by wjw on June 25, 2014

SeaLife DC1400 
You thought from the title that this was going to be about the TV show, didn’t you?

Nope, I’m here to introduce you to an invertebrate.  This is an arrow crab (Stenorhynchus seticornis).  You can see the pale stripe across the carapace that gives it its name.

It’s maybe six inches across if you stretch those incredibly thin legs out to their maximum extent.  I gave my macro lens a workout on my recent dive trip.

The picture has been pretty seriously Photoshopped, because the photo was taken at night under indirect light.  (If I shone my light directly onto the target, the resulting photo would have been completely washed out.)

My Sealife camera can take both photo and video, and this trip all the really spectacular pictures were video, which take up too many megabytes to post here.  All the pictures of sharks cruising by at close range, then circling to cruise again.  The pictures of barracudas doing likewise.  The tarpons, big night-hunting predator fish clad in bright silver scale mail, each scale the size of a quarter, who hung in lines over the reef to wait for nightfall, and who then followed our lights to find food.  The two dolphins who raced through the frame when I was trying to take a picture of the tarpons, and who caused the tarpons to scatter.  (Pictures of submerged dolphins are relatively uncommon, and I was happy to get these.)

I also got terrific video of big sea turtles, moray eels, hermit crabs, and the dive to Blue Hole, the latter of which I now propose to tell you about.  (The best still photo is here.)

I trained on the Blue Hole in New Mexico, which is a big sinkhole in the same limestone formation as Carlsbad Caverns.  Water carves out big cave systems in limestone, and then the top crashes in, and you’ve got a great big water-filled hole in the ground that leads to further caves below.

There’s a similar limestone formation in Central America, and many Mayan settlements formed around cenotes, as they called the sinkholes over there (and which Autocorrect keeps changing to “denotes”).

The Blue Hole in Belize is on the reef system, fifty nautical miles out to sea, and drops over 400 feet.  It’s bell-shaped, just like the Blue Hole in New Mexico, wider at the bottom than at the top, though the Belize hole is much, much wider.

Most of our dives were fairly unsupervised— you could go with a guide, or you could just jump in the water with your buddy and do whatever you liked.  But the Blue Hole dive wasn’t just supervised, it was regimented.

Once assembled in the shallow water on the edge of the hole, we’d drop to 130 feet, swim around for five minutes, and then commence our ascent.  We’d do our safety stop in the shallow water, and then return to Sun Dancer.  There would be one guide at the front, and another at the back.  You’d come up with a fair amount of air still in your tank.

Those of us who dove on Nitrox— a mixture of 32% O2, with the rest being nitrogen— were given a much leaner mix, 24% oxygen, just a little over the normal content of air.  That’s because oxygen can grow toxic at greater depths, so you want less of it.  I was okay with the leaner mix, as I have an unshakeable prejudice against convulsions and death.

Most of the precautions were to minimize the dangers of against nitrogen narcosis, known more poetically as “rapture of the deep,” which is another problem that can happen if you go too deep.  Most people who suffer from this get hilariously drunk, which can be problematic if you’re dealing with complicated equipment 130 feet below the surface.  (And in fact one of our group did get narked, which my Autocorrect insists is “marked,” and either came up by himself or didn’t, depending on who you talk to.  I won’t get into that, not having witnessed anything myself.)

So down we went under the eye of John, who I think of as the Oldest and Wisest of the Divemasters.  Down we went, the hole growing more wide as we descended, until at about 110 feet we began to see stalactites from the original cave system.  They were large and impressive, big enough to embrace with two arms, not that we did.  (They were covered with sharpish marine growth.)

I started out near the front of the column, but people kept elbowing me aside to get to the front, which I thought a bit rude.  I ended up near the back and saw the same stuff seen by the people at the front, except maybe with more bubbles in the picture.  It was too dark to to take still photos, the flash being swallowed up by the hugeness of the place, but the video came out fine.

And then the five minutes was over and it was time to head for the surface, passing through two layers of progressively warmer water until we were on top of the reef and able to begin our safety stop.  When I came up, my tank was still a third full.  Because we went deep, we didn’t get a second morning dive, and instead were dropped off on Half Moon Caye to wander around looking at palm trees, hermit crabs, iguanas, and the official sanctuary of the Red-Footed Booby (which was pretty cool actually).

This is what’s called a “bounce dive”— you bounce down, then back up.  It’s still an open question in my mind as to whether it’s worth all the fuss.  I get bragging rights, I suppose, and the stalactites were cool, but was five minutes’  bottom time worth two regular dives?

Clearly, I should have asked the Oldest and Wisest of the Divemasters.

DensityDuck June 25, 2014 at 8:16 pm

I love how they call it the “arrow crab” when there’s nothing remotely arrow-like about crab or marking.

I guess it’s the same kind of marketing strategy that gets applied to all animal names. “This ‘ere is the narrow-gill blue-teated linefish.” “It’s green, it’s spherical, and there is not a teat to be seen.” “Sure, but ‘big ugly toothy eeal thing’ was already taken.”

wjw June 26, 2014 at 3:32 am

Probably the name “stripey crab was taken.”

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