Brown Tide Eruption Creeps Into Long Island’s Great South Bay

PATCHOGUE, NY — An intense and damaging brown tide has erupted, threatening marine life like hard clams, across Great South Bay on the south shore of Long Island, according to scientists at The Gobler Laboratory of Stony Brook University.

Monitoring on Wednesday in Patchogue Bay showed a brown tide “rapidly intensifying” to more than 300,000 cells per milliliter — the highest brown tide cells count recorded on Long Island since 2017, Christopher Gobler, the endowed chair of Coastal Ecology and Conservation in the School of Marine and Atmospheric Sciences at Stony Brook University who runs the lab, said in a news release.

There were also densities well over 100,000 cells per milliliter present in the water from Bellport to Sayville, but lower levels of brown tide were found to the east and west of the region, Gobler said. Any density above 35,000 cells per milliliter can be particularly harmful to hard clams.

The south shore is highly vulnerable to brown tides and the area has experienced the events almost annually since 1985, but Gobler called this year’s strain “the most intense and widespread brown tide in four years.”

“The timing of the current brown tide is particularly troubling for hard clam populations, as June marks the once per year event when they reproduce, and newly spawned hard clams are highly vulnerable to brown tides,” he said. “The fate of these young-of-the-year clams may rest on the duration of the current brown tide which usually intensifies through June and into July until water temperatures get into the mid-70s.”

The brown tide alga, known in the scientific world as Aureococcus anophagefferens, caused the demise of the largest bay scallop fishery on the U.S. east coast in the Peconic Estuary, making it notorious throughout Long Island.

Scientists have largely attributed the loss of eelgrass across the island, as well as the inhibition of hard clam recovery efforts in Great South Bay since the 1990s to the destructive algae.

Brown tides originally occurred across the south shore and the east end from 1985 through 1995, but the Peconic Estuary on the north shore has been free of it since 1995, according to Gobler.

Past Stony Brook research has identified high levels of organic nitrogen and poor flushing as factors promoting blooms on Long Island, and while the new ocean inlet in Great South Bay has improved water quality in Bellport Bay, that inlet is getting smaller and has never improved water quality in central Great South Bay, according to Gobler.

“Great South Bay has the precise combination of conditions that leads to brown tides and other harmful algal blooms: Intense nitrogen loading from household septic systems into a shallow water body that is poorly flushed by the ocean,” Gobler said, adding, “As efforts by Suffolk County move forward to address septic nitrogen loading, this region should improve as a result.”