DIGESTION TIME AND FEEDING INTENSITY OF THE LARVAL CTENOPHORE MNEMIOPSIS LEIDYI A. AGASSIZ (CTENOPHORA, LOBATA)
Keywords:
Mnemiopsis leidyi, digestion time, microzooplankton, clearance rate, ingestion rate, feeding rate, daily rationAbstract
Effect of nutrition conditions (food species and concentration, prey and predator sizes, prey number in stomach) on digestion time and ingestion rate in lobate ctenophore Mnemiopsis leidyi larvae have been studied Digestion time of the larvae in length range of 0.5 – 9.5 mm feeding on nine food species, that varied in their size one order of magnitudes (from 0.15 – in Acartia sp. nauplii to 1.8 mm in Palaemon larvae) depended on food species, larvae size and prey number in the stomach and decreased as larvae size increased and prey size reduced. Relationships between ingestion rate (R, ind ind –1) and food concentration (N, ind l –1) were described by linear equations R = 0.04N – 0.71 and R = 0.02N + 2.4 in 5 and 9 – mm larvae feeding on Acartia sp. nauplii, correspondingly. In the range of wet weight from 0.5 to 120 mg the linear relationship have been found between clearance rate (F, ml ind–1 h–1) and wet weights of the predators feeding on metazoan microzooplankton (WW, mg) F=0.148 WW + 6.96 and F= 0.128 WW + 11.38 when they fed on ciliated protozoans. Carbon specific clearance rate value was power function of carbon content in larva body and did not depend on food species as on separate Infusoria species as on metazoan microzooplankton Carbon specific total daily ration on microzooplankton was very high in the smallest larvae (0.25 mm) (2550 % С) and decreased to 56 % C as larvae length increased to 3 mm. The share of ciliated protozoans in the total ration also reduced from 82 – 68 % in small (0.3 – 0.6mm) to 18 – 11 % in larger larvae (1.5 – 3.0 mm). Displayed high feeding rates testify that in some years during the peak of abundance the predatory impact of M. leidyi larvae on microzooplankton can be as high as 25 % of microzooplankton biomass.
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