Story last updated at 10:32 a.m. Thursday, September 12, 2002

Sea butterflies make rare appearance
by Sepp Jannotta
Staff Writer

Editors note: Due to an editing error part of this story was missig in the print copy. The following copy contains the full story.

Members of the science community are often heard to speak of Kachemak Bay as a unique and dynamic mixing cup for the great cauldron that is the Pacific Ocean. The combination of oceanic forces and life-giving nutrients plays itself out each summer in a dramatic display of the marine food chain in motion.

It is a process that most people see demonstrated by the teeming schools of salmon or the flight of the seabirds or the presence of breaching whales.

But a couple of weeks ago, a rare but prolific occurrence of tiny planktonic snails -- a type of gastropod commonly known as a sea butterfly -- gave ample proof to some Kachemak Bay residents that the local waters are host to a highly complex web of life that is constantly in flux.

Residents of Seldovia began to notice the presence of these very unusual creatures roughly the size of a pencil point in their bay around the third week of August. A closer look revealed that some of them had tiny shells and some didn't, but all of them were equipped with a pair of wing-like appendages that they flutter back and forth to move.

As the presence of sea butterflies began to spread along the south side of the bay, calls began to come in to the Department of Fish and Game, the Kachemak Bay Research Reserve and the Center for Alaskan Coastal Studies. All the callers were asking roughly the same thing of Homer's scientists: what are these little snails, and where did they come from?

Homer resident Anne Wieland was kayaking with a friend in Eldred Passage near the mouth of Sadie Cove last week when she and her paddling partner found themselves awash in the tiny sea butterflies.

"We had come from an area where there were none of these (sea butterflies), and then we paddled into an area that was rich in these things," Wieland said. At first she thought they were bits of broken off barnacle parts, but then she captured one and recognized it as a tiny planktonic snail known scientifically as a pteropod.

"It was very remarkable," she said.

In 28 years of boating on Kachemak Bay, Wieland had only encountered them on one other occasion, about 10 years ago.

Carl Schoch, who in his capacity as research director with the Kachemak Bay Research Reserve spends a lot of time scuba diving in the bay, also obtained some pteropod samples. A lab study confirmed them to be a pelagic, or open-ocean, form of snail, from the genus Clione.

As is commonly the case, there were two distinct forms of the sea butterflies present in Kachemak Bay recently. The first, which grows to approximately 10 millimeters in length, was a shell-bearing variety that feeds on microscopic zooplankton and phytoplankton. Schoch described this creature's highly effective feeding methods as resembling those of a fisherman -- the snail casts out a net of mucus that traps the smaller organisms and then consumes the whole lot before making a new net. Their wings allow them to move up and down in the water column with the phytoplankton, which tend to be near the surface during the day but go deeper as the night falls on the water.

The other form of pteropod is a carnivorous snail. It was far less abundant and grows quite a bit larger than its counterpart, which Schoch said ends up being the bulk of the carnivore's diet.

"It is very common to see them together," Schoch said. "But to see them here in the bay is odd."

So for Schoch, an intertidal oceanographer by training, the presence of this kind of zooplankton in Kachemak Bay is highly significant.

A bloom here supports the notion that the coastal current flowing along Alaska's gulf coast from east to west often swirls around on itself in giant eddies, the largest of which can be hundreds of miles across. Using satellite imagery that tracks the movement of plankton blooms caught in the gulf's coastal current, researchers at the University of Alaska Fairbanks have shown a particularly active eddy, known as the Seward Eddy, pushing off the Kenai Peninsula's outer coast.

These same images have shown that Kachemak Bay is often very insulated from the influences of the Gulf of Alaska current, with the bay usually receiving it's biggest push of coastal current in the fall.

Schoch said he assumed that event was a rare combination of upwelling in the Gulf of Alaska and an unusually strong swirl of coastal current that pulled the nutrient-rich ocean water toward shore. But he added that by using satellite images, the Research Reserve hopes to pinpoint just where this pteropod bloom originated.

It is these brief shots of coastal and even open-ocean water that sets Kachemak Bay apart from much of the rest of Cook Inlet, scientists say.

For Schoch and others who watched the progression of the sea butterfly bloom, the most incredible thing about them was how efficiently they cleared the water of phytoplankton and other algae.

"It was absolutely amazing how quickly the water cleared," Schoch said, noting that the water is rarely very clear in the summer. "When we first saw these (pteropods), we were diving with a visibility of 15 to 20 feet. In a few days, that went to a visibility of at least 40 feet. It just gives you an idea how many were out there."

While the sea butterflies were giving a vivid demonstration of the lower end of the food chain in action, Schoch said, the upper end of the food chain was certainly involved as well.

According to Schoch, it is reasonable to assume that the snails were on the menu of both seabirds and the large runs of silver salmon moving into the bay. And it is likely no coincidence that around the same time the sea butterflies arrived, boaters began reporting humpbacks feeding in Eldred Passage.

For Wieland, the sea butterflies were just more evidence of how incredibly rich Kachemak Bay's marine environment remains.

"The whole thing was just surreal because there were so many of them," she said. "It was like (paddling) in the soup."

Sepp Jannotta can be reached at sjannotta@homernews.com.

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