Assessing the Clearance Rates of Dolioletta gegenbauri fed different size particles

Studies on the rate of different size doliolids feeding under simulated or real environmental conditions require that food composition, abundances, and size distribution resemble that of the natural environment. There have been several studies conducted on feeding rates and retention efficiencies of salps, doliolids, and copepods on natural and different sized particles. This study shows that the presence of large diatoms can affect the clearance rates of gonozooids of D. gegenbauri on smaller, co-occurring cells. The clearance and ingestion rates of 3.5 mm to 5.5 mm Dolioletta gegenbauri gonozooids on three phytoplankton of different sizes, Rhodomonas sp. (Rho.) at 8 µm, Thalassiosira wessfloggii (Tw) at 12, and Rhizosolenia alata (R. alata) at 49 µm cell diameter, was determined at 20 ^oC. The objectives were to quantify the rates at which each size zooid could ingest three concentrations (21, 46,100 µg C/l) of R. alata, and how these rates will affect the clearance rates of Rho and Tw at a constant concentration of 60 µg C/l. The study also compared the rates from experiments where gonozooids were offered 60 µg C/l of Rho + Tw only. The clearance rates of R. alata, Rho, Tw, and the Rho+Tw combination were not significantly different at the low concentration of R. alata for all gonozooid sizes, but some differences were found in clearance rates at the medium and high concentrations. The results from these experiments suggest that as Dolioletta gegenbauri gonozooids increased from 3.5 to 5.5 mm, their ability to ingest R. alata increased. The small and medium sized gonozooids have the ability to ingest large and small cells at similar rates, while the larger gonozooid’s clearance rates, at higher concentrations of R. alata, reduce the grazing pressure on smaller cells. The ingestion of these large diatoms increases the amount of carbon ingested per day, and may increase their rates of growth and reproduction.