Physiological recovery from prolonged ‘starvation’ in larvae of the Pacific oyster Crassostrea gigas

Abstract

Previous studies of energy metabolism in larvae have described a developmental “point of no return” (PNR), a time by which larvae of planktotrophic marine species must feed in order to survive and grow. This study investigated the effects of long-term food deprivation on developing larvae of the oyster Crassostrea gigas with the goal of providing a biochemical and metabolic description of larvae at the PNR in this species. Mortality of unfed larvae was low for the first 14 days without the addition of phytoplankton foods. Even after 33 days without food, larvae were still swimming. Unfed larvae did not lose their ability to capture and digest algal cells when provided with food after 33 days. Growth, metabolic rate and biochemical constituents all increased at the same or greater rates in larvae whose feeding was delayed for 5, 8, 11, 14 or 17 days compared to larvae fed at 2 days old, when feeding was possible. These results show that larvae of C. gigas can survive long feeding delays while maintaining a constant rate of metabolism. These results suggest that oyster larvae have the capacity to survive ‘starvation’ using alternative sources of energy. If there is a “point of no return” beyond which larvae of C. gigas must feed on microalgae to survive, our findings suggest this point may be set by the availability of detrital material or dissolved organic carbon that can fuel maintenance metabolism for extended periods equivalent to over four times the predicted lifespan.