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Photo: Christine Ewers
Participation fee $0
Expenses $0
Spend the time outdoors
Location East coast of the United States
Appropriate for kids yes
Teaching materials no


Required Gear:

Camera: your phone or digital camera


Horseshoe crabs as homes


Discover what species live on horseshoe crabs.
Spot and share sightings of animals living on horseshoe crabs.

You are walking along the beach on a sunny spring day. But what is that? Something is moving slowly out of the water. It looks like a large crab, covered in barnacles and mussels. Creepy? Ugly? No, its home! At least for all those critters that live on Horseshoe crabs. Horseshoe crabs have been around for more than 250 million years, unimpressed by dinosaurs and ice ages.

Since then, Horseshoe crabs have played a key role in coastal ecosystems: the eggs are eaten by shore birds, juveniles are food for sea turtles, and adults aerate the ocean floor through their digging activity.

We believe Horseshoe crabs serve yet another important function: as substrate for many invertebrate species such as mussels, barnacles and snails. Many marine species require hard substrates to live on, and such substrates are historically rare on the predominantly sandy beaches of the Eastern US. In more recent times, docks and boats may offer new opportunities for intertidal species - but what about animals that do not like the tidal influence? Are there even species living on Horseshoe crabs that we have not discovered yet?

Help us decipher who lives on Horseshoe crabs! Take clear pictures of Horseshoe crabs and their critters when you see them on the beach, and send them to us. Just let us know when and where you saw the crab. That's it.

In return, we will post the best pictures on our website and explain every animal that you discovered on the Horseshoe crab. New species will be featured on the site, and we would like to name our most successful discoverers.

With your help, we will be able to address the following questions: Which region has the highest diversity of animals attached to Horseshoe crabs? When are the crabs found the most? The least? Moreover, we will build a valuable resource for school classes, beach walkers and everybody else who ever wanted to know: What is that thing sitting on the Horseshoe crab?

Horseshoe crabs come to the beaches to mate and lay eggs when the tides are highest. This happens at full and new moons. So be on a lookout for them!




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