Saturday, March 1, 2014

Limulus polyphemus- I love horseshoe crabs

Here are some of the reasons I love horseshoe crabs:

Picture from
 photo horshoecrabgirl_zps087a53ab.jpg

1. Horseshoe crabs are cool-looking, like an alien space helmet with spider legs, pincers, and a spike tail.
 photo horseshoe_crab_zps3eea33da.jpg

2. Horseshoe crabs' oddly-positioned compound eyes are large and shaped such as to give them an inscrutable and vaguely menacing glower. In addition to their two main eyes, they have some less obvious eyespots further forward on their carapace.

 photo limuluseye_zpsd79a2073.jpg

3. The horseshoe crab lineage has maintained the same body form since the Ordovician period 450 million years ago. During that time all their close relatives have perished, making them the sole modern representatives of a prehistoric group that included such monsters as the Eurypterid "sea scorpions." Their closest living kin are the terrestrial (land dwelling) spiders and scorpions... but you could hardly call them close because they diverged from a common ancestor about 480 million years ago! Calling them "crabs" is misleading, because they're even further separated from the crustaceans (which include crabs) than they are from spiders and scorpions.

 photo eurypterid_zps603418d6.jpg

4. Horseshoe crabs are scarily amazing when you pick them up and turn them over to reveal their numerous legs, claws, and flap-like gills. But they don't pinch too hard, so go ahead and pick one up to take a look. Just watch out for the spike tail (the "telson").

 photo horseshoecrabupsidedown_zps4fcceb33.jpg

5. There are no horseshoe crabs on the West Coast so I never saw a live one when I was growing up. That makes getting to see them in action here on the East Coast extra cool. The Atlantic Horseshoe Crab (Limulus polyphemus) is pretty tolerant of a wide range of temperatures, so it lives from the Gulf of Mexico all the way up to Canada. There are also some three species of horseshoe crab that live in the Indo-Pacific region.

 photo distr_horseshoecrab_zpse1b1c4bd.jpg

6. Horseshoe crabs are ecologically important. Beside playing a role as low-level predators and sediment-stirrer-uppers in benthic (sea-bottom) food chains, they provide a vital food source for loggerhead sea turtles. Also, horseshoe crab eggs are a critical food for migrating shorebirds (sandpipers and such). Horseshoe crabs lay eggs in massive numbers on sandy beaches, and shorebirds time their arduous arctic - tropic migrations to make a refueling stop on the beaches where the horseshoe crab eggs will be. If there are no eggs to eat, the birds die of exhaustion and starvation before completing their migration.

 photo HorseshoeCrabbirds_zps8f126015.jpg

 photo Horseshoe-crab-eggs_zpsf5bbdae4.jpg

7. Horseshoe crabs are important to humans, but also threatened by human activities. In increasing order of the unique value of their services, horseshoe crabs have provided us with 1) agricultural fertilizer,

 photo horseshoefertilizer_zps30b59e96.jpg

2) bait for eel and whelk traps
 photo horseshoecuttinginhalf_zpsc483531e.jpg
and 3) a blood-cell extract called LAL that can be used to check for bacterial contamination of fluids and medical devices before they are put into the human body. The LAL story has been getting around a lot lately and was recently a feature article in the The Atlantic magazine. While I'm strongly opposed to the wasteful use of horseshoe crabs for fertilizer and bait, I think the blood harvest is pretty important... as long as it's done sustainably. Some progress has been made towards that end. For instance, we no longer kill the beasts to take their blood- we just partially drain them and then release them, whereafter they have about an 80% survival rate.
 photo horseshoecrabbloodharvest_zps60d90419.png
Scientists are now working to make a synthetic version of LAL so we don't need to suck horseshoe crab blood to get it. Let's hope that works out.


Lady Notorious said...

Great blog! Was this spurred on by that horseshoe crab I found while we were SUPing the other day?

That opening picture is the best :)

Just goes to show you:
Naked Lady + * = win

James Douglass said...

Lady Notorious- Yep, it was largely inspired by that one we found at Wiggins. Next time we find a * sea creature let's test your mathematical theorem.