Mark E. Hay is Co-Director & Regents Professor, OSE & Harry and Linda Teasley Chair at Georgia Tech's School of Biological Sciences, and specializes in marine ecosystems, marine ecology, coral reefs, and marine conservation. He joins the show to discuss his work and insight on these topics, especially as it relates to coral reef conservation. Press play to discover:

• To what degree coral life cover has changed over the last 40-50 years in different areas, and the consequences of these changes
• How the loss of coral reefs can threaten food security for some villagers living in coastal regions
• How corals sense and behave in response to chemical cues in order to settle in areas where they are most likely to live

Coral reefs are not only of the most diverse ecosystems in the ocean, but on earth itself. However, the presence and health of corals has changed dramatically in recent decades. Since Hay began studying coral reefs in the Caribbean during the mid-70s, about 80 to 90 percent of those corals have died.

Up until this point, most of the management efforts to conserve coral reefs have been herculean and have failed to produce the intended outcomes. With this is mind, Hay is focused on how small changes can cause large, positive effects on marine ecology. In part, this involves trying to better understand the chemical signaling that contributes to coral reef health or lack thereof.

Off the coast of Fiji, Hay's work revealed that almost all juvenile fishes and most coral babies can smell and are attracted to marine-protected areas; they can also smell and are repelled by overfished areas. Additionally, corals smell nearby organisms that are similar to them, as well as the type of seaweed that commonly grows on damaged reefs. Depending on what they sense, they will either move toward or away from an area. This sheds light on how corals have evolved to be extremely selective about where they settle—after all, it's a decision that can't be undone. It also sheds light on how we might be able to enhance the probability of juvenile fish returning to certain areas and growing into populations that will keep the reef healthy. In turn, this could lead to greater overall health of ocean life and marine ecosystems.

Hay explains the difference between coral reef recovery in the Caribbean after coral bleaching, and coral reef recovery in the Pacific Ocean after coral bleaching. Hay is investigating why it is that some coral reefs recover well, while others don't seem to recover much at all. This question is becoming increasingly pressing, since major bleaching events are occurring more and more frequently.

Tune in to learn about all of this and more, including some of the innovative ways people are trying to counter the negative impacts on marine ecosystems. Available on Apple Podcasts: apple.co/2Os0myK