Rust tide, an algae bloom that is lethal to shellfish and finfish, has returned for the 11th consecutive year to several East End bays, but this year it has returned late and in lower concentrations than in recent years.
The low intensity of the bloom could be a boon to the Peconic Bay scallop industry, which suffered in 2012 and 2013 from a large die-off of scallops due to the heavy concentration of rust tide algae.
The Gobler Laboratory of Stony Brook University’s School of Marine and Atmospheric Sciences has recorded the rust tide algae at densities exceeding 10,000 cells per milliliter in eastern Shinnecock Bay, exceeding 3,000 cells per milliliter in western Shinnecock Bay, and exceeding 1,000 cells per milliliter in the western Peconic Estuary.
They’ve detected lower levels as far east as Sag Harbor.
Rust tide densities above 500 cells per milliliter have been shown to be lethal to marine life.
The rust tide algae, Cochlodinium, first appeared in Long Island waters in 2004. This year’s bloom has proved to be later and in lower densities than in recent years. Scientists believe this is due to the drought we’ve experienced this summer.
“Historically, blooms have emerged in mid-August and reach peak densities by early September,” said Professor Christopher Gobler of SOMAS, in an announcement to the press Sept. 8. “This year’s bloom has been delayed and is, thus far, less intense than in the past.”
“We know that increased nitrogen loading makes these blooms more intense and more toxic,” said Dr. Gobler. “Nitrogen, originally from septic tanks and cesspools, is delivered to our bays via groundwater and groundwater flow is driven by rainfall patterns. Rainfall levels on Long Island are 60 percent below average since April, meaning there is less nitrogen entering the bays to fuel these blooms.”
Dr. Gobler pointed out that this year’s bloom shows what could happen if less nitrogen entered the groundwater and traveled from there into the bays.
“The ability of this organisms to form cysts or seeds assures it will return every summer,” he said. “This year’s occurrence suggests efforts to reduce nitrogen delivery to bays may lead to more years like 2014 and 2015, when there was less nitrogen and the blooms are shorter in duration.”
The milder rust tide may also benefit Peconic Bay scallop populations.
In years with particularly bad rust tides, such as 2012 and 2013, bay scallop populations in the Peconic Estuary declined dramatically during the bloom, which was at its peak just two months before the November opening of scallop season.
In contrast, last year there was also late summer a dry spell, the rust tide was mild, and scallop harvests were the best in decades.
“While nothing is fully certain, if the drought continues and the bloom does not intensify, there will likely not be a large die-off of bay scallops this fall,” said Dr. Gobler. “This would bode well for another robust harvest come November.”