April 18, 2008 -- Some make your limbs feel numb. Some give you the stomach flu. Others will even kill you.
These are the scary consequences of shellfish poisoning caused when populations of certain types of toxic algae grow rapidly, or "bloom," in a given spot in the ocean, accumulating in oysters and other shellfish that feed on them -- and then become our dinner.
Now seafood-loving Texans can thank an underwater instrument designed by researchers with the geeky goal of studying plankton ecology for detecting a surprise bloom of a diarrhea-causing algae in the Gulf of Mexico -- just days before a major oyster festival.
The researchers believe more widespread use of this sea sentinel could improve early detection of harmful algal blooms, preventing future outbreaks of shellfish poisoning.
The instrument is the Imaging Flow Cytobot, designed by Rob Olson and Heidi Sosik at Woods Hole Oceanographic Institution in Woods Hole, Mass. It sits on the ocean floor, photographing every cell in samples of water drawn in from its surroundings, around the clock for up to six months at a time.
The Cytobot also measures laser light scattering from each particle, and sends all the information back to the lab to a central a computer that identifies each cell.
"It's something we envisioned for helping us to answer very basic questions about the diversity and ecology of plankton in the ocean," Sosik said.
But the team thought it might be useful for detecting blooms of harmful species, so they collaborated with Lisa Campbell at Texas A&M University in College Station to post another instrument in the Gulf of Mexico, to look for seasonal blooms of Karenia brevis, which can cause shellfish poisoning.
They found a bloom, but it wasn't Karenia brevis.
Since installing the instrument in the Gulf last fall, Campbell checked the output from the instrument daily to develop a set of images of the local plankton species. She planned to use those images to train the computer to automatically identify samples from the Cytobot.
"Around the middle of February, I started to notice this organism called Dinophysis," she said, which she knew was toxic, but which had never before bloomed in the Gulf. "I'm wondering, 'Should there be this many?' I started seeing more. One day, I really see a lot, and I'm thinking, 'This is crazy. I don't want to cry wolf, but I should probably tell someone.'"
Subsequent tests confirmed the presence of actionable levels of the Dinophysis toxin, okadaic acid, in the water and in local shellfish, prompting the Texas Department of State Health Services to close local shellfish beds and recall shellfish harvested in the first week of March.
"Nobody was looking for this type of toxic bloom. It's not part of the ordinary monitoring," Sosik said. "We can't be sure that people would have gotten sick, but there was plenty of toxin in shellfish from that area."
Even if official tests had been looking for Dinophysis, they might have missed it, Campbell pointed out, because the populations varied by as much as 10 times at different times of day, perhaps because of tides or swimming patterns of the algae.
"Normal routine monitoring might be once a month," Campbell said. "Even if you go twice a month, you might not get it at the right time."
Because of the large amount of data collected by the instrument, the researchers can now go back and try to understand why Dinophysis bloomed when it did, and they will continue to look for the usual suspect, Karenia brevis.
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