Energetics of larval swimming and metamorphosis in four species of Bugula (Bryozoa)

The amount of energy available to larvae during swimming, location of a sui table recruitment site, and metamorphosis influences the length of time the y can spend in the plankton. Energetic parameters such as swimming speed, o xygen consumption during swimming and metamorphosis, and elemental carbon a nd 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 is about a fi vefold difference in larval volume among the four species, which scales lin early with elemental carbon content and, presumably, with the amount of end ogenous reserves available for swimming and metamorphosis. Mean larval swim ming speeds (in centimeters per second) were similar among species. Specifi c metabolic rate and larval size were inversely related. For larvae of a gi ven species, respiration rates remained similar for swimming and metamorpho sis; however, because metamorphosis lasts about twice as long as a maximal larval swimming phase, it was more energetically demanding. Larger larvae e xpended 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 th e energy expended during larval swimming calculated on the basis of oxygen consumption and on the basis of elemental carbon decrease suggests that lar vae of Bugula spp. may not use significant amounts of dissolved organic mat erial (DOM) to supplement their endogenous energy reserves.