SPEAKER: It seems nearly every day now that we hear reports of more damage to the environment. Coral reefs are no exception. As we look throughout the planet, we continue to find significant decline in the health and richness of coral reefs.
We recently looked at the prevalence of disease in marine organisms, and found a real increase over the last three decades in many species. And during the fall of 2005, there has been widespread coral bleaching throughout the Caribbean. In fact, the worst we've seen since the 1998 El Nino, which caused a devastating, global-scale bleaching event that resulted in a lot of coral death.
While there are many indicators of coral reef decline, I'd like to focus on three main symptoms-- coral disease, coral bleaching, and the overgrowth of reefs by algae.
Now, coral diseases can be caused by a number of stresses, including infection by viruses, bacteria, and fungi. You may not have thought about it before, but coral reefs can get bacterial, viral, and fungal infections just as humans do. Infections can be worsened by conditions such as increased sea water temperature, sediments, and pollutions.
So how can you tell that a coral is sick? Do they get sniffles? Actually, they're more akin to measles or pox. Some diseases move across the surface of living coral in colored bands. Others appear as tumors or blotches or spots. Some diseases look like patches of dead tissue spreading across the coral.
Sometimes, coral bleaching can be caused by infectious agents. We say that corals have bleached when they lose their symbiotic algae, which are called zooxanthellae, and then they turn white. Studies have shown that not only heat stress, but also an infection by the bacterium Vibrio shiloi, can cause this loss of zooxanthellae.
Coral bleaching can also be caused by a variety of physical stresses, the most important one being long periods of increased temperature. As higher ocean temperature becomes more common, so do coral bleaching events around the world.
Finally, declining coral reefs often appear to be overgrown by green algae. The abundance of algae is normally kept in check by fish and other herbivores that feed on the algae. When herbivore populations drop-- due to disease or overfishing, such as happened in the mid-1980s-- and when nutrients increase, the algae can grow out of control and take over surface area inhabited by coral.
Now, when nutrients increase due to things like runoff, they act as a sort of fertilizer for the algae, which then grows more quickly over coral colonies. In 1994, scientists in the Caribbean called it a phase shift when corals were replaced by algae on many Caribbean coral reefs.
My research here at Cornell focuses on coral disease and how coral organisms resist disease. I'm particularly interested in sea fans, a type of soft coral. These corals make a variety of biologically-active defense compounds, some of which help them fight fungal and bacterial infections, where they also act as deterrents to fish and other predators.
We are looking now at how sea fans protect themselves from a specific fungal pathogen called aspergillus sydowii. In the picture of the sea fan, the lesions are caused by the fungus, and the bright purple halos is the sea fan immune response to fungal infection.
This project has many facets and involves research being conducted by postdocs, graduate, and undergraduate students I'd like to take the opportunity now to introduce them and let them tell you about the work they're doing.
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Over the last 20 years we have observed coral reefs declining at an alarming rate. What is causing this catastrophe and what can be done to prevent further damage?
This study room examines the causes of coral reef decline, including increasing ocean temperatures, overfishing, and runoff from coastal areas. The room describes research on coral disease and how coral organisms resist disease. The research is being conducted by graduate students, undergraduate students, and researchers, who describe their work in their own words.
This video is part 3 of 10 in the Coral Reef Sustainability series.