Researchers explain bioluminescence in Salt River Bay


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ST. CROIX - The darkness reveals a little magic in the water at Salt River Bay.

Trail your hand through the sea at nighttime in the small mangrove lagoon, and the sparkles come shimmering off your fingertips.

The paddle from your kayak lights up the water.

The bioluminescence glimmers.

Researchers have, for more than a year, been studying what makes the water go aglow when something moves in a small mangrove lagoon at Salt River Bay, a little bay within the bay.

Recently, they presented their findings, delving into the nature of the organism that causes the glow and its long-term population and growth in the bay; along with the bay's water quality, sedimentation and water exchange.

The species responsible for the glow is Pyrodinium bahamense - the same species that is commonly found in other bioluminescent bays in the Caribbean, including Mosquito Bay on Vieques, said Jay Pinckney, the principal investigator for the Salt River Bay study.

"It's important because we didn't know who was responsible for the bioluminescence in the lagoon," he said.

Bioluminescence is the production and emission of light by a living organism. In the sea around St. Croix, there are two areas that are known for bioluminescence: one at Salt River and the other at Altona Lagoon.

In certain areas at Salt River Bay where the concentration of the one-celled bioluminescent organisms is high, any movement in the water agitates them and causes them to light up. Pyrodinium bahamense are part of a group of one-celled, two-tailed organisms called dinoflagellates.

According to Pinckney, the water quality in the little lagoon where the dinoflagellates seem to thrive is very good, with good concentrations of oxygen and nutrients, and good pH.

"It's very similar to the water that's in Salt River Bay," he said, noting that in his presentation, he referred to it as "an appendage of Salt River."

David Goldstein, the chief of education and interpretation for the National Park Service sites on St. Croix, said he feels that the relationship between Salt River and the little mangrove lagoon - and the need for more data - is the important take-home message from the research.

"We've got to focus on the health and well-being of the bay as a whole," he said. "Ground water seepage, overall water quality, the impact of storm drainage management, the impact of the roadways and sedimentation, even what's living in the bay. A lot of that management data isn't clear at this time."

Conservation efforts need to focus on the entirety of Salt River Bay, Pinckney said.

The studies on the bioluminescence came as officials begin planning for a proposed Salt River Bay Marine Research and Education Center that they want to build on a piece of National Park Service land, with access to Salt River Bay through the lagoon where the bioluminescence seems to be thriving.

Although bioluminescence is a natural phenomena, the mangrove lagoon where it is concentrated is actually man-made.

The shoreline in that area of Salt River Bay was changed drastically in the 1960s, with dredging and construction as a proposed hotel development in the area started to take form. Although construction began and a hotel building was erected, the project never fully materialized and the work stopped in the 1970s, before the Park Service bought the land.

According to Pinckney, the study clearly determined that "these dinoflagellates have been in mangrove lagoon since not too long after it was dredged in the mid-1960s. They've been in that lagoon for at least 50 years."

The dinoflagellates can transform themselves into cysts, and the cycts were found throughout the sediment at the bottom of the lagoon, Pinckney said.

There are multiple hypotheses about why the bioluminescent organisms might transform into cysts, including that they do so when they are under stress, he said.

"Stress can come from lots of different things: low nutrient concentrations, the water gets too fresh, the water gets too salty," he said.

The bioluminescence also may appear brighter or dimmer at times, and the intensity varies even in different locations within the lagoon itself, according to Pinckney.

Mosquito Bay in Vieques - one of the best-known bioluminescent bays in the world - went dark in January, and, although it has regained some bioluminescence, the light has dimmed, leaving scientists, government officials and others concerned, according to media reports. Some activities in that bay have been restricted.

Pinckney said bioluminescence like that which is found in the mangrove lagoon in Salt River Bay is not all that common.

"The bioluminescence, this particular type is only found in a few places in the Caribbean and a few places in the Pacific," he said. "There's just a few places where this is a natural phenomena. And the mangrove lagoon is one of the few places where it happens year-round, so it's an important eco-tourism feature."

Currently, four companies take kayakers to see the bay at Salt River at night.

Although interest in seeing the bioluminescence from tourists may be growing, officials said some local residents still are not aware of it.

Part of the grant from the U.S. Department of Interior that funded the bioluminescence study went to outreach, with a goal of informing more residents about the phenomena.

"I did high school outreach. I arranged for 200 kids to go out," said Marcia Taylor, marine adviser at the University of the Virgin Islands. "The purpose was to expose more people who live here to the bay. We found that very few people who live here actually know about it."

Taylor went into classrooms first, providing a presentation about the bioluminescence.

For the students who got to explore the bay first-hand, "they just loved it," she said.

Taylor said she believes residents need to learn what they can about the bioluminescence.

"If we're talking about the possibility of development around that area, people need to know what's there so we can make an informed decision," she said.

- Contact reporter Joy Blackburn at 714-9145 or email jblackburn@dailynews.vi.

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