Marine & Freshwater Environmental Education
Even though they have ten legs – not, eight – we’ve always said horseshoe crabs are members of the arachnid family. It was first theorized by E. Ray Lankester in 1881. But, until recently, it had not been proven in terms of genetics. Scientists at the University of Wisconsin-Madison studied the molecular evolutionary patterns of Limulus polyphemus to confirm Lankester’s theory. So they are still a great addition to your Halloween decoration box.
Image (c) factzone.com
No joke. I like horseshoe crabs, but not more than my family. Especially my mom. Let me tell you a story about how incredible she was one particular evening in early June. It was probably about 2002 and I was a seasonal employee for the NJ Division of Fish and Wildlife. The job was awesome in every sense. Except the hours … either really early for tagging stripers along the Delaware Bay or really late to survey HORSESHOE CRABS!
In case you haven’t heard watching the horseshoe crabs come up to the wrackline to spawn is an incredible experience (check out my post on the short and sweet of horseshoe crab spawning here). You might see some Limulus polyphemus the nights near a full moon or new moon right as the sun is going down. But, it’s not until the tide is at its highest point that the ancient fossils really come out of their hiding spots. 
My co-workers and I went about as normal for this event and used the quadrat to estimate the amount of females and males every six steps (the females are much bigger!). We’d log the numbers on a clipboard. After the length of the beach that was our responsibility we’d head home. It was about 2am one particular morning when we finally made it back to the van. I also worked as a waitress in the summer so it had been a long day. The data sheet was my responsibility. It blew away. It’s really windy by the sea usually!
We didn’t fudge any numbers. I went back the next night … but, not alone. My amazing, overprotective mom came with me. After all, I had to drive about an hour to a small town along the Delaware Bay in the middle of the night. It was going above and beyond. I mean, she’s not a nature-type so this was in pure mama bear mode that she made the trek with me. It was incredible … my mom was totally amazed by the phenomenon too. One minute there were about fifteen horseshoe crabs and the next hour as soon as high tide occurred they were covering the beach! That night I was able to share my love of teaching and horseshoe crabs with someone I loved. She exuded such enthusiasm that I have no doubt it’s one reason I keep this blog and it’s focus of all things horseshoe crabs going. She might have been pulling my arm and thought the whole experience was really gross and icky, but parents know how to let their kids shine and that’s just fine with me.
NOAA’S Ocean Today provides a great view of the field experience, too. Yes, I did wear a headlamp like those citizen scientists.
What citizen science projects have you participated in lately? Check out what’s going one here.
Once a horseshoe crab reaches their full size they stop molting. Their shells then come to host many sessile creatures, including slipper snails.
All horseshoe crabs molt – until they reach adulthood. They grow on average a quarter of their size each time they shed. Females grow to be about two feet across and males a bit smaller. Molting occurs several times during the first few years and slows as they age. It usually takes 17 molts to reach sexual maturity at age 9-11.
Studies have proven that adults do not molt because the age of organisms living of the crab’s shell. For instance, scientists Bottom and Ropes (1988) completed a study to determine that large slipper snails (Crepidula fornicata) were at least 8 years old on a sample of specimens. This would then make the average age of horseshoe crabs in the Delaware Bay to be 17 years old.
Also, the deteriorated carapace of some horseshoe crabs, as well as the presence of internal chitinous rods that hold the carapace in place are also evidence that older horseshoe crabs do not molt.
Horseshoe crabs use hemocyanin to distribute oxygen throughout their bodies. Hemocyanin is copper-based and gives the animal its distinctive blue blood. We use an iron-based hemoglobin to move oxygen around.
The blood of this living fossil has the ability to clot in an instance when it detects unfamiliar germs, therefore building up protective barriers to prevent potential infection. This adaptation has made the blood of the horseshoe crab quite desirable to the biochemical industry.
Image (c) wired.com
In case you have not had the opportunity to get your hands on the new book, Horseshoe Crabs and Velvet Worms, about animals that have remained unchanged through time (Richard Fortey) here is a video from the BBC on how the horseshoe crab has been able to survive through the ages.
I am particularly fond of this clip because the horseshoe crab expert notes that the horseshoe crab, while an opportunistic and a generalist, is not an aggressive animal.
Please feel free to comment if you’re one of the few that has eaten horseshoe crab eggs.
