Looking Out for Horseshoe Crabs

Horseshoe crabs spawning. Credit: Bill Hall, Univ. Delaware Sea Grant

Horseshoe crabs spawning.
Credit: Bill Hall, Univ. Delaware Sea Grant

Horseshoe crabs spawning on a beach. Credit: FL Fish & Wildlife Commission

Horseshoe crabs spawning on a beach.
Credit: FL Fish & Wildlife Commission

The female is the larger of the two horseshoe crabs. Credit: Fotosearch -Stock Photo

The female is the larger of the two horseshoe crabs.
Credit: Fotosearch -Stock Photo

Spring is here and that can only mean one thing, horseshoe crabs! That’s right it’s horseshoe crab survey time!

Each spring the scientists with the Florida Fish & Wildlife Conservation Commission (FWC) look for volunteers to report horseshoe crab sightings around the state as part of their annual horseshoe crab survey.

So, if you would like to be part of the research team, all you need to do is get out and walk along the beach and let FWC researchers know when you see horseshoe crabs. Please see the information at the end of this article for submission information. The following is some background information on horseshoe crabs.

About Horseshoe Crabs

  • The horseshoe crab is found on shores of the western Atlantic Ocean ranging from Maine to Mexico. Fossils of horseshoe crab ancestors show that these animals have been around for over 350 million years – before the age of dinosaurs. Therefore, it is no surprise that scientists typically refer to horseshoe crabs as “living fossils.”
  • Interestingly, horseshoe crabs are not really crabs at all! As it turns out, they are more closely related to spiders and scorpions than they are to true crabs. This is because unlike true crabs, horseshoe crabs do not have antennae or jaws, and their legs are similar to those found on spiders.
  • Currently, horseshoe crabs are being harvested commercially for three purposes in the United States: bait (conch & eel fisheries); marine life (aquarium trade, research, etc.); and biomedical (for blood).
  • Compared to other states, especially along the Atlantic coast, Florida does not have a large horseshoe crab fishery.  The primary harvest in Florida is for marine life.
  • Horseshoe crabs are ecologically important. During certain times of the year, horseshoe crabs lay billions of eggs on beaches. These eggs are an important food source for migrating birds and the marine wildlife.
  • Horseshoe crabs are also directly important to humans because research on their compound eyes has lead to a better understanding of the human visual system.
  • In addition, horseshoe crab blood is widely used by the biomedical industry. Special cells in their blood (which by the way is blue) are used to test for bacterial contamination in our blood supplies and in the production of many commercial drugs. A horseshoe crab’s blood contains hemocyanin, a copper – based molecule that gives it a blue color.
  • Finally, the material that makes up their exoskeleton (chiton) is used to make contact lenses, skin creams, and hair sprays.
The blood of the horseshoe crab is blue because it is copper-based. Credit: FL Fish & Wildlife Commission

The blood of the horseshoe crab is blue because it is copper-based.
Credit: FL Fish & Wildlife Commission

Horseshoe Crab Anatomy

  •  The tail of the horseshoe crab is often thought to be a weapon by many people. However, the horseshoe crab is actually harmless and the tail is used to dig through sand and to turn the crab upright if it is accidentally turned over.
  • The first pair of legs can be used to distinguish between males and females. Males use their specialized front legs, called claspers, to hold on to the female during spawning.

Project Objectives and Goals

Currently, horseshoe crabs are being over-harvested in some states. The management plan issued by the Atlantic States Marine Fisheries Commission requires that all Atlantic coastal states must identify horseshoe crab spawning beaches.

With your help! – FWC’s goal is to identify horseshoe crab spawning beaches around Florida.

How can you help?

FWC is asking the public to report sightings of horseshoe crab activities. The information that the researchers would like to collect from you is the following:

  • Date and time of your sighting.
  • Location of your sighting.
  • Whether or not horseshoe crabs were spawning.
  • A rough estimate of the number of horseshoe crabs seen.

Spawning behavior of horseshoe crabs is best observed within three-days before and after a full or new moon on sandy beaches with low wave action.

