Algae suspect in Pamlico fish kill

Chesapeake Bay had similar events

The largest fish kill on the Pamlico River in more than a decade could be linked to a potentially toxic algae that researchers only recently have begun to focus on in North Carolina waters.

State investigators collected water samples after the death of an estimated 3.9 million fish on Aug. 5-6 on the Pamlico River near Broad Creek. The preliminary lab results show significant numbers of a potentially toxic microscopic algae, Karlodinium. The algae are not known to affect human health but have been linked to fish kills in the Chesapeake Bay and elsewhere.

Karlodinium, one-celled algae that propel through water with a whiplike motion, are common in brackish waters along the Atlantic Coast. In large numbers, the algae can produce brownish or "mahogany" tides and can release toxins that are lethal to fish. In North Carolina, blooms associated with fish kills have been rare.

"It's hard to say whether Karlodinium was the culprit," said Jill Paxson, leader of the state Division of Water Quality's Pamlico River rapid response team, which investigated the fish kill. "It was a large number of Karlodinium. It's important to continue to look into it and not overlook it."

Harmful strains of Karlodinium release a toxin that damages the gills of fish and can cause them to suffocate. The fish kill consisted primarily of one species, juvenile menhaden, suggesting the event was more likely caused by a toxin rather than a drop in oxygen levels in the water, which would kill multiple species, Paxson said.

Hans Paerl, a professor at UNC-Chapel Hill's Institute of Marine Sciences in Morehead City, said Karlodinium blooms have been recorded since the 1960s in the Chesapeake Bay, where water monitoring has been in place longer. In a recent paper, Paerl and other scientists linked a dense bloom of Karlodinium in October 2006 to four subsequent fish kills on the Neuse River.

"It's not as though this is a new organism," Paerl said in an interview. "We're getting better at monitoring it and pinpointing it and linking it to fish kills that might occur a week later."

Paerl said the Karlodinium blooms require certain natural conditions to develop, such as stratified layers of fresh water and salt water. Under those conditions, excessive nitrogen and phosphorus that wash into the river in runoff and treated sewage fuel growth of algae.

Paerl said it's important to develop a better understanding of what kind of reductions in pollutants are needed to minimize the blooms.

"The frequency and intensity of the blooms may very well be related to nutrient loads in our estuaries," Paerl said.

While not all strains of Karlodinium produce toxins, Allen Place, a professor at the University of Maryland Center for Marine Biotechnology, said large blooms typically are toxic. The Chesapeake Bay had 13 blooms of Karlodinium last year, resulting in 13 fish kills.

"It's a global issue," Place said. "The problem has been in the past this organism was thought to be nontoxic."

Heather Jacobs, the Pamlico-Tar Riverkeeper, said the fish kills are a symptom of a larger problem -- an ecosystem out of balance.

State regulators declared the Tar-Pamlico River basin sensitive to nutrients in 1989 after algal blooms, low oxygen levels and increased numbers of fish kills pointed to excessive amounts of nitrogen and phosphorus in the water. Regulators required reductions in nitrogen discharged by sewage treatment plants and limits on runoff.

"We've been working on reducing nutrients in the Tar-Pamlico," Jacobs said. "I think we're going to find we're going to have to do a lot more."