In Poppy On Monday, Gone By Tuesday, Harmful Algae An Omen Of What’s To Come
By: Brian Kehrl
A species of algae that can kill fish was detected in Popponesset Bay this week, in what may be the first time the bay has been found to be host to a harmful algal bloom.
Shellfish Constable Richard H. York Jr. detected the cochlodinium algae, often known as “rust tide,” on Monday during routine water quality monitoring conducted every month near Gooseberry Island in the main body of Popponesset Bay.
“That is the first time we have seen what could be a problem algae in the 20 years that I’ve been here,” Mr. York told the Mashpee Shellfish Commissions during separate meetings this week. “It is a problem worldwide.”
Mr. York said the rust tide was present at 800 cells per milliliter, making it the most prevalent algae in the water column when measured by weight.
By Tuesday, afternoon, however, the bloom had dropped down to 2 cells per milliliter, a change that Mr. York attributed to an overnight drop of 6 degrees in water temperature. Such large drops in temperature can occur in cool, windy conditions, Mr. York said.
The rust tide is not toxic to humans or a risk for people in contact with the water. But it can kill fish, due to its production of hydrogen peroxide, which damages the fish’s gills. The invasive algae, thought to be transported around the globe in ship ballast water, have been a severe nuisance to the fishing industry in southeast Asia and the Mid-East.
Mr. York said there were no reports of fish kills in Popponesset this week.
Shellfish can also be affected as the rust tide is too large for them to eat and crowds out other sources of food.
It is unclear what caused the cochlodinium (pronounced cock-lo-din-ium) bloom in Popponesset, but it comes after the same species was identified this summer in Buzzards Bay and Nantucket Sound, Mr. York said.
It has also been found in the Three Bays system in Cotuit and Osterville in the past.
According to news reports this summer, the bloom in Buzzards Bay was thick enough in some areas to turn the water a brown, rusty color. At times it reduced visibility in the water column down to just a few inches.
Rust tide grows best in warm water with high nutrient levels, according to the Buzzards Bay National Estuary Program.
According to Mr. York and news reports of the Buzzards Bay event this summer, the bloom is caused in part by the excess nitrogen in area waters, primarily from septic system wastewater.
According to information from the Woods Hole Oceanographic Institution, the algae blooming once makes it more likely to bloom in the future, due to the presence of cysts to spawn future growth and an indication that the conditions are right to host the algae.
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