WENDT, D.E.: Energetics of Larval Swimming and Metamorphosis in Four Species of Bugula (Bryozoa)

The amount of energy available to larvae during swimming, location of a suitable recruitment site, and metamorphosis influences the length of time larvae can spend in the plankton. Energetic parameters such as oxygen consumption during swimming and metamorphosis, and elemental carbon and nitrogen content were measured for larvae of four species of bryozoans, Bugula neritina, B. simplex, B. stolonifera, and B. turrita. The larvae of these species are aplanktotrophic with a short free-swimming phase ranging from less than one hour to a maximum of about 36 hours. There exists approximately a 5-fold difference in larval volume among the four species, which scales linearly with elemental carbon content and, presumably, with the amount of endogenous reserves available for swimming and metamorphosis. Specific metabolic rate and larval size were inversely related. For larvae of a given species, respiration rates remained similar for swimming and metamorphosis; however, because the duration of metamorphosis is about twice as long as a maximal larval swimming phase, it was more energetically demanding. Larger larvae expended more energy to complete metamorphosis than did smaller larvae, but in terms of the percentage of larval energy reserves consumed, swimming and metamorphosis were more ‘expensive’ for smaller larvae. A comparison of the energy expended during larval swimming calculated on the basis of oxygen consumption and on the basis of elemental carbon decrease suggests that larvae of Bugula spp. may not use significant amounts of dissolved organic material (DOM) to supplement their endogenous energy reserves.