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MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps13627

Effect of the prey selectivity and trophic cascades induced by mesozooplankton on the dynamics of phytoplankton

Mianrun Chen, Yueyue Si, Liuyu Han, Xin Liu, Bangqin Huang, Chang-Keun Kang*

*Corresponding author:

ABSTRACT: Mesozooplankton are key component in the marine environment, linking the microbial food web and the classic food chain. Yet, uncertainties remain on how mesozooplankton mediate the dynamics of prey communities through their complex feeding patterns. To examine mesozooplankton-mediated trophic interactions, we performed shipboard incubations using food removal and dilution methods during four cruises in the Pearl River estuary (PRE), Southern China. Our results revealed that mesozooplankton had diverse effects on different size fractions and taxonomic groups of phytoplankton via a combination of strong feeding selectivity and trophic cascades. High ingestion rates of mesozooplankton suppressed the accumulation of microphytoplankton (> 20 μm), whereas low ingestion rates of mesozooplankton and high trophic cascades promoted the biomass of nano-sized (2–20 μm) and pico-sized (0.7–2 µm) phytoplankton. Among phytoplankton groups, diatoms were passively selected by mesozooplankton despite of high concentrations in natural seawater, whereas dinoflagellates and cryptophytes were actively preferred by mesozooplankton in spring and autumn. Similarly, ciliates were also preferred by mesozooplankton despite of lower biomass compared with phytoplankton, which induced a trophic cascade that indirectly increased the biomass of smaller phytoplankton. The overall feeding effect of mesozooplankton on phytoplankton was determined by the balance between the direct grazing rate and the indirect compensation with trophic cascades. The carnivory degrees of mesozooplankton, which determine the strength of trophic cascades, varied among seasons, resulting a week control of algal bloom by mesozooplankton. Our findings provide insights into the complex trophic interactions between mesozooplankton and other plankton groups in dynamic natural ecosystems.