Collaborative Research: Deep-sea larvae as grazers in the midwater microbial loop

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Although it is generally assumed that metazoan (multicellular) animals do not feed directly on the microbial loop, ciliated invertebrate larvae are small enough to exploit this food source directly. Billions of larvae are produced each year by benthic invertebrates, and probably comprise a higher proportion of the plankton at midwater depths than in shallow waters dominated by crustacean zooplankters. The food sources for deep-sea larvae remain largely unresolved. In preliminary studies, bathyal echinoderm larvae reared in natural water from below the deep chlorophyll maximum consumed significant numbers of cyanobacteria, organisms so small that they should not easily sink into those depths. The implication is that these deep-sea larvae may swim actively up to shallower depths for the purpose of feeding. In this project, the investigators will examine the vertical distributions of larval forms and their potential microbial food sources in the Gulf of Mexico and the Bahamas, focusing especially on the potential role of cyanobacteria, picoeukaryotes, and heterotrophic bacteria as food sources for migrating deep-sea larvae. A multidisciplinary team will measure larval metabolism, swimming and feeding activity; and the physiological status of potential food organisms in deep water. Empirical data will be incorporated into an energetics model that predicts the likelihood of ontogenetic migration to the euphotic zone for larvae originating at bathyal depths. In keeping with their past record outreach and education at both the college and k-12 levels, the investigators will provide extensive and intensive learning opportunities for graduate and undergraduate students in hands-on multidisciplinary research. A college course, Biology of the Deep-sea Benthos, will be taught at sea, as it has been during previous NSF sponsored projects. Cruises will have internet components that will engender excitement in the adventure of science through web postings directly from the cruises. The investigators also will continue their involvement with outreach efforts including a regular public lecture series and a university program that provides seminar speakers to undergraduate and predominantly minority institutions.