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Public Radio's Environmental News Magazine (follow us on Google News)

Red Tide Mystery

Air Date: Week of


CURWOOD: It's Living on Earth. I'm Steve Curwood. At first, the experts had no clues. Something was killing fish last year in the creeks upstream from Delaware's great inland bays. Five million fish to be, well, somewhat exact. But recently, scientists did find the culprit. Bruce Schimmel reports on how they unraveled the mystery.


SCHIMMEL: One Friday afternoon in early August, Bill Winkler played hooky from his souvenir shop near Rehoboth Beach to do some surfing.

WINKLER: We paddled out, and as soon as I jumped in the water I saw this foamy, like brown stuff. And I thought "What the heck?" I said. And as I went out a little bit further, I was the first one in the water, I noticed that the water was reddish brown, more red than brown. It looked like a reddish brown tea.

SCHIMMEL: The spry 52-year-old was surprised by the brown foam, because the water near Rehoboth Bay is known to be among the clearest on the Delaware coast. So Winkler filled a bottle with a sample and took it to a state lab for analysis. But the scientists there found nothing unusual. Kevin Donnelly is director of Delaware's Division of Water Resources. His lab, he says, was looking for the wrong thing.

DONNELLY: This past summer, we've had the worst record, the highest number of fish kills that we've had in 20 years. Almost twice the number that we've ever had. We were looking for pfisteria. We were looking at low dissolved oxygen as a problem.

SCHIMMEL: Low levels of oxygen and pfisteria, a toxin-producing microorganism, are problems in Delaware's bays, exacerbated by pollution from leaking septic systems and agricultural runoff, among other things. But the lab didn't find any pfisteria in this sample. Winkler wasn't satisfied. He feared his surf water was laced with a toxin known to cause massive fish kills off the coast of Florida. But the algal bloom, known as red tide, had never been found this far north. Winkler persisted, and sent his sample to Daniel Baden, director of the Center for Marine Science at the University of North Carolina.

BADEN: I think we went in objectively thinking it's something poisonous in the water, and we did find it.

SCHIMMEL: But weeks had passed since Winkler collected his sample, and Baden needed a fresh one to pin down if the algae producing the poison was the same one responsible for Florida's red tides. Fortunately, just as Baden's lab called for more, a friend of Winkler's, another surfer, happened upon a fish kill in a small cove inside the bay. The sample contained brevetoxin. But it also held the culprit which produced it. Baden's colleague, marine cell biologist Carmello Tomas, took a look. This was his reaction:

TOMAS: Astounding to see all these little green things that were swimming through our microscope fields.

SCHIMMEL: Tomas had been tracking these particular little green things, called chattonella for several years. Chattonella has been implicated in fish kills in Norway and Japan. But scientists hadn't been able to confirm what kind of toxin it produces. Tomas had seen chattonella in the waters of several eastern states, though never in such a concentration. He was at a loss to explain the density he found here.

TOMAS: The number of cells per liter in other states normally has been very, very low. Whereas the Delaware situation here is one which was inordinately high, to the point of having ten million cells per liter or more at the highest concentrations. Those concentrations are really alarming.

SCHIMMEL: The density of chattonella from this inland bay sample was 100,000 times greater than he'd seen before. Tomas could now confirm that chattonella produces red tide toxin. What's more, unlike Florida, where red tides affect only open waters along the coast, here was a bloom in an inland waterway.

TOMAS: This organism can occur in areas where we had never previously thought that they existed before. So there should be some kind of surveillance.

SCHIMMEL: Finding brevetoxin in inland waters, such as bays and estuaries, says Tomas, is like finding a poison in your back yard. Since these areas are close to where people live and play, this heightens the need for algal bloom monitoring. Although brevetoxin isn't known to be fatal in humans, the spray from affected waters can cause a skin irritation, burning eyes, and respiratory problems. In addition, people can become sick from eating shellfish tainted with breve. And the highest concentration of shellfish beds are found in inland waters. The state of Delaware is developing a plan to detect chattonella blooms, and, if necessary, close off shellfish beds. But even the best monitoring plan, Tomas says, can only do so much.

TOMAS: In many cases, we really can't control these large-scale events like blooms in open bays.

SCHIMMEL: But, he says, we can reduce their frequency and duration by reducing the amount of pollution runoff.

TOMAS: That is, increasing the water quality or making the water quality better, so that the essential materials that these blooms feed on is not being provided to them in excess.

SCHIMMEL: Tomas cannot say if pollution caused this particular outbreak. But pollution will certainly exacerbate and prolong harmful algal blooms. For Living on Earth, this is Bruce Schimmel in Rehoboth Beach, Delaware.

CURWOOD: The thought of a windswept, snow-lined beach may send a shiver down the spine of many northerners at this time of year. But the beach is the place to be. Creatures you would never spot on a summer stroll on the hot, crowded sand suddenly appear undisturbed and unfettered by the presence of a solitary human. For commentator Sy Montgomery, it's a naturalist's paradise.




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