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Kachemak Bay's foamy brown bloom of phytoplankton proves to be strange visitor

Yereth RosenAlaska Dispatch News
The phytoplankton species Karenia mikimotoi, a substance that has caused major fish die-offs elsewhere, was found in Kachemak Bay this summer -- the first time the species has been documented in Alaska waters. Courtesy Catie Bursch

Scientists have now solved one mystery about a strange root-beer-like substance that covered much of Kachemak Bay this fall, but other questions remain.

The growth that that turned much of the bay brown and foamy for weeks starting in late September turns out to be a massive bloom of the phytoplankton species Karenia mikimotoi, a substance that has caused major fish die-offs elsewhere. It was the first large bloom of this species documented in Alaska, said officials with the Kachemak Bay National Estuarine Research Reserve, a joint federal-state science center. 

This type of phytoplankton is usually found farther south, said Catie Bursch, a community monitoring coordinator at the research center. The hot summer that baked Kachemak Bay and other parts of Alaska may be implicated, Bursch said Tuesday. Because it takes time for water to absorb ambient air temperatures, the bay’s temperatures usually peak in September, possibly setting up friendly conditions this fall for the Karenia mikimotoi bloom, she said.

“This thing did like that warm water, I guess,” she said.

The region seemed to dodge any major ill effects from its Karenia mikimotoi encounter. Only a few dead fish were found in Kachemak Bay, as well as some unpleasant slimy residue left in some intertidal zones by dying phytoplankton cells, Bursch said. However, there were concerns about shellfish, particularly among Kachemak Bay’s oyster farmers, she said. Blooms of this phytoplankton tend to be more threatening to mariculture operations than free-swimming wild fish, she said.

Identification of the bloom was made by experts at the National Oceanic and Atmospheric Administration’s Beaufort Laboratory in North Carolina, who tested samples sent from Alaska.

Still unclear is how this phytoplankton wound up in Kachemak Bay. “Nobody really knows," Bursh said, but it could have come from a vessel's ballast water.

Elsewhere, Karenia mikimotoi blooms have caused massive fish kills and other serious problems.  This type of phytoplankton was first described in Japan in 1935 and spread in subsequent decades to the Atlantic, its blooms triggering fish kills in Norway, Scotland and Ireland, among other sites, according to the North Sea Alien Species Database.

A 2004 bloom off western India killed massive numbers of fish, produced bad odors and caused respiratory problems for children. There was a repeat occurrence five years later.

It is unclear exactly how Karenia mikimotoi kills fish, but the general belief is that the blooms tax oxygen supplies, Bursch said. Some scientists believe this type of phytoplankton also produces some toxins, she said.

But Kachemak Bay’s bloom has been persistent, she added, lasting about two months. Past blooms of other species in the bay have usually lasted only a week or two, but remnants of the Karenia mikimotoi bloom were found last week, and some of it may still be lingering, she said.  

Investigation of the bloom is timely. The Kachemak Bay research reserve is planning a scientific conference in February on phytoplankton and harmful algal blooms.

Contact Yereth Rosen at yereth(at)alaskadispatch.com