Too few fish in the sea?February 23rd, 2012
Fish feces seem an unlikely tool to help preserve the world’s much-stressed coral reefs. John W. Turner Jr. in the Department of Physiology and Pharmacology knows better; he and his team of researchers have been using fecal material from parrotfish in the Virgin Islands to link their stress with that of the reefs.
The project, funded in large part by conservation groups, centers on cortisol, a hormone produced by the adrenal gland in response to stress. The hormone serves as an excellent biomarker and stress monitor for both mammals and fish, and is detectable in their waste matter.
For a fish, stress goes beyond the presence of hungry predators. Nitrite — present in water due to fertilizer runoff — creates the condition as well, eventually impacting their numbers. That in turn affects the reefs. “One of the biggest threats facing coral reefs today is that we’re seeing much lower diversity in fish populations, lower reproductive success and slower growth rates in those who do reproduce” says Turner. “The bottom line is fewer fish.”
It‘s a fraught line because fish play a critical role in reef ecology. Take parrotfish: Grazing on the coral’s surface, the colorful fish eat away algae that unchecked would block sunlight from the coral and prevent vital photosynthesis.
“Parrotfish are part of most coral reef systems worldwide, so if you can find a reliable biomarker for the parrotfish family, you can apply it to almost any coral reef system,” Turner explains.
Cortisol was the first stress biomarker the researchers identified by analyzing parrotfish fecal matter. Taking a further step, they began looking at gene expression associated with stress response, and with the fish’s reproductive success. “We’d like now to know what genes are being turned on and off by stress. If we know, we have a template to tell us what type of stressor is affecting that area,” Turner says.
Recently the team was able to isolate RNA from four specific genes. The discovery encouraged them to begin developing a hierarchical biomarker system to detect and isolate individual stressors in an environment.
That would create a powerful tool for everyone interested in conservation, Turner notes. “It’s to the advantage of resort builders, for example, to know what the conditions are before they begin to build near a pristine coral reef area, then what they are as they build, open and operate.
“The relationship between developers and biologists used to be antagonistic, but that’s counterproductive. Everybody, including the public, benefits from knowing about the environment before and after. It makes constant monitoring possible.”
Far from spurning fish poop’s Ew! factor, Turner is excited: “Coral reefs are in bad enough shape as it is, and we’d all like to stem their degradation. We think this is the path to do it.”