The toxic rust tide has returned again to the East End's bays
The toxic rust tide has returned again to the Peconic Estuary | 2012 photo courtesy Bill Portlock

At this time last summer, marine biologists working to replenish the scallop population in the Peconic Bays were finding record numbers of scallops and baymen were getting their dredges ready for a banner season. Then, just before the start of scallop season, biologists taking test dredges began pulling up scores of empty shells. The scallop boom had quickly become a bust.

Rust tide, an algae bloom that is toxic to finfish and shellfish but not to humans, has appeared to some extent in the East End bays for each of the last ten years, and last year’s large bloom is believed by some scientists to have been a major culprit in last fall’s scallop die-off. This week, the toxic algae bloom has returned again to the Peconic Bays and Shinnecock Bay.

Dr. Chris Gobler’s laboratory at Stony Brook University’s School of Marine and Atmospheric Sciences reported Monday that the rust tide algae is now at densities exceeding 10,000 cells per milliliter in the western end of the Peconic Estuary. Densities exceeding 1,000 cells per milliliter were found in Shinnecock Bay and Flanders Bay and tributaries of Flanders Bay such as Meetinghouse Creek.

The rust tide algae, a dinoflagellate called Cochlodinium, can be toxic to marine life at densities above 500 cells per milliliter, while the East End’s other most problematic algae, brown tide, isn’t harmful to marine life until it reaches concentrations of 50,000 cells per millileter. It is a different organism from red tide, which is toxic to humans who ingest shellfish contaminated by the algae, and brown tide, which led to the major decline in scallop populations in the Peconics in the mid-1980s. Brown tide, which thrives in warm water with poor tidal flushing, has returned to Shinnecock Bay each of the last seven years.

Dr. Gobler said he believes a new inlet to the ocean created by Hurricane Sandy in eastern Great South Bay may have helped keep the rust tide bloom out of that bay this year, after it was found there the past two years. His research team at Stony Brook Southampton is closely studying rust tide.

“In the last year, we have published two important, new discoveries that help explain the chronic recurrence of these events,” said Dr. Gobler. “First, we have discovered the organism makes cysts or seeds which wait at the bottom of the bay and emerge each summer to start a new bloom. At the end of the bloom, they turn back into cysts and settle back to the bay bottom. This allows for the blooms to return every year. Second, we have found that nitrogen loading makes these blooms more intense and more toxic. As nitrogen loading has increased into our bays, these events have intensified.”

In the past year, activists have been pushing the Suffolk County Health Department to require better septic systems in the Peconic Estuary watershed in the hopes of decreasing the amount of nitrogen from human waste that is entering the bays.

Dr. Gobler’s experiments have shown the rust tide alga can kill fish in a matter of hours and shellfish in a matter of days. His extensive report to the Suffolk County Department of Health Services is available here.

“Last fall, bay scallop densities in the Peconic Estuary declined by ten-fold in some regions during the rust tide, causing great disappointment among baymen and lovers of this delicacy,” he said in a press release Monday. “The impacts of this year’s bloom will likely depend on its duration. The rust tide is expected to spread in the coming days and weeks and typically extends into the fall or until water temperatures drop below 60 degrees.”

Beth Young
Beth Young is an award-winning local journalist who has been covering the East End since the 1990s. She began her career at the Sag Harbor Express and, after receiving her Masters from the Columbia University Graduate School of Journalism, has reported for the Southampton Press, the East Hampton Press and the Times/Review Media Group. She founded the East End Beacon website in 2013, and a print edition in 2017. Beth was born and raised on the North Fork. In her spare time, she tinkers with bicycles, tries not to drown in the Peconic Bay and hopes to grow the perfect tomato. You can send her a message at

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