Sunday, April 14, 2019

Creature Feature: Crabs Rule in Providencia





Sign along the western road announcing the closure for crabs
You might know that Anne is a crab geek, not surprising since she spent nearly twenty years doing crustacean research for the State of Florida. And Chris likes to eat crabs. So, we were intrigued by the signs we saw on Providencia regarding the black land crab Gecarcinus ruricola. Travelling in the Caribbean, you’ve probably seen the holes that these crabs occupy in forested areas, often far from the water, or wondered W.T.F? upon finding a crab claw high up a mountain. They’re also often found in the market or on the menu if you want a taste. The species is nocturnal, and their skittering about in the dark, clicking across a road or rustling through the undergrowth, can be unnerving if you don’t know what it is. Anyway, it’s precisely these wanderings that bring attention to the crab during mating season. Though terrestrial as adults, larval development occurs in the ocean. Adults migrate from the forest to the ocean to spawn, then back to the forest. Initial larval development occurs at sea, then megalopal-stage larvae (looking mostly like little crabs at this point) migrate back ashore and head to the forest. And these are not small migrations; the population on Providencia was estimated at three million. If a road lies between forest and ocean…well, you can imagine the mess. Consequently, from April 1 to July 31, a portion of the road that runs along the western side of Providencia is closed to all vehicles. Since the road around the island is a loop, this means a lot of detouring back around the eastern side of the island. Time-consuming, perhaps, but it’s done for the purpose of conserving the species, which is good thing. They show a film of the black land crab migration at the Lighthouse Café/Cinema/Art House, but we unfortunately didn’t make it. Fellow crab geeks can find detailed analyses of black land crab population biology and reproduction on Providencia and San Andrés in these articles from the Journal of Crustacean Biology. And if you want to feel a little squirmy, check out this video of migrating adult and larval red land crabs (related species) on Christmas Island – not the exact species as on Providencia, but related, and the same general idea.


Crab information alongside the trail to the Peak

Crab migration documentary at the Lighthouse

The black land crab is even featured at a bus stop


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