Evolution News: Earth Day: Horseshoe Crabs And Shorebirds Who Eat Them Going Extinct

Horseshoe_crab_big
Elaine Meinel Supkis

Horseshoe crabs have been around longer than cockroaches. And now humans are destroying them. And the other members of their ecosystem are going down, too. We must protect this earth, we won't be given another one, magically. No matter what we want to believe. Treasure what we have, today!

National Geographic:

John Roach
for National Geographic News
April 18, 2006
The food web around the horseshoe crab—one of Earth's oldest species—is beginning to unravel, scientists say.

Certain species of migratory shorebirds depend on excess crab eggs to fuel the final leg of their spring journey to the Arctic. Researchers are concerned the birds are in jeopardy.

"Right now we're in that real dangerous period where nobody can say what's going to happen for certain," said Larry Niles, a biologist with the New Jersey Division of Fish, Game, and Wildlife in Trenton.

The birds feed on the crab eggs in the Delaware Bay, an estuary sandwiched between New Jersey and Delaware (map) that harbors the world's largest horseshoe crab population. But human harvest of horseshoe crabs has reduced the egg surplus.

In the race to keep birds—especially the red knot, which feeds exclusively on the crab eggs—from extinction, scientists and fisheries managers are considering increased protections for the crabs.

Many years ago, on a full moon, springtime tide, I was walking at sunrise on the beach, my first spring in NYC, living on Coney Island's Grave's End, I saw an amazing parade of prehistoric creatures come trundling out of the surf, hundreds of them scrambling over each other, in an ancient sexual struggle, in the broiling waters that hissed and sighed into the dense sands, these creatures crept along on many small feet, sharp, sword tails wiggling after them, the sunlit fog making a romatic haze for this primordial dance.

I loved watching them and they pretty much ignored me as they laid their eggs. Sea birds flocked to this scene d'amore, squabbling with each other as sharp beaks scooped up the bounty of shiny eggs. The female horseshoe crabs would wait until the very edge of the water running up the beach would enfold them and then lay the eggs. Everyone knew what to do, each working hard to take advantage of numbers and tides.

Then the crabs return to their deep, watery home and not be seen again until a year later.

Well, we might not see anyone eventually. Greedy humans fished the vast schools of cod fish mercilessly to the point of near extinction and every time the poor fish try to come back, we assault them again. Now, in a desperate attempt to save them, it is forbidden to fish them at all so substitutions are made and one is to hunt fish that eat horseshoe crabs.

With no cod to catch, fishers started to go after conch. "And the best bait for conch was horseshoe crab," Niles, the New Jersey biologist, said.
As the conch harvest expanded, so too did the horseshoe crab harvest, he added.

By the mid-1990s the annual horseshoe crab harvest increased to 2.5 million from a few hundred thousand. The horseshoe crab population plummeted. Density dropped 90 percent, according to Niles.

So we will eat all the conch and kill off all the horseshoe crabs and in addition, kill off all the sea birds who need to eat the eggs each spring. This is most depressing. Our desire to consume everything is consuming everything and remove just one key species and an entire complex can come crashing down.

A general rule of nature: the lower the creature on the eating/evolutionary totem pole, the more vital it is for survival of all other organisms in the vacinity and the older the entity, the more dangerous it is to remove it entirely. In the oceans, we can kill off many different creatures without much impact on the ecosystem but kill off most of the krill and the entire life systems of the oceans can and will collapse into a serious extinction event!

So today, Earth Day, is a good time to appreciate our ancestral entities. We don't have tribolites anymore but we have their near-relatives, the singular horseshoe crabs. And losing them will be a very unhappy thing. After all, the Great Permian Extinction is when Tribolites disappeared. And do note that nearly everything else went with them!

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