Climate Change and Ocean Acidification cause a variety of pressures to the local stressors on coral reef, this problem is a big challenge for coral reef managers. Coral Reefs vulnerability should be taken into consideration in the national frameworks to improve the resilience and management interventions to reduce these vulnerabilities. The anthropogenic activities have an important role in coral reef vulnerability, the local stressors such as overfishing, pollution, sedimentation and sewage discharge contribute to climate change and ocean acidification. They also affect recovery process and reduce the coral reefs resilience.
Coral reefs are important for local communities, livelihood, they provide various environmental services that meet their needs such as fisheries production, shoreline protection and livelihoods for ecotourism. The influx of sewage is not beneficial for people and for marine life, untreated sewage can produce excess nutrients that can disrupt the battle between corals and the seaweed for space, light, and food.
The extent of sewage pollution is alarming, about 85 percent of wastewater that enters in the Caribbean Sea is not treated and it produces changes in the environment such as poor water quality from the sources of pollution in the land. As a result of the population growth, the urban development changes the landscape; and it produces an increase of run off from the land. This can carry large quantities of sewage outflows, petroleum products as well as high levels of nutrients from agricultural areas, inorganic nutrients, suspended solids, heavy metals, and other toxins. Also, the excess in nutrients can affect the quality of water, as a result it decreases the oxygen and increases the nutrients like phosphor and nitrogen in the ocean. This process is called eutrophication; and it leads the increase in algal growth on coral reefs, which degrades the ecosystem.
Studies claimed that there is an evidence of chemical stress, solid deposition, nutrient enrichment, and bacterial contamination on coral reefs, which come from different hotels. The sewage discharge raises the proliferation of benthic algae as well as filter feeding invertebrates such as sponges, tunicates, bryozoans, and a decrease in the diversity and abundance of hermatypic corals.
Furthermore, the sediments that come from the sewage discharge are deposited into coral reefs and interfere with their growth, their reproduction, and their feeding. It even leads the increase of pathogens into the ecosystem. An example of this is the Serratia marcescens which are associated with coral disease known as a white pox.
Pollution caused by sewage can lead to coral reef bleaching and other coral diseases. The elevated levels of nitrogen and phosphorus may double the amount of coral bleaching. After researching the effect of the sewage on coral reefs, researchers found the “dark spot syndrome”, this disease was found on 50 percent of corals; and it decreases when the entry of nutrients stops. This is evidence that nutrients facilitate the growth of pathogens on coral reefs. Perhaps the only solution to stop it is to make decisions to conserve coral reefs resilience such as cleaning up the water. Even if it seems to be the biggest challenge, it is necessary because sewage discharge has been one of the causes that affect coral reefs health.
Any change in the physical and chemical conditions outside the given tolerance ranges can be detrimental to the growth of the corals and their survival (Johannes and Betzer, 1975; Endean, 1976; Pearson, 1981; Pastorok and Bilyard) When pollution destroys the hermatypic corals, many species which depend on coral reefs for their shelter, food, and refuge from predators, are threatened and would die (Johannes, 1975). The effects of the toxins can be enhanced when there is an increase in water temperature which likely happens in coral reef ecosystems; the effects of these high temperatures are faster biotic uptake, greater toxicity, and increased solubility
Currently, coral reefs managers are challenged by a lot of pressures and stressors which make these ecosystems vulnerable including local communities that depend on their goods and services. To sum up, coral reefs are vulnerable to climate change, ocean acidification, the effects of anthropogenic activities (e.g. overfishing, pollution, deforestation, among others). The challenge to reduce those stressors and support the coral reef resilience from these threats has been faced by researchers, managers, governments. Focusing on the resilience will provide effective approaches to the conservation, Adaptive Resilience Based Management (ARBM) has been developed from a variety of studies of ecological and social systems; and it can be only successful if there is an integration of fundamental principles in ecosystem vulnerability.
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