Glowing worms in Bermuda

Reproduction is a complex business, and often requires that the partners meet. Polychaete worms belonging to Odontosyllis have developed a highly elaborate mating behavior that includes bioluminescent signals. During a recent stopover on the Bermuda islands, on a sailing trip across the Atlantic, I was able to witness the fascinating mating dance of Odontosyllis enopla. The species normally spends its life in shallow water on rocky or sandy bottoms. Once a month, 2-5 days after full moon and around 55 min after the astronomical sunset, the animals start ascending to the sea surface. Here the circling female tries to attract a male by emitting green light and the repeated release of green glowing clouds. The male signals its presence via bioluminescent flashes. In the course of this dance — which may last from 10 to 30 min — the animals spawn and the sea turns black again as they go dark. Remarkably, the worms undergo severe modifications of their body and behavior when switching from the bottom dwelling mode of living to the free floating form. In the case of the males this means, amongst other things, a considerable enlargement of the eyes. After spawning the worms return to the bottom and can potentially swarm again. The photo above, by Greg Rouse, is of the Californian species Odontosyllis phosphorea in its benthic phase. Data from Dimitri Deheyna and Michael Latz suggest the involvement of a photoprotein in the bioluminiscence of this species.

--Stefan Siebert