WOODSHOLE - Bangor Daily News Bangor, ME (BNGR)
Red tide algae may be natural
Brief study shows high occurrence
Orna Izakson Of the NEWS Staff
When red tides first showed up in force on Maine's shores in 1972, the logical conclusion of land-based people was that humans somehow had polluted the water and that the toxic algae blooms were the unfortunate -- and costly -- result.
But that land-bound myopia began to wash away this summer when researchers from the University of Maine and other institutions took to the sea and found healthy concentrations of the unhealthful algae in the clean waters offshore in the Gulf of Maine.
David Townsend, an oceanography professor at the University of Maine, explained that the results are still only preliminary, based on quick observations of samples taken during three 12-day cruises this summer, with detailed laboratory analyses yet to come. But the indications so far are that Alexandrium tamarensis, the alga that causes red tides, is a prevalent and natural element of the Gulf of Maine when certain conditions are right.
Red tides occur when Alexandrium goes into a massive growth spurt. When such "blooms" occur close to shore, the algae can emit a toxin that contaminates clams and mussels with paralytic shellfish poisoning -- putting them off limits to human consumption and costing the commercial digging industry as much as $500,000 a year.
Townsend, along with UMaine colleagues Neal Pettigrew and Andrew Thomas and researchers from the Woods Hole Oceanographic Institution in Massachusetts, the University of New Hampshire and Bigelow Laboratory for Ocean Sciences in West Boothbay Harbor, this summer surveyed currents, water salinity and temperature and took water samples to check for the prevalence of Alexandrium.
"Based on preliminary counts during those three months, it began to be obvious to me anyway that a trend was developing," Townsend said. "We could see that the trends of Alexandrium were not close to the coast. They are apparently a naturally occurring species that occurs offshore, but only when the right combination of light and nutrients is together."
The researchers found most of the algae along a swirl of current that comes out of the Bay of Fundy at Grand Manan off New Brunswick, heads southwest along the Maine coast, then veers offshore somewhere between Jonesport and Mount Desert Island.
Usually during the summer, the water in the Gulf of Maine separates into two relatively distinct layers, with warmer water floating on top and holding cold water underneath. Like all plants, algae need both light and nutrients to grow, so the separate layers provide a conundrum: The warm water gets the most light, but is poor in nutrients; the colder water has lots of nutrients, but not enough light for plants to thrive.
The current coming out of the Bay of Fundy is active enough that the distance between the warm, sunlit water and the cold, nutrient-rich water is small enough that Alexandrium can move between the two and get everything it needs to thrive.
"The inshore occurrence of Alexandrium appears to be when this offshore water gets blown in for one reason or another," Townsend said.
If that theory holds up when the summer's samples go through a rigorous laboratory analysis, the oceanographer said, scientists may be able to provide advance warning of Alexandrium blooms before they hit shore, much like a weather report announcing an incoming storm.
The curve in the current explains why some sections of the coast, such as the Jonesport area, appear to be relatively immune to red tides. It also explains why Monhegan Island has been such a hot spot for the toxic blooms -- the island sits right along the current's path.
By late summer, however, the warm layer along the offshore current thickens and the cold-water nutrients grow too distant for Alexandrium to reach.
"That's why this is a late-spring, early-summer phenomenon, except in extreme eastern gulf and the Bay of Fundy, where more mixing and nutrients come closer to the surface," Townsend explained.
But the natural occurrence of Alexandrium tamarensis doesn't get pollution off the hook as a culprit in the blooms, he added.
Fresh water polluted with excess nitrogen and phosphorus -- two of the nutrients necessary for all plant life, including algae -- also floats on top of salt water, giving algae both the light and the food they need to thrive. So polluted water can exacerbate blooms that blow into shore, or mimic the conditions that work so well for Alexandrium offshore.
Townsend said his group has not yet done a detailed study of how pollution affects Alexandrium blooms. But researchers working under the same $5 million federal grant are looking at the problem at the mouth of the Kennebec River in Casco Bay, he said. Currents there can take that pollution, and the red tides, down the coast to Massachusetts.
The UMaine oceanographer stresses that the results so far are preliminary, not yet based on rigorous, quantitative analysis in a laboratory. Nevertheless, he added, the initial results show great promise for understanding what until now has been a considerable mystery.
"Our spirits are bolstered that we have, perhaps, gained a very, very important insight into what causes these things," he said.
Caption: Alexandrium tamarensis, the algae that produces potentially toxic red tides, is natural and common offshore in the Gulf of Maine under certain conditions. David Townsend, an oceanography professor at the Unive Maine, spent 36 days at sea last summer sampling water temperature, currents, salinity and algae counts to learn about red tides in the Gulf of Maine. (Photos courtesy of the University of Maine) Thomas Pettigrew