Oyster Love

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By John Page Williams

No, there’s no 'R' in June, but this is perhaps the most important month for oysters. Even when many of us aren’t thinking about eating them, they have lives of their own and oyster business to do. When the Chesapeake’s water temperature finally reaches 74 degrees Fahrenheit, they begin producing the next generation. 

The oysters have been working on this process since the sun’s rays began warming the water in late February, driving a slow increase in body temperatures and a growing concentration of phytoplankton in the water column, which they filter out and eat. As their energy reserves build from winter’s meager diet, they invest most of that energy into developing eggs and sperm. The youngest oysters are all males. Most older, larger oysters have turned female and are developing eggs in roughly direct proportion to their size (bigger oyster, more eggs) and in quantities of nine figures, 100,000,000 or mores. This process has been going on since the late February thaw. 

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Now, when the water temperature hits the magic mark on each reef, young male oysters release sperm, triggering an orgy for their mates on the reef around them. The more oysters on the reef, the greater the cloud of sperm and eggs. Oyster spawning is an exercise in big data. The odds of sperm meeting eggs and of fertilized egg survival are lower than those for a big Powerball jackpot, but, on what the National Oceanic and Atmospheric Administration (NOAA) defines as a healthy reef (15-50 oysters per square meter, over a quarter-acre or more), the numbers boil down to a healthy total.

Are those unconnected sperm and eggs wasted? No indeed. They get swept into the gills of the oysters and other filter-feeding critters such as barnacles and hooked mussels on the reef around them, and converted into biomass. Nothing gets wasted. Remember that concept.

An oyster egg that is lucky enough to be fertilized will begin to develop as a free-floating larva, feeding for a couple of days on energy stored by its mother before beginning to draw in June’s rich phytoplankton bloom. Over two weeks, it will develop a thin shell and the ability to swim toward light at the surface, drifting with currents driven by the tides, river flow, and the wind. If it escapes being drawn in by a larger filter feeder, it will grow a “foot” and sink toward the bottom. If it lands on a hard, clean surface such as an old oyster shell, a granite block, or a concrete reef ball, it will make a life-long commitment by cementing its left side to this substrate, settling into a life of filter-feeding whatever the currents bring, and spawning with oysters that have “struck” around it. The rules of big data bring great success if the strike is good with lots of spat (baby oysters) attaching, but slim pickings if not.

What comes next is the big deal about our Eastern oyster: that strike begins a new generation of oysters, living on the crusts of previous generations in the hard calcite (calcium carbonate) shells that they develop as they grow, extracting the raw materials from the water around them, as well as the phytoplankton that nourish their living tissues. Unlike the Chesapeake’s other bivalve mollusks such as soft clams and hooked mussels, eastern oysters (AKA Virginia, Wellfleet, American, or Atlantic oysters) grow together, building reefs that are our Bay’s equivalent of the tropical coral reefs. 

Two centuries ago, Chesapeake Bay had huge “live-bottom” reefs that formed keystone communities in the ecosystem. These reefs hosted huge concentrations of living creatures, from barnacles and red-beard sponges to grass shrimp, mud crabs, small fish, blue crabs, and big predator fish. The foundations were generations of oysters, spawned in big data revels (oyster orgies—you heard it here first) like the ones taking place in Bay waters as the water warms to 74 degrees. Those reefs are the basic groundwork of the Chesapeake ecosystem, which builds and rejuvenates over time from the oyster love that begins this month. It matters. 

CBM Editor at Large and author John Page Williams is a licensed captain and Maryland fishing guide. He has been on staff at the Chesapeake Bay Foundation as an educator, writer and senior naturalist, saving the Bay since 1973. In 2013, the State of Maryland proclaimed him an official Admiral of the Bay, something we knew all along.