Tuesday, January 31, 2017

The Definition of Insanity . . .

Is reputed to be doing the same thing time after time, and expecting the result to be different: Chesapeake losing its oyster reefs faster than they can be rebuilt
The Chesapeake Bay has an oyster problem — but more fundamentally, it has a shell problem.

Put simply, there aren’t enough oyster shells available to support a large-scale restoration of the Bay’s depleted bivalve population. And the way things are going, there may not even be enough to sustain the wild fishery a whole lot longer, at least in Virginia.

Decades of overharvesting, habitat destruction, disease and poor water quality have reduced the population of oysters in the Bay to less than 1 percent of its historic levels. And in much of the Bay, oyster reefs — made up of the shells of living and dead bivalves — are wearing down and disappearing faster than they’re being built up.

Scientists, managers and others worry that there aren’t enough shells to go around to sustain the traditional wild fishery as well as a growing aquaculture industry, not to mention ambitious large-scale efforts by both states and the federal government to restore the Chesapeake’s oyster population for its ecological value.

“We don’t have the habitat,” said Bruce Vogt, manager of ecosystem science and habitat assessment for the National Oceanic and Atmospheric Administration Chesapeake Bay Office. “Even if we had adequate spawning stock to revive the population over time, the habitat just isn’t there.”

It’s the classic chicken-or-egg dilemma. Oysters make their own habitat, building reefs out of the shells they produce. But juvenile oysters need a hard surface — customarily, another oyster shell — on which to grow. The problem now is that there are many fewer shells than there used to be on which the shellfish can live and reproduce.

The losses stem from a variety of factors. In the last century, as much as 70 percent of the 450,000 acres of oyster reef habitat that once blanketed the bottom of the Bay and its tributaries has been lost to siltation, according to an environmental assessment done in 2009 by the U.S. Army Corps of Engineers. Reefs have been smothered by a deluge of silt washing off the land, which has yet to let up.

Oyster shells are being lost in other ways, too. Their shells are broken up by predators, such as cownose rays, black drum, crabs, boring sponges and shell-boring snails known as oyster drills. Shells are removed by harvesting, too, and not always returned; and the gear used to dredge up oysters scatters and breaks other shells.

Finally, perhaps most significantly of all, the shells themselves dissolve naturally over time. While oysters are alive, they keep producing new shell from carbon and calcium that they filter out of the water. But after the bivalves die, dissolution takes over; the shells begin to corrode. One study estimated shell loss ranging from 2 percent to 70 percent per year, depending on water conditions. The saltier or more acidic the water, the faster the process.
70% is just a silly number, why might apply to the small, thin shells of the newly set spat. The dissolution of CaCO3 is a complicated issue, but in much of the bay, where salinity and alkalinity are similar to sea water, calcite is actually supersaturated and tends to spontaneously precipitate from the water. In Maryland's fresher, less alkaline water, it does tend to dissolve, albeit rather slowly. Shells are protected by protein matrix, both on top of the shell, and embedded within.

And yet, 14,000 years ago there was no Chesapeake Bay, just a valley with a fresh water river at the bottom. But as the sea rose at the end of the ice age, somehow, the oysters managed to settle on what ever substrate was available and spread to cover huge areas. Just as they had the four previous times of the great glaciations. So lack of substrate is not the fundamental problem

No, the fundamental problem with oysters is oystering faster than the oysters can keep up. And until they manage the fishing at a level that permits enough oysters to survive and reproduce to expand the population, the same cycle of unsuccessful restoration efforts, and failing populations will continue.

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