Red Knots and Horseshoe Crabs

Most of you who have recently taken an ecology or environmental science class have probably hear of the classic story of the horseshoe crabs and red knots on the beaches of Delaware Bay. For those of you who have not, here’s the story: horseshoe crabs come up onto the beaches in the summer to spawn. Their mating is pretty cool in and of itself, with males competing for space literally on the females (sort of like frogs, actually), but it’s really the eggs the female lays that are the crux in this story. Those eggs are laid all across the beaches of Delaware Bay, and are little bundles of energy and nutrients.

Red knots, a bird species that migrates from the southernmost tip of South America to the Canadian arctic every year, have a migration route that takes them by those very same beaches for a high-caloric snack of horseshoe crab eggs. If the birds don’t eat the eggs (for instance, if not enough eggs are laid for all of the migrating birds), then they are much less likely to make it all the way to the Canadian summer breeding grounds. And if they can’t make it to their breeding grounds, then fewer new birds will be born for the next year’s migration, and you can see how this could easily spin out of control.

Well, it’s already started to spin. Horseshoe crabs are caught as bait for more economically-important fish, and their fluids are also used for some medicinal purposes. In recent years, they have been overfished, despite regulations in some states on the fishery. However, just like with species that span country borders, these crabs cross state borders, and not all states have stringent limits on the fishery. It has led to decreased amounts of eggs deposited on the beaches of Delaware, which in turn has led to dramatic drops in the numbers of red knots.

Luckily, initial data from this year seem to indicate that both species have had a good year. However, one good year does not mean that there is a comeback poised and ready to happen. It will take much longer for both species to recover. I just hope it won’t be too late for the red knots.

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