Temporal stability of marine phytoplankton in a subtropical coastal environment |
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Authors: | Bingzhang Chen Hongbin Liu |
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Institution: | (1) Division of Life Science, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong;(2) Present address: State Key Lab of Marine Environmental Science, Xiamen University, Xiamen, People’s Republic of China |
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Abstract: | We investigated the temporal stability of phytoplankton at a subtropical coastal site for 9 months by conducting chlorophyll
and flow cytometric measurements at relatively high frequency (roughly at 2–5 day interval). Phytoplankton cells were grouped
based on their sizes obtained from flow cytometric signals. We also conducted dilution experiments to estimate the growth
and grazing mortality rates of different phytoplankton groups to assess whether the temporal stability of phytoplankton abundances
was related with phytoplankton growth/grazing rates. Based on size-fractionated chlorophyll measurements, there was some indication
that smaller phytoplankton cells were more stable than larger ones. However, by cytometric counting, there was no evidence
for greater stability in small cells. Synechococcus, which had the lowest stability and dominated the <1 μm size class, showed a strong seasonal cycle that was highly dependent
on temperature whereas eukaryotes did not have evident seasonal cycles. In general, biomass of a phytoplankton group consisting
of several size classes was more stable than that of its sub component, consistent with the hypothesis that higher diversity
leads to higher stability, probably related with the effect of statistical averaging (portfolio effect). Stability of heterotrophic
bacteria was much higher than that of phytoplankton, leading to the speculation that bacteria were more diverse than phytoplankton.
Phytoplankton stability was not related with their growth or grazing mortality rates. Our study suggests that species diversity
should be taken into account when considering the temporal stability of phytoplankton. |
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