Bivalve as savior, threat


Solution? Crassostrea ariakensis, an Asian oyster, looks promising as a way to address a shortage of the native population. But if it's not introduced properly, it could be a disaster.

January 04, 2002|By Tom Horton | Tom Horton,SUN STAFF

NEW YEAR, new oyster.

Learn to say Crassostrea ariakensis. You will hear much about this Asian bivalve in the next year or two as a savior of the Chesapeake Bay -- also as a major threat.

With overharvest and disease having reduced the native Eastern oyster, Crassostrea virginica, to a remnant population, the ariakensis oyster indeed looks attractive.

It resembles the native bay oyster, tastes as good, grows twice as fast and is highly resistant to MSX and Dermo, the two diseases plaguing C. virginica.

Since 1996, researchers at the Virginia Institute of Marine Science have been producing sterile versions of ariakensis for use in controlled studies. These "triploid" oysters have three sets of chromosomes and cannot reproduce like natural, "diploid" oysters with two sets. This virtually eliminates the risk of the new oyster spreading into the bay.

But now ariakensis is attracting such interest from Virginia's seafood industry that some scientists, and the Chesapeake Bay Foundation, fear someone might be tempted to release reproducing versions of the new oyster (readily available from West Coast hatcheries).

We do not need to speculate on the worst that could happen from introducing an exotic species. We know.

The MSX parasite that has devastated Chesapeake oysters since the early 1960s almost certainly came from someone introducing, without any scientific controls, another Asian oyster, Crassostrea gigas.

The gigas oyster never survived in the Chesapeake environment -- or in Delaware Bay, where MSX also appeared -- but the parasite did. Harmless to gigas, with which it evolved, MSX remains deadly to our native oysters after four decades.

MSX might even be credited with a human victim, Clyde A. Phillips, a prosperous oyster planter from the Delaware Bay, who was one of the first to see it.

In August 1956, Phillips had just taken on substantial debt to enlarge his shucking and packing operation when he inspected his oyster beds a few days before the season's opening.

Everything there was dead. Rutgers University would later identify the culprit as MSX. The night before the oyster season opened, Phillips suffered a fatal heart attack. "The oysters were what killed him," his daughter-in-law, Mary Phillips, told me a few years ago.

Virginia oystermen probably feel they have little left to lose. Oyster harvests in their part of the Chesapeake have been almost nonexistent in recent years.

Maryland, by contrast, still manages 200,000 to 400,000 bushels a year. The lower salinity in the upper bay depresses MSX's impact somewhat.

The Virginia Seafood Council, an industry group, is expected to seek state permission soon to grow experimentally a million sterile ariakensis oysters in parts of the bay. That would be up from the 60,000 triploid oysters they grew last year.

And at a recent symposium on ariakensis, Virginia watermen and seafood packers said they want introduction of reproducing, diploid ariakensis oysters in the bay by next year. Five tidewater counties in Virginia have passed resolutions calling for the same thing.

It's too soon for that. From MSX to mute swans and nutria, from kudzu and zebra mussels to gypsy moths and the hemlock adelgid, we've seen too many examples of exotic species spreading throughout ecosystems not adapted to them.

On the other hand, not all introductions are disasters. The Asian gigas oyster that wrought havoc on the bay has become the cornerstone of huge shellfish industries on the West Coast and in Europe. Brown trout became a popular sport fish so long ago (1880s) that most people think they are a native.

Also, it is absolutely critical to bring oysters back to the bay for their immense ecological values -- filtering polluting algae from the water and providing stellar habitat for other marine life in the nooks and crannies of the reefs they form.

Continued research into whether ariakensis is the best way to do this, or the only way, ought to be vigorously pursued, with every precaution against their contaminating the natural ecosystem.

Some interests would have us embark now on building an aquaculture industry that could use only sterile oysters; but the Virginia scientists who are producing those warn it is inevitable that some of these triploids will sooner or later revert to diploids and spread into the wild.

Before we risk that, a lot of questions need to be answered: Would ariakensis build reefs like virginica? There is some evidence it won't. Would it survive and grow as well in the real bay, with hungry blue crabs and other environmental forces not present in controlled lab and aquaculture experiments?

Would it outcompete and obliterate the native oyster, or coexist with it? Would it occupy habitat now used by other bay species? We will never be able to predict the outcome completely, but in a few more years, research could tell us a lot more.

Meanwhile, years of effort to build a restoration program for the native virginica oysters are paying off, with about $7 million a year in state and federal money going toward a goal of increasing native populations tenfold by 2010.

It would be crazy to derail that, or to abandon research into MSX and into breeding disease-resistant native oysters, based on this early infatuation with a promising but little-known species.

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