If you want to be more involved, you can contact the FWC researchers about collecting data on abundance of male and female horseshoe crabs, and on sizes of individuals. You can contact FWC using any of the following methods:

Go to MyFWC.com/Contact and click on the “Submit a Horseshoe Crab Survey” link, then “Florida Horseshoe Crab Spawning Beach Survey,” or go directly to http://www.surveymonkey.com/s/horseshoe_crab

  1. You can also report findings via email at horseshoe@MyFWC.com
  2. Or call toll-free at 1-866-252-9326

If you have any questions please let me know. Enjoy your beach walks and “crab” watching.

(Bill Mahan is a FL Sea Grant Agent and Director of the Franklin UF-IFAS Extension Program. Contact him at (850) 653-9337, 697-2112 x 360; via e-mail at bmahan@ufl.edu; or Facebook http://www.facebook.com/UFIFASFranklinExtension

Sinkholes in the Florida Panhandle, Facts and Resources

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This tiny sinkhole appeared in my yard during the heavy March rains. Although only 3 feet wide, it was 5 feet deep. My dog looks both curious and jealous that it wasn’t one of the holes he’s dug!

During our heavy March rainfall events a tiny sinkhole appeared in my yard.  While it was only 3 feet across, it was over 5 feet deep!  After reading about the various types and causes of sinkholes, I decided it was most likely a “subsidence incident” sinkhole caused from collapsed underlying organic material (perhaps an old tree root?).  Read on to learn more about sinkholes, their causes, and their prevalence in Florida.

Sinkholes are a fascinating, common, and sometimes tragic characteristic of Florida’s landscape.   They are one feature of “karst” terrain which is quite prevalent in Florida.  Other features of karst terrain include caves, springs, disappearing streams, and underground drainage systems.  Karst terrain “is a type of topography that is formed by dissolution of bedrock in areas underlain by limestone, dolostone or, as in some western states, gypsum….The term karst, therefore, refers to the terrain and the term sinkhole is one of the types of drainage features reflected by that type of terrain.  Other subterranean events can cause holes, depressions or subsidence of the land surface that may mimic sinkhole activity. These include subsurface expansive clay or organic layers which compress as water is removed, collapsed or broken sewer and drain pipes or broken septic tanks, improperly compacted soil after excavation work, and even buried trash, logs and other debris… Such an event is called a “subsidence incident.” (Source: Florida Dept of Environmental Protection http://dep.state.fl.us/geology/geologictopics/sinkhole.htm)

According to the United States Geological Survey and the Florida DEP Bureau of Geology, panhandle Florida’s limestone bedrock is overlain with from zero to over 200 feet of sediments.  The depths and types of these overlying sediments are major factors in the prevalence and characteristics of sinkholes and other karst features.  View this map to see an overview of sediment depth and sinkhole activity in your county.  Leon County, in eastern panhandle Florida, boasts its geologically active Lake Jackson, not only for its famous largemouth bass fishery, but also for its periodic disappearances through underlying sinkholes!  This 4,000 acre lake has a history of virtually draining through underlying sinkholes about every 25 years.  Its most recent draining event was in 2006.

This is the sinkhole that drained Leon County’s Lake Jackson in 2006.  The author is kneeling at its edge.

Please visit the following links for more information, including answers to questions such as:

  • I think I have a sinkhole in my yard. What should I do?
  • How do I fill in a sinkhole?
  • Will watering our lawn lower the water table level and thus, cause sinkholes to develop in our neighborhood?
  • Is there a government agency that will come and inspect my sinkhole?
  • What is the sinkhole risk factor associated with my area?
  • Is there a database showing all sinkholes in Florida?
  • Our insurance company has informed us that the area where we are going to purchase property is listed as a sinkhole area. What does this mean? What can we do about it? Should we buy in that area?

Florida DEP, Bureau of Geology, All about Sinkholes, Questions and Answers.

Sinkhole Type, Development, and Distribution in Florida – A Map

UF/IFAS Disaster Handbook – Sinkholes

Sinkholes and Catastrophic Ground Collapse: What Every Floridian Should Know