Bacterivory in seawater samples estimated by a dual radioactive-labelling technique

Author： Zubkov Mikhail V. Sleigh Michael A.

ISSN： 1464-3774

Source： Journal of Plankton Research, Vol.19, Iss.2, 1997-02, pp. : 209-219

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Abstract

A dual radioactive-labelled bacteria technique using Vibrio (DRLV), developed for laboratory studies on bacterivory, has been refined for use at the concentrations of prey and predators typcially found at sea. Experiments with estuarine water collected in spring and in autumn showed that bacterivorous nanoflagellates (HNF) (concentration 1.38±0.35×10³ HNF ml⁻¹) ingested 2.7±0.96 DRLV flagellate1⁻¹ h⁻¹ at concentrations of 0.8–2.2×10⁶ DRLV ml⁻¹ in the presence of 2.04±0.68×10⁶ natural bacteria ml⁻¹. The method was also applied to samples collected in October in the Celtic Sea, when on average 1 ml of water from the surface layer contained 1.41±0.16×10⁶ natural bacteria, 14.6×10³ cyanobacteria, 530±170 HNF, 7.3±3.0×103 phototrophic nanoflagellates (1.5–4 μm), 49.0±26.5 phototrophic dinoflagellates, 36.3±12.6 heterotrophic dinoflagellates and 21.3±9.5 Leucocryptos marina. Under these conditions the grazing rate in most samples did not exceed the coefficient of variation of the method (2%), although we estimate the grazing rate was -1.6 DRLV HNF⁻¹ h⁻¹ and on one occasion a rate of 2.45 was recorded. The gross growth efficiency for protein of -30% displayed by natural HNF means that they could release about ∼70% of inorganic nutrients derived from their food.