Florida Horseshoe Crab Watch – Linked with Limulus


map of Florida showing locations of horseshoe crab watch program

Current and future monitoring sites of the Florida Horseshoe Crab Watch.

Ancient and distinctive, most Floridians recognize the American horseshoe crab (Limulus Polyphemus) in our marine waters by its smooth, helmet like carapace, scientists refer to as the prosoma. Perhaps surprising to many Floridians, the stock status of horseshoe crabs is poorly understood, thus spurring on the need for this study. The program is a collaboration with Florida Sea Grant, and several NGOs across the state that engages citizens in monitoring established horseshoe crab spawning beaches through the citizen science group, “Linked with Limulus.” Volunteers are a vital part of this study, so engaging volunteer coordinators in coastal Florida counties to establish new volunteer groups is a priority. The data from this study will be incorporated into the next Atlantic States Marine Fisheries Commission Horseshoe Crab Benchmark Stock Assessment and inform state managers, in Florida and beyond, to population and spawning trends.

Horseshoe crabs are important for several reasons: shorebirds rely on their eggs as a primary food source during their long migrations (the decrease in horseshoe crab abundance has contributed to notable declines of many shorebird species); they are used as bait in the eel and whelk fisheries; and are of extreme importance in the biomedical industry – their copper-based blue blood is used to test the sterility of all injectable drugs and medical equipment.

Surveying horseshoe crab spawning beaches provides much needed data on spawning population trends, sex ratios and other biologically important information. Like sea turtles, they come ashore to sandy beaches to mate and lay eggs. Beaches are surveyed in the spring and fall, during the full and new moon at high tide, coinciding with peak spawning. At each beach, volunteers survey 3 consecutive days around the new and full moons. Data collected during each survey includes number of animals, mating pairs or aggregations, and any tagged animals. A subsample of crabs is collected for tagging with a U.S. Fish and Wildlife Service horseshoe crab tag. Prior to tagging, sex, age, prosoma width, weight, injuries, and mating status is recorded.

Current sampling areas include beaches in Hernando, Hillsborough, Pinellas, Brevard, Manatee, Volusia, Indian River, Martin, Franklin, Nassau, Dixie, Levy and Taylor counties. FWC is actively working to incorporate sites in Monroe, Charlotte, Lee, Palm Beach, Collier, Miami-Dade and Broward counties.

  • measuring width of horseshoe crab

    Florida Horseshoe Crab Watch volunteers measuring the prosoma width of a horseshoe crab before tagging.

  • attaching tag to horseshoe crab

    Florida Horseshoe Crab Watch volunteers tagging a crab with USFWS tags. Crabs are resighted during subsequent surveys and public beach combers.

  • attaching tag to horseshoe crab

    A male horseshoe crab that has just been measured, weighed, and tagged by Florida Horseshoe Crab Watch volunteers. The crab will be returned to the water, in hopes of being resighted by volunteers and the public.

The paucity of Florida-specific data have not allowed the State of Florida to conduct Atlantic and Gulf of Mexico population assessments, and further limited the capacity of the Atlantic States Marine Fisheries Commission horseshoe crab stock assessments. The stock status of Florida horseshoe crabs is poorly understood, due to the limited amount of targeted fishery sampling along the Atlantic coast. In addition to the scientific goals, volunteer involvement from the public has increased knowledge of biology and fishery specific issues, and further supported conservation of Florida natural resources.

Training events are held to train volunteer coordinators on how to conduct surveys, manage volunteer involvement, develop sampling schedules and train volunteers. Volunteer training events educate and train volunteers on horseshoe crab biology and management, as well as the importance of collecting scientifically accurate data.

FWRI staff and Florida Sea Grant/ IFAS will continue finding interested persons willing to serve as volunteer coordinators in coastal counties with horseshoe crab populations. Criteria for site selection, is determined by using public reporting data collected since 2002. Training events will be scheduled to specifically train volunteer coordinators on how to educate, and train volunteers on the scientific collection of data, coordinate sampling events and select sampling locations. Additionally, volunteer training events will be held to properly educate and train citizens who will be collecting seasonal horseshoe crab spawning data. In addition, the Trained coordinators and volunteers will be responsible for the collection of data from 21 established beaches, in 6 locations as well as 5 locations, and 14 beaches to be added at the beginning of the funding period. Beaches are surveyed each year in the spring and fall coinciding with peak spawning, the full moon and high tides. At each beach, volunteers will survey 3 consecutive days around the new and full moons.

Florida Sea Grant is a key partner in this project. Claire Crowley serves as principal investigator from FWRI. Berlynna Heres is the Florida Horseshoe Crab Watch coordinator and organizes all volunteer coordinators throughout the state, conducts trainings, and actively samples at beaches on the west coast of Florida. Savanna Berry, researcher with the University of Florida Sea Grant/IFAS, serves as the Cedar Key volunteer coordinator, and worked extensively to develop protocols, and training videos, used at all locations.