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Red Tide Returns, With A Deadly New Twist

Blooms of a “red tide” algae stained the East End’s bays once again this week, the ninth straight year the organism known as cochlodinium has emerged here, and this year’s blooms appear to be on track to be among the densest and most harmful experienced since the species first appeared in local waters, scientists say.

Already the blooms have set a destructive new milestone, as they are being blamed for the first time for the death of hundreds of wild fish in a creek off Flanders Bay. Lab tests had long ago shown the organism to be toxic to fish and shellfish but this week is the first time scientists have seen direct evidence of the blooms killing free-swimming fish in the wild.

According to scientists from Suffolk County and the Stony Brook University School of Marine and Atmospheric Sciences, hundreds of menhaden, striped bass, black sea bass and smaller baitfish that died suddenly in Chase’s Creek in Aquebogue were covered in a reddish slime that is associated with cochlodinium blooms.

Stony Brook professor Dr. Chris Gobler, one of the world’s foremost authorities on the brown tide blooms that devastated East End fisheries in the 1980s and 1990s, said that water samples taken from the creek on the morning of the fish kill showed that low oxygen levels, a common cause of fish kills, were not an issue in the creek and that the red tide algae counts were extremely high throughout the creek.

“I don’t know how much more definitely we could say it was from one of these blooms,” Dr. Gobler said this week. “When we got there, some of the fish were still expiring. We took samples and oxygen levels were super-saturated … much higher than normal waters, so that was not the problem. But there was a very intense cochlodinium bloom going on. The fish that were dead were covered with this rust-colored slime that is caused by cocholodinium. We’ve had fish kills in pound nets and in tanks at our marine lab … where the fish can’t move, but this is the first time we’ve seen a wild population of fish dying from one of these blooms.”

The red tide blooms, which appear as reddish-brown to crimson red striations on the surface of local bays in late morning and afternoon, popped up early last week in eastern Shinnecock Bay and throughout the Peconic Bay Estuary. The late July bloom is three to four weeks earlier than the blooms have appeared in most previous years, though it is about a week later than it appeared in 2010.

Dr. Gobler said the early appearance is probably due to the high temperatures in July. In 2010, he said the early emergence, combined with high temperatures, led to denser and more widespread cochlodinium blooms, a pattern that this year’s bloom appears to be following as well.

“In 2010 we found that the blooms got really intense, and there were times when all of Peconic Bay was covered with them, whereas in other years its been more patchy. We might be headed there again.”

Soon after cochlodinium was first detected in local waters, scientists discovered that the organism, a dinoflagellate that can propel itself through the water column, sinking to the bottom of the bays at night and rising to the top during the day, was highly toxic to most marine species like fish and shellfish. It is not harmful to humans, however, unlike another species of red tide algae that has been found blooming in western Shinnecock Bay in recent years, leading to closures of shellfish harvesting there in the late spring and early summer.

Dr. Gobler said that the blooms of cochlodinium also thrive on elevated levels of nitrates in water and that runoff and groundwater tainted with fertilizer from farm fields just north of Chases’s Creek in Aquebogue probably fed the dense blooms there that killed the fish.

It was a group of scientists from Stony Brook led by Dr. Gobler that issued a report last year on years of research linking the emergence of harmful algal blooms, like the red tide and brown tide, to nitrogen seeping into local tidal waters from septic systems of homes within the watershed.

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