To fluoresce

A while ago, I bought a fluorescent flashlight to use while diving on coral reefs. My theory was that the fluorescence would help me find coral spat - the single-polyp recruits that will eventually grow to become whole coral colonies. I took the flashlight to Palau in November, but I never got a chance to try it out. When we were packing for this trip, I threw it in my bag to give myself another shot. 

We headed out for a night dive off the pier at our dive resort, fluorescent flashlight in tow. It looks like a radar gun - thin handle, large-diameter shooting end - and comes with these yellow light filters you're supposed to wear over your mask. I shined the blue beam on the corals, placed the filter over my mask, and scanned the reef. Oh my goodness, you guys. 

Ok, it's a horrible picture, but this is the best we could get of
anything fluorescing. 

Fluorescence occurs when light of a particular wavelength excites electrons and makes them jump up to a higher-energy state (a higher orbital in whatever atom they're in). Then when the electron falls back down to its normal energy state, it releases light at a different wavelength. Lots of things fluoresce. On coral reefs, there are a number of species of stony corals, octocorals, and mobile invertebrates with fluorescence - not every species, but a good number of them. 

In Bonaire, Montastrea cavernosa fluoresces orange or green. It's one of the most common corals on the reefs here, so it was everywhere I looked with my flashlight. Some colonies reflected back at me bright orange, but others were green. I started wondering if the two colors represented different subspecies - I'm not sure if anyone has ever looked into that. 

As I swam along, I noticed these fluorescent blue things. They were pretty convoluted, with multiple folds of flexible tissue, like a complex flower with numerous petals. They didn't remind me of anything I had seen in daylight, but they were very common. I removed my yellow light filter, turned off the fluorescent flashlight, and switched to my regular white light. The animal was a nudibranch! A lettuce slug (Elysia crispata) to be precise. They must only come out at night!

Swimming a little further on the reef, I noticed a dull brown animal. It was rather large and strangely shaped, like a lobster that had gotten smashed in a panini press. I knew I had seen something like it a few years ago, also on a night dive. It was a Spanish slipper lobster, Scyllarides aequinoctialis. 

Our last find of the dive was on the way back to the dock. A plate-sized brown lump on the sand. At first I thought it was a rock, but then I got close enough to see the star pattern on the top and the faint fuzz covering its body. It was a sea biscuit! Meoma ventricosa.

Coral reefs are completely different after dark, and I was glad for the chance for a fluorescent night dive in Bonaire!