Park Service Studies Tiny, Glowing Mysteries in Salt River

The bioluminescent lagoon in Salt River has become a hallmark tourist attraction on St. Croix, but scientists aren’t sure exactly why the phenomenon occurs or how long it will last. Researchers from the University of South Carolina and the University of North Carolina Wilmington are joining the National Park Service and the University of the Virgin Islands to learn more about the lagoon’s beautiful glow and safeguard it for the future.

According to Zandy Hillis-Starr, chief of resource management for the national park, the bioluminescence may be a fairly new occurrence, starting between 10 and 15 years ago. She said that prior to that, there were no recorded bioluminescent events in the area.

The lagoon where it occurs is also a relatively new addition to the island. Previously the lagoon was a small saltwater pond, but in the 1960s a hotel developer widened it, dredged it and opened a channel to Salt River to build a marina. The development flopped in 1971, however, and construction was never completed.

The area was subsequently added to the Salt River Bay National Historical Park, and Hillis-Starr said the lagoon area is being considered as the site for a marine research and education center.

Before construction can take place, however, Hillis-Starr says the park service wants to better understand the bioluminescent phenomenon to ensure they don’t disrupt it.

“We need to find out the various essential components,” she said. “Will it continue? Will it survive? Is there something we have to do to maintain the phenomenon over time? And, certainly, will there be any conflict if we’re doing small boat operations out of the bay for the marine lab?”

To that end, the park commissioned the universities to study the phenomenon using a $128,000 grant from the Office of Insular Affairs Coral Reef Program.

The focus of the study is on pyrodiniumbahamense, microscopic organisms known as dinoflagellates that photosynthesize like plants but are capable of propelling themselves through the water.

These tiny creatures are what are glowing in the lagoon. That much is known. Why they glow, what causes them to prosper and even where they came from is still a mystery.

The research has been split into two major parts. Chad Lane, an assistant professor of geography and geology at UNC Wilmington, is studying the distribution of the dinoflagellates in the lagoon.

He and his assistant, master’s student Paula Reidhaar, are taking core samples of the muck at the bottom of the lagoon and searching for microscopic “cysts.”

Lane explained that dinoflagellates have the ability to enter a seed-like resting phase. Counting the number of dormant creatures, known as cysts, under a microscope allows the scientists to extrapolate how many live in that area of the lagoon.

So far their data has found the dinoflagellates prefer the tip of the lagoon farthest away from the channel to the ocean, a finding in line with the anecdotal accounts of kayak tour operators who say the glow is most vibrant in that area.

Lane is also taking core samples of the lagoon floor and searching for cysts several feet below the surface. This, he said, was an attempt to gauge when the creatures may have arrived on the island. He said it was unclear if they arrived shortly before the bioluminescence began or if they’ve been here for years before.

Lane said that the creatures can remain in their dormant cyst phase for decades waiting for the right conditions for them to bloom and return to their active state.

What those conditions might be is the research topic of Michelle Zimberlin, a master’s student at USC. Aided by UVI researchers who have been gathering water samples from the lagoon for her weekly, Zimberlin has experimented with adding various nutrients to the water to see just what combination of factors allow dinoflagellates to thrive.

In order for the bioluminescent effect to be visible, dinoflagellates must be present in large quantities in the water. For some reason, this particular lagoon is well suited to their needs, and Zimberlin wants to know why.

She has experimented with different nitrogen, phosphorous and even vitamin B12 levels. She’s been most successful stimulating dinoflagellate growth by simply adding mangrove leaves to samples, however, suggesting the key may lie in the plants ringing the lagoon.

The researchers plan to finish their research by December and a report will be issued to the Park Service after that.

In the meantime, Marcia Taylor, a member of UVI’s outreach faculty, is trying to share the mystery of bioluminescence with local students.

Through the grant, she secured funding to take around 200 high school students on evening kayak trips through the lagoon so they can see the phenomenon for themselves.

Taylor said the students, many of whom have never been in kayaks before, let alone been to the lagoon, are amazed by the experience, and she is hoping to expand the project.

Taylor said she wanted to share the phenomenon with as many locals as possible because it’s usually tourists who get an opportunity to see it.

“So many of the people who live on St. Croix don’t know that it’s there. They don’t understand the phenomenon. They don’t know anything about it,” she said.

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