If you’ve kept on eye on the sandy shores of the Atlantic Ocean or eastern Gulf of Mexico over the past twenty years you’ve noticed a significant decline in the number of horseshoe crabs, Limulus polyphemus, covering the beach. As a marine educator and naturalist in my past life, I always said the decline was due to over harvesting for bait and pharmaceutical needs. This is only half the reason. Recently scientists also noted that climate change, with the sea level rise and temperature fluctuation, may be a cause of the decline.
Tim King, a scientist with the United States Geological Survey, thinks that what happened during the Ice Age could happen again. With climate change comes a loss of habitat and a loss of diversity. These issues could have severe implications, not only for horseshoe crabs, but also for species that rely on them for sustenance. For instance, along the Delaware Bay the red knot eats the horseshoe crabs eggs at the midpoint of their migration. In the Chesapeake Bay, loggerhead sea turtles are struggling to find one of their favorite food sources, horseshoe crabs, and are retreating elsewhere to find food. Now that the link of a decline in the horseshoe crab population and climate change has been made fisheries managers can take this into consideration.
Images (c) Greg Breese, US Fish and Wildlife Service
First of all, let’s chat biotechnology, or, ‘biotech’, as those in the industry call it.
The concept of biotech has been around for ages, just, not given the fancy term. For instance, planting seeds to produce food, fermenting juice for wine and churning milk into cheese (that are tested with the help of mycotoxin testing kits for the quality) are all processes that use some derivative of a plant or animal to benefit mankind. In the biotechnology and pharmaceutical fields of today, the Atlantic horseshoe crab (Limulus polyphemus) blood is a very important component in the process for testing drugs that can benefits humans that can be produced using nonhuman primate CRO method.
Their blood is used for the Limulus Amebocyte Lysate (LAL) test is used to test for gram negative bacteria contamination in certain products before being released to the public. Horseshoe crab blood cells (amoebocytes) attach to harmful toxins produced by some types of gram negative bacterias. What is unique with the LAL, is that LAL does not distinguish between living or dead gram negative bacteria and detects either.
You do not want anything with a gram negative bacteria contamination. Gram negative contamination include: Escherichia coli, Salmonella, Neisseria meningitidis, Hemophilus influenzae, Klebsiella pneumonia.
The blood of the horseshoe crab has this unbelievable property where it will congeal in the presence of either living or dead gram negative bacteria (both are undesirable). This adaptation has never been able to be duplicated and consequently horseshoe crabs are often captured to have their blood drained and then released, all in the name of science.
Do you have another great question? Check out www.beachchairscientist.com and let us know what you always ponder while digging your toes in the sand!
No. I mentioned in the very first BCS blog entry that the horseshoe crab is a “sweetheart of an animal” and I will continue to defend that statement. Some people may think that the tail spine, or telson, is poisonous. What the telson is simply used for is to flip the animal over when a wave turns it onto its carapace. The tip of the telson is jabbed into the sand and the horseshoe crab rights itself over, somewhat like the act of throwing a javelin.
Do you have another great question? Check out www.beachchairscientist.com and let us know what you always ponder while digging your toes in the sand!
Many horseshoe crabs you see this time of year along the shore are probably “molts”. You can tell if the exoskeleton seems hollow. Insider science tip: If the horseshoe crab has a slight opening at the opposite end of the telson (i.e., pointy “tail”) – it’s a molt.
However, if you see a live one that has been stranded on shore, you may want to help the living fossil out and flip it. But, be sure to do it carefully and handle it in the safest manner. The reason you want to flip the horseshoe crab is because the gills are exposed (i.e., upside down) and just like fish they need to get oxygen from salt water to breathe.
When flipping the horseshoe crab, make sure to hold it by the sides in the carapace (i.e., upper exoskeleton) and not the telson. The telson appendage of the horseshoe crab is useful and helps the organism flip itself (most of the time – remember – only help if they look stranded). If you pick the organism up this way tje telson may risk breakage. Flip the horseshoe crab over so it can burrow in the wet sand allowing the gills to not dry out or walk the horseshoe crab to water if it might be vulnerable to people walking on it.
Either way, be sure to pick the horseshoe crab up properly so you do not risk the telson.
Last year I was pretty proud of my sea & sky pumpkin featuring constellations, a sunset, fish, a seahorse, and horseshoe crabs and I’m at a loss on what to do this year. I started a template for a much larger horseshoe crab so I thought I would share it with you (HSC_template).
I actually cut out and created some artwork for my office.
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