A clever technique that exploits 'glow-in-the-dark' marine microorganisms now enables scientists to visualize how water flows over the surfaces of dolphins as they swim. The luminous patterns observed by researchers might lend insights into some of the unique adaptations dolphins have evolved to survive in their marine environment.

Bioluminescence is the ability of an organism to produce visible light. Creatures possessing this ability include various species of bacteria, dinoflagellates, fireflies, and fish. Bioluminescent organisms are able to produce light via chemiluminescent reactions—chemical processes that produce energy in the form of light.

Numerous species of marine plankton are bioluminescent. These microscopic, glowing invertebrates are most commonly found floating in large colonies in the deep, open waters of the world's oceans. The light emitted by bioluminescent marine plankton is created by organs in their skin called photophores.

The reasons for bioluminescence in marine plankton is not clear. Some scientists believe it helps members of the same species to recogize one another, while other scientists believe it serves to lure prey or distract predators.

Dinoflagillates, a type of bioluminescent plankton, inhabits the shallower coastal waters and, as a result, was an ideal organism for the "dolphin swim" studies. Because dinoflagillates glow more intensely when disturbed or stressed by objects passing through their colonies, they provide detailed, luminous images of the water flowing around the swimming dolphins.

In their research, physicist Jim Rohr, biologist Michael Latz, and their colleagues used trained dolphins to swim through colonies of dinoflagillates. As the dolphins disturbed the tiny bioluminescent organisms, they created intricate light patterns. By attaching video cameras to the dolphins, the scientists were able to capture image-intensified video recordings of these light patterns. By closely studying the videos, Rohr's team was able to quantify the flow of water over the dolphin's skin. They found areas of low bioluminescence where there was high surface shear stress, such as front of the dolphin's head and the leading edges of their fins.

This research not only lends insight into how dolphins are adapted to their environment, but also offers information useful to better design of boats, submarines, and other marine vehicles.

Find out more:

• Herring, P.J. Dolphins Glow With the Flow. Nature. 393:732-733 (1998).
• Rohr, J., Latz, M.I., Fallon, S., Nauen, J.C. and Hendricks, E. Experimental Approaches Towards Interpreting Dolphin-Stimulated Bioluminescence. Journal of Experimental Biology. 201:1447-1460 (1998).
• Burnie, D. and D.E. Wilson. Animal. Dorling Kindersley. London. 2001.

Photo © Hiroshi Sato / iStockPhoto.