On the Significance of Doliolids as Consumers and Producers

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9633401 Paffenhofer This project will investigate the ability of doliolids (Tunicata, Thaliacea) to control the abundance of protozoa and free-spawning calanoid copepods. Pelagic tunicate feeding rates have been difficult to quantify, particularly for Thaliacea. In this work, Drs. Paffenhofer and Verity will quantify simultaneously the feeding, growth and reproduction rates of doliolids, which repeatedly have constituted a major component of neritic zooplankton in temperate and subtropical waters. The main hypotheses are that:(1) doliolid assemblages above ~ 600 large zooids m -3 are able to control phytoplankton, protozooplankton and free- spawning calanoids, and (2) that such high concentrations of large doliolids are rapidly attained by intense reproduction of two consecutive asexual stages, and high individual grown rates. The significance of these studies is several fold: first, to obtain environmentally-realistic and simultaneous information on rates of consumption and production of the different doliolid zooids; second, determine experimentally at which concentrations doliolids control phytoplankton, protozooplankton and free-spawning calanoids; third, develop a model describing the direct and indirect effects which a doliolid assemblage can have on these prey populations. ***