Horseshoe crabs - IFAS Tyler Jones

Horseshoe crabs (Limulus polyphemus) are a common sight on sandy beaches and other nearshore habitats in Florida. They mate along beaches, especially during full and new moons of the fall and spring months. This behavior makes study of population numbers convenient because researchers simply need to walk along the beach and count. A citizen science program in Cedar Key, started earlier this year by the University of Florida, FWC, and the Friends of the Lower Suwannee NWR, takes advantage of this behavior to collect valuable information about breeding horseshoe crabs. In addition, a subset of the crabs are tagged with a small white disc (shown below, right) that helps track crab movements and reappearances on beaches.

Why study the crabs?

Horseshoe crabs are an important species ecologically and are also used in biomedical testing. Many marine species eat horseshoe crab eggs, including shorebirds that depend on the eggs for energy during migration. These crabs are also used as bait (conch and eel fisheries) and are captured live for display in aquaria and for research. The blood of horseshoe crabs also is vital for medical testing – the FDA requires that all injectable medicines, devices used for injection, and internal prosthetics (e.g., heart valves) undergo testing with an extract only found in horseshoe crab blood (Limulus Amebocyte MAR 22 CITY SCILysate). 2016-08-30 13.35.34If you have ever received a vaccine, horseshoe crabs have helped you! Their importance in different industries means that there is a demand for wild-caught horseshoe crabs and a moderate fishery for these animals exists in Florida. The FWC is required to collect data on fisheries within the state, but limited resources prevent detailed surveys from being completed by state biologists. Therefore, citizen scientists are providing an important service by helping the state keep track of population numbers and better manage these important marine animals, to ensure that the ecological function of horseshoe crabs is not impacted negatively by harvest.

What can you do?

Keep your eye out for tagged horseshoe crabs the next time you are walking the beach or near the water. If you see a tagged crab (like the ones in the photo above), snap a picture of the tag or record the number on the tag. Try to limit disturbance to the crab (try not to pick it up and if you must pick it up, NEVER pick it up by the tail) and DO NOT remove the tag. Make a note of the date and time you saw the crab and the location. You can then report this data MAR 22 MAR TIF Citizen Scientistsusing the online form at ( or by calling 1-888-546-8587 (1-888-LIMULUS). This data goes into a national database maintained by the US Fish and Wildlife Service and contributes to knowledge about horseshoe crab movements and population numbers.

If you would like information about how you can be involved in the citizen science surveys, please contact me at We are hoping to expand this program to other areas of the Nature Coast!




HSC Tag Resighting Flyer

UF IFAS Publication on Horseshoe Crabs:

Cedar Key News Article about First Round of Citizen Science Sampling:

Horseshoe Crab Fishery in Florida:

Horseshoe Crab Facts:

Photo Credits:

Top – UF IFAS Communications, Tyler Jones

Middle Right – UF IFAS NCBS, Savanna Barry

Middle Left, Bottom Left – UF Biology/Maria Sgambati