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)

9 pages, 3 figures, 2 tables.-- Data Availability Statement: Publicly available datasets were analyzed in this study. This data can be found here: https://doi.org/10.20350/digitalCSIC/14561..-- It is a contribution of the Marine Zooplankton Ecology Group (2017 SGR 87)., We exposed Gyrodinium dominans and two strains of Oxyrrhis marina to temperatures well above (25°C) and below (12°C) their maintenance temperature (18°C) to study the mechanisms controlling the overall physiological response to thermal stress. As variables, we measured growth, ingestion, and respiration rates (this latter with and without food). The growth rates of O. marina strains plotted as a function of temperature showed maximum values at the maintenance temperature, as expected in a typical unimodal functional response. However, G. dominans showed similar growth rates at 12 and 18°C, and even a marked decrease in growth rates at 25°C, happened to be not significant. G. dominans ingestion rates were not significantly different at all temperatures (although apparently decreased at 25°C), whereas both O. marina strains showed higher ingestion rates at 18°C. The respiration rates of G. dominans were unaffected by temperature, but those of O. marina strains increased with temperature. The specific dynamic action (respiration increase produced by feeding activity) ranged from 2 to 20% of the daily carbon ingestion for all organisms investigated. The calculated energetic budget indicated that the responses to temperature were diverse, even between in strains of the same species. G. dominans maintained similar growth at all temperatures by balancing metabolic gains and losses. In O. marina strains, on the other hand, the decrease in growth rates at the lowest temperature was driven mainly by reduced ingestion rates. However, increased respiration seemed the primary factor affecting the decrease in growth rates at the highest temperature. These results are discussed in the light of previous studies and on its suitability to understand the response of wild organisms to fluctuations in temperature, This research was funded by Grant PID2020-118645RB-I00 by Ministerio de Ciencia e innovación (MCIN)/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”. 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). [...] With the institutional support of the ’Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

10 pages, 6 figures, 3 tables, supplementary data https://doi.org/10.1016/j.marenvres.2022.105693, Sudden environmental changes like marine heatwaves will become more intense and frequent in the future. Understanding the physiological responses of mixoplankton and protozooplankton, key members of marine food webs, to temperature is crucial. Here, we studied two dinoflagellates (one protozoo- and one mixoplanktonic), two ciliates (one protozoo- and one mixoplanktonic), and two cryptophytes. We report the acute (24 h) responses on growth and grazing to a range of temperatures (5–34 °C). We also determined respiration and photosynthetic rates for the four grazers within 6 °C of warming. The thermal performance curves showed that, in general, ciliates have higher optimal temperatures than dinoflagellates and that protozooplankton is better adapted to warming than mixoplankton. Our results confirmed that warmer temperatures decrease the cellular volumes of all species. Q10 coefficients suggest that grazing is the rate that increases the most in response to temperature in protozooplankton. Yet, in mixoplankton, grazing decreased in warmer temperatures, whereas photosynthesis increased. Therefore, we suggest that the Metabolic Theory of Ecology should reassess mixoplankton's position for the correct parameterisation of future climate change models. Future studies should also address the multigenerational response to temperature changes, to confirm whether mixoplankton become more phototrophic than phagotrophic in a warming scenario after adaptation, This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 766327. [...] Thanks for financial support are also due to the ERASMUS + traineeship program and to the Grants CTM2017-84288-R and PID2020-118645RB-I00 funded by MCIN/AEI Spain/10.13039/501100011033 and by “FEDER Una manera de hacer Europa”. This work is a contribution of the Marine Zooplankton Ecology Group (2017 SGR 87) with the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX 2019-000928-S), Peer reviewed

This article is a contribution from the Marine Zooplankton Ecology Lab at the ICM-CSIC.-- 10 pages, 5 figures, supplementary data .-- Data availability: The data will be deposited in the DIGITAL.CSIC repository after
publication https://doi.org/10.20350/digitalCSIC/15171. DIGITAL.CSIC http://hdl.handle.net/10261/303804, We assessed the effects of nutrient imbalanced diets on the feeding, reproduction and gross-growth efficiency of egg production of the copepod Paracartia grani. The cryptophyte Rhodomonas salina, cultivated under balanced (f/2) and imbalanced growth conditions (N and P limitation), served as prey. Copepod C:N and C:P ratios increased in the imbalanced treatments, particularly under P limitation. Feeding and egg production rates did not differ between the balanced and N-limited treatments but decreased under P limitation. We found no evidence of compensatory feeding in P. grani. C gross-growth efficiency averaged 0.34 in the balanced treatment and declined to values of 0.23 and 0.14 for the N- and P-limited treatments, respectively. Under N limitation, N gross-growth efficiency increased significantly to a mean value of 0.69, likely as a result of increasing the nutrient absorption efficiency. P gross-growth efficiency reached values > 1 under P limitation, involving the depletion of body P. Hatching success was >80%, with no differences among diets. Hatched nauplii, however, had lower size and slower development when the progenitor was fed a P-limited diet. This study highlights the effects of P limitation in copepods, which are more constraining than N, and the presence of maternal effects driven by prey nutritional composition that ultimately may affect population fitness, This research was supported by Grant [PID2020-118645RB-I00] funded by MCIN/AEI/10.13039/501100011033. [...] The open-access publication fee was covered by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

This article is a contribution from the Marine Zooplankton Ecology Laboratory at the ICM-CSIC.-- 11 pages, 6 figures, 2 tables, supporting information https://doi.org/10.1002/lno.12327.-- Data availability statement: The data that support the conclusions of this study are openly available in Digital.CSIC repository at https://doi.org/10.20350/digitalCSIC/15130, Under the current ocean warming scenario, multigenerational studies are essential to address possible adaptive changes in phenotypic traits of copepod populations. In this study, we exposed the calanoid copepod Paracartia grani, reared in the laboratory at 19°C, to warmer conditions (22°C and 25°C) to investigate the changes in key phenotypic traits in the 1st, 10th, and 11th generations. Development rates and adult body size were inversely related to temperature in all generations. We also found a decline in copepod egg size at higher temperatures. Temperature had positive effects on the ingestion and egg production rate of females in the first generation, but the thermal response of the copepods diminished significantly in the consecutive generations. The decrease in thermal effects on feeding and egg production rates after multigenerational exposure cannot be explained only by the shrinkage in body size at warmer temperatures, but also involves the action of physiological compensation. These adaptive processes did not appear to have a significant cost on other traits, such as egg hatching success, gross growth efficiency, and sex ratio. Our findings have implications for the prediction of ocean warming effects on copepod activity rates and highlight the importance of physiological adaptation processes after multigenerational exposure, This study acknowledges the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928.S). This research was funded by Grants [CTM2017-84288-R and PID2020-118645RB-I00] by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe.” C.J. was supported by Grant [PRE2018-084738] funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future.” The open access publication fee was covered by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI), Peer reviewed

This article is a contribution from the Marine Zooplankton Ecology Lab at the ICM, CSIC.-- 13 pages, 6 figures, supporting information https://doi.org/10.1111/1365-2435.14356.-- The datasets generated for this study can be found in the Digital CSIC repository https://doi.org/10.20350/digitalCSIC/14754. (Calbet & Saiz, 2023), The temperature–size rule suggests that there is a negative relationship between the size (volume) of an ectothermic organism and the environmental temperature experienced during its development
We question how to validate this hypothesis for the particular case of some algivorous protozoans because in many of these unicellular organisms, body size is directly related to the consumption of prey and, on most occasions, the true size of the cell is uncertain.
In our opinion, to approach this question, the actual size of the protozoan should be measured when the prey are fully digested.
To prove our arguments, we designed a series of experiments with the heterotrophic dinoflagellate Oxyrrhis marina, including functional and numerical responses, time-dependent acclimation responses and the estimation of the protozoan volume during absence of food.
We found that after the digestion of the prey Rhodomonas salina, the size of our long-term thermally acclimated strains of Oxyrrhis marina was the same regardless of the temperature (16 and 22°C).
We believe that previous reports showing protozoan size reduction because of temperature might actually reflect imbalances between ingestion and digestion of prey, perhaps amplified by insufficient acclimation.
In support of the previous argument, we found evidence that short-term temperature exposure experiments may suggest a negative relationship between well-fed protozoan size and temperature, although this was not observed after long-term acclimation.
In light of the results presented here, we suggest that the actual evidence supporting the temperature–size rule in algivorous protozoans may not be sufficiently conclusive because most of the