State of the Bays: Rotting Seaweed & Nitrogen Could Pose Human Health Risks

Pictured Above: A photo of Dasysiphonia japonica posted by the Gobler Laboratory from the East Islip Marina in October 2019

As the Covid-19 pandemic reminded us all of the interconnectedness of the world’s ecosystems, other environmental threats are quickly going global.

Dr. Christopher Gobler, who this year held his annual State of the Bays address via Zoom meeting May 28, has been following the progress of the fibrous red seaweed Dasysiphonia japonica into Long Island’s bays and harbors.

Craig Young, a researcher in Dr. Gobler’s lab, has documented this algae, which is native to the Pacific Ocean and jumped to the East Coast of the United States from Europe in the late 2000s.

It is now widespread and covering much of the bottom of the Great South Bay, Moriches Bay, Shinnecock Bay and even the Peconic Bay system, said Dr. Gobler.

Mr. Young performed an isotopic analysis of the nitrogen in the tissue of the seaweed and found out that 90 to 100 percent of that nitrogen is from wastewater.

While seaweed by itself might not seem like a problem, Dr. Gobler said there have been reports around the world of decaying Dasysiphonia causing major health problems due to a release of sulphur gas.

He pointed out a recent paper in the scientific journal The Lancet which showed that 8,000 people reported acute exposure to sulphur from rotting seaweed during an eight-month period on the Caribbean island of Martinique, with at least three people requiring intensive care treatment.

Dr. Gobler said that silverside fish exposed to decaying Dasysiphonia seaweed in his lab face about a 100 percent mortality in one week.

“It’s not a low oxygen or ammonium effect,” he said. “There’s some sort of additional compound coming from the seaweed that is lethal to fish.”

Dr. Gobler said some communities along the South Shore have already reported “big seaweed stink events” in recent years.

“There’s emerging medical evidence this can have very serious consequences,” he said. “In Europe, there were reports of animals and people dying from exposure to sulfur in seaweed.”

Dr. Gobler, a professor at the School of Marine and Atmospheric Sciences at Stony Brook Southampton College, is well-known throughout the region for his work researching harmful algae blooms and the sources of nitrogen that feed those blooms.

Dr. Gobler is also looking this year at the health effects of nitrogen in drinking water, due to the high level of nitrogen in Suffolk County’s drinking water due to on-site septic systems.

“Suffolk County’s nitrogen level in groundwater is among the highest in the United States,” he said, which is about 3.8 milligrams per liter. About 200 million of the U.S. population of 350 million people have drinking water nitrogen levels below 1 mg/L.

The U.S. Environmental Protection Agency has set a drinking water standard of 10 mg/L of nitrogen, but Dr. Gobler wonders if that standard is low enough.

He pointed out research from the Mayo Clinic that shows a significant increase in risk of bladder and ovarian cancer when people have drinking water with greater than 2.46 mg/L of nitrogen.

“The EPA is looking at nitrate and nitrite in drinking water as a health concern,” he said. “The International Agency for Research on Cancer classifies nitrates and nitrites as probably carcinogenic to humans.”

Dr. Gobler shared many Peconic Bay Scallop researchers’ sentiments that a massive die-off of adult bay scallops in 2019 was due to warmer than usual water temperatures, along with the presence of a parasite.

“That contributed to mortality, though the manner in which that happened is not fully understood,” he said.

Dr. Gobler said there’s no evidence of algae blooms or increased nitrogen contributing to this scallop die-off.

Beth Young

Beth Young built her first boat out of driftwood tied together with phragmites behind her family’s apartment above the old Mill Creek Inn in Southold. Nowadays, she spends most of her time kayaking, learning about shellfish, writing newspaper stories, trying to sail a Sunfish, and watching the way the bay changes from day to day. You can send her a message at

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