Rust Tide Has Spread Here

What began as isolated patches of Cochlodinium, or rust tide, in Sag Harbor and Three Mile Harbor in East Hampton earlier this month has spread across the Peconic Estuary.

Christopher Gobler of Stony Brook University’s School of Marine and Atmospheric Sciences reported Cochlodinium at densities exceeding 3,000 cells per milliliter on Tuesday. While rust tide is not a threat to human health, densities above 500 cells per milliliter can be lethal to marine life. Prior rust tides have resulted in kills of finfish and shellfish on eastern Long Island.

“We have identified climate change and, specifically, warm summer temperatures as a trigger for these large, widespread rust tides,” Dr. Gobler said in a statement. “In the 20th century, summer water temperatures were significantly cooler than they are today. When we have extended summer heat as we have seen this summer, a heavy rust tide often follows.”

By September of 2013, a rust tide had reached East Hampton waters after migrating from the western reaches of the Peconic Estuary. It was found in Three Mile and Accabonac Harbors the following year, but was gone by September. Dr. Gobler described both years’ rust tide incidents as muted, citing lower water temperatures.

A 2012 paper from Dr. Gobler’s lab identified excessive nitrogen as an equally important factor in the intensity and toxicity of rust tides. The study also referred to the rust tide organism’s flexibility with regard to nitrogen, being able to feed off high levels in near-shore regions but also able to persist at lower levels in more open water sites.

“The links between these toxic blooms and excessive nitrogen loading are now well established and are playing out again this year,” Dr. Gobler said. “Near-shore regions on the East End experience intense nitrogen loadings from wastewater and farms and get these events first, after which they are transported to open water regions. It is likely that the recent, intense rainfall will intensify the rust tide in the coming week.”

The last major rust tide, in 2012, coincided with a die-off of scallops in some regions. The effects of this year’s event will depend on its duration, coverage, and intensity, Dr. Gobler said. “We anticipate the rust tide will intensify in the Peconics and spread to Shinnecock Bay in the coming weeks.” Blooms typically persist into the fall or until water temperatures drop below 60 degrees, he said.