Evidence of partial thermal compensation in natural phytoplankton assemblages

Whether phytoplankton growth is solely constrained by temperature (hotter is better) or compensated by thermal adaptation is still under debate. We measured the temperature sensitivity of natural phytoplankton communities at both short-term and seasonal timescales using temperature manipulation experiments. The activation energy across communities (mean ± SE: E_i = 0.51 ± 0.12 eV, Q₁₀ = 1.98) is significantly lower than that within communities (E_a = 0.80 ± 0.10 eV, Q₁₀ = 2.80). Moreover, using a larger dataset of phytoplankton growth rates measured in (sub)tropical waters, we estimated the across-community activation energy as 0.33 ± 0.06 eV (Q₁₀ = 1.56), which is also lower than E_a. Our study is the first to suggest the “hotter is partially better” for natural phytoplankton communities, indicating that the phytoplankton communities can show some thermal adaptation capability. Our results highlight the importance of incorporating the differential temperature sensitivities at different timescales into the biogeochemical models to better evaluate how marine ecosystems will respond to climate changes.