Temperature Dependence of Freshwater Phytoplankton Growth Rates and Zooplankton Grazing Rates

Jennifer Pulsifer,Edward Laws

doi:10.3390/w13111591

Abstract

Phytoplankton growth rates and zooplankton grazing rates were estimated on 16 occasions over a period of 17 months in University Lake, a highly eutrophic lake on the campus of Louisiana State University. Phytoplankton growth rates and chlorophyll a concentrations averaged 1.0 ± 0.2 d−1 and 240 ± 120 mg m−3, respectively. Chlorophyll a concentrations were at or above the inflection point of the Holling type I curve that described the relationship between zooplankton grazing rates and chlorophyll a concentrations. In most cases, it was necessary to dilute lake water by more than a factor of 4 before zooplankton grazing rates became sensitive to chlorophyll a concentrations. Chlorophyll a concentrations were positively correlated with temperature and were roughly fourfold higher at 30 °C than at 15 °C. An analysis of the temperature dependence of the growth rates and grazing rates in this study and 87 other paired estimates of limnetic phytoplankton growth rates and zooplankton grazing rates revealed virtually identical temperature dependences of growth rates and grazing rates that were very similar to the temperature dependence predicted by the metabolic theory of ecology. Phytoplankton growth rates exceeded zooplankton grazing rates by 0.13 ± 0.05 d−1 at all temperatures over a temperature range of 8.5–31.5 °C. The Q10 for both phytoplankton growth rates and zooplankton grazing rates was 1.5 over that temperature range.

Highlights

In 1972, Eppley published a now-classic paper [1] in which he concluded, based on analysis of an extensive dataset of growth rates of approximately 130 species or clones of freshwater and marine algae in culture, that at temperatures below 40 ◦ C, the maximum growth rates of phytoplankton increase exponentially with temperature
Kremer et al.’s [4] analysis was based on application of the so-called metabolic theory of ecology (MTE), and when they reanalyzed the Eppley [1] data accounting for “functional group and mass”, they concluded that the temperature dependence implied by those data was very similar to the results of their MTE analysis
Because of the highly eutrophic status of the lake, we assumed that phytoplankton growth rates were not limited by nutrient concentrations, and we hypothesized that the Q10 of the growth rates would be either 1.53 or 1.88

Summary

Introduction

In 1972, Eppley published a now-classic paper [1] in which he concluded, based on analysis of an extensive dataset of growth rates of approximately 130 species or clones of freshwater and marine algae in culture, that at temperatures below 40 ◦ C, the maximum growth rates of phytoplankton increase exponentially with temperature. We used the dilution technique originally developed by Landry and Hassett [6] to estimate phytoplankton growth rates and zooplankton grazing rates in the lake.

Results

Conclusion