All organisms ranging from the simplest bacterium to the most sophisticated multicellular animal need energy for metabolic maintenance, growth, and reproduction. It is thus not surprising that a wide variety of mechanisms have evolved for acquiring the energy needed to carry out these vital processes. One such system that has developed among aquatic organisms involves cellular transport and utilization of dissolved organic matter (DOM) directly from the surrounding medium. The work from this project will add much needed direct evidence on the ecological and energetic role of DOM for marine invertebrate animals. Most of the current studies examining use of DOM by marine invertebrates are limited to indirect evidence based on comparisons of metabolic expenditure and potential contribution of DOM calculated from uptake rates of dissolved compounds. Although this approach is useful in determining the theoretical contribution of DOM, it does not directly characterize the realized contribution to an animal's energy budget. A more direct approach based on comparisons of metabolic expenditure of animals in the presence versus absence of DOM is needed. The proposed work seeks to establish this for the bryozoan Bugula neritina through a series of laboratory and field experiments examining how the availability of DOM during larval swimming and metamorphosis effects ecological relevant parameters such as, larval swimming duration, metamorphic competence, size after metamorphosis, adult growth rate, and onset and amount of reproduction. In addition, direct evidence for incorporation of DOM into larval tissues and those of early post-metamorphic stages will be established through autoradiographic techniques. These data will provide insight into how and when the transported compounds are being used (e.g., for swimming, metamorphosis, early juvenile growth). Taken together, the proposed experiments will provide direct evidence on the realized contribution of DOM to the nutritional biology of invertebrates, adding significantly to our current understanding of the ecological and energetic importance of DOM.
