Stability of plankton community structure in a long-term biomanipulated eutrophic shallow lake in southeast China: Evidence from particle size spectra

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To characterize the plankton size structure and evaluate plankton community stability in Longhu Lake, a shallow eutrophic lake in southeast China that has been biomanipulated for ~20 years, the biomass-size spectra of the plankton were seasonally studied from August 2017 to November 2018. The plankton-size spectra revealed a typical bimodal structure in all seasons. The higher peak consisted of small-sized phytoplankton ranging from 10 to 30 μm, while the lower peak consisted mainly of rotifers and ciliates ranging from 66 to 83 μm. Compared with other eutrophic lakes, the size classes of the bimodal structure in Longhu Lake were relatively smaller, indicating individual miniaturization in the lake's plankton community. There was also a trough in the 90 to 370 μm region of the size spectra, indicating a low biomass for crustacean zooplankton in the lake. The slope (b = −1.27 ± 0.04) of the normalized size spectra was lower than that of the theoretical equilibrium state (b = −1), suggesting high energy transfer from the large phytoplankton (>30 μm) and zooplankton (>90 μm) to the planktivorous silver and bighead carps via filter feeding. Although the seasonal size spectra fluctuated with the water temperature (positively) and nutrients (negatively) in Longhu Lake, their patterns and coefficients of determination did not significantly vary with the seasons (R2 = 0.98 ± 0.01, p < 0.05), indicating the plankton community is stable in this long-term biomanipulated eutrophic lake.