The carrying capacity of a 2.4 ha Manila clam Venerupis philippinarum farm, using mechanised harvesting in North Puget Sound, WA, USA, was determined by means of an ecological model; the results were also scaled to Puget Sound as a whole. An individual Manila clam growth model was developed, calibrated and validated for the commercial farm, together with a macroalgal model to simulate fouling of the predator nets by seaweeds. Both models are based on our previously developed generic frameworks for bivalves (AquaShell) and seaweeds (AquaFrond). For the most part, equations are taken or adapted from the literature and parameterised for the studied site. The individual models were incorporated into the Farm Aquaculture Resource Management (FARM) model to simulate the production cycle, environmental effects and economic optimisation of culture. Both the individual and farm-scale models are built using object-oriented programming. Potential effects of clam production on seaweed growth were analysed and found to be about 10% above background. The FARM model was also used to classify the farm area with respect to its eutrophication status, by applying the Assessment of Estuarine Trophic Status (ASSETS) model. Farm production ranging from 32 to 45 t of clams per year is well reproduced by the model. Harvest yield is very sensitive to mortality, and profitability is very sensitive to seed costs. Manila clam culture provides a potential nutrient credit trading value of over US $41 000 per year, over 1000 Population-Equivalents (PEQ, i.e. loading from humans or equivalent loading from agriculture or industry) with respect to eutrophication control. The potential income would add 21% to the annual profit ($194 900) from clam sales. A scaling exercise to the whole of Puget Sound is in reasonable agreement with declared production (difference of 16%), and suggests that clams provide a significant ecosystem service, of the order of 90 000 PEQ per year.

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During a detailed survey of Pacific oyster Crassostrea gigas juvenile health at intensive rearing facilities, an episode of persistent morbidity and mortality occurred over an 8 wk period in 1997. Affected oyster seed were typically between about 1.0 and 2.4 mm in shell height. Abscesses were formed in the extrapallial space resulting from invasion by straight bacterial rods along the inner shell surface. The abscesses contained host cells and bacteria. The infection appeared to be chronic, was associated with relatively low numbers of bacteria cells, and caused alterations of the underlying mantle and abnormal shell deposition. No signs of any other type of Infectious agent were found associated with the lesions. After a chronic time course, 2 outcomes were possible: either the mantle was breached, leading to an overwhelming terminal bacterial infection or, in some cases, host cell debris and bacteria were sequestered by new shell deposition and the infection was resolved. The condition can cause mortality and significant loss of growth in intensively cultured juvenile oysters.

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