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Underwater Wakulla- September 7, 2017

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Two New Crabs for the Aquarium By GREGG STANTON

Two New Crabs for the Aquarium

We are trying to run our 26 foot Mako boat out to “K” Tower every week, weather permitting. On a recent trip, Makenzie (a recent student of mine) and I were looking for creatures to enhance our aquarium. She pointed to a sponge that promptly moved off when I tried to capture it. When Makenzie captured it, I pulled the zip-lock bag out only to find whatever this creature was, was on the loose again.  Simple enough, we just kept looking carefully on top of the barge at 40 feet depth until we saw another small sponge making its getaway! Once in the clear bag, it was obviously a crab with many small and colorful sponges attached to it’s carapace (back), claws and arms. After swimming around the entire barge, we came back to the place we first lost our first mysterious creature, only to find it again. They both reside in our aquarium for all to see.

Imagine the scene, sinking through schools of Minos that swirl around in large bait balls being attacked from all sides by predatory fish. They part to let us drop to the darkened barge below causing Goliath Grouper to begrudgely move over, grunting their displeasure as they move under vertical stanchions rising up from the deck. We scour the deck for lost anchors, lead sinkers, Tiger Scallops, and Turkey Wings, and now crabs. Once we have collected what we need, we move off the barge and down to the ocean floor at 60 FSW. There we encounter Arrow Crabs, a long legged stripped creature that hangs over anemones and sponges. These are abundant and easily caught. Unlike the Decorator Crab, this creature uses it’s very long claws to capture food originally collected by their host Anemone or Sponge. Long legs keep it out of harm’s way. The arrow crab also has a long rostrum, or tip to its carapace, upon which it grows a garden of algae, upon which it will occasionally feed.  

We swim the circumference of the barge, finding all manner of fish, big and small. The Bat Fish is always a delight to find, as it walks about and can be picked up and closely admired without injury to either party. We collect a few small fish, but more on them in another column. A short 40 minutes later, our breathing gas is low so we must find the anchor line. We return past the Goliaths, up through the bait ball and back to the sun drenched sea surface. Specimens are quickly put into an air pumped seawater bucket for safe transport back to the shop. Plankton is also collected.

None of the taxonomic keys that I use accurately described what we first caught. But Cypress at Gulf Specimen described this crab as a Decorator Crab. I will include a picture for the website. I am more familiar with the Arrow Crab as it is found around the Caribbean hovering over many anemones and some sponges, and referred to as having a commensal relationship. Technically, that means each member relies on the other for survival. The crab gets the occasional morsel of food while the anemone uses the crab as a lure to attract prey. I’m not so sure what the sponge gets out of putting up with the crab.

But now we can watch them every day in the shop. Come join us some time.