Old-growth coral reveals clues to its survival

Taking to a living organism with a large pneumatic drill might not sound like the best way to protect it.

But that’s just what UNC marine scientists did to a distinctive species of coral off the coast of Belize, in an effort to determine how to help conserve coral reef systems.

Coral reefs are important natural resources for certain states in the U.S. and developing countries such as Belize, a small nation just below Mexico in the western Caribbean. There, the Mesoamerican Barrier Reef – the second largest in the world – acts as an environmental and economic attraction for humans and marine creatures.

The UNC researchers, Karl Castillo, Justin Ries and Jack Weiss, tapped the natural internal archive of massive starlet corals, which can grow to almost 4-feet across over a period of about 100 years.

“Massive starlet corals are like old-growth trees in a forest,” says Castillo, a postdoctoral research associate in the College of Arts and Sciences. “In much the same way that land-based biologists analyze tree rings to determine the age of trees and the impact of past environmental events, the cores of these corals reveal the same kind of information.”

What Castillo and Ries found indicates a troubling change. By measuring annual growth bands in the cores, they could tell that in the early 1900s, corals on the outer reef grew faster than those closer to shore. But over the past century, the pattern has flip-flopped; open ocean corals’ growth rates slowed, while the others have remained relatively stable.

Their new findings suggest that massive starlet corals closest to the open ocean are having the most trouble weathering the effects of environmental changes, such as warmer-than-average water temperatures due to climate change and higher pollution levels.

Ries, assistant professor of marine science, says that may be because seaward corals have not had time to adapt to these recent human activity-related stressors. In contrast, for millennia, landward corals have probably been exposed to greater baseline stressors and possibly built up more immunity to them.

“When coral growth slows down, reefs may erode more quickly than they’re being built, which could ultimately cause the reefs to decrease in size or even disappear,” says Ries. “Local economies rely on these reefs and the organisms that inhabit them for their fishing and tourism industries. These corals must be actively producing new reef material to support a thriving ecosystem.”

The research holds special significance for Castillo, a native of Belize.

“As a kid, my stepfather took me out to the reefs,” he says. “I’ve actually seen the changes that have occurred over time. I wanted to try to find out and answer these questions so that we can eventually, if possible, make conservation or management decisions to try to conserve coral reefs in the face of climate change.”

The work was partially funded by a grant from the National Science Foundation.