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Getting Crabby For A Cause: Scientists Look For Help Documenting Horseshoe Crabs

A horseshoe crab is measured and weighed
Florida Sea Grant
Measuring, counting and weighing horseshoe crabs is part of a citizen scientist project in Florida.

Horseshoe crabs have been around for a long time. Hundreds of millions of years. But their population has never been assessed in Florida. And the state is looking for help from citizen scientists to gather data.

Marine biologists in the Keys already know horseshoe crabs are part of the marine ecosystem. Now they want help figuring out how many crabs are here—and what they're up to in the water.

"We know they're here year-round," said Shelly Krueger, a marine biologist and agent with Florida Sea Grant in Monroe County. "We suspect they're breeding year-round because a lot of the reports we get, the smaller male is attached to the larger female, which means they're in their breeding mode."

That breeding mode can last for a few weeks, with the females carrying the males up to the beach to lay eggs, then back into the water to feed.

Krueger said Sea Grant also gets reports throughout the year of dime- and quarter-sized baby horseshoe crabs.

"Obviously when they're little, they don't migrate very far. So we know they're actually hatching in the Keys, but we just haven't been able to find any dedicated nesting beaches," she said.

Now Florida is embarking on its first stock assessment of horseshoe crabs, which are watched more closely in the mid-Atlantic where their eggs are an important food source for birds like the endangered red knot.

"Here we don't have as robust a population, but they still are important food for birds. That's part of why we're trying to find out more about the population in Florida, to find out if it's stable, increasing or decreasing," Krueger said.

And the horseshoe crabs — which aren't really crabs, but are more closely related to spiders and ticks — play other roles besides providing food.

"When they go through looking for worms or clams, it's called bioturbation. They're actually aerating the soil and bringing oxygen into the sediments and making better places for other animals to settle—like sponges and corals and different animals like that," Krueger said.

The state is offering a free online course to learn how to collect data about horseshoe crabs. Krueger said, in the Keys, once people complete the virtual training, she'll meet with them individually to decide where they will monitor and how to tag, weigh, sex and count the crabs. The horseshoe crab count is taking place in every coastal county in Florida, she said.

If you don't want to take the online course but still want to report horseshoe crab sitings, you can do so through the FWC Reporter app.

Copyright 2020 WLRN 91.3 FM

Nancy Klingener covers the Florida Keys for WLRN. Since moving to South Florida in 1989, she has worked for the Miami Herald, Solares Hill newspaper and the Monroe County Public Library.