Collaborative Research: Energy Sources for Reproduction and Development in a Cold-Seep Mixotrophic Mussel

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Heterotrophic deep-sea animals require a downward flux of material in order to survive and reproduce, whereas animals with chemoautotrophic symbionts at hydrothermal vents or cold seeps should theoretically be capable of producing gametes more-or-less continuously without the benefit of surface-derived detritus. Mixotrophic mussels at cold seeps are intermediate between these two situations. They can grow and survive using only methane or sulfide as an energy source, but are also capable of filter-feeding on detrital particles or plankton in the benthic boundary layer. Available evidence suggests that supplemental filtration on bacterioplankton may be necessary to provide sufficient nitrogen to the mussels. The cold-seep mussel Bathymodiolus childressi, which lives at methane seeps on the Louisiana slope, demonstrates periodic rather than continuous reproduction, a pattern not predicted by the commonly accepted paradigm that food limitation controls reproductive timing in the deep sea. Thus, mixotrophic mussels present a unique opportunity to investigate the role of detrital input in the control of gametogenic timing in the deep sea. Lipid biomarkers and compound specific stable isotopes will be used to determine if energy from surfacederived detritus is differentially partitioned between the gonads and somatic tissues of B. childressi. In the deep-sea megafauna, seasonal breeders virtually always produce feeding larvae, suggesting a possible mechanistic or evolutionary link between surface production and larval success. Crisp's rule, the prediction that animals with planktotrophic larvae will time their breeding to assure optimal nutrition for the larvae, is one such possible link. Crisp's Rule will be examined in this study by rearing the larvae of B. childressi in natural water collected at various depths.