Horseshoe Crabs

I find horseshoe crabs fascinating - their helmet-like appearance, their prehistoric nature, and the fact that they're closely related to arachnids. 

• Horseshoe crabs originated 450 million years ago, so they are "living fossils"
• Horseshoe crabs have the rare ability to regrow limbs
• Sometimes described as "walking museums" for the large number of organisms that attach to their carapace (below you can see mainly barnacles attached!)
• They have 6 appendages under the front "horseshoe" part of the carapace which are mainly used for passing food into the mouth in the middle part of this region
• The second set of appendages are used for walking. They have a leaf-like structure used for pushing
• The tail/caudal spine/telson is used for steering in the water and also for flipping the crab over if it gets stuck! This is crazy to watch and looks weirdly painful
• It has a total of 9 eyes - 2 compound and 7 simple
• They become sexually mature around age 9, but have to shed their shell around 17 times before then!!

There are certain beaches that are laden with horseshoe crab carapaces, either from stranded individuals or from when they shed their carapace and leave the old one behind. There are other spots where I often see horseshoe crabs up in the intertidal zone. Upon doing a little research (aka calling my dad and googling) I found out that they prefer gently sloping beaches that are on a shoal or inlet. This makes sense for the area I took these photos and videos. We walk about 4 miles of shore that's facing the Atlantic and I don't notice many horseshoe crabs, but the second we round the corner to the inlet-facing south end of the island the shore looks like it's moving with all the horseshoe crab activity!

A few weeks ago the horseshoe crabs were especially abundant - mating time. 

This last week was apparently time for them to be spawning. We experienced the new moon and it was a supermoon, so we were dealing with crazy low and high tides here! Apparently this is great for those female horseshoe crabs and their egg laying.

Here is some more information from a site called The Horseshoe Crab:

Horseshoe crab spawning season varies according to latitude, but it generally peaks in May and June, with peak spawning occurring on evening high tides during the full and new moons. The adults seek beaches that are at least partially protected from surf, within bays and coves.

When the Limuli head for shore, the males patrol along the foot of the beach, awaiting the females. The female horseshoes give off chemical attractants called pheromones, which the males can detect. Although there may be other means of identification, these attractants, the directional movement and the number of males involved (often several times the number of females) reduce the liklihood of a female reaching the beach unattended.

Males, who are about 20% smaller than females, use a specially developed appendage to "clasp" themselves onto the back of the female. During peak spawning times, the horseshoes will form a dense "huddles" along the edge of the water, with 5 or 6 males grouped around one female.

By the beginning of the spawning season, each female will have developed about 80,000 eggs, which are located in dense masses near the front of her shell. She will return to the beach on successive tides, laying 4-5 clutches of eggs with each tide. Each cluster contains about 4,000 eggs and a female will lay about 20 egg clusters each year. (http://www.horseshoecrab.org/nh/spawn.html)