Toxic levels of "rust tide" -- a lethal late summer threat to Long Island marine life -- are blooming slower and less frequently in East End bays this year because of a lack of rainfall, according to Stony Brook University scientists.

Researchers with the university's school of marine and atmospheric sciences recently recorded densities of rust tide algae exceeding 10,000 cells per milliliter in eastern Shinnecock Bay, said Professor Christopher Gobler Tuesday, adding that densities above 500 cells per milliliter are lethal to marine life.

But rainfall is down on Long Island by 60 percent since April, leading to delayed and less intense blooms, said Gobler, a marine science professor at Stony Brook.

Typically, rainfall boosts groundwater levels and nitrogen loading as the element leaches from septic tanks and cesspools and into waterways.

"Historically, blooms have emerged in mid-August and reach peak densities by early September," Gobler said. "We know that increased nitrogen loading makes these blooms more intense and more toxic."

At a Stony Brook conference in June, Gobler spoke about the hazards of nitrogen loading. Suffolk County Executive Steve Bellone has said nitrogen reduction is a key issue in his administration.

advertisement | advertise on newsday

In the Stony Brook study, scientists found densities of more than 1,000 cells per milliliter of rust tide algae in the western Peconic Estuary, Gobler said.

The less intense bloom this year and a similar pattern in 2014 show the potential benefits to marine life of restricting nitrogen loading, he said.

The mild rust tide is expected to help Peconic Bay scallop populations, Gobler said. In the severe rust tide of 2012 and 2013, bay scallop levels dropped dramatically. In 2014, also a low rainfall year, scallop harvests were the best in decades, scientists said.

"If the drought continues and the bloom does not intensify, there will likely not be a large die-off of bay scallops this fall," Gobler said. "This would bode well for another robust harvest come November."