Can you feel it? It’s almost here. Horseshoe crabs are getting ready for another busy breeding season.
Soon after the herring have migrated upstream to spawn in selected rivers and waterways around the harbor, horseshoe crabs begin to have similar urges to reproduce.
Days are getting longer, the sun is climbing higher in the sky, and the thermometer responds accordingly. Water temperatures are starting to get warm, with readings in the mid to upper 50s, some shallow parts of the lower bay even have readings in the 60 + degree range. Mother Nature is setting the stage for a busy breeding season for horseshoe crabs.
The need to breed must be strong. Starting in early April, people, including myself, have been encountering crabs crawling out of the ocean or bay looking for love on the beach. Yet, the time wasn’t ready yet.
Each year, the event happens during May and June. Adult horseshoe crabs will quietly migrate into shallow areas of the bay from wintering sites in deeper waters of the harbor or out in the Atlantic Ocean on the continental shelf, sometimes travelling up to 50 miles to local estuarine waters. Large numbers of the crabs will crawl up onto sandy beaches to mate and lay eggs, synchronized perfectly with full moon and new moon events and the highest tides of the month. Tides rise and waters will nourish the eggs by keeping them moist and hot sands during low tide will incubate the eggs.
In about two weeks, the eggs will hatch and little horseshoe crabs will emerge and make their way to the bay. Larvae usually swim around in the shallow intertidal areas near the beaches where they were spawned until they settle to the bottom and molt. Juvenile horseshoe crabs spend their first and second summer on the intertidal flats before moving to deeper waters to feed.
For many local residents, this spring might be their first encounter with a horseshoe crab. Walk along the beach right now and you may see a small weird sea creature the size of a dinner plate that looks like it belongs to the dinosaur age. It’s a horseshoe crab, and in fact, it’s older than dinosaurs.
Horseshoe crabs are one of the oldest living species on our planet. Fossils of horseshoe crabs have been dated around 360 million years old. They evolved in the shallow seas of the Paleozoic Era (540-248 million years ago) with other primitive arthropods called trilobites, a long extinct close relative of the horseshoe crab.
Actually, horseshoe crabs are not really crabs or crustaceans like lobsters, blue crabs, and other crabs. They’re more closely related to arachnids, eight-legged creatures that include spiders and scorpions.
The horseshoe crab plays an important ecological role in our local aquatic food web. Several species of shorebirds depend on horseshoe crab eggs, exposed on the surface by waves and storms, as a source of food. Horseshoe crab eggs and larvae are also eaten by several species of fish including the American eel, killifish, striped bass, weakfish, kingfish, silversides, summer flounder and winter flounder. In addition, sea turtles are known to feed on adult horseshoe crabs.
So if you are taking a beach walk around the harbor, please show some regard for an ancient mariner, the horseshoe crab. Never pick up a horseshoe crab by its tail. The delicate hinge will not support the crab’s weight and will tear off. The tail acts as an important rudder for a crab. Also, when you see a horseshoe crab that is stranded upside down on the beach, just flip it over by the edge of its shell. No need to be scared, a horseshoe crab doesn't bite or sting and its claws are very gentle and won't hurt you.
Horseshoe crabs have been around for more than 350 million years. They have outlasted the dinosaurs. These ancient sea creatures certainly deserve our respect.