ABSTRACT
To investigate how the pico-level micro food loop transfers energy and material to higher trophic levels, five size spectrum experiments were designed and each was performed at eight levels (3 μm, 5 μm, 10 μm, 20 μm, 50 μm, 100 μm, 200 μm, and pico-2 μm) in August 2011. Environmental factors including temperature, light, nutrients, chlorophyll and initial population were fully taken into account. These physical and chemical parameters were set at the most appropriate level to minimize their influence on the experimental results. After 24 h incubation, the community was analyzed to determine the interactions between the components which were not significant under the experimental conditions. As other limitations were eliminated, the predation pressure was highlighted. The results indicated that the picophytoplankton (including Synechococcus and picoeukaryotes) showed five trophic cascades (2 μm, 2–5 μm, 5–20 μm, 20–50 μm and 50–200 μm). The trophic cascades of heterotrophic bacteria were indistinct, with the exception of the strongest predation pressure at the <5 μm level. The confusion in trophic levels was caused by regurgitation feeding in larger plankton and the grazing selectivity of bacterivory.
