Written by: Rowan Mulder, SSCW Marine Ecology Intern
Today is the 5th annual International Horseshoe Crab Day! This holiday is dedicated to protecting and learning about one of the most important (and underappreciated) species in our coastal ecosystem. Horseshoe crabs support the places and people that we love every day – and in more ways than one. Interestingly, these humble little critters are not crabs, but chelicerates, more closely related to spiders than crustaceans. There are four horseshoe crab species in the world, and only one of which lives in Salem Sound. Horseshoe crabs are known as “living fossils” because they’ve remained relatively unchanged for more than 450 million years. In fact, they’re about 200 million years older than the dinosaurs and have survived 5 mass extinctions.
Horseshoe crabs live in shallow, coastal waters and arrive at intertidal beaches in the spring and summer during high tides to reproduce. In one year, a single female can lay about 80,000 eggs, which are buried under the sand until they hatch. These eggs are a vitally important food source for other animals, especially migrating shorebirds, such as the threatened red knot. These birds rely on horseshoe crab eggs for nutrients as they fly thousands of miles to their northern breeding sites. Adult horseshoe crabs also support local wildlife: their shells act as a moving habitat for the many animals that grow on them, including sponges, mussels, barnacles, and snails.
Horseshoe crabs are beneficial to humans, too. They’re harvested as bait for whelk, conch, and eel fisheries. What’s more, they can save lives! If you’ve ever had a vaccine, shot, or medical implant, you have horseshoe crabs to thank. Their blue, copper-based blood reacts to dangerous bacterial endotoxins, which allows us to test for harmful substances in injections and implanted devices before using them. This substance (called LAL) is very important for avoiding deadly infections. Although the animals are released after the procedure, harvesting the blood has a 15% to 30% mortality rate. Horseshoe crabs are listed as vulnerable on the IUCN Red List, and much of this is due to overharvesting. In Massachusetts, fisheries and medical industries are allowed to catch 340,000 horseshoe crabs each year. Habitat loss is another harmful factor, as coastal development restricts the beach habitats where horseshoe crabs spawn.
This year, we have good reason to celebrate horseshoe crabs – they’ve just received new protections! In March, the Massachusetts Marine Fisheries Advisory Committee (MFAC) approved stronger regulations which ban all harvests during the main spawning season between April 15 and June 7. This is largely thanks to your public advocacy: the Division of Marine Fisheries proposed similar protections last year, but without as much public support, they were never passed. The new regulations will ensure that horseshoe crabs can safely reproduce, and their populations will remain stable so that we don’t lose the important services they perform for us and our environment. At Salem Sound Coastwatch, we’re doing our own work right now to learn more about horseshoe crabs through our community science Horseshoe Crab Survey, which will help us better understand where these creatures are living and breeding on the North Shore.
Get outside today to look for horseshoe crabs, and don’t forget to say thank you!