Loggerhead turtles help sustain delicate dunes
Web posted at: 2:00 PM EST
By Environmental News Network staff
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, research at the University of Florida shows.
Eggs laid by threatened loggerheads along Melbourne Beach, Florida hold essential nutrients that may strengthen vegetation along the shore and could be preserving the dune system, according to the research.
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.
Nesting beaches typically are nutrient poor because sandy soils don't retain nutrients and salt spray can limit vegetation growth, says Karen Bjorndal, a UF zoology professor and director of the Archie Carr Center for Sea Turtle Research.
Sea turtles nest along the East Coast of the United States from Florida up into the Carolinas. Melbourne Beach has one of the largest loggerhead nesting colonies in the world and the densest nesting along the East Coast.
The nesting season for loggerheads at Melbourne Beach stretches from May to August. The sea turtles climb up onto the beach and dig a hole in the sand between eight to 18 inches deep, and lay their eggs. Then they return to the sea, and never come back to tend the nest. About 50 days after the eggs are laid, the hatchlings emerge -- at night to avoid predators -- and head for the sea en masse. 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.
The sea turtles laying the eggs have sometimes traveled from as far as 1,500 miles away. They bring the nutrients from their feeding grounds -- the Bahamas, Cuba, the Dominican Republic, the Florida Keys and other locations along the Eastern Seaboard -- to the nesting beach.
The nutrients found inside the eggs can be distributed throughout the ecosystem in multiple ways, Bouchard says. Nests may be disturbed by predators such as raccoons, crabs or birds that eat the eggs and scatter them across the dune. 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. And 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.
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, according to Bjorndal.
Dunes naturally 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.
Studying the turtles and understanding the benefits they bring to the dune ecosystem can help improve management practices involving both the dunes and turtles, says Bouchard, and can lead to better regulation of the dunes and more turtle protection.
For instance, sometimes nests are moved into protected areas so more eggs will hatch, 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.
For more information, contact Sarah Bouchard, (352)392-2355 or Karen Bjorndal, (352)392-5194.
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