Horseshoe crabs are ancient organisms – they have been in existence for hundreds of millions of years! This is much longer than the average lifespan for a species on Earth and, therefore, horseshoe crabs are considered living fossils. Earlier this year, citizens in Cedar Key were trained by FWC and University of Florida biologists to collect data on horseshoe crabs. Citizen scientists in Cedar Key finished up the final 2016 survey of nesting horseshoe crabs this past Monday the 17th. In total, over 20 volunteers completed 45 separate surveys of nesting horseshoe crabs at 5 sites around Cedar Key. In the photo above, three citizen scientists are working together to collect data on a subset of crabs they observed nesting on the beach. Over 200 crabs were tagged with a small white disc, each with a unique number that allows that crab to be identified if seen again. Keep your eye out for these tags next time you are walking the beach!
Horseshoe crabs are different from most other invertebrates in that they take a long time to reach maturity – about 10 years on average! Therefore, adult horseshoe crabs found nesting on beaches are usually at least 10 years old. Citizen scientists studying nesting crabs begin by checking the condition of the crab’s hard outer shell (carapace), legs (appendages), and tail (telson). This helps estimate the age of the crab – a smooth, shiny shell indicates the crab is younger while a scratched, pitted, and barnacle-encrusted shell indicates the crab is older. After estimating the age of the crab, citizen scientists measure the weight and width of the crab. They also determine if the crab is male or female by examining body size (females are larger) and appendages. The crab in the picture to the right appears shiny and smooth and is relatively small – this crab was a young male.
After taking the measurements, citizen scientists apply a small white tag to the left side of the crab. This is done by making a small puncture in the shell and pushing a fastener into the hole (this does not harm the crab). The crab in the photo on the left is being tagged at the City Beach in downtown Cedar Key. The tag gives a unique identifier to the crab that receives it and this information is linked to the data collected on that crab, such as weight and location.
Anyone can report a tagged crab – Just make note of the number on the tag and use the hotline (1-888-LIMULUS) or the website (www.fws.gov/crabtag) to report the number, sighting location, and condition of the crab. Researchers use the tags to collect valuable information about population numbers and movement of crabs between nesting beaches. See this post for more information about why citizen scientists are helping collect this valuable data.
For more: Horseshoe Crab Fact sheet: https://www.nwf.org/Wildlife/Wildlife-Library/Invertebrates/Horseshoe-Crab.aspx