When one pictures a dream vacation, their mind typically wanders to a tropical paradise with soft white sand that fills the spaces between their toes, water so clear they can see the ocean floor, along with the thousands of beautiful brightly colored fishes swimming amongst vibrant coral reefs. An ecosystem is “a biological community of interacting organisms and their physical environment”, and although this wonderland covers less than 1 percent of the entire globe, they are one of the most diverse ecosystems known to mankind, second only to tropical rainforests (Oxford Dictionary). In a sense, reefs are the rainforests of the ocean. Even more astounding, these reefs have an immense value to humans medically, economically, as well as environmentally. Though many know of coral reefs, it is not commonly understood what they are composed of, nor that they are the driving force behind much of the life on this planet.
This ecosystem is typically found in shallow waters surrounding an island as shown in Figure 1, and in warm seas near the equator. Corals are hard stony substances made from the secretions of zooxanthellae; an algal cell they coexist with and use in order to create a coral reef. Coral reefs are “a ridge of rock in the sea formed by the growth and deposit of coral” (Oxford Dictionaries). There are also soft and deep water corals, but for the most part, the stony type found near the shore are the most common. Coral reef growth is a slow process but can lead to massive sizes, ultimately depending on the species of coral, food source availability, water temperature, amount of salt in the sea, as well as how clear the water is.
Figure 1 Typical coral reef zonation of a tropical island, from Genny Anderson, Typical Coral Reef Zonation; Marine Science; 30 June 2003; Web; 18 November 2017
Reproduction comes into play in regards to growth. Coral reproduction is unique in the aspect that reproductive methods vary, depending on the species of coral. Hermaphrodite species will eject trillions of both eggs and sperm at once into the outer water through the mouth (NOAA). This phenomenon known as coral spawning only happens once a year. Once the egg and sperm join, larvae is created. Other species will have colonies that eject only sperm or eggs. The larvae can then fertilize within the polyp. Once the larvae has finished maturing within the mother’s body, it is spit out through the mouth. The larvae will swim to the surface near the sunlight, and eventually sink back down to attach itself to a hard surface. From there, it is capable of turning into a polyp, which will clone itself, eventually creating a massive colony.
Coral reefs are composed of thousands of individual polyps, and understanding their composition is key to knowing how they connect to the rest of the world. A single polyp as shown in Figure 2 is composed of the mouth covered by the tentacles, which are used for defense as well as catching food. Within the tentacles are nematocysts, cells used to sting any foreign creature presenting a Figure 2 Anatomy of Coral, Coral Anatomy; danger. At the base, is a calcium carbonate skeleton.
Algone; n.d.; Web; 16 November 2017
Nematocysts are capable of delivering deadly amounts of toxins to catch prey. In this case, their prey consists of microscopic animals ranging from zooplankton to small fish. When prey comes into contact with the tentacles, it stimulates the nematocysts to open the flap known as the operculum, causing the thread to unwind and shoot barbs into the animal.
Figure 3 Nematocysts cell, NOAA, Diagram of Nematocyst Cell, Ocean Service Education; 06 July 2017; Web; 16 November 2017
Once the animal has weakened, the tentacles will move it towards the mouth for consumption. From there, the food moves to the stomach for digestion, and waste is then expelled back to the outside world. This is similar to the way a jellyfish would sting, as they also have nematocysts in their tentacles.
Yet, one of the most important cells that live within the tissue of polyps are tiny plant cells known as zooxanthellae. Zooxanthellae are photosynthetic algae, which coexist with coral through a mutualistic relationship. Mutualism, also known as symbiosis, is a relationship where both parties benefit from each other; it’s a win-win situation. How exactly do they benefit from each other? Basically, coral acts as the bodyguard; it provides a home, protection for this delicate cell, as well as compounds needed for photosynthesis. In return, coral and its polyps receive a myriad of advantages. Zooxanthellae will remove waste, produce oxygen, supply the necessary nutrients for the creation of calcium carbonate -what the coral skeleton is composed of- , and give coral astonishingly beautiful colors. Since this algal cell is photosynthetic, it must be constantly exposed to sunlight, which is why coral is commonly in shallow waters through allows for warm waters.
Figure 4 Colorful coral reef found near the surface near the equator, where the most sunlight of the ocean is common, but to find it at greater is provided. The equatorial area is a depths is rare, from Volodymyr Goinyk, Coral utopia, because the sunlight radiating Reefs, Grapevine; July 7 2017; Web; 16 Nov 2017
Though this ecosystem appreciates warm waters, it is very selective, in that it can only tolerate a slim difference of temperatures ranging from 23-29℃, as well as a certain pH. Unfortunately, “global warming due to anthropogenic -or human- causes, is making it extremely difficult for coral to adapt to their rapidly altering environments”(Saving Coral Reefs). Currently, ⅓ of coral reefs are at risk of extinction, and are constantly in danger due to both global and direct threats. When regarding climate change, “ninety-seven percent of publishing climate scientists agree that global climate change is real and a result of human activity. By reducing the human use of fossil fuels, we can curb carbon dioxide emissions (CO2), slow the pace of climate change and give coral reefs the critical time they need to adapt”(Coral Reef Alliance).
Climate change is due to an increase of carbon dioxide (CO2), which comes from an excessive burning of fossil fuels. Oceans absorb about 30%, and because this compound is heat trapping, the Earth’s temperature increases, causing glaciers to melt and sea levels to rise. This rise in sea level means coral is deeper underwater. When coral is too deep underwater, this prevents the proper amount of sunlight to reach zooxanthellae, leading to Figure 4 A diver checks out the bleaching at difficulty in proper growth. All of this “…stress on corals can cause them to expel their algae, a phenomenon known as coral bleaching. With the algae gone, the white limestone of the coral is visible, and the corals die if stress is not relieved” (Saving Coral Reefs). Coral bleaching removes all beautiful color, and life from the reef, leaving behind the dead white skeleton.
Heron Island on the Great Barrier Reef, from Richard Vevers, onEarth NRDC; The Ocean Agency, June 16 2017; Web; 16 Nov 2017
Yet if this ecosystem is in its prime state, the biodiversity is quite impressive. More than a million species rely on coral reefs to be their home. For example, the intricate structures of the skeleton serves as a great hiding spot for the small fish seeking refuge from predators. The fallen waste produced from polyps becomes the food source for the bottom feeders. Other fish graze on the algae produced from zooxanthellae, which prevents coral from becoming smothered and not receiving the necessary amount of sunlight. Larger predators help regulate those grazers, because zooxanthellae is still essential to the coral’s well being. This biodiversity can also benefit humans, as it provides many services including: food from fishing, medicine, protection from storms, and huge amounts of income from tourism.
One of the most significant reasons this ecosystem benefits us, is medically. The biodiversity within this little world is crucial to finding medicines and cures to diseases. Drugs have already been created to be used for treatment of cancer, arthritis, bacterial infections, and other viruses. Through tourism and fisheries, billions of dollars are made in profit. Yet one of the most valuable services they provide is protection against natural disasters. These giant structures have a great strength, and play a big role in protecting shorelines against harmful waves. This protection prevents billions of dollars in property damage, and huge loss of human life. Unfortunately, these types of natural disasters will damage the reefs, and bring in colder water, imitating the effects of coral bleaching. The Paris Climate Agreement was a huge step forward in progress for Americans and mother nature, as it placed restrictions on industry to reduce the releases of greenhouse gases. Though with Trump’s decision to withdraw from the Paris Agreement, a positive future for coral reefs and the environment seems unlikely.
Of course, there are still many ways in which an individual may contribute to the salvation of this diverse habitat. Living sustainably and reducing one’s carbon footprint helps immensely. Eating sustainable seafood which discourages overfishing, and reducing the amount of trash one produces through reusable lunch containers, compost bins, and reusable grocery bags aids in eliminating large amounts of waste that ends up in the ocean. Finally, becoming an advocate for this planet through calling and emailing government officials would be an amazing tactic toward saving an ecosystem that does so much for everyone.