Survival and biochemical changes during metamorphosis of the American oyster Crassostrea virginica (Gmelin) and the Pacific oyster Crassostrea gigas (Thunberg)

Abstract

Metamorphosis is the transition between two distinct life-history stages in oysters. During this period of a few short hours, dramatic morphological changes occur, transforming the motile larva to a sessile juvenile. Despite the physiological and ecological significance of metamorphosis in the biology of the oyster, metamorphosis is less well studied than other life-history stages. This is in part due to experimental difficulties. The use of epinephrine to induce simultaneous metamorphosis in large numbers of oysters was proposed as an experimental tool whereby physiological and biochemical studies would be made feasible. As a prerequisite, it was necessary to validate the use of epinephrine for this purpose. Controlled laboratory experiments pairing larvae treated with epinephrine and untreated control larvae were conducted to quantify survival rates and examine the effects of epinephrine (Chapter 1). While the mortality rate was variable and often high, it could not be attributed to the use of epinephrine. It was hypothesized that the variable and often high mortality observed during metamorphosis was the result of an energetic deficit incurred during metamorphosis. Levels of lipid, carbohydrate and protein in pediveligers and utilization of these substrates during metamorphosis was measured and compared with the results of calorespirometry in order to assess the catabolic demands of metamorphosis (Chapter 2). All substrate reserves were found to be heavily utilized during metamorphosis. Positive correlations were found between survival and both the pre-metamorphic levels of carbohydrade and the utilization of carbohydrate during metamorphosis. Thus radioisotopic tracers were used to measure the utilization and fate of glucose during metamorphosis. A highly active pentose shunt pathway was indicated and labeled carbon appeared to be incorporated into nucleic acids and proteins (Chapter 3). The roles of neutral and polar lipid as catabolic and anabolic substrates were then examined. Specific changes in the fatty acid classes of each lipid type were measured in pediveligers and metamorphosing oysters. Nuetral lipids were heavily utilized, while polar lipids appeared to be conserved (Chapter 4).