Posts Tagged ‘marine extinction’


Well, I had a treat last week! I went to watch horseshoe crabs being tagged for research — kind of like birdbanding, but for crabs. The woman with the funny expression above was actually enjoying the whole thing and helping to take notes for the scientist, Kim Gaffett.

Kim, who may be best known to New Shoreham visitors for birdbanding, has been working for some years with Connecticut’s Sacred Heart University on an initiative called the Limulus Project. The idea is to learn more about the amazing horseshoe crab, a species that, depending on whom you ask, has managed to survive between two and five mass extinctions on Planet Earth, including the one that wiped out the dinosaurs.

In spite of their amazing record of survival, the crabs are considered threatened today, so it’s important to study them and try to find out what’s going on. As I wrote a few years ago, their blood has the ability to clot in the presence of bacteria, so it has become invaluable to pharmaceutical companies. Researchers are supposed to draw the blood as one would for a human and then have the fishermen return the crabs to the ocean, but that may not be happening consistently.

I asked Kim how she knew she would find any crabs that particular morning, and she told me that when there is a high tide and a full moon in June (flood tide), the horseshoe crabs come up to the shore to mate. The male has one claw like a boxing glove, with which he attaches to the female’s shell in order to be available when she drops her eggs. The eggs are fertilized outside the body. Sometimes other males are hanging around, and it’s possible for one batch of eggs to get fertilized by more than one male.

All sorts of marine life forms attach themselves to horseshoe crabs — seaweed, barnacles, slipper shells. Kim calls the crabs “their own ecosystem.” The crabs’ fellow travelers don’t usually cause any trouble, but as you can see below, a quahog had snapped onto a claw of one crab. A citizen scientist is shown detaching it.

From Phys.org, I read this about horseshoe crabs’ survival: “They have a special kind of blood, which … coagulates when it encounters bacteria. They can ‘wall up’ any wounds they receive.

“Another key to their survival seems to be their tolerance of habitats that fluctuate in salinity (levels of salt). When environmental changes happen, they can move to safety.

“An ability to live with low levels of oxygen is also important. [Natural History Museum expert Richard Fortey] adds, ‘The horseshoe crab was able to cope with periods of oceanic deoxygenation that were fatal to many marine organisms.’ ”

I was also interested in what Quartz had to say: “These amazing crab species are among the handful of species referred to as ‘living fossils’ because their current form resembles those found in the fossil record. Externally at least, the crab hasn’t changed much in nearly 450 million years. In that time, it has survived all five of Earth’s great mass extinctions, the worst of which killed off an estimated 95% of all marine species, and the most recent of which did away with the dinosaurs. …

“The crab’s blue blood contains a chemical called limulus amebocyte lysate (LAL), which thickens when it comes in contact with toxins produced by bacteria that can cause life-threatening conditions in humans. Labs use LAL to test equipment, implants, and other devices for these toxins.”

Kim says she hopes labs will start using the synthetic version of LAL more and give the horseshoe crab a break.

Note the tag below. Kim found one crab with a tag from a previous year, and she attached another tag to a newer find.




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