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Horseshoe crabs outlasted dinosaurs, but can they survive today's challenges?

The Wildlife Forecast

Tuesday, October 05, 2010

Media contact: Patricia Behnke

The ancient arthropod moves along the beach searching for clams with its 10 eyes. It eats while walking, using its legs to crush prey and bring it to its jawless mouth. The horseshoe crab has survived unchanged for approximately 300 million years and existed 100 million years before the dinosaurs.

My first sighting of a horseshoe crab coincided with my first visit to salt water. For a 10-year-old from Central Michigan, I'm not sure what astounded me more - the vast and fierce Atlantic Ocean pounding against Montauk Point on Long Island or the armored and fierce-looking horseshoe crab.

After moving to Florida, I learned horseshoe crabs are not what they seem. They are not crabs, nor are they fierce. But they are ancient. Horseshoe crabs can be found in Florida from St. Vincent in the Panhandle, to the Atlantic coast, all the way down to the 10,000 Islands area.

Today their population is declining at a rate not experienced since the end of the last Ice Age, according to a study published by the U.S. Geological Survey (USGS) in August.

"Extensive harvest has played a role in the decline of the horseshoe crab," said Ryan Gandy, crustacean research biologist with the Florida Fish and Wildlife Conservation Commission (FWC). "The species is harvested as bait for the eel and whelk fisheries and is used in both pharmaceutical and biomedical research. Harvesting and habitat loss has created a situation where severe population declines resulted in intensive management along the Northeast coast of the United States."

The USGS study predicts climate change will further exacerbate horseshoe crab declines and further stress the many other species that depend on them.

A ripple effect already can be seen among species dependent upon the horseshoe crab. Migratory birds - 11 species in Florida alone - depend upon the 90,000 eggs one horseshoe crab can lay in a season. The red knot's decline is linked to the decline in horseshoe crab eggs in Delaware Bay, the major refueling point for the little bird in the sandpiper family known to fly as much as 9,300 miles in one season, from the Arctic Circle to Tierra del Fuego. Essential to its journey are the stopovers where the birds eat horseshoe crab eggs to gain weight needed to get them back to the Arctic Circle for breeding. With the decline in horseshoe crabs, the red knot has less and less fuel for its journey. Studies conducted by the FWC along with scientists from New Jersey and the U.S. Fish and Wildlife Service show the population of red knots wintering in Southwest Florida decreasing.

Another species, the loggerhead turtle, shares some common characteristics with the horseshoe crab: both remain unchanged after millions of years, and both face an uncertain future. And loggerheads prey upon horseshoe crabs, or at least they did. A loggerhead diet study conducted in the Chesapeake Bay recently revealed that the turtles have shifted away from eating horseshoe crabs. Although there is no direct link between the decline in horseshoe crabs and the decline of loggerhead nests in recent years, loggerhead declines did prompt the U.S. Fish and Wildlife Service to consider a change in the loggerhead's status from threatened to endangered this year. Loss of prey species is just one of many threats to loggerheads. Other threats include mortality from fisheries, illegal harvesting, habitat loss, pollution from litter, and lights on the beach during nesting season.

"Protection of nesting beaches is an important component of sea turtle conservation," said Blair Witherington, biologist with the FWC. "I'm happy to say, loggerheads nested in above-average numbers in 2010, but this was not enough to reverse the declining trend we've seen over the past decade."

To protect all the species impacted, restrictions on the harvest of horseshoe crabs in the past few years in Delaware Bay has helped increase the population, according to the USGS.

As the wildlife managers do their job through research, monitoring and regulating to prepare for future climate changes, individuals must take steps such as lowering their carbon dioxide output, a major contributor to climate change. For example, I'm on a campaign to combine errands into one trip. I keep lists of errands, and when I leave my house or workplace, I visit places close together. I also do some tasks over the Internet so I don't have to drive at all.

That horseshoe crab survived before and after the dinosaur, and with a little help from all of us, it will weather climate change as well.

FWC Facts:
The star coral may live for several centuries and grow to the size of an automobile. Its growth rate ranges from about 1/4 inch to 3/4 inch of yearly outward expansion.

Learn More at AskFWC