By Abbey Green | Courtesy of ecoRI News[divider style=”solid” color=”#eeeeee” width=”1px”]
Older than dinosaurs, horseshoe crabs have survived plenty. But human impact may be the threat that could wash them out of the Atlantic.
For more than 350 million years, these living fossils have crawled ashore underneath the light of a full moon and laid their eggs in the sand. These hard-shelled crustaceans are a keystone species, making them vital to the ecosystem. Their eggs are a critical food source for many migratory shorebirds, and their ocean floor walks rototill the bottom, keeping the seafloor healthy.
The Atlantic States Marine Fisheries Commission reports horseshoe crabs were hunted heavily from the 1800s to the early 1900s, with catches averaging from 1 to a whopping 5 million crabs a year. Total catch numbers dwindled over time, all the way down to 42,000 crabs by the 1960s. However, millions more were being harvested unreported and at a detriment to the horseshoe crab’s survival.
Bob Prescott, sanctuary director at the Mass Audubon’s Wellfleet Bay Wildlife Sanctuary, said the sanctuary’s research into the ecosystem importance of horseshoe crabs began in 1999. Some fisheries didn’t see the benefit of horseshoe crabs at the time, and were more concerned with, say, their clam harvest than anything else.
“There was virtually no oversight by the (Massachusetts) Division of Marine Fisheries, and all of the shellfish departments and shellfish wardens were happy to get rid of this predator from their systems, thinking they’d get more clams,” Prescott said. “But, as we now know, the horseshoe crab is a really important part of the ecosystem, and you may even end up with less clams with less horseshoe crabs.”
By 2001, state-by-state harvest quotas were required by the Atlantic States Marine Fisheries Commission Horseshoe Crab Management Plan, and harvests have decreased in an effort to save the crabs.
Today, these crabs have two big threats looming over their oddly shaped heads. Horseshoe crabs are a popular bait for conch and eel fishermen, and they are wanted for their blood. Horseshoe crab blood is used for biomedical research and product manufacturing involving the detection of gram-negative bacteria, which can be harmful to humans.
Overfishing is the species’ primary threat, according to Scott Olszewski, marine biologist at Rhode Island Department of Environmental Management (DEM). He said a stock assessment taken in 2012 indicated that the Mid-Atlantic stock was stable, but the southern New England stock had low abundance.