Research - Shellfish

Several types of mollusks are, or have been, investigated at WMC. Promising species include hard clams, oysters and bay scallops. MRRI and WMC biologists have been developing clam farming techniques for many years. This research fostered a very large commercial clam aquaculture venture and several small operations. The commercial operations use land-based hatchery and nursery facilities with growout in estuarine enclosures. Recent refinements include work on a tidal-powered floating nursery and upwelling nursery silos deployed in ponds.

Final growout of clams in ponds has being investigated as well to see if it is possible to avoid deploying equipment in the estuary all together. Clams in initial and follow-up pond growout trial are reached market size in two years at a density of one million per hectare.

Some work; however, has been performed growing on scallops in ponds. Scallops were deployed in various types of net enclosures. Fouling of the netting typically results in high mortality. Releasing scallops free on the pond bottom has not been attempted.

A research emphasis in the past two years has been pond growout of oysters, either as a monoculture crop or cultured in a closed system with fish or shrimp. Oysters grew rapid but it was discovered that the oysters needed to be supported off the bottom to prevent suffocation. Inexpensive support hardware has been developed and the oyster carrying capacity in ponds appears to be a maximum acceptable density of one million oysters per hectare.

The possible human health risks associated with consumption of oysters grown in ponds must be addressed before the technology can be commercialized. Initial results indicate that pond oysters may be less likely to transmit pathogens to humans than oysters taken directly from the estuary.

In many respects, oysters make an excellent polyculture candidate. The dense algae blooms resulting from intensive feeding of shrimp or fish provide an abundance of oyster food. The use of oysters to improve water quality from fish and shrimp ponds prior to discharge has been studied.

Oyster polyculture is but one aspect of a larger project which seeks to minimize the environmental impact of coastal aquaculture. Of particular concern is the high biochemical oxygen demand, suspended solids and nutrients of pond effluent. Several approaches have been investigated including cleaning effluent, minimizing effluent and completely eliminating discharge.