Diverse herbivorous protists show common response in growth-temperature dependency

Gayantonia Franzè, Institute of Marine Research Bergen, Plankton Lab, Flødevigen, Norway and Susanne Menden-Deuer, University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, United States
Temperature is a fundamental driver of physiological rates and impacts biological processes at a global scale. Addressing temperature effects, including temperature fluctuations, on growth and feeding physiology of key consumers of marine primary production, unicellular herbivores, is of pivotal importance to quantify and predict cellular processes, ecosystem properties and, ultimately produce reliable carbon cycle predictions. While phytoplankton growth dependence on temperature is recognized and quantified globally, no similar relationship exists for herbivorous protist. Here we investigated herbivorous growth responses across an ecological relevant temperature gradient (0-22°C) representing the polar to temperate ocean. We tested species well adapted to laboratory conditions as well as newly isolated organisms established from Narragansett Bay through a seasonal cycle. The laboratory cultures presented commonalities useful to predict response to short term temperature fluctuations and long term warming of the ocean such as: 1. a common rate of increase in growth with increasing temperature, with a greater increase in biomass based (0.062±0.05 d-1 ºC-1) compared to abundance based rates (0.043±0.02 d-1 ºC-1), 2. a similar rate of acclimation, slower to cold and faster to warm temperature and, 3. a linear response of growth to increasing temperature, implying a weaker temperature effect on growth than the commonly assumed exponential dependency. While still testing wheatear similar trends apply to new isolated species, these results raise questions on the accuracy of productivity models based on rates and trends that do not represent the potential carbon availability within food webs and, show the necessity to settle these significant questions in order to accurately predict predator prey dynamics in microbial food webs in a rapidly changing ocean.