Great Barrier Reef Eutrophication

One of the earth’s most diverse and unique ecosystems, the coral reef, is dwindling due to anthropogenic stressors. Coral reefs across the globe provide habitat to approximately 550,000 to 1.3 million different species of organisms (Wear and Thurber 15). Although reefs can take thousands of years to form, over just the past 27 years, the world’s largest coral reef, The Great Barrier Reef, has seen its coral cover decline by over 50% (Kroon 1987). What is causing such an immense deterioration and what can be done to stop it? Various academic journals such as, Evidence of Large-Scale Chronic Eutrophication in the Great Barrier Reef, claim that fertilizer and sediment runoff are two of the leading causes of coral reef debilitation. By paying closer

The coral provides a protected habitat for the zooxanthellae and the zooxanthellae provide nutrients that the coral utilizes to survive and thrive. Fertilizer runoff occurs when fertilizer flows over the surface of the land and is carried by rain water into streams, rivers, lakes, and the ocean. Once in the ocean, the nitrogen found in fertilizer is absorbed by algae resulting in large algal blooms and excess macroalgae growth; this process is known as eutrophication (Kroon 1987). The overabundance of algae negatively affects zooxanthellae, and thus coral, because the algae and zooxanthellae compete for resources such as space and sunlight and zooxanthellae need sunlight for photosynthesis (Bell et al., 364). When zooxanthellae do not obtain an adequate amount of sunlight they become stressed and either leave their coral shelter or die (Bell et al., 364). It is the zooxanthellae which give coral their vibrant colors and thus the phenomenon of zooxanthellae withdrawing from coral is known as coral bleaching. Coral bleaching is problematic for coral because as a result the coral loses a major source of nutrients. Research has found that a decrease in zooxanthellae correlates with a decreased rate in calcification of coral’s carbon skeleton (Brodie and Waterhouse 7). Eutrophication does not only pose a significant threat to zooxanthellae but it also results in other stressors which harm overall coral reef