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), R ates of development from a four-arm to a six-arm larval stage were not affe cted by food availability. The respiratory cost of development to the six-a rm larval stage (day 60) was 14.0 mJ for fed larvae and 8.2 mJ for unfed la rvae. We observed three phases of metabolic regulation during development. During embryogenesis (day 0-22), increasing metabolic rates were proportion al to increases in cell numbers. During early larval development (day; 22-1 7), the differences in respiratory rate between fed and unfed larvae were n ot accounted for by cell number, but by cell-specific metabolic rate (respi ratory rate normalized to DNA content). Once an advanced larval stage had b een reached (day 47-60), cell-specific respiratory rate and mitochondrial d ensities (citrate synthase activity normalized to DNA content) were more eq uivalent between fed and unfed larvae, suggesting that size-specific metabo lic rates were determined at a level of physiological regulation that was i ndependent of cell numbers or feeding history.