Reliability of qPCR for quantitative gut content estimation in the circumglobally abundant pelagic tunicate Dolioletta gegenbauri (Tunicata, Thaliacea)

Gelatinous metazooplankton play a crucial role in marine planktonic food webs. Because of methodological difficulties encountered while studying them in situ relatively little is known about their ecology, including their diet or in situ rates of feeding. In this study we report the development of a differential length amplification quantitative PCR (dla-qPCR) assay targeting the 18S rRNA gene to validate the use of qPCR-based approach to quantify consumption of specific plankton prey by the doliolid Dolioletta gegenbauri. We also present an initial application of a qPCR-assay to estimate consumption of the centric diatom Thalassiosira spp. on the southeastern continental shelf of the United States where doliolids stochastically bloom in response to upwelling events. Results indicate that prey DNA was not significantly digested during passage through the gut of D. gegenbauri. Molecularly estimated feeding rates were in the same range as those estimated from clearance rates in laboratory feeding studies. In the field, the centric diatom Thalassiosira spp. was detected in the gut of wild caught D. gegenbauri at very low abundance that was consistent with its relative rarity in the water column at the time of collection. Thus, both experimental and field investigations support the hypothesis that a qPCR approach will be useful for the quantitative investigation of the in situ diet of D. gegenbauri without introduced biases associated with cultivation.