Imogen Aley
Coral reefs are incredible expanses of living organisms that are essential to more than 25% of the ocean’s life. Corals get their trademark bright colors from algae called Zooxanthellae that live on the structure made by thousands of tiny organisms called polyps, which secrete the limestone that give corals their classic shape. These reefs provide food, protection, and shelter and are one of the world’s most diverse ecosystems. For example, thousands of tiny organisms called polyps secrete limestone and give coral their classic shape, while algae called Zooxanthellae that live on the structure give coral their trademark bright colors and provide a source of nutrients to an environment that is void of hospitable conditions. Humans also rely on these expansive ecosystems for food, medicine, and income; coral reefs bring in hundreds of millions of dollars a year out of tourism alone. Coral reefs also provide the coastlines with protection from erosion from storms and wave action, and with billions of people living on the coastline during a time where storm intensity and sea levels are rising, our coastlines need all the protection they can get. Despite their importance, human activities are destroying these beautiful coral reefs.
Corals and their algae have a symbiotic relationship. Through the process of photosynthesis, algae uses CO2 to create glucose, a source of energy. However, they often overproduce these sugars, thus allowing the polyps to consume this energy rather than catching their own food. The consumption of these sugars produces CO2 for the algae to feed on, thus producing more sugars. These sugars are also eaten by tiny bacteria, which provide food for larger organisms that feed on the bacteria, creating a food chain. Any waste excreted by organisms is taken up by algae in the form of nutrients, creating a complex system of nutrient cycling. However, this complexity is extremely fragile.
Global climate change has contributed significantly to the decline of coral reefs. Increased CO2 levels have lowered the pH of the ocean, causing coral bleaching events. When their surroundings change, the algae living in the corals’ structure become stressed and release harmful toxins to the coral and so the corals are forced to expel the algae to protect themselves. This causes the corals to look white, and the corals become starved without the algae producing food for them. While corals do not actually die during bleaching events, and the Zooxanthellae may return, the lack of algae is detrimental for organisms who rely on the reefs to survive, since the delicate nutrient cycling system is disrupted. Increased acidity also slows the growth of the corals, and may even damage the coral beyond repair. Along with climate change, other human activities are responsible for destroying coral reef systems. Fishing techniques like trawling or using explosives to startle the fish destroy corals. Moreover, runoff pollutants like chemicals and fertilizers enter water systems from land and cause algal blooms that smother corals.
Without corals, the marine food web would be disrupted and many marine organisms would therefore no longer have access to food and shelter. Biodiversity and organism populations would decrease. This would also affect humans as our food supply would drastically decrease since many coastal areas that rely heavily on marine life would struggle to survive. Furthermore, a lot of these areas rely on tourism and so their economies would be severely disrupted if corals were to die.Around one billion people rely on corals for food and income; if the effects of climate change were to continue to increase, these one billion people would be without food and income. However, there is some good news. The Great Barrier Reef is seeing some of its highest coral cover levels in history, indicating that even through extreme bleaching events like those seen in 2016, corals can and will recover
Citations
“Coral Reef Ecosystems,” National Oceanic and Atmospheric Administration, https://www.noaa.gov/education/resource-collections/marine-life/coral-reef-ecosystems
“Anthropogenic Threats to Coral,” National Oceanic and Atmospheric Administration, https://oceanservice.noaa.gov/education/tutorial_corals/coral09_humanthreats.html
“How is Climate Change Affecting Coral Reefs?” Florida Keys National Marine Sanctuary, https://floridakeys.noaa.gov/corals/climatethreat.html
“Are Corals Animals or Plants?” National Oceanic and Atmospheric Administration, https://oceanservice.noaa.gov/facts/coral.html
James Lee, “Maroon Fish on Corals” Pexels, 03/18/2019 https://www.pexels.com/photo/maroon-fish-on-corals-2016941/
Nils Rädecker and Claudia Pogoreutz, “Why are Coral Reefs Hotspots of Life in the Ocean?” Frontiers, 12/17/2019 https://kids.frontiersin.org/articles/10.3389/frym.2019.00143