New Research Shows Loggerhead Sea Turtles Sustain Delicate Dunes

November 05, 1998

GAINESVILLE --- Nesting sea turtles may do more than hatch future generations of loggerheads -- they also may be ensuring the future of the nation's fragile coastline, new research at the University of Florida shows.

The results of the research shows eggs laid by threatened loggerheads along Melbourne Beach hold essential nutrients that may strengthen vegetation along the shore and could be preserving the dune system.

Sarah Bouchard, a UF student who studied the nesting turtles for her master's thesis, monitored the beach for energy, nitrogen, phosphorus and lipids left behind by turtle eggs and the possible effects those nutrients had on the beach ecosystem.

Karen Bjorndal, a UF zoology professor and director of the Archie Carr Center for Sea Turtle Research, said nesting beaches typically are nutrient poor because sandy soils don't retain nutrients and salt spray can limit vegetation growth.

Sea turtles nest along the East Coast of the United States from Florida up into the Carolinas, Bouchard said. She said Melbourne Beach has one of the largest loggerhead nesting colonies in the world and the densest nesting along the East Coast.

Loggerhead turtles nest at Melbourne Beach from May to August. About 50 days after the eggs are laid, a hatchling will emerge. Turtles nest on average every few years with each turtle laying several clutches, or nests. Each year, about 65,000 nests are laid along Florida's beaches. Although no statistics are available yet, Bjorndal said preliminary indications show this year's nesting season was successful.

The nests are laid by sea turtles that can feed as far as 1,500 miles away from beaches where they lay their eggs. Sea turtles swim to nesting areas and carry nutrients from feeding grounds to sandy beaches. Feeding grounds are near the Bahamas, Cuba, the Dominican Republic, the Florida Keys and other locations along the Eastern Seaboard.

Bouchard said the nutrients found inside the eggs can be distributed throughout the ecosystem in multiple ways. Nests may be disturbed by predators such as raccoons, crabs or birds that eat the eggs and scatter them across the dune.

She said some eggs escape predators but are damaged when the roots of plants grow toward the egg and break through the shell to reach the nutrients inside.

If the eggs survive and a hatchling emerges, the fluid inside the egg remains in the ground and still provides nourishment for the dune ecosystem, Bouchard said.

"There has not been enough attention paid to the impact turtles have on the ecosystem," Bjorndal said. "We've never quantified those impacts."

Bjorndal said possible consequences of a beach losing the nutrients provided by the sea turtles include loss of plant growth, which can lead to dune destabilization and erosion. In addition, insects and other herbivores that eat dune vegetation would suffer.

Without the turtles, Bjorndal said, dunes receive nourishment from rain water, algae tossed up by waves and terrestrial animals from behind the dune system that wander across the sand. But sea turtles provide a much greater quantity of nutrients to the dune system than these other sources, which is why it is important to understand their role.

Bouchard said studying these turtles and understanding the benefits they bring to the dune ecosystem can help improve management practices involving both the dunes and turtles and can lead to better regulation of the dunes and more turtle protection.

Some nests are moved into protected areas so more eggs will hatch, she said, but moving the nests also removes the nutrients from the original nesting areas.

The next step, she said, is to help "management agencies understand the ramifications of moving the nests on nutrition in the dunes." Future research will follow the pathways of the nutrients through the food chains in the beach ecosystem and seek to determine what would happen if sea turtles no longer nested in those areas.
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Writer: Kristen Vecellio, vecellio@ufl.edu
Sources: Sarah Bouchard, 352-392-2355
Karen Bjorndal, 352-392-5194
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University of Florida

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