After a trip to China and Japan to learn about the Suminoe oyster in its native habitat, oyster scientist Mark Luckenbach returned to his Chesapeake Bay laboratory with as nearly as many questions as he left with.

The Virginia Institute of Marine Science researcher found Crassostrea ariakensis oysters which seemed to build oyster reefs—and oysters that seemed only to grow in the mud. He found oysters that were supposed to be the same species, but went by different names—the red oyster and the white oyster.

Tests in the Chesapeake Bay have found the foreign oyster grows exceptionally fast and resists disease, offering hope to advocates that if a reproducing population were placed in the water, it could quickly populate the estuary.

But Luckenbach said that C. ariakensis was not the dominant oyster anywhere he visited in China, where it is a native species, nor in Japan, where it was introduced. The oyster seemed to be growing slowly in Southern China, and was being crowded out by nonnative species in Northern China. “I guess I have added to the confusion,” Luckenbach said.

The confusion stems in part from the fact that so little is known about the oyster that has fueled so much interest in the Chesapeake. A National Academy of Sciences report released this summer concluded a lack of knowledge about the basic biology of the Suminoe oyster made it impossible to evaluate the risks and benefits of introducing a breeding population into the Bay.

The lessons from laboratory experiments have also raised questions.

Luckenbach’s work, using small C. ariakensis in a quarantined laboratory, has suggested that the Suminoe oyster tends to spread horizontally over a flat surface, rather than growing vertically, as does the native oyster. At small sizes, the native C. virginica can crow up and over C. ariakensis, although more recent lab work shows that if crowded together, C. ariakensis may grow upward as well, though not as fast.

Other lab studies have raised concerns about larvae behavior. Larvae from some C. ariakensis oysters float in the water column, while other C. ariakensis oysters sink to the bottom. Such differences, from what may be different genetic strains of the same oyster, could dramatically affect the impact—and potential success—of any effort to introduce reproducing oysters into the Bay.

The reef-building question is particularly important, as some scientists have said that if the C. ariakensis had the characteristics of a “rock oyster”—covering solid substrates but not forming vertical reefs—it would have less habitat value in the Bay than the native oyster, whose reefs are used by a variety of species.

“If there is a difference between stocks and their ability to form reefs, then we probably want to know that in terms of which one we want to use in the Chesapeake,” Luckenbach said. “If this is going to be introduced, it would be nice to do it right.”

To start collecting field information, Luckenbach this summer visited sites in Japan and China where C. ariakensis grows in the wild or in aquaculture. But observations from his trip, funded by the Campbell Foundation, suggest C. ariakensis is an oyster that behaves very differently from place to place. It’s unclear whether that is because they represent different genetic strains or because environmental factors are influencing how the oysters grow.

In Japan’s Ariaki Bay, where the oyster is an introduced species, it grows primarily in mud flats, popping up like “pin shells” from the bottom, Luckenbach said. “If we just looked at ariakensis from the Ariaki Sea, we would have called it a mud oyster,” Luckenbach said.

But across the Yellow Sea, in China’s Bo Hai Bay, the oyster is found almost exclusively on large reefs. Luckenbach accompanied local fishermen to a reef about 20–30 acres in size which resembled an “upside down egg crate” with mounds of oysters rising 3–10 meters in height, and sometimes coming within 2 meters of the surface.

Luckenbach was told by area fishermen that they never observed individual C. ariakensis growing in the mud, as was common in Ariaki Bay.

The perceptions of the oysters also varied sharply between the two locations. In Ariaki Bay, fishermen harvested other oysters for sale, but not C. ariakensis. “If they catch ariakensis, the fishermen just take it home,” Luckenbach said.

In Bo Hai Bay, C. ariakensis was clearly the preferred oyster. But in the bay, C. ariakensis was on the decline, apparently because the reefs have been invaded by C. gigas, the most widely grown oyster species in the world. “The fisheries managers lamented the invasion of gigas,” Luckenbach said.

A surprising finding was that in Southern China, the oysters are grown in low-salinity areas in aquaculture, where they grow large—but slowly. Often they take three to five years to reach market size. Luckenbach said growers in the area told him that C. ariakensis grew poorly in higher-salinity areas and that they grew C. gigas instead.

That’s the opposite of the Bay experience, where the oyster tends to grow faster in high-salinity waters. “We can grow it to market size in well under a year in high salinities—at least the stocks we’ve worked with,” Luckenbach said. “They are saying they can’t grow it in high salinities. The picture from Southern China has me confused.”

Luckenbach said the southern oysters were likely a different strain, and possibly even a different species. In other locations in China and Japan, Luckenbach said it was impossible to determine the growth rate of C. ariakensis because they were grown in the wild, rather than in aquaculture, where their age is tracked.

The oysters used in experiments in the Bay came from the West Coast, where they were accidentally introduced several decades ago with other oysters from Ariaki Bay in Japan. Genetically, they are the similar to the northern China C. ariakensis found in Bo Hai Bay.

VIMS researchers are presently testing growth rates of several different strains C. ariakensis. So far, there seem to be only slight differences between them, and all are growing markedly faster than native C. virginica in side-by-side tests, said VIMS researcher Stan Allen. But, he added, VIMS probably does not have a strain from Southern China to test.

Luckenbach’s trip was the third by Bay scientists to the region. Last year, VIMS researcher Allen, who had made two previous trips, visited China along with Kevin Sellner, director of the Chesapeake Research Consortium, an association of universities conducting Bay-related research.

Allen agreed that it was hard to determine how C. ariakensis behaved in the wild. “Most of what we saw was aquaculture, and the same applied for [Luckenbach],” he said.

They saw no indication of C. ariakensis growing on pilings or other manmade structures, which could make them a nuisance species in the Bay, Allen said. Mostly, they were confined to deeper parts of rivers, he said.
In some cases, he said, divers tried to explain what they saw on underwater reefs through a series of four interpreters. Because of such difficulties, Allen said researchers have discussed finding other places to study wild populations, such as Korea.

“That would certainly be the northern strain,” Allen said. “And there is a possibility that communication would be better, and there may be some natural populations that would be observable on the western and southern side of Korea.”