An algal bloom known as "red tide" that is devastating to fish populations has returned to East End bays as expected, and this summer has also been spotted in the Great South Bay for the first time.
Red tide is caused by cochlodinium polykrikoides, a type of phytoplankton, said Chris Gobler, Ph.D., an associate professor at the Stony Brook University School of Marine and Atmospheric Science.
“It’s something that we’ve never seen in Long Island waters until 2004, and we’ve seen it every summer since then,” he said. “It typically shows up some time around the middle of August.” This summer is no exception."
Even after Tropical Storm Irene passed through the area, Gobler said the red tide persists.
Aerial photographer Jeff Cully of Quogue, who contributes photos to Patch and has photographed red tide for years, said the red tide is the worst he has ever seen it. “It's particularly bad around Shelter Island,” he said.
Red tide has been detected in Shinnecock Bay and Peconic Bay, and “it’s also happening in Great South Bay for the first time ever,” Gobler said. “Up until last year, it’s been confined to the Peconic Estuary — between the North and South Forks from Shelter Island all the way to Riverhead.”
Red tide is caused by the same type of organism as brown tide, which has ravaged local bays since the 1980s, with some key differences on top of the difference in pigment.
Red tide is found in patches, but with brown tide the water is uniformly brown, Gobler said. Brown tide blocks out the sun, killing off eelgrass beds, a habitat of larval shellfish.
While both are harmful, Gobler said red tide is particularly lethal to fish.
Citing a recent experiment using red tide water from Great South Bay and larval fish, Gobler said, “Some fish don’t make it more than an hour, and none of the fish survive more than six hours.”
Gobler also pointed to pound net fishing, in which fish swim into nets and then cannot swim back out. When the red tide comes in, and the fish cannot escape it, they die, he said.
Scallops are very sensitive to red tide, he added.
Gobler said that under normal circumstances algae are typically eaten by fish in the environment, other plankton and shellfish, but nothing eats up the red tide phytoplankton because it’s toxic.
“Thankfully, this algae does not make a toxin that affects humans,” he said.
Gobler said it is not certain why red tide shows up when and where it does. “It’s probably a combination of environmental triggers,” he said. “We’re just starting to piece it all together.”
Temperature contributes, but it can’t be the whole story because the same water temperatures can be recorded in June, he said.
Also contributing to red tide are nutrients in the water, phosphorous and nitrogen — particularly nitrogen, Gobler said. The nutrients come from storm water runoff, lawn fertilizers, septic systems and other sources of effluent, such as boats.
“It typically persists through September,” Gobler said. “When it really starts cooling off in October, it starts clearing up.”
The tide impacts the fish population and fishermen have logged fewer catches, according to Gobler, who said it is evident that when red tide comes in, the fish go out.