Lecithotrophic larvae of the cheilostome bryozoan, Bugula neritina (L.), lose metamorphic competence 12 to 24 h after release from the maternal zooid. The high respiration rate of newly released larvae (mean=306.3 pmol O2 larva-1 h-1, range= 149.3 to 466.6, n=18 trials, 22.5 °C) from adults collected at Link Port, Fort Pierce, Florida during the winter/spring of 1990-1991 reflects their active swimming behavior. The average energy con¬tent per larva was 15.24 mJ (range: 13.35 to 20.17 mJ ind-1, n=5 groups). If all cells have an identical energy content and metabolic rate, then 2 and 20% of the total en¬ergy content would be consumed by the onset (2 h post-re¬lease) and the loss (24 h post-release) of metamorphic competence. Larvae of B. neritina are a composite of both larval and juvenile tissues and the loss of metamorphic competence may be due to regional depletion of labile en¬ergy stores in transitory “larval" cells, particularly the ciliated cells that comprise the locomotory organ, the corona. Although "nonfeeding", B. neritina larvae can acquire nu¬trients from the environment in the form of dissolved or¬ganic materials (DOM) in seawater. Both the amino acid alanine and the fatty acid palmitic acid can be transported from seawater ([S]=1 µM, 22.5°C). The rates of alanine influx (aptpearance of label in tissue) averaged 0.366 pmol larva-1 h-1 and, based on comparisons between rates of so¬lute transportand metabolism, would contribute little (<1% of required energy) to offset the metabolic demand. The average rate of palmitic acid influx was 4.668 pmol larva-1 h-1 and, assuming that the measured influx equals the net solute flux, could account for 21 to 72% of energy requirements. These data suggest that the duration of planktonic life of B. neritina larvae is principally regulated by the amount of endogenous energy stores, but may be mod¬ulated by available DOM in seawater. Originally published in Marine Biology and used with permission.