Scientists say blooms of a red algae that have plagued local bays each summer for more than a decade have appeared in some of the densest concentrations they’ve seen in several years.
The algae blooms appearing this week in Sag Harbor Cove were at densities more than 60 times the level that has been shown to be lethal to fish and shellfish exposed to it in laboratories for as little as an hour. Less dense blooms also were recorded in Three Mile Harbor and Accabonac Harbor in East Hampton.
The researchers who track algae blooms in local waters had been expecting them to emerge any day but still were caught somewhat by surprise that they appeared in Sag Harbor, Three Mile Harbor and Accabonac Harbor first. In past years the blooms had generally emerged first to the west, in eastern Shinnecock Bay and the western creeks of the Peconics, before gradually spreading east.
“Historically, we have tracked a west-to-east migration of the rust tide, with blooms typically emerging in the tributaries of the far western Peconic Estuary in mid-to-late August,” said Christopher Gobler, Ph.D., a marine science professor at Stony Brook University’s School of Marine and Atmospheric Sciences and the leader of the team of researchers who track algae blooms across Long Island for the New York State Department of Environmental Conservation.
“Late last week we saw rust tide at moderate levels in East Hampton and thought it might be a blip,” he continued. “However, this week, the rust tide spread to at least three distinct harbors and reached a level in Sag Harbor we have not seen anywhere on Long Island in several years.”
The algae, a swimming dinoflagellate known as Cochlodinium, is referred to as “rust tide” by the scientists who track it due to the brownish-red tint that it gives the water where it blooms, and to differentiate it from another species of red algae that blooms in late spring and early summer and can be dangerous to humans.
At densities of just 500 cells per milliliter of water, Cochlodinium has been shown to be lethal to fish and shellfish. The levels in Sag Harbor this week were measured at 30,000 cells per milliliter, and at 1,000 cells per milliliter in Accabonac and Three Mile harbors.
Dr. Gobler said last week’s observations had still not revealed any evidence of blooms to the west, though scientists are sure they will emerge there eventually.
“While this is somewhat uncharted territory, we anticipate the rust tide will spread and emerge in the western Peconics and Shinnecock Bay in the coming weeks,” Dr. Gobler said. “Blooms typically persist into the fall or until water temperatures drop below 60 degrees.”
Last year the Cochlodinium blooms first appeared on August 16 in the western Peconics, and not until early September in East Hampton waters. They lasted well into October.
The Stony Brook scientists have published a series of reports in recent years tying the growth in number, range and intensity of the blooms by several different species of harmful algae to increasing nitrogen levels in local waters, fed primarily by septic system pollution of groundwater tables that flow into the bays. Along with the “rust tide,” the species of algae that produced the infamous brown tides of the 1980s and 1990s still appears each year in western Shinnecock Bay. Another species of red algae, called Alexandrium, also appears in some local creeks, including Sag Harbor, in late spring and has forced the closure of shellfishing because it can be harmful or even lethal to humans. Cochlodinium does not pose a health risk to humans.
Cochlodinium first appeared in East End waters in 2004. Their migrating blooms, which drift across bays with the wind during the day and sink to the bottom at night, have been blamed for several instances of fish kills in small harbors and in fishermen’s traps over the last several years. The blooms were also fingered as a likely cause of a massive die-off of what had been expected to be large bay scallop set in the Peconics and Gardiners Bay in the summer of 2012.