Estuaries may be in a deep stew without oysters.
Oyster reefs aren’t much to look at. Most shallow-water recreational fishermen view oyster reefs in two distinct roles–as fish-attracting devices and as a way to create employment opportunities for boat mechanics. Colliding with an unseen bar is a common—though not highly recommended—technique for discovering new fishing venues. Scraped hulls, mangled props and lower units usually mark this adventuresome, low-tech approach to fish-finding.
Plus, if you rip up a clump of oysters, you ruin the day for a lot of critters besides the oysters. Mussels and sea squirts cling to their displaced residence. Slithering red worms, shrimp, small crabs, juvenile lobsters–even tiny fish—tumble from the crevasses, suddenly in the market for a new home.
The collective countless cavities of the vertical oyster reef are the unpretentious highrise waterfront condos of the shallow-water world. Even one-story oyster beds house an amazing abundance and assortment of marine life, including just about every predatory gamefish under the sun. But its capacity to host other creatures only begins to describe an oyster’s worth. If the full significance of that unbecoming clump of shells had been recognized and appreciated a hundred years ago, perhaps some of our estuaries would be facing less questionable futures today.
Unfortunately, only in the last 30 years or so have we begun to recognize the value of the lowly oyster without an accompanying spicy horseradish cocktail sauce. And until much more recently than that, little has been done to reverse the demise of an environmentally vital creature whose biomass was historically so great as to pose a threat to ship navigation. Many of our waters are now paying a stiff price for that oversight.
Oysters haven’t changed much in the 190 million years since they developed in the Triassic Period. The only dramatic change simply occurred in their numbers after Europeans invaded North America. A couple centuries of commercial over-exploitation is all it took to reduce oyster populations to one percent of their original numbers in some Mid-Atlantic areas. At the height of commercial harvesting, 14 million bushels of oysters a year were gouged from Chesapeake Bay alone. Oyster dredges towed behind “skipjacks” leveled many of the three-dimensional oyster communities of the Mid-Atlantic. Oyster colonies a century ago probably populated depths to 100 feet. Reefs now rarely occur below 30.
Since oyster larvae attach themselves to existing oysters, the destruction of oyster reefs promises not only smaller brood stocks, but also fewer habitats for larvae to recruit to. Pollution and diseases like MSX (Haplosporidium nelsoni) and Dermo (Perkinsus marinus) in recent years have decimated remaining reefs, wiping out as much as 95 percent of stocks in estuaries as dissimilar as Long Island Sound and the Louisiana delta.
Predatory fish are attracted to oyster reefs for a very fundamental reason–that’s where the food is. Along with four different types of shrimp and a variety of crabs, a South Carolina Department of Natural Resources study identified 17 piscatorial prey species present at high tide. As in spartina salt marshes, high tides deliver a whole new cast of temporary transient characters to the long list of full-time residents. Tidal flows often scour deepwater troughs paralleling the bars, enhancing accessibility. Predators come nosing around the nooks and crannies in search of the unwary, and the visiting prey species create a temporary buffet until departing tides force a retreat.
Anglers expect shallow-water predators–red and black drum, spotted seatrout, weakfish, sheepshead, flounder, snapper, stripers, snook—to be seasonal visitors, but in the northern Gulf of Mexico, pelagic surprises like Spanish mackerel and cobia are known to follow menhaden, mullet and anchovies onto the bars.
High tides allow fishermen to work topwater plugs, weedless spoons and soft plastics over shallow bars. Popping corks keep jigs and live baits like pinfish and shrimp from descending into a virtually guaranteed cutoff among the razor-edged oysters.
However, oysters deserve a much higher status than as mere hosts to other species and anglers, or as slimy culinary delights and alleged sexual enhancers, although those attributes most certainly should not be overlooked.
Oysters may be one of the keys to the ongoing health or recovery of entire estuary ecosystems.
In 1988, Roger Newell, a researcher at the University of Maryland Center for Environmental Science, made the extraordinary claim that even without the assistance of since-decimated menhaden schools, the oyster population of Chesapeake Bay in the late 1800s was capable of filtering every drop of water in the nation’s largest estuary every six days. Today’s oyster population, probably at less than one percent of historic levels, now takes more than a year to accomplish that feat, even with each and every surviving oyster straining up to five liters of water an hour, 24 hours a day. With trawlers transforming water-filtering menhaden into chicken feed, and considering the number of pollution sources in the densely populated coastal area, water quality has predictably declined right along with the oysters.
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? FS