Impact of micro- and nanograzers on phytoplankton assessed by standard and size-fractionated dilution grazing experiments

Calbet, A.; Trepat, I.; Almeda, R.; Salo, V.; Saiz, E.; Movilla, J.; Alcaraz, M.; Yebra, L.; Simo, R.
Aquatic Microbial Ecology
Grazing by microzooplankton is typically assessed by dilution experiments of the whole natural community. However, in many ecosystems these experiments actually include not only micrograzers but also nanograzers. We discerned the relevance of micro- and nanograzers under contrasting trophic situations in the coastal NW Mediterranean throughout a seasonal cycle. We measured the grazing upon total, 10 mu m chlorophyll a in 11 standard dilution experiments. We also conducted simultaneous dilution experiments with the 10 mu m primary production consumed daily, range 23 to 71 %). When the entire microbial community was size-fractioned by 10 pm, the potential impact of nd August) the size distribution of the grazers' community slightly shifted towards ly control the primary producers during the cold season (winter and most of the autumn), switch to nano-sized heterotrophic prey during spring, partially suppressing the impact of this group on phytoplankton, and finally are replaced by nanograzers during the warmer months (end of the summer period), heavily impacting the dominant small primary producers.
Mediterranean coastal waters, Microbial food web, Marine ecosystems,Trophic interactions, Community structure, Microzooplankton, Growth, Carbon, Volume, Bloom
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