Energy metabolism during embryonic development and larval growth of an Antarctic sea urchin

Developmental energetics of an Antarctic sea urchin, Sterechinus neumayeri, were quantified to describe the physiological bases underlying ontogenetic changes in metabolic rate at extreme cold temperatures (−1.5 degrees C). Rates of development from a four-arm to a six-arm larval stage were not affected by food availability. The respiratory cost of development to the six-arm larval stage (day 60) was 14.0 mJ for fed larvae and 8.2 mJ for unfed larvae. We observed three phases of metabolic regulation during development. During embryogenesis (day 0–22), increasing metabolic rates were proportional to increases in cell numbers. During early larval development (day 22–47), the differences in respiratory rate between fed and unfed larvae were not accounted for by cell number, but by cell-specific metabolic rate (respiratory rate normalized to DNA content). Once an advanced larval stage had been reached (day 47–60), cell-specific respiratory rate and mitochondrial densities (citrate synthase activity normalized to DNA content) were more equivalent between fed and unfed larvae, suggesting that size-specific metabolic rates were determined at a level of physiological regulation that was independent of cell numbers or feeding history.