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Harbor Branch researcher examines stresses on coral reefs
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By WILIAM LARRY JENNINGS
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Coral reefs make up less than 1 percent of the earth’s surface, and yet they are among its most biodiverse environments.

But they’re disappearing at an alarming rate. And Sara Edge, a research associate at Harbor Branch Oceanographic Institute at Florida Atlantic University, is trying to discover why.

Edge has customized a piece of machinery, called a microarray, to detect a coral’s response to stress, both in her lab and in the environment. Her “gene expression profiling” microarray has been used to research the stressors on the coral species montastrea.

Such stressors can range from elevated sea temperatures to sedimentation or even pollution.

To be able to conduct her research with her microarrays, Edge extracts total RNA (all of the RNA contained within a single cell). She then converts it to cDNA (copy DNA) by a process called "reverse transcription reaction" to isolate the genes that she wants to research.

“This way,” Edge explained, “I am only focusing on genes that have been transcribed and not all of the genetic material within a cell.”

Microarrays show what genes are more expressed than others in the form of a grid. In the case of Edge’s microarray, the lesser that genes are expressed, the more green they show on the grid. The more expressed, the redder they appear.

It was during her graduate work at Georgia Institute of Technology, under Professor Terry Snell, that Edge became interested in developing a microarray to research on the stressors of coral.

“I was interested in [Dr. Snell’s]) lab,” Edge recalled, “because of his research on corals using molecular biomarkers as indicators of stress.”

Wanting to progress from biomarker research, which worked with only a single gene at a time, Edge saw an availability for microarrays, which can handle anywhere from 150 to thousands of genes at a time.

“Microarray technology was being used in human health … at the time,” Edge said. “I became interested in using [it] to study coral stress.”

The first "coral-stress array" that Edge developed was for a study in Bermuda to assess the health of coral that existed at varying distances from the Bermuda dump.

“The array was small at the time and consisted of 32 genes,” Edge said. “It was technically a macroarray.”

Edge’s first full microarray, consisting of over 150 identified genes, was used in a 2005 study to analyze populations of montastrea cavernosa on reefs just off the coast of South Florida.

In addition to Bermuda and Florida, Edge has also conducted research in Fiji and the Bahamas.

The ability to examine the gene reaction of coral, as with humans, can also lead to identifying susceptibility to diseases, toward which Edge would like to expand microarray research, as well.

“I’m interested in … the molecular response of coral to disease infections,” Edge said. “I’m also interested in understanding cellular communication between the coral host and its symbiotic algae.”

The disappearance of coral across the globe begs the question: what could cause such global-wide effects?

“This is not a simple question,” Edge admitted.

“It’s clear that there is no single factor that is definitively causing coral decline,” she explained, “but climate change acts as a catalyst, causing increased bleaching [the colored algae leaving the coral host, causing the white appearance], decreased ability to recover, higher rates of disease and death.”

Long periods of elevated water temperatures also add to local stress experienced. In regard to the South Florida area, the local stress is the cause of humans, Edge said. “The single most influential local stressor,” she said, “is human pressure due to development.”

Such activity includes overfishing, pollution, sedimentation and the input of both freshwater and sewage into the ocean.

To further her research, Edge not only wants to expand to more genes, but also to discover the origins of coral existence.

“In essence,” she explained, “I am interested in how [the algae and the coral host] talk to each other and how they make sense of their environments using molecular signals.”

 

 
 

 
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