The Coral Catastrophe: Ocean Acidification, Climate Change, Coral Bleaching, and the Death of the Reefs
2018, High School, Prose
“Coral reefs represent some of the world’s most spectacular beauty spots, but they are also the foundation of marine life: without them many of the sea’s most exquisite species would not survive.”
— Sheherazade Goldsmith, environmental activist
Slipping on your flippers, you tumble backwards off the edge of the boat, plunging into the crystalline water. After hastily righting yourself, you blow through your mouthpiece to clear your snorkel and duck under the surface, immersing in the shallow tropical waters off the coast of Australia. And that’s when you see it. Only the snorkel in your mouth prevents you from gasping in awe. Below you lies a vast, colorful reef exploding with life. Around you swim thousands of brilliant fish in all colors, shapes, and sizes, from the size of your fingernail to twice the size of a person. Among the coral there reside hundreds of strange and unique creatures who all depend upon the beautiful, diverse coral polyps that form enormous structures upon the sea floor. Swimming further, you glide like one of the sharks around over the vast expanse of the reef. But then you reach a sharp divide. Behind you lies a teeming reef, but before you stretches a barren wasteland, with the bleached, stony skeletons of long-dead corals reaching forlornly for the sky. What has happened here?
Across the world, hundreds of reef ecosystems are in constant danger due to the escalating threats of global warming, ocean acidification, and harmful human activity. Cyanide and dynamite are used to collect or kill fish, while at the same time fracturing the very foundations of reef ecosystems. Chemical pollution leaves a lingering effect on countless marine habitats such as coral reefs, causing stretches of coral to wither and die. Yet the two most widespread concerns for coral reefs, and the hardest problems to stop, come from slowly but surely increasing ocean temperatures and carbon dioxide absorption. Rising ocean temperatures stress, bleach, or kill hundreds of coral reefs, while increasing ocean acidity from carbon dioxide absorption dissolves and weakens coral structures. Every year, the number of coral reefs affected by higher marine temperatures and acidity are growing at unprecedented rates, and since these problems are caused mainly by rising levels of atmospheric carbon dioxide, the global crisis cannot be quickly or easily resolved.
Coral reefs are built over hundreds of years by soft-bodied organisms called coral polyps. These coral polyps secrete calcium carbonate in layers to form a protective limestone skeleton called a calicle. These calicles — usually found as a small cup shape in which the polyp resides — are then joined into colonies that vary in size and form, which gives certain species of coral their unique shape (Stone). Over time, colonies of coral polyps expand and combine into a coral reef. Although coral polyps are transparent organisms, each polyp in a colony is a host for zooxanthellae algae, which contain colorful pigments that give the corals their stunning colors and are part of a symbiotic relationship with the coral polyps. During the day, zooxanthellae provide the polyps with sugars gained through photosynthesis, while the polyps provide the zooxanthellae with a protected environment and the compounds necessary for photosynthesis. Although coral polyps can feed at night by catching microscopic zooplankton, most of their food is gained through photosynthesis (Stone).
Coral reefs are one of the most biologically concentrated and diverse ecosystems on Earth. Often called “the rainforests of the seas,” they cover only 0.1 percent of the ocean’s surface, but they host a quarter of all life in the Earth’s oceans (“Coral Reef Ecosystems”). While most reefs are found in the shallow tropical waters off the coasts of islands, deep-sea coral reefs can be found up to 300 feet below the surface of the ocean. Coral reefs are a feeding and breeding ground for ocean migrants such as fish and sharks and sustain a food web that is essential for hundreds of marine organisms. Algae, coral, sponges, and a few species of invertebrates are the base of this food web, supporting fish, snails, and crabs that consume them to keep the coral clean and healthy. Smaller fish and invertebrates find shelter among the coral, while larger predators prey upon these reef occupants. Some organisms, such as parrotfish and crabs, help to clean up the reef by breaking down and decomposing old or dying corals (“Coral Reef Biodiversity”). Collectively, the reefs and their dependent organisms create an oasis for life in the ocean.
Ocean acidification and warming, two concerning factors of climate change that affect reef development, both stem from the role of the ocean as a climate mediator. Large bodies of water, such as lakes and oceans, absorb excess heat and atmospheric gases such as carbon dioxide (CO2). Temperature absorption and mediation occurs seasonally as the ocean absorbs heat in summer and releases it in winter, always staying a more moderate temperature than the atmosphere. Although this process can also have fluctuations in average temperatures over thousands of years, recent climate trends show that average atmosphere temperatures are rising in response to increases in greenhouse gases (Gershwin). This is causing the ocean to absorb more heat at a faster rate, leading to water temperatures that are increasing too quickly for marine organisms to adapt.
The same is true for carbon dioxide. Saltwater has a lower ph measurement than freshwater, around 8.1 to 8.2, and absorbs carbon dioxide from the atmosphere, which is necessary for phytoplankton respiration (Brewer). The absorbed CO2 makes the water more acidic, lowering the ph. But as atmospheric CO2 increases, so does the amount the ocean absorbs, causing acidity to rapidly increase, which can harm the natural processes and development of ocean organisms such as phytoplankton and zooplankton. Even lowering the ocean ph to 8.0 can have significant impacts on the health of marine plankton (“Ocean Carbon Uptake”). The heightening ocean temperatures and acidity can both be linked to one main cause: the increase in carbon emissions from the burning of fossil fuels and agricultural deforestation.
