An Odd Highlight for a Wall Dive: Slipper Lobsters in Action!

[Continuing my diving adventures in February 2008 off Maui with Mike Severns Diving.]

Molokini Crater lies a couple miles southwest of Maui. An extinct vent of the massive Haleakala volcano that comprises about two-thirds of the island of Maui, the crater walls only enclosed three-quarters of a circle that measures about 1800 feet across. The crater formed as hot ash spewed into the air about 230,000 years ago – it was all above water back then – and was pushed by the steady trade winds to form the crater walls, with a permanent gap facing into the steady winds.

Now a good portion of the crescent-moon-shaped crater, the cliffs of which rise only about 160 feet above the surface, is underwater. The submerged rocky walls themselves have been overgrown with corals and sponges and the many lifeforms that live upon them, and the interior of the crater is filled with coral outcroppings and the sand formed by coral’s decay. The interior of the crater has a number of moorings used by both diving and snorkeling boats, but some of the best diving is in the deep water – you don’t hit bottom until about 300 feet – around the curved back side of Molokini.

The wall is nearly vertical. Holes and cracks ranging from fist-sized to twenty feet long run vertically, horizontally, and every degree in between. Surf washes up against the rock in a perpetual tumble of turquoise and white. There are no moorings on this side, so when you’re diving, you gear up, wait for the okay, and jump over the side of the boat when the captain says “Go.” You plunge into deep blue water that’s refreshingly cool after standing in the sun in your thin wetsuit, pop to the surface, give the “OK” sign to the guys still on the boat, and kick away from the boat towards the wall. The other divers make their entries and you all group up on the surface, do one last equipment check, and submerge.

The boat “stays live,” motoring and drifting along, keeping our bubbles in sight as we descend to eighty feet. Over the rumble of the motor, which cuts in and out as Andy maneuvers the boat to stay within easy pick-up distance at the end of our dive, I hear the low, elongated moans and whoops of a nearby male humpback. Glancing down to the sandy bottom some 220 feet below me, I watch a white tip reef shark working its way along the crater wall until it vanishes into the murky blue.

I glide along the wall, admiring the coral formations that jut from the underlying rock and playing hide-and-seek with the fish and moray eels tucked into their sheltering crevices. I keep an eye on the other divers strung like a line before and behind me, and we point out to each other particularly beautiful or interesting sights: a pair of fountain shrimp advertising their cleaning services, a bright yellow trumpetfish that must be three feet long hanging suspended dead-center in a vertical crack, a yellow-margin moray eel ribboning its way from hiding spot to hiding spot through stubby branches of finger coral. I check my depth gauge with near paranoid frequency, knowing how easy it is to lose track of one’s depth on a wall with visibility at 200 feet like this. And I spin around like an underwater dervish to stare out at the deep blue water, hoping for another glimpse of a white tip reef shark, or a passing humpback, or – that Holy grail of all divers – a whale shark.

Turning back from one of these perusals of the deep, I notice one of my fellow divers hovering to my left and maybe fifteen feet above me, semaphoring his long arms wildly over his head to get my attention. I make eye contact and decide he’s not out of air or in some other emergency situation. I start running through my catalog of hand signals for cool critters he might have seen: the waving fingers of an octopus, the hand-on-head-like-a-dorsal-fin that signifies shark, the little pinky wave that says shrimp, the flapping arms that mimic the majestic wings of a manta ray.

Shaking his head emphatically, he points with both hands to something on the wall just beneath him. I fin over and up, scanning the wall curiously, and am totally WOWWED by the vision of two slipper lobsters – the animal in it’s entirety looks just like the meaty tail of the succulent Maine lobsters I grew up on – tearing apart and devouring a red slate pencil sea urchin.
I whoop through my regulator and give my fellow diver the double-OK signs that are the diver equivalent of a surfer’s “awesome, dude!” I snap a couple of pictures and watch in awe as these two slipper lobsters, the urchin trapped between them, take turns reaching nasty-looking pincers into the center of its underside – which is facing up and out towards us, the way the lobsters are holding it – and yank out chunks of meat. The meat vanishes beneath the raised carapace of the lobster, and then the voracious claw is back for more.

While it’s true I feel a twinge of pain and sadness for the sea urchin, this is at the heart of my love of wildlife watching: not just seeing an animal and making a note in a guidebook about the place and date where I encountered it, but really seeing it in action, exhibiting a natural behavior, giving me a glimpse of how it lives its life.

The encounter brought up far more questions than it answered…Had one or both lobsters come upon the urchin hale and hearty and wrestled it into its present predicament? Or had they found the urchin lying upside down, perhaps already partially eaten by some other predator? Were these two lobsters competing? Cooperating?

I’ve seen hundreds of slipper lobsters and other crustaceans all over the world. While some have been bizarrely, almost frighteningly large, I've never considered one to be the highlight of a dive before! Seeing these slipper lobsters in action gave me a whole new perspective and reminded me how little I know about even the simplest organisms I share the planet with.