New Toxic Seaweed Species Has Exploded In Long Island Bays

Stony Brook University lab technician Craig Young is working with the new seaweed species in the lab at the Marine Science Center to try to determine what makes it so toxic when it dies. Michael Wright

A new species of seaweed that can be extremely toxic to fish and shellfish has spread throughout Long Island’s bays in the last three years and could pose a dangerous threat to many marine species, marine biologists from Stony Brook University announced this week.

Speaking publicly about the new species of seaweed for the first time, the leader of Stony Brook’s water quality research team, Dr. Christopher Golber, said on Thursday that the seaweed was first identified in Great South Bay three or four years ago, and that a broad survey by students and scientists last summer revealed it has established itself across all of the South Shore bays and is likely spread throughout the Peconics as well.

The stringy reddish-brown seaweed is technically a red algae, a large-format cousin of the microscopic phytoplankton that cause toxic “red tides” here and throughout the world.
The scientific name of this so-called macro algae is Dasysiphona japonica, but the scientists call it just “Dasy” for short — pronounced like Daisy.

Since emerging a few years ago, it’s fronds have sprouted in dense carpets in areas of the Great South Bay, where it attaches itself to rocks and wood dock pilings, and when it dies in summer has cloaked areas of shoreline with dense, stinking mats.

It has not taken quite as dominant a foothold in Shinnecock Bay, where it is most prevalent locally, but is a worrisome new threat, Dr. Gobler said.

“When these kind of algae first show up, they expand rapidly,” Dr. Gobler said. “Right now in Shinnecock Bay, it is not as dominant as it is in Great South Bay, where it just coats the bottom in some places — but we’ve seen pretty significant growth by the [Ponquogue Bridge].”

While alive, the seaweed is somewhat toxic to fish or shellfish that are engulfed in it. But when it dies in large amounts, the Stony Brook researchers have found, the decaying process appears to emit some substance that is highly toxic to both fish and shellfish.

“It’s nearly 100-percent mortality in a week,” Dr. Gobler said in announcing the first findings on his lab’s research into the weed, during his annual “State of the Bays” presentation on water quality events throughout Long Island during the past year. “There is some additional compound coming from the decaying process that is lethal.”

In laboratory studies, he said, about 20 percent of a common minnow species died after being exposed to the live algae for seven days. But when exposed to the decaying algae, nearly half of the minnows died within two days, and nearly all died within seven days.

With hard clams, the mortality was about 80 percent when exposed to the decaying weeds.
This is a concern, Dr. Gobler said, because the macro algae has been found to be particularly sensitive to warm water temperatures and died off in huge amounts in the Great South Bay last July.

“This stuff doesn’t like the hot weather,” Dr. Gobler said in an interview on Friday. “It’s super happy and growing like nuts for 10 months of the year, but then when you have a those peak temperatures, it dies off. It definitely could lead to fish kills, particularly if it gets into an enclosed area.”

The exact source of the extreme toxicity of the decaying process is still a mystery, Craig Young, one of the researchers studying the emergence of the weed at Stony Brook, said.

“We don’t really know what the potential of this is, it’s such an emerging species,” Mr. Young said on Saturday at the Stony Brook Southampton Marine Science Center. “It hasn’t gotten to the densities yet that can cause real problems. We haven’t seen it in action yet.”

Dr. Young said that the odor of the decaying weed, alone, could cause health issues for some people caught in areas where dense mats of the dying weeds wash ashore. On Florida’s west coast, entire downtown areas of resort towns have been forced to close because of the stinging vapors of red algae seaweeds washing ashore at nearby beaches.

While the Stony Brook biologists found some of the Dasysiphona growing at the Peconic Bay end of the Shinnecock Canal last year and assume that it is widespread in the Peconic Estuary now, the deadly weed does not appear to have been responsible for the massive die-off of bay scallops in the estuary in late summer, which has been linked to record high water temperatures and possibly the effects of a parasite found in the estuary’s shellfish.

