26 Jan 2013 – Titanic crabs, vampire fish and a miraculous mask

A coral reef at dawn is a magical place.  The night fishes are getting ready to tuck in for the day.  The day fishes are awakening, eager to break their night-long fast.  This is a time when an early-bird diver can see the most amazing diversity of species, and the most unusual behaviours from reef denizens.

Luis, Emily and I have been diving at dawn on patch reefs in RSunriseock Sound at the southern tip of Eleuthera, in the Bahamas.  For 4 days last week, and 4 more days this week, we met on the dock at 06h15 and headed east, towards the dawn’s first light, on the Simon Says (our snazzy research boat).  Our goal was to see what lionfish – infamous invaders from the Indo-Pacific – do in the early morning.

The first trickle of water into the wetsuit at that hour is always a little shock.  The temperature has been dropping over the past month and is now 22oC.  In the crepuscular gloom, Luis and I head towards the reef patch, already a hive of activity.

This morning, our survey of lionfish is delayed by a stunning display of brawn by two enormous reef spider crabs.  Each must measure at least 40 cm from leg to leg. They are built like Hummers with spines all over.  It’s not clear what the subject of their dispute is but these titans are facing each other, threatening claws waving.  The claws sometimes make contact for a short bout of arm-wrestling, and then the crabs return to their staring match.  Luis films some of the encounter, which eventually fizzles out, with one of the contestants retreating.

Back to lionfish.  They are out, over the reef, over the seagrass, hunting.  A lionfish hunting is a beautiful sight – it’s just a shame it’s happening in the wrong oceLionfishan!  When on the prowl, lionfish fan out their large, feathery pectoral fins, and advance ever so slowly towards their prey, a small fish, crab or shrimp.  I have seen them patiently herd fish into a corner, cutting all escape routes with their spread fins.  And then they strike, fast as lightning, extruding their jaws and sucking in water, fish and all, like the most powerful of vacuums.   This is what they are doing this morning, slowly emptying the reef of small fishes.

We leave the reef patch, get back on Simon Says, and zoom over to another reef.  As we speed along, I lean over to clean my mask (oooh, rookie mistake!), lose my grip on it, and then it’s gone.  No!  What to do?  Go look for it or go survey the last patch?  There is a spare mask on the boat so work wins.  Disheartened, I jump in, with a leaky mask, to count lionfish.   When the sun rays hit the reef, poof!  As swiftly as vampires repelled by light, the lionfish disappear into caves and crevices.  This is where they will stay until dusk. Our window of work time has closed for the morning, just 45 min after sunrise.

Clever Luis then reveals that he marked the spot of the sunken mask on the boat’s GPS.  I’m still doubtful that we’ll find it since we were going so fast when it happened.  But sure enough, Emily and I spend only two minutes looking from the surface, and she shouts ‘Found it!’.  I hold on to it tightly all the way back.

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