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
"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.