Apr 13, 7:40 PM

Loggerheads nest earlier on Space Coast

Study points to climate change

BY JIM WAYMER
FLORIDA TODAY

Loggerhead sea turtles lay eggs on Brevard's beaches 10 days earlier than they did 15 years ago, a shift that three University of Central Florida biologists believe was caused by global warming.

"Since turtles are so driven by temperature, we are showing that we have a potential signal of climate change," said John Weishampel, a UCF biologist who co-authored a paper set to be published within the next six months in the scientific journal Global Change Biology.

Other scientists doubt whether 15 years is long enough to read any significant global temperature trend.

The UCF researchers calculated median nesting dates between 1989 and 2003 on beaches from Patrick Air Force Base to Sebastian Inlet. That's as far back as Florida has used consistent methods for monitoring sea turtle nesting.

Biologists consider the 25-mile stretch the most important nesting area in the western hemisphere for threatened loggerhead sea turtles.

The researchers found that turtle nesting peaked sooner and sooner during the past 15 years: about June 19 in 2003 vs. June 29 in 1989.

Within that timeframe, loggerhead nesting stayed statistically flat throughout Florida, said Llew Ehrhart, a marine turtle biologist at UCF and co-author of the paper. Since 1982, loggerheads increased in south Brevard and in Indian River County. Nesting dropped in the past five years.

"I guess I'd have to admit, it did surprise me," Ehrhart said of their discovery of earlier nesting.

Warmer May waters may be triggering earlier nesting, the researchers said.

They noted a 1.44-degree Fahrenheit ocean temperature increase for the month of May -- since 1989 -- at the weather buoy closest to Brevard's nesting beaches. That's 23 miles off Cape Canaveral.

Weishampel suspects warmer temperatures in the Caribbean also may spur turtles to nest sooner.

But a century of tide gauge data from the Caribbean to South Carolina shows no significant temperature change, said George Maul, a professor of oceanography at Florida Tech.

He said temperature changes at one buoy could represent normal climate cycles, with difficult-to-determine influences on wildlife.

"Scientists are not sure how good those temperatures represent exactly what's going on where the organisms are," Maul said. "I think we just need to be cautious before we jump to conclusions about things."

Earlier loggerhead nests might affect the ratio of male to female turtles, Ehrhart suspects. When sand warms beyond 82.4 degrees Fahrenheit, nests produce more females. When cooler than that, more males tend to hatch. But the influence of earlier nesting is uncertain, he said.

"Maybe, so far as the turtles and the eggs are concerned, there's not much difference," Ehrhart said.

An earlier season could benefit the turtles, if it puts the hatchlings out of harm's way during peak hurricane season, he added.

"It depends a lot on the timing," Ehrhart said.

Loggers take about 50 days to hatch.

The researchers suspect an earlier season also could apply to Florida's other four species of sea turtles.

The researchers said that earlier nesting raises questions for future studies, such as whether the turtles' diet of shrimp, crabs and other invertebrates would be as available when hatchlings venture from beach to sea.

While the impact on sea turtles has yet to be determined, Ehrhart said he's convinced global warming is real.

"I think there is a legitimate argument about what's causing it. That it is happening is almost beyond question," he said. "I think we'll be seeing these kinds of effects on animals and biological systems for as long as the global-warming phenomenon persists."

Contact Waymer at 242-3663 or jwaymer@flatoday.net