No Shortcut to a Clean Chesapeake

Too much of a good thing can have unintended consequences -- even for a body of water. Excess nutrients are engorging this country's waterways, generating massive dead zones in some of the world's most valuable ecosystems, including the Chesapeake Bay.

In the scramble for a solution, some regulators are casting about for quick fixes that, unfortunately, could cause more harm than good. In the Chesapeake, for example, the National Oceanographic and Atmospheric Administration and several state agencies are considering the mass introduction of an exotic oyster species to clean the bay's waters.

Nutrient pollution is a difficult problem to solve. Human and agricultural waste contains large amounts of nitrogen and phosphorus that make their way into runoff and then into the bay. Although state and federal agencies are attempting to reduce this pollution source, progress is slow, and once in the water, the excessive nutrients cause uncontrollable algae growth. The huge quantity of algae clogging the Chesapeake does more than make the water pea-soup green and create a stench as it decays on the beaches. Rotting algae drains oxygen from the water, often suffocating fish and shellfish.

A study published in March by scientists from Brown University painted a dramatic picture of the interaction between shellfish and nutrient pollution. During the spring of 2001 an unusually large crop of baby mussels carpeted the bottom of Narragansett Bay, the Chesapeake's neighbor to the north. The mussels filtered microscopic algae from the bay, which left the water uncharacteristically clear -- temporarily. When low-oxygen conditions set in that summer, though, most of the tiny mussels suffocated, and the water reverted to being an opaque green.

In any case, the native oyster populations in Chesapeake Bay are hardly up to the task of filtering the bay waters in a similar fashion. Pollution, overharvesting and disease have ravaged the oyster population despite long-standing efforts to restore the fishery. Because the native oysters are not thriving, environmental agencies are looking at introducing a disease-resistant species of Asian oyster -- known as the Suminoe oyster -- to the Chesapeake.

While cleaning the bay's waters with oysters is an appealing idea, the introduction of an alien species is not the answer to nutrient pollution. Small trial projects in the Chesapeake are using a mutant Suminoe oyster that can't reproduce. But even a carefully cultured mutant population can produce a few normal oysters capable of reproduction, and a few spawning Suminoe oysters could precipitate an invasive species' takeover of the bay.

We should have learned our lesson about the dangers of tinkering with an ecosystem after the disastrous invasion of the Great Lakes by zebra mussels. In the absence of predators, beginning in the late 1980s, these creatures spread wildly through the Great Lakes. They now hog habitat, clog water-intake pipes and filter water so efficiently that they have removed nearly all of the microscopic algae from the water, starving native species.

If Suminoe oysters get loose in the Chesapeake, they could rapidly crowd out the remaining native oysters and irreversibly damage the ecosystem we are trying to protect.

Reducing nutrients in the bay may be a slow and arduous process, but it is the only sure route toward a cleaner, healthier bay.

-- Emily Saarman

is a science writer based

in Santa Cruz, Calif.

esaarman@ucsc.edu