The 2017 Hermit Crab Migration

Something very cool happened at Honeymoon Beach yesterday, and Steve Simonsen was lucky enough to catch it on film. Here’s what he wrote on his Vimeo page:

“This morning August 30, 2017 Ranger Laurel Brannick telephoned me to tell me that there was a hermit crab migration taking place at the rock peninsula just below the ranger residence between Solomon Beach and Honeymoon Beach. I quickly made my way back to the house loaded the appropriate number of cameras in the truck and with special permission to drive in. I went directly to Honeymoon Beach and began filming the spectacle of the hermit crab migration again on St. John.

“In nearly every watershed around the island hermit crabs will make an annual pilgrimage to the sea to release their egg into the ocean. Today I was able to film the actual release of the eggs into the water in close proximity to individual hermit crabs. This may be the first time that is been filmed. while this migration was not nearly as large as the one in 2012 that occurred at Nanny Point and numbered hundreds of thousands of hermit crabs the migration that took place today was estimated at several thousand individuals. It begins at about six in the morning as the sun comes up and it’s finished sometime between 11 AM and 1 PM.”

Check out the video:

Here’s some information as to why this happens courtesy of the Smithsonian’s National Museum of Natural History:

These hermit crabs are Coenobita clypeatus, the Caribbean hermit crab (also known as the soldier crab), which are native to islands throughout the Caribbean region. I typically think of hermit crabs as a marine phenomenon, but the adults of this species live in wet inland areas, hiding between tree roots or in caves. They mostly eat iguana poop (from Cyclura stejnegeri), although they can also climb up tree trunks to snack on soft wood.

And every summer, thousands of these hermit crabs migrate from the woods to the sea to release their eggs.

The hermit crabs begin creeping along the forest floor towards the shore in July or early August to meet up with others of their kind. On the way, they mate by partially removing their bodies from their shells, allowing the males to drop off their sperm packets. Then each female lays thousands of fertilized eggs and carries them around for about a month as they grow larger and deplete their yolky energy stores — and the crabs continue their trek, sometimes navigating distances over 3 miles (5 kilometers).

Signaled by the crescent moon at the end of August or early September, the female crabs wade into the water. Upon contact with the salt water, the eggs burst and the larvae float into the waves. Over the course of three or four days, they “wash” their eggs in the water to make sure each gets touched by seawater. And then, all together, the hermit crabs make their way across the land back to the forest – the migration filmed in the video.

It’s not known whether the females make this journey alone or if the males join them. “In some [Coenobita] species it’s just the females that migrate, and they release their zoea larvae into the ocean when they get there,” invertebrate zoologist Jan Pechenik of Tufts University wrote in an email. “But in some species both males and females migrate to the sea,” mating along the way.

Hermit crab sex aside, the crabs in the video are either creeping towards the sea to release their larvae as zooplankton, or moving back home to snack on iguana poop until the following summer.

Pretty neat, isn’t it? Have a great Thursday everyone! I’m heading over to the BVI today, so keep checking our Facebook page for some new live videos!

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