Revolutionary Coral larvae study gives hope to aiding Coral Reef decline

By: Ashley Gustafson

It is no secret that thPorites astreoides e alarming decline of coral reefs is only increasing. It is nearly certain that without some sort of change, coral reefs will cease to exist in the wild as they once were. Coral reef health is in critical condition around the globe. Many studies and experiments have been performed in order to try to understand what is causing this swift decline in coral reef health around the world. The main culprits of the coral reef decline are pesticide run off, general pollution, and the raise in overall ocean temperature. Although some communities and organizations have put regulations on the use of pesticides, waste disposal, and toxic run-offs it has not been enough to make a great enough impact on the seemingly exponential decline of wild corals. In order to gain insight into a more specific cause of coral reef decline, a first of its kind study has taken the initiative to look at the combined effects of mosquito pesticides and rising sea-surface temperatures in a new, innovative way. The basic idea of these researchers is to expose coral larvae to specific combinations and concentrations of pesticides and temperatures. Their hope is that these combined effects will give a clearer picture to what we can due to slow coral reef decline.

The man behind this idea is Dr. Cliff Ross, an associate professor of biology at the University of North Florida in Jacksonville, FL. With the help of Mote Marine Laboratory scientists, Dr. Ross was able to expose coral larvae to various concentrations of pesticides and various water temperatures. The coral larvae used in this experiment was Porites astreoides which is a species of coral found in a wide range of the Caribbean, the Gulf of Mexico, Florida, Bermuda, the Eastern Atlantic, and the Bahamas. It is an abundant and dominant coral that is found in deeper waters than the average coral and although the larvae are short-lived they exhibit a high level of recruitment. Compared to other Porites species it is more disease resistant which allows it to be more resilient to habitat loss and reef degradation making it a fairly stable coral and good test subject.

Pesticides to Blame?

The major pesticide issue of many coastal environments is that of mosquito-control and thus the focal point of pollution in this study. Many coastal communities have substantial human populations that rely on tourism which motivates the increase in use of mosquito pesticides that can cause harmful run-off into the coastal waters not only causing harm to coral reefs, but all the marine life that reside along these coastal habitats.

This pioneer study was recently published in Ecotoxicology by Dr. Ross and his colleagues Kevin Olsen, Michael Henry, and Dr. Richard Pierce. The experiment exposed a number of interesting qualities these corals display when exposed to adverse conditions. One characteristic the coral larvae displayed was that they showed a moderate amount of resistance against any short term exposure to ecologically relevant concentrations of pesticides at an elevated temperature. Simply put, they found that the coral larvae were able to handle and survive short term exposure to common current concentrations of pesticides in the ocean in combination with normal elevated water temperatures that could currently be seen in nature. Dr. Ross both collected and then exposed coral larvae to specific concentrations of two major mosquito pesticide ingredients, naled and permethrin, as well as seawater elevated 3.5 degrees Celsius. He was able to see that after 18 to 20 hours of being exposed to these conditions that the subjected larvae had significantly lower survivorship than that of the control larvae groups. He did not see this reduce in survival in the presence of permethrin nor that of the elevated temperature. In addition to the previous results, the researchers did not see any significant change in larval settlement, post-settlement survival, or bleaching with any of the treatments. Another round of tests was done to evaluate the sub-lethal stress response of the larvae in the various treatments. This was done by taking several cellular and molecular assays, much like a human blood test, to determine if the larvae were being stressed by their conditions. The results of these tests showed variable responses to the pesticides and were contingent upon the type of pesticide the larvae was exposed too along with the specific biomarker being employed. There was some variation between cases. One example, in the case of the protein carbonylation and catalase gene expression, the effects of the naeld exposure in conjunction with the rise in temperature were inactive. In a different example, the pesticide exposure of both chemicals failed to induce any sort of sub-lethal stress response at all.

These results supply researchers with significant data about the resistance of baby corals to the new higher temperature oceans, and harsher, chemical filled waters they must survive in to become adults. If baby corals can’t withstand the rapid increase in stressors in their natural environment, they will not be able to survive to adulthood to reproduce and maintain a population. Overall, Dr. Ross and his fellow researchers were able to conclude that this specific species of coral larvae have a moderate degree of short-term resistance against the rising temperatures and increasing concentrations of mosquito pesticides in coastal waters. While Dr. Ross is happy with the results and success of this new study so far, he knows there is much more to discover as there is neither a single chemical nor a single stressor to the wide variety of corals in the wild. Hopefully, by uncovering the unique stress signals and resistance of corals, Dr. Ross will be able to find solutions for the changing conditions of the world’s oceans. This is just the first results of a very exciting and innovative new way to study coral reefs and their intensifying decline around the world.



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