July 28, 1999 -- Scientists Say Brown Tide Was Twice as Intense as Previous Outbreaks

Researchers Continue

To Track

New Concentrations

Teri Frady
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NMFS Northeast Fisheries Science Center

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Highlands, N.J.-- Federal scientists say that the brown tide that appeared in the Barnegat Bay system and Great Bay this spring reached roughly twice the intensity of previously documented outbreaks before subsiding to presently low levels.

“The level of Aureococcus was virtually undetectable in February, but by June we registered the largest concentrations that we’ve recorded so far,” says Dr. John B. Mahoney, a NOAA Fisheries algal bloom expert at the J.J. Howard Marine Science Laboratory at Sandy Hook.

Aureococcus anophagefferens is the scientific name for the tiny golden-brown alga that causes brown tide. NOAA Fisheries is the federal agency that has among its responsibilities maintaining healthy habitats for marine life.

“Although the warmer water temperatures caused by an early July heat wave suppressed the bloom, this is a persistent organism. If conditions are right, it may reassert itself,” says Mahoney. He is presently sampling for the organism weekly, and will continue to track levels through the winter. “We want to determine if the 1999 bloom provides a massive seed population for a bloom next year,” says Mahoney.

Brown tide algal growth is related to several natural factors, including water temperatures, faring best at 70-77oF. These temperatures were prevalent in June, when algal cell concentrations reached roughly 2 billion per quart of water–more than 60 times the highest concentration observed in 1998.

Growth is diminished when water temperature is greater than 80oF. Water temperatures during the heat wave were 81-84oF. At present, Mahoney says the cell concentrations have returned to a few thousand cells per quart of water, about the same as in April of this year.

Mahoney leads a field study that has been tracking the incidence of brown tide in the area since late 1997. The study was initiated after major brown tide events in New Jersey in 1995 and 1997. Each of those outbreaks lasted about two months, and affected the survival, feeding, and growth of hard clams at commercial aquaculture facilities in the Little Egg Harbor area and nearby. Brown tide cells produces a compound that can inhibit the feeding of a number of other shellfish species such as the hard clam, blue mussel, and bay scallop.

“We have no information about brown tide effect on natural shellfish populations in New Jersey,” says Mahoney, “but with this most recent event, we have some evidence that brown tide in Long Island may not be correlated with brown tide in New Jersey.” He says, “There’s been no major brown tide outbreak in Long Island embayments this summer, so to some important degree the natural factors regulating development of a bloom appear to differ between the two areas.” Since the initial outbreak in 1985, there have been more brown tide incidents in Long Island waters than in New Jersey. There was a moderate outbreak this spring in Maryland.

New Jersey was spared an outbreak in 1998 because El Nino weather kept water salinity unseasonably low during the normal May-June algal development period. After that, high water temperatures through the rest of the summer worked to keep growth suppressed.

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