What is clear about “Dasy” is that it is thriving in the bays that have high levels of nitrogen from residential “wastewater” seeping out of obsolete residential septic systems, Dr. Gobler said.

In studying the make-up of the plant, the researchers found that nearly all of the nitrogen it is soaking up, fueling its rapid growth, had the distinct chemical signatures of residential wastewater, as opposed to those of fertilizers, animal excrement or natural sources.

During his presentation on Thursday, Dr. Gobler said that the ongoing study of the dynamics of the dozens of algae blooms in Long Island’s bays and ponds shows that nitrogen from human waste is continually making algae blooms more severe and more toxic to both marine species and mammals. The Stony Brook scientist was on the team of marine biologists that first proved the concrete links between the toilets of residential neighborhoods with cesspools or the obsolete septic systems common in Suffolk County and the explosion of destructive algae blooms across eastern Long Island over the past 35 years.

Nearly 30 individual bays, harbors and ponds experienced harmful algae blooms in Long Island waters in 2019, and there were more than 50 total incidents of algae blooms and other “impairments” to water bodies, like disastrously low oxygen levels spurred by the high water temperatures during what was the third straight summer to set a record as the hottest ever measured globally.

Almost all of the algae blooms were seen in Suffolk County, and most of those on the South Fork. The density of residential development and the lack of sewer systems and sewage treatment plants, like in western Suffolk and Nassau County, has made the East End, and particularly the South Fork, the epicenter of the toxic onslaught.

One of the “red tide” algae that has bloomed in western Shinnecock Bay and Sag Harbor Cove over the last decade, a species known as Alexandrium, emits a toxin that is 1,000 times more toxic than cyanide, Dr. Gobler told the Zoom audience for his virtual “State of the Bays” presentation.

And there were more than a dozen blooms in South Fork ponds of blue-green algae, which also naturally emits a toxin that can be harmful to humans and fatal to pets that ingest water tainted with it. Nationwide, 10 dogs died last year from drinking water in ponds where blue-green algae was blooming.

Suffolk County has seen more blue-green algae blooms than any other county in New York State over the last five years.

The county is in the top 5-percent of counties nationwide with the highest levels of nitrogen in drinking water, as well. Around the country, 200 million people are serviced by drinking water that has less than 1 part per million of nitrogen in their drinking water and another 75 million have less than 2 parts per million. Suffolk County’s water has 3.8 parts per million on average, Dr. Gobler said.

He noted that studies have found that drinking water high in nitrogen can leave compounds in the stomach that are also seen in smokers and that people who drink water with more than 2.4 parts per million of nitrogen have a statistically higher incidence of bladder cancer — as Suffolk County residents do.

Dr. Gobler called the nitrogen issue a “threat to our public health and economy,” and said that global warming will intensify the problems.

The good news, he said, is that there are finally steps being taken to address the matter. The implementation of new nitrogen-reducing septic systems, which are now mandated in new construction and being encouraged with grant funding from Suffolk County and the East End towns’ Community Preservation Fund, are starting to lessen the flow of nitrogen into groundwater and the bays — though vastly more of the new systems will be needed to show results even decades from now. The university itself is working on developing a septic system that reduces nitrogen levels released in wastewater to below 10 parts per million and costs less than $10,000 — about a third of what the current systems are costing.

More immediately, Stony Brook’s Shinnecock Bay Restoration program has shown that re-introducing huge numbers of shellfish to local bays can help tamp down algae blooms, while also boosting the economic prospects of baymen. Shinnecock Bay has not seen a bloom of the infamous “brown tide” that nearly wiped out shellfish and eelgrass in the 1980s and 1990s, in two years, but has seen a 1,700-percent increase in the haul of little neck clams by baymen.

And the university’s scientists are now experimenting with growing seaweeds in controlled farms that will soak up nitrogen from the water and then can then be harvested and used as organic fertilizer or even consumed by people.

“I don’t think we have seen the end of brown tides,” Dr. Gobler said. “But we have made the system more resilient.”