Knowledge: Biological Function of Fluorescence in a Marine Organism – Mantis Shrimp

A team led by NIGHTSEA founder Charlie Mazel discovered and videotaped fluorescence in a mantis shrimp in the Bahamas in May of 2002. The discovery led to a new research project into the contribution of the fluorescence to the color pattern of the animal, and its functional role in visual ecology. The results were published in the journal Science in January 2004. Click here to download a pdf of the paper.

 

Mantis shrimp

Mantis shrimp are stomatopod crustaceans that live in tropical and subtropical seas. They are fearsome predators with remarkable (incredible!) vision and lightning-fast striking appendages. They come in two varieties – smashers and spearers. As the names imply, the smashers have blunt-tipped claws used to stun prey, while the spearers have sharp tips. Some varieties are small, just a few centimeters long, but others can grow up to 30 cm (12 in.).

The discovery

In May of 2002 Charlie Mazel was leading a small research team at the Caribbean Marine Research Center, Lee Stocking Island, Bahamas. The general goal of the project was to explore for new examples of fluorescence in the sea, and we were finding a variety of shrimp, crabs, anemones, fish, and other critters in which fluorescence had never before been documented. On one night dive I was under the dock at CMRC testing out a video camera rigged for fluorescence, while my incomparable team (talented artist and diver Sharon McGauley and the irrepressible Joel Albertson of Girdwood, Alaska) had wandered out into the sand to explore. I caught up with them stretched out on the bottom with their lights pointed at an animal filling the opening of a hole in the sand. It was a mantis shrimp, and it had two bright yellow fluorescing spots. I settled in to film it, and was lucky to capture the clip of the mantis shrimp spearing a fish that you see at the top of this page.

The research

After the trip I sent a copy of the video to Dr. Tom Cronin at the University of Maryland, Baltimore County. Tom is an expert in mantis shrimp vision, and he was excited about the possible significance of the fluorescent spots. We added Dr. Justin Marshall (University of Queensland, Australia) and Dr. Roy Caldwell (University of California Berkeley) to the team. Justin is also an expert in mantis shrimp vision, and Roy is a leading researcher on mantis shrimp ecology and behavior. We investigated the fluorescence excitation and emission spectra and how those interacted with the available light at different depths and with the mantis shrimp visual system. Normally colors are absorbed as you go deeper in the water, leading to the washed-out blue you see in underwater photos taken without flash. The fluorescence of the yellow spots keeps them from losing their color with depth, so that they stay bright and obvious – especially to another mantis shrimp of the same species. Work that Roy Caldwell did with subjects in his lab showed that the fluorescent spots are important in the animal’s threat display behavior. Details are in the paper.