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Thursday, September 29, 2022
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Bioluminescence Lights Up Night Waters

Michelle Pugh, left, and Marcia Taylor. There are lots of strange and wonderful sights to see in the Virgin Islands, especially in the underwater world. Longtime residents Marcia Taylor and Michelle Pugh take divers on night dives to see the spectacular light displays from marine organisms, called bioluminescence, that occurs in our inland waters at night.

Bioluminescence is the phenomenon of living things giving off light. This occurs in many ways in our waters. The way most people may see this is to swim or look into the water on a dark, moonless night and see tiny “sparkles,” or individual flashes of light, as water is disturbed or breaks on the beach. This is caused by very small, single-celled organisms called dinoflagellates. When a particular bay has a high concentration of these it is called a phosphorescent bay, like Bio Bay in Vieques.

Here on St. Croix we have a vivid phosphorescent bay in Salt River estuary.

Another animal that provides a spectacular light show for divers are ostracods. Ostracods are sesame-seed-sized crustaceans that live on the reef or in the sediments around reefs.

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Earlier this month, Taylor, a marine scientist at the University of the Virgin Islands, and Pugh, owner of the dive shop Dive Experience, took a group of 15 divers from the St. Croix Dive Association to a site near Christiansted where these animals are found in abundance. About an hour after sunset, the first ostracod bioluminescence was seen. The group of divers settled on the sand and turned off their underwater lights and saw the amazing light show.

Ostracod courtship displays in the Caribbean are among the most spectacular natural light shows ever reported. When mating, the males leave the sea bottom and ascend to send out coded messages to females of their species. They secrete a substance from one set of tiny nozzles on their upper lips, and enzymes from two others. These mix in the water to produce a sustained, discrete pulse of bright blue light. They repeat this as they swim to produce a species-specific, coded display. To the diver the display looks like a string of pearls being sequentially lighted from top to bottom.

As the divers looked around thousands of these “string of pearls” displays were seen all around.

“It’s like being in Times Square at night” Taylor said.

The display lasts about 30 to 45 minutes and ends as suddenly as it starts.

There may be 7 or 8 different species of ostracods displaying in the same area. Each species has a distinct display. Some displays are only a few centimeters long, while others may extend meters. Some move downward, others upward, others laterally. Some make relatively long lasting pulses of luminescence, 10 to 20 seconds, while others are like little strobe lights, 50 to 100 microseconds. One can see these displays throughout the Caribbean, and each island has different species from most others. 60 species have been discovered so far in the Caribbean but scientists believe there are many more.

These displays appear to be restricted to the Caribbean and have not been observed anywhere else.

This moonless event produces a symmetry of star lights above and sea creature lights below that is unforgettable.

Further information on this or other marine phenomenon can be obtained by contacting Taylor at UVI, 692-4046 or sending her e-mail at mtaylor@uvi.edu.

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