that smothers the reefs and reduces photosynthesis. Additionally, toxins are found in runoff that originates from highways, farms, and residential lawns, discharged in sewage and found in oil spills.  But the fastest growing and more difficult to manage danger to coral is ocean warming. When water temperatures rise high enough, the algae inside the tissues of the coral are expelled. The result is that the coral loses an essential source of nutrients as well as their color. The loss of color or whitening of the coral is described as bleaching.

An increase of 1.8–3.6 degrees Fahrenheit during a period of several weeks may result in coral bleaching. Bleached coral is not necessarily dead. It can survive short-term bleaching events. They are, however, stressed by the event which makes them less resistant to other threats and thus more likely to die. When the bleaching episode is prolonged, the coral will die. Reefs around the world including the Great Barrier Reef in Australia and the Northwestern Hawaiian Islands in the United States have experienced mass bleaching events. The bleaching event in 2026 and 2017 of the Great Barrier Reef  caused 50 percent of the coral to die.

Supercoral. Is it the Solution?

Some issues that negatively impact coral (e.g., sedimentation) can be addressed on a local level and others like improper fishing practices may require regulation on a country or regional level. The issue of global warming is much more difficult to address because it involves global involvement to achieve a solution. Limiting the increase in ocean temperature to a range required for the survival of coral reefs cannot be achieved without significant actors taking meaningful action. As the IUCN noted: “Other measures alone, such as addressing local pollution and destructive fishing practices, cannot save coral reefs without stabilised [sic] greenhouse gas emissions.”

While the need to address rising global temperatures is required for far more than the survival of coral reefs, there is at least a partial strategy that has shown promise in the effort to forestall the extinction of coral. Stephen Palumbi of Stanford University’s Hopkins Marine Station is one of the researchers studying what are referred to as super reefs. Coral in these reefs have a tolerance to temperatures that typically lead to bleaching and death in less tolerant species. Palumbi  examines reefs in search of the more heat-tolerant species. The goal of his and other researchers is to test if these coral can be used to restore what once were vibrant communities that are currently being decimated by warming temperatures. Palumbi says: “Our mission is to save as much as possible, so that when the world gets better—and it will get better, because this is going to be solved—then there’s something to grow back from. 

Information about super reefs is one part of a wider strategy that the Reef Resilience Network, initiated by The Nature Conservancy and NOAA’s Coral Reef Conservation Program, and other  knowledge-sharing networks like them are using to inform marine practitioners around the world. Armed with the latest science and management approaches, there may yet be hope that these extremely important ecosystems survive and once again flourish.