Corals Survived Two Mass Extinctions

Climate change is an issue that threatens many aspects of marine life and its survival as we know it. The first example focused upon by Palumbi in this lecture is the occurrence of ocean acidification and its detrimental effects on both the organism and the surrounding environment. Examples of harmful effects include: malfunctioning nervous systems, making it harder for the organisms to protect themselves, and eventually large upsets in entire ecosystems. Another example that Palumbi primarily focuses on are rises in ocean temperature, in which he looks first at coral and its role over the course of about 250 million years. Although coral had survived two mass extinctions, many things have affected their survival rates recently. In recent decades coral cover loss is roughly up 40%, due to things such as sedimentation, pollution, overfishing, and of course, coral bleaching.

He then proposes two different hypotheses to answer why coral is suffering; either that the environmental change is too unprecedented, or we have yet to see how they adapt to extreme conditions. With the use of two graphs, Palumbi compares the rate of temperature change per century from the last 150,000 years to the increase in global average temperatures in the oceans over the last 100 years and find shocking results. The rise in temperature is 11 times higher, proving that mankind has escalated temperature much more than the recovery from an ice age. This increase in temperature can bring about coral bleaching, a process that involves the expulsion of the algae that give some coral its color, known as symbiodinium.

Palumbi then goes into further explanation of this process using a coral reef located on Ofu, an island in American Samoa. Through an animation, we learn that the symbionts are inside the coral cell’s gastrodermis, one of its two cell layers. Symbiodinium is an orgaism refered to as a dinoflagellate, which is photosynthetic. The increase in temperature and light breaks the photosystem by overloading them with energy. Now that the photosystems don’t function correctly, the excess of energy now creates reactive oxygen cells. These cells hurt the coral cell and forces it to expel the symbiote, thus bleaching eventual colonies and killing them. In order to help find solutions to coral bleaching conditions, Palumbi and others found that the same Ofu Island has thriving coral with surprising heat resistance. The researchers simulated different coral samples of the same species in mock Ofu reef heat.

They found that the same species from a cooler part of the reef was completely bleached while the other, which was from a warmer part, was not. By transplanting coral to the opposite type of temperature area in the reef (those in a cooler area to a warmer area and vice versa) researchers were able to discover that after repeated testing, the group living in areas with warmer temperatures repeatedly showed higher resistance. The results prove that to an extent, coral can acquire heat resistance trait through a process known as acclimation. Acclimation (defined as “The adjustment of an individual’s physiology to new conditions”) is described as being one of two responses to environmental change with the other being adaptation (or “Natural selection for the individuals that have the right genes for new conditions”).

Although adaptation is difficult to observe, as it requires generations of studies which, as humans, we simply don’t have access to. Luckily enough, Palumbi is a geneticist and can give us insight on how the alleles differ in corals in response to the water temperature. All of these studies shown reveal that corals have the capacity become resistant to climate change through both adaptation and acclimation, although this ability is limited. Corals will never be able to acclimate forever, as they posses limits, and finding and pushing these boundaries is something researchers are constantly looking into.

The fact that the coral has the ability to adapt at all allows professionals to continue their research in hopes to find a solution. We can use this research to argue that the pools along Ofu island beach are to be protected from human endeavors, as they have genes needed to survive no matter what future conditions hold. While results may be unknown, Palumbi and his team are attempting to transplant this type of coral elsewhere in order to built more heat resistant reefs. The team has predicted that after the coral has grown, it should have retained partial heat resistance. Lastly, Palumbi answered a student’s question related to whether