11/29/2020 How does Coral Bleaching occur?In this article I want to talk about how coral bleaching occurs. If you haven't already read my article about Coral Bleaching, I recommend reading that first: https://coralconservancy-crcp.weebly.com/whats-happening/whats-happening Ever heard of bright, fluorescent algae? Symbiotic dinoflagellates known as Zooxanthellae are a great example of these wonderful types of algae which are found inside coral cells. If we zoom into a coral tentacle, there are two layers of double cells with an open space in between. Like this: The algae are taken in and distributed into the space between the layers. After moving into the space, they shift into the cells through phagocytosis. Phagocytosis is the process by which cells use their plasma membranes to take in particles, substances, or in this case, algae, making space internally for the algae to live safely. Phagocytosis is a type of endocytosis. Endocytosis is the process of a cell taking in matter with intent to form a vacuole. Let’s zoom into one cell and specifically identify each component within: In this diagram, we see photosynthesis occurring. The natural light is being absorbed by the algae, which provides sugars, carbon dioxide, oxygen, etc. There are also many nutrients being created, such as glucose, glycerol, and amino acids, which is a result of photosynthesis. Since the coral is providing the algae safe shelter, and the algae are providing the coral with what it needs for it to survive, creating a symbiotic relationship. Zooxanthellae is providing the coral with over 90% of its energy. Now that we know about the relationship between the algae and the coral, let’s talk about how exactly the bleaching is occurring. The temperatures on Earth are increasing at an alarming rate because of the increase of carbon dioxide on an atmospheric level. The intense carbon dioxide levels are damaging the “Photosystem II” inside the algae’s chloroplasts. These photosystems complete photosynthesis, so when these photosystems are damaged, they die. All the products of photosynthesis that was talked about earlier are not possible and are gone. This symbiotic relationship no longer exists since the coral doesn’t have the energy to supply both itself and the algae with what it needs to survive, causing the coral to expel the algae. Keeping in mind that the algae provides the coral with all the fantastic, vibrant coloring, when the algae is expelled, the coral is considered “bleached” or is a bright white, colorless organism. The coral, however, is not dead. Yet, since 90% of the energy is gone, the corals will die if the ocean temperatures continue to rise. Since the ocean temperatures are continually rising at an exponential rate, the bleached corals have a low chance of survival. Ocean acidification is consistently occurring in the oceans as well. Ocean acidification is the constant decrease of pH levels in ocean waters. Normal ocean pH levels would be around 8.2 which is slightly basic. Over time, the pH levels have decreased to 8.1 which may not seem like a huge difference, however, the pH scale is logarithmic which indicates that everything is occurring on a tenfold change. Ocean Acidification rids the ocean of its carbonate at an exponential rate. The corals depend on the carbonate to produce their carbonate shells, which is the backbone of the coral’s skeleton. With ocean acidification occurring and the increase in global temperatures, we see a few significant reasons for the intense coral bleaching crisis. pH source |
|