Since the beginning of the industrial age, the world’s population has drastically increased the amount of fossil fuels such as coal, natural gas, and oil that are burned in order to supply the energy needed for global growth. However, this growth comes at a cost. Fossil fuels are ancient deposits of organic carbon that are mined and then burned to create energy, but they release carbon dioxide as a byproduct into the atmosphere, where it either contributes to the greenhouse effect or is absorbed by the ocean. Mass deforestation contributes to the increase of CO2 when carbon is released into the atmosphere from burned trees and the soil bared for agricultural operations. Deforestation also disrupts the natural carbon cycle, resulting in a loss of carbon uptake through plant respiration (World Weather). Since the 1970s, global carbon emissions have increased by 98 percent, averaging around 10 gigatonnes of CO2 being released annually. In recent decades, this has caused ocean temperatures to increase at nearly twice the rate. Every year, 25-30 percent of these carbon emissions are absorbed by the ocean, causing the average ocean acidity to increase by over 30 percent in the past few years (“Global Carbon Emissions”).
Ocean warming and acidification, both caused by the increase in carbon emissions that lead to climate change, directly affect the health of coral reefs. As ocean temperatures rise, the symbiotic zooxanthellae algae within coral begin to produce toxins that can stress the polyps in which they reside, resulting in the zooxanthellae being ejected from the polyps’ tissue. This event, called coral bleaching, leaves the coral either white or transparent from the lack of the pigments found in algae. Although bleaching relieves the coral of the toxins the algae were producing, it also rids the coral of its main food source. Corals can survive for short periods of time without zooxanthellae, but the coral polyps will eventually die if they do not regain algae and the process of photosynthesis (“What is Coral Bleaching”). Coral bleaching can be caused by even slight increases in temperature, as little as one degree Celsius higher than normal, if it lasts for extended periods of time. In recent years, a marine “heat wave” has caused one of the largest coral bleaching events in history, during which 70 percent of the ocean’s coral reefs experienced bleaching over a three-year period (“What is Coral Bleaching”).
Ocean acidification, although slower to affect the health of coral reefs, has a longer-lasting impact. The diverse range of coral structures all rely on a stony skeleton for protection and support. This skeleton is created from calcium carbonate (limestone), which will dissolve when subjected to an acidic environment. As ocean acidity increases, the calcium carbonate secreted by coral polyps will dissolve or be considerably weakened, leaving them without a protective skeleton (Gattuso). This effect of acidity, although not yet recorded at dangerous levels in coral, has also been witnessed in the development of mollusk shells. Over several decades, the calcium shells of mussels, clams and other shellfish have grown thinner and weaker in relation to increased ocean acidity, causing them to be more susceptible to parasites. With the ocean’s acidity levels rising by over 30 percent more than before, it is projected that ocean acidification will soon become a critical dilemma for the formation and survival of new corals and coral reefs (Gattuso).
The death or decline of coral reefs, if not prevented, could have serious consequences not only for marine life, but also for the survival of people and their economy. If reefs are removed from the worldwide marine biome, the entire food web will collapse and thousands of unique species will be lost forever. Deprived of a major food source, the only surviving organisms would be those that could subsist solely on drifting plankton and deep ocean invertebrates for food. Many species of fish that are harvested for human consumption rely on reefs for food and reproduction, so the seafood in our diet would either change drastically or disappear altogether. In addition, coral reefs are one of the largest tourism hotspots on Earth, with the Great Barrier Reef alone having two million visitors and earning four to five billion dollars in tourism a year (Brewer). If reefs become nonexistent, the loss of such profitable attraction would have serious impacts on the economy worldwide.
In the modern age, climate change has become a major obstacle for struggling ecosystems around the world. However, the effects of ocean warming and ocean acidification on ocean ecosystems are global impacts of climate change that are not as well known. Although solutions to these dilemmas will take time to implement, there are several possible answers to the question of stopping climate change and its effects on the oceans. Several proposed responses include: reducing atmospheric pollution and carbon emissions, halting deforestation, and implementing green energy sources (“Ten Climate Solutions”). Monitoring and limiting the carbon dioxide and other pollutants emitted in the process of creating energy can limit the greenhouse effect that leads to global warming, while a decrease in deforestation could help preserve the natural carbon cycle. Green energy options such as wind, solar, and hydroelectric could potentially help solve the problem of climate change by having a smaller carbon footprint than traditional options.
Every year, the number of marine ecosystems affected by harmful human actions is rising in record numbers. Every year, more and more animals, habitats and marine systems are stressed, harmed, or destroyed by the many forms of pollution caused by human populations. Every year, more and more coral reefs fall prey to coral bleaching, while rises in ocean acidity pose a growing concern for the basic structure of coral reefs. The effects of global warming and ocean acidification pose a great threat not only to the oceans and countless marine organisms, but also to us. The death of the reefs would lead to the loss of one of our most important food sources and even affect our economy. Because of our actions, the careful balance of the Earth’s natural systems such as the carbon cycle has been upset, and it is up to us to restore this balance. By ending our massive global pollution, we can help protect one of the most important and beautiful habitats on Earth: the coral reefs.
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After learning more about global warming and ocean acidification -- more specifically, how they affect the health of coral reefs and their ecosystems -- I feel that they are perhaps the two most important types of pollution affecting reefs, not only because of their detrimental impacts but also because of the time-consuming process of resolving them. And though there is a chance of stopping climate change, however slim, it will take action from everyone to help save one of the Earth’s last wild frontiers: the ocean.