Prehistoric survivors: Horseshoe crabs endure eons
Long before dinosaurs roamed the Earth, hard-shelled, spear-tailed sea creatures crept along the ocean floors. Four hundred million years later, their form and lifestyle is virtually unchanged.
Today, a Fairfield researcher has studied these primordial beings for more than a decade -- and whether the tides of time are turning against them.
Horseshoe crabs, a common sight in the months of May and June along Connecticut's shoreline, have been the focus of this comprehensive study by Jennifer Mattei, PhD, an associate professor of biology at Sacred Heart University. Called Project Limulus (the Latin term for the crabs), the study tags and tracks the creatures with the goal of learning more about them and their prehistoric legacy.
An SHU faculty member for 16 years, Mattei said that 11 years ago she started helping a colleague with a Connecticut Audubon Society program focused on horseshoe crabs. "Questions arose about their migratory patterns and if, like sea turtles, they returned to familiar breeding ground every year," she said. "We got a kit from a tagging company with the intention of tagging the crabs to track their annual travel, starting in the Milford Point area. We affixed tags to 50 horseshoe crabs that first summer."
Unfortunately, the pair saw none of the tagged creatures return the next summer. "That was probably because the tag quantity was so minimal," she said.
In 2001, Mattei applied for a grant through the state's license plate program dedicated to Long Island Sound preservation. "I decided to expand our work into a community research project, involving the Audubon, Maritime Aquarium, members of the Nature Conservancy and high school teachers," she said. "I did talks, trainings and gave out tag kits. We were able to get a few thousand horseshoe crabs tagged."
Mattei said the program continued to expand. This past May and June, over an eight-week period more than 16,000 horseshoe crabs were tagged.
With regard to findings of the study, the biologist said, "About 10 percent return, indicating that they are not like sea turtles. There is some affinity -- about half of those that have returned were originally tagged at the same beach."
Mattei said the study indicates the crabs don't seem to travel in any particular pattern and a small percentage cross the Sound. "When they're not ashore, they appear to live out in the middle of the Sound and bury themselves," she added. "We've sonar tagged a few which has given us these results."
The mating ritual is quite unique to the species. "Typically, in March, a male chooses a female at random and attaches himself to her hindquarters," she said. "When she emerges from the water and deposits her eggs in the sand, he fertilizes them externally. She carries up to 30,000 eggs and will return several times during the season to make deposits. The male is still attached throughout that time, through August."
Surrounded by posters depicting such topics as the evolution of life and age of reptiles and several coastal survey maps, the professor expressed concerns about the status of the region's horseshoe population. "They are not endangered and have been around since the Ordovician period, though recent observations are showing a building trend of females coming up on the beaches without a mate," she said. "The density of animals is low here, which makes it difficult for the animals to find each other and may, over time, contribute to a decline in their overall numbers."
She said it's ironic that creationists have used horseshoe crabs as proof that organisms don't evolve. "They're actually the epitome of evolution," she said. "Their bodies have been conserved relatively unchanged over time by natural selection."
Mattei said a new finding this year is the discovery of various insects that live in and around the horseshoe crab eggs. "We've seen a predacious beetle that may eat fly larvae," she said, eager to learn any relationship between the species.