First there was the brown tide, then the red tide and now, floating in waters at either end of the Peconic estuary system, are patches of what New Englanders informally call “rust tide.”
It poses no threat to humans but can be deadly to finfish and shellfish.
Rust tide is a collection of microscopic algae that’s been showing up in the Peconics in late summer during the past several years, but when the water cools, they’re gone.
Dr. Steve Tettelbach, a biology professor at Long Island University, got about as close to the algae as anyone could a few weeks back but suffered no ill effects.
As part of a research team working on rebuilding the depleted bay scallop population, hard hit by past brown tide blooms, Dr. Tettelbach donned scuba gear late last month to check on scallops in the Orient Harbor spawner sanctuary. He found patches of the rust tide floating on the surface directly above the scallops,
“We’ve seen it many times and have driven through it, but I’ve never actually dived through it before,” he said.
He passed through and back unharmed, and in between found the scallops to be thriving.
“Some people call it red tide, but to me that’s the really nasty one that kills people,” said Dr. Tettelbach.
Earlier this year the state Department of Environmental Conservation temporarily closed 92 acres of Mattituck Inlet and Mattituck Creek to shellfish harvesting after the discovery of a naturally occurring toxin, the same found in true red tide outbreaks, that causes shellfish poisoning.
That neurotoxin, known as saxitoxin, is produced by certain types of algae.
The rust tide, Cochlodinium polykrikoides, is a type of phytoplankton — a plant algae — known as a dinoflagellate capable of movement. It is a different species from the algae that caused the inlet and creek closures.
During the day, the tiny cells swim up from the bottom to the surface to absorb solar energy and then return to the bottom at night. Unlike the brown tide, which can fill a body of water from the surface to the bottom, the rust tide usually appears on the surface in long streaks or patches.
It began appearing in the Peconics some eight to 10 years ago, but whether it was always here in low concentrations or was introduced from elsewhere isn’t clear, said Dr. Tettelbach.
Research conducted by another marine scientist, Dr. Chris Gobler of Stony Brook University’s School of Marine and Atmospheric Science, showed that 24-hour exposure to the rust tide is fatal to finfish and shellfish. That timing is critical to the long-hoped-for return of the bay scallops, all but wiped out with the brown tide algae, Aureococcus anophagefferens, that first appeared in the Peconics in the late 1980s. That species has bloomed almost yearly in South Shore waters, but has not returned to the Peconics in significant numbers since 1995.
Since the rust tide moves up and down through the water column, its contact with scallops is limited, said Dr. Tettelbach.
“We have not seen any evidence that it is impacting scallops locally,” he said. “Maybe it is, but we just haven’t seen it. Even if this was killing some, the scallops are coming back. If there is an impact, the rebuilding of the scallop population is occurring despite that.”