Algae blooms, dead zones hurt Long Island waters in 2023, report says

Last summer was the worst on record for harmful algae blooms in Long Island waters, according to a new report by Chris Gobler, a marine and atmospheric sciences professor at Stony Brook University who has monitored local waterways since 2014.

The assessment was based on sampling conducted by the Gobler Laboratory at Stony Brook every week throughout the summer and data from the Long Island Sound Study, a research collaboration funded by the U.S. Environmental Protection Agency. It's the latest in a series of annual evaluations by the lab. 

"During the months of April through September, every major bay and estuary across Long Island was afflicted by harmful algal blooms … oxygen-starved dead zones, and fish and turtle kills," Gobler said in a statement Tuesday.

According to Gobler and many environmental advocates, the cause is not a mystery: excess nutrients — that is, sewage.

Nitrogen leaches into the groundwater from sources such as aging septic systems, and from there makes its way into Long Island’s creeks, bays and estuaries. The oversupply of nitrogen encourages runaway growth of algae; when the algae dies and decays, it consumes the dissolved oxygen in the water, without which marine life cannot survive. 

Other experts note there are other contributors to excess nitrogen in waterways besides faulty septic systems, including runoff from lawn and crop fertilizers.

Old septic systems common

Almost 75% of homes in Suffolk County use standard septic systems rather than newer models that reduce nitrogen. Earlier this year, a proposed referendum to raise funds through a one-eighth of a percent tax increase for septic system improvements and sewer expansion was dropped by the Suffolk County Legislature.

Kevin McDonald, senior policy adviser for The Nature Conservancy, a nonprofit environmental group, said between 65% and 70% of nitrogen entering the Great South Bay and other Long Island bodies of water is from septic systems.

"Eliminating this pollution source will allow water quality to be restored, thus the great need to change out septic systems in favor of clean water systems and strategic sewering," McDonald said.

Focus on septic systems misplaced?

Some experts say the focus on septic systems as the trigger for algae blooms is misplaced. Royal Reynolds, a sanitation engineer who worked for 30 years for the Suffolk County Health Department, said the county "overestimated the nitrogen loading from septic systems" based on faulty modeling. 

If septic systems were the main culprit, Reynolds suggested, then excess nitrogen and algae blooms in the Great South Bay would have been eliminated decades ago when South Shore communities from Queens to Oakdale were sewered.

There are many other sources of nitrogen that could be feeding the blooms, he says, such as atmospheric nitrogen, over-fertilizing of lawns and crops and even droppings from geese and ducks. 

Toxic algae species detected

Whatever the cause, this year four toxic algae species were detected off Long Island's shores, according to Gobler's report.

One harmful alga that had never before been found in New York appeared this year on Long Island: pseudo-nitzschia, which spread from Islip through Quogue and all or parts of the Great South Bay, Moriches Bay and Shinnecock Bay, the report said.

Pseudo-nitzschia can produce the neurotoxin domoic acid, which can be fatal to fish and to wildlife that may eat the fish, including water birds and sea lions. (Alfred Hitchcock’s classic film “The Birds” was based on an incident in Monterey Bay, California, when sea birds began exhibiting bizarre and sometimes aggressive behavior; testing later determined that the birds had been poisoned by domoic acid.)

In humans, the toxin can cause short-term memory loss, headaches, confusion and seizures.

Three more familiar harmful algae species made an appearance this year, starting as soon as water temperatures began to warm in the spring, according to the report.

"The wild card is climate change," says Kevin McAllister, founder and president of Defend H20, a nonprofit based in Sag Harbor. Hotter summers and warmer water also contribute to rapid algal growth, creating "a perfect stew of chronic blooms," he said.

Concentrations of Dinophysis — which contains a gastrointestinal toxin called okadaic acid — increased, according to Gobler's report. Twelve years ago, Dinophysis levels reached 2 million cells per liter, the highest ever recorded. This summer, Gobler said, the levels reached 100 million cells per liter. That bloom led to another shellfish bed closure, in Moriches Bay.

A bloom of Alexandrium, which produce a biotoxin that can be fatal to shellfish and to humans who eat them, led to the closure of five shellfish beds in April and May. And a rust tide caused by Cochlodinium appeared in mid-July, spreading from Shinnecock Bay through the Peconic estuary. It was also the longest-lasting rust tide ever observed in the area, lasting from July into October.

For some local ecologists, reports of the dire state of Long Island's waterways are overstated. John Tanacredi, an estuarine ecologist at Molloy University in Rockville Centre, says his weekly monitoring of the Great South Bay shows excellent health over the past decade.

"Long Island's coastal community is robust and has dramatically improved," Tanacredi said.