Symbiosis between Algae and Coral Reefs
Symbiosis between Algae and Coral Reefs
A symbiotic relationship is one in which there is a mutual dependence between two or more different organisms. In an aquatic ecosystem, the most dominant symbiotic relationship is that between the coral reefs and algae (Baker, 2003). The species of the algae that is found within the gastrodermis cells of coral reefs is zooxanthellae, which is unicellular (Mostafavi, Ashrafi, and Dehghani, 2013). Notably, the relationship between these organisms is called obligate symbiosis since the survival of one organism depends on the presence and metabolic activity of the other. This paper, therefore, will delve into the symbiotic relationship between coral reefs and zooxanthellae algae as well as the effect on the coral bleaching.
One of the mutual benefits between the two is that corals offer the protection to the zooxanthellae algae and the materials necessary for photosynthesis. These materials are usually waste products from the corals. In return, zooxanthellae supply oxygen to the coral and aid in the removal of waste products. Additionally, they provide coral reefs with carbohydrates which are an essential organic material of photosynthesis. Since the coral reefs need to manufacture fats for survival, they utilize these compounds as building blocks. Furthermore, these waste products from the algae are important in the synthesis of calcium carbonate skeleton of the corals. Most importantly, the zooxanthellae algae are crucial organisms to the survival and health of reef-building corals because the coral tissues use almost 90% of their photosynthetic-manufactured materials (Yamashita, Suzuki, Kai, Hayashibara, and Koike, 2014).
The other symbiotic relationship between the two is color. Zooxanthellae algae give the corals their beautiful characteristic color since they produce pigments that are visible through the transparent coral polyps. The color produced by the algae varies from brown to golden-yellow and hence the color of the host. Nevertheless, the variation of these colors is dependent on the intensity of light subjected to the environment in which the host and the symbionts are exposed. Since the algae are photosynthetic, when the intensity of light is lower than normal they may increase in number so as to increase the green coloring matter to sustain ideal levels of photosynthesis. On the contrary, when the intensity of light escalates, photosynthesis normally increases thus producing a high level of oxygen in the tissues of corals. These high levels of oxygen are toxic to the corals (Hagedorn and Carter, 2015). To control the level of oxygen, there are usually two actions that result. Either the corals may eject some algae or the zooxanthellae may minimize the levels of chlorophyll within them.
When the corals expel excessive algae, it leads to a situation in which the corals appear white due to the transparency of their tissues and the white color of their skeleton caused by the calcium carbonate. This phenomenon is known as coral bleaching. Moreover, bleaching rates may also accelerate due to higher temperatures (Reaser, Pomerance, and Thomas, 2000). Eventually, the corals begin starving due to the absence of the algae and most of them struggle for survival. However, not all the corals are affected adversely by bleaching since some can feed themselves sufficiently. Consequently, the corals are susceptible to diseases and their growth as well as reproduction is reduced significantly. The corals may completely die out if the bleaching is persistent. Recovery of the coral reefs from bleaching may take long periods of time.
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