BUSCADOR RECOLECTA

Association for the Sciences of Limnology and Oceanography Aquatic Sciences Meeting (ASLO 2019), Planet Water - Challenges and Successes, 23 February - 2 March 2019, San Juan, Puerto Rico, The impact of the oceanic temperature raise due to climate change might have profound consequences for key components of marine food webs, such as zooplankton. In general, the fate of a species facing a temperature change in its habitat will depend on the coupling among the different thermal sensitivities of key ecophysiological activities. In this regard, thermal windows define the tolerance range of temperature for a given species, and are a good indicator of its vulnerability to changes in habitat temperature. Here, we report preliminary data on short-term responses (1 day) to temperature changes (range from 5ºC to 34ºC) on microzooplankton. We built thermal windows for two heterotrophic dinoflagellates (Gyrodinium dominans and Oxyrrhis marina) and one ciliate (Strombidium sp.) grown for multiple generations at 19ºC. The variables considered were growth, ingestion rates, and growth gross efficiency. The experiments showed the ciliate to be the more resistant to changes in temperature and the one benefiting the most from a rise in temperature. These contrasted responses between ciliates and dinoflagellates, if confirmed for other species, could have profound implications for the structure of marine communities under future climate change scenarios. In the future, we aim to investigate the thermal sensitivity of key ecophysiological activities of zooplankton to long-term (multigenerational) changes in temperature, and to determine how the coupling of these different thermal sensitivities may result in adaptive advantages or disadvantages for a given species.

13 pages, 6 figures, 3 tables.-- Data Availability Statement: The raw data supporting the conclusions of this article can be found at the open repository (Digital.CSIC, http://hdl.handle.net/10261/262244, https://doi.org/10.20350/digitalCSIC/14517).-- It is a contribution of the Marine Zooplankton Ecology Group (2017 SGR 87), Proper thermal adaptation is key to understanding how species respond to long-term changes in temperature. However, this is seldom considered in protozooplankton and mixoplankton experiments. In this work, we studied how two heterotrophic dinoflagellates (Gyrodinium dominans and Oxyrrhis marina), one heterotrophic ciliate (Strombidium arenicola), and one mixotrophic dinoflagellate (Karlodinium armiger) responded to warming. To do so, we compared strains adapted at 16, 19, and 22°C and those adapted at 16°C and exposed for 3 days to temperature increases of 3 and 6°C (acclimated treatments). Neither their carbon, nitrogen or phosphorus (CNP) contents nor their corresponding elemental ratios showed straightforward changes with temperature, except for a modest increase in P contents with temperature in some grazers. In general, the performance of both acclimated and adapted grazers increased from 16 to 19°C and then dropped at 22°C, with a few exceptions. Therefore, our organisms followed the “hotter is better” hypothesis for a temperature rise of 3°C; an increase of >6°C, however, resulted in variable outcomes. Despite the disparity in responses among species and physiological rates, 19°C-adapted organisms, in general, performed better than acclimated-only (16°C-adapted organisms incubated at +3°C). However, at 22°C, most species were at the limit of their metabolic equilibrium and were unable to fully adapt. Nevertheless, adaptation to higher temperatures allowed strains to maintain physiological activities when exposed to sudden increases in temperature (up to 25°C). In summary, adaptation to temperature seems to confer a selective advantage to protistan grazers within a narrow range (i.e., ca. 3°C). Adaptation to much higher increases of temperatures (i.e., +6°C) does not confer any clear physiological advantage (with few exceptions; e.g., the mixotroph K. armiger), at least within the time frame of our experiments, This research was funded by Grant CTM2017-84288-R by Fondo Europeo de Desarrollo Regional (FEDER)/Ministerio de Ciencia, Innovación y Universidades-Agencia Estatal de Investigacioìn (AEI), and by Grant PID2020-118645RB-I00 by Ministerio de Ciencia e innovación (MCIN)/AEI/10.13039/501100011033 and by ERDF A way of making Europe. [...] With the institutional support of the Severo Ochoa Centre of Excellence accreditation (CEX2019-000928-S). The open-access publication fee was partially covered by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI)