DOAG: The Eastern Oyster in Long Island Sound

This article appeared in the November 28, 2012 edition of the Ag Report


The Eastern Oyster in Long Island Sound

By Hillary Kenyon, from The Dredge, Volume 5(1) Fall 2012


The eastern oyster, Crassostrea virginica, is a keystone species in Connecticut’s coastal environment.  Like the wedge-shaped keystones of ancient Roman arches, the oysters of Long Island Sound (LIS) bring together the building blocks of the ecosystem and bear the weight of maintaining its healthy state.


As the predominant filter-feeding organisms, Connecticut oysters are critical to preserving water quality.  By filtering plankton, these oysters make a tasty smoothie of the water column and cleanse it of harmful pollutants in the process.


Natural oyster beds in LIS are large areas where old shell, or cultch, from past oyster generations cover the sea floor. These beds provide a hard, three-dimensional surface where oyster larvae may attach.  Here the seed oysters, or spat as they are called just after settlement, may grow free from the adversity of the suffocating sediment.


In addition to these ecosystem services, the eastern oyster is a major economic asset to Connecticut.  A resilient species, they flourish throughout the coast, and over 86,000 acres of Connecticut’s sea floor are mapped and managed shellfish growing


It is necessary to note, however, that only a mere fraction of this area can be considered natural oyster beds. The majority of the growing areas are privately leased from the state to be farmed and harvested by the hardworking harvesters that rely on the Sound for their livelihood.


The industry has seen considerable fluctuations in years past. Despite a resurgence of oystering in the 1980s and 1990s due to enhancements made on the natural seed oyster beds, disease outbreaks and extensive time periods with no natural sets have caused years with minimal harvests and overall irregularity in the industry. 


The protozoan parasite Haplosporidium nelsoni (MSX) is responsible for considerable oyster mortality in Connecticut.  Following the devastating outbreak of 1997, there were no commercially significant sets on record, and a period of low production followed.  Such a profound gap in natural oyster sets struck a blow to the industry.


In response, Connecticut Sea Grant has provided funding for a research project that aims to devise a technique for enhancing the state’s natural oyster beds, which provide the seed that the vast majority of the industry depends upon.  In the case of a disease epizootic, or during a time with little to no natural recruitment, this method would provide an economic cushioning for the oyster industry.


Headed by Dr. Inke Sunila, shellfish pathologist at the Connecticut Department of Agriculture’s Bureau of Aquaculture, the research employs a biodegradable mussel netting or sock used to deploy remote-set hatchery reared oysters. The idea behind the project is that the socking provides a degree of protection from predators.


Conventional culturing practices involve hatchery-raised oyster larvae settling on tiny shell fragments.  This produces single (cultchless) oysters that require a nursery stage, elevated from the sea floor in either submerged cages or bags. 


Remote setting, however, circumvents this phase and allows oyster larvae to settle on full shells as they do in the wild.  Just as natural set, settling on cultch enables hatchery-raised oysters to grow directly on the bottom.  In simple terms, remote setting simulates Connecticut’s existing practices of collecting set from natural oyster beds and transplanting them to be grown on private leases.   There is the added benefit of selective breeding—potential for increased oyster survival and growth. 


The “Clinton” strain of oysters has shown significant resilience and was chosen for the experiments. “Clinton” broodstock were obtained from Clinton, Connecticut, following the MSX outbreak of 1997 and have been selectively bred over numerous generations. 


The plan was to manually deploy the oysters on the lease, now marked with bamboo poles and cinder blocks.  In due time, the oysters were released over the boat edge, half with the biodegradable netting, and half without. 


Two types of netting were utilized as potential predator control:  one made of pure cotton, the other with a polyester base material. Both served as predator deterrents in the early weeks after deployment when growth is most critical. Bare (seedless) cultch was also deployed on the lease to serve as a comparison to natural oyster recruitment for this season.


In order to track growth and survival rates, the researchers have begun a monthly sampling of the oysters that will continue into the next year. They predict that this approach of using biodegradable netting for oyster bottom culture has the potential to promote Connecticut oyster production in many ways. 


In addition to filling the gap between natural oyster sets, this form of remote setting disease-resistant oysters could potentially enhance currently unproductive natural beds and provide further economic prosperity.  In terms of ecological significance, establishing successful beds will also promote improved water quality and overall improved biodiversity and health of Long Island Sound.