Victims of Lake Okeechobee's pollution, dead oysters line Florida's St. Lucie River shore.

Although Newell’s numbers were probably in need of some fine tuning, his assertion that oysters do a far better job of managing water quality than we have is now widely accepted, and restoration efforts on varying scales are under way throughout Atlantic and Gulf coastal regions, even in areas where oysters are not managed for their commercial value.

As with many aspects of the environment, cause and effect is often hard to pin down. Did the effects of dirty water dictate the decline of the oyster, or did the commercial extraction of the oyster predict the dirty water? Whether in the Chesapeake Bay or Florida’s Indian River Lagoon, biologists continue to analyze the complicated relationship involving nutrient-rich runoff, water turbidity, erosion, salt marshes, seagrasses and oyster beds.

Seagrass and oysters have a stabilizing effect on shorelines and estuary bottoms. Each buffers wave action and prevents suspension of particles, helping to sustain the water clarity necessary for sunlight penetration and photosynthesis vital to seagrass communities. Oysters contribute directly to water clarity by filtering plankton and other particles from the water. In the case of Chesapeake Bay, however, less than 15 percent of the grass beds from just 50 years ago still exist, so their contribution is minimal.

So now water managers tasked with cleaning up Chesapeake waters face the daunting task with a limited number of tools at their disposal. Nutrient-rich runoff feeds an algae orgy. An overabundance of algae, along with particle suspension, plays havoc with re-establishing seagrass beds. As the uncontrolled algae dies and settles to the bottom, the decomposition process removes oxygen from the water, creating dead zones where oyster larvae don’t live long enough to get attached to their predecessors.

While nutrient-rich source runoff can be greatly reduced, it can’t be eliminated. And with as much as 30 percent of the nitrogen entering the Bay literally raining from the sky from sources as far away as smokestacks in the Midwest, water managers face a Catch-22 dilemma.

Historic numbers of oysters and seagrass tracts working in concert with menhaden could possibly remove enough algae and suspended particles to clarify the water. But sea grass in the quantities necessary can’t survive until the water clears, and many areas of the Bay won’t support enough oysters to do the job, even if the resources to plant huge new reefs were available. So here’s the catch: How do you clean up the water sufficiently for oysters and sea grass to survive without using oysters and sea grass to do the job in the first place?

Given optimal salinity and water quality, oysters have the capacity to rebound quickly. Oysters produce extraordinary numbers of larvae. Year-old oysters spawn as males, but switch to female roles over the following several years as their energy reserves develop. In other words, female oysters, as in their human counterparts, do most of the hard work when it comes to reproduction. A single adult female oyster can release 10 to 100 million eggs annually. The larvae, or spat, free-swim for two to three weeks. Chemicals released by older oysters attract the youngsters, which eventually find a place to settle, usually on another oyster’s shell. Oyster larvae are popular items on crab and fish menus. Natural survival in a successful spawning cycle is less than two percent. The massive East Coast oyster structures that greeted early European explorers resulted from untold generations of oysters piling on.

Researchers continue to study the biomass of oysters necessary to improve water clarity. The inadvertent introduction of exotic zebra mussels to the Great Lakes and the resultant clear water in Lake Erie are evidence of what bivalves can accomplish. The Chesapeake Bay Program calls for a minimum tenfold increase of oysters by 2010. Efforts will focus on planting oysters in oxygen-rich areas with the greatest chance of improving water clarity to aid seagrass survival. A regional group of Mid-Atlantic scientists are collectively working on research projects to develop disease resistant strains. And just as stemming commercial excesses has rejuvenated populations of redfish, seatrout and stripers, managers now recognize the necessity of placing some areas off-limits to commercial harvesting. These sanctuaries would serve as brood stock reserves and larvae recruitment centers.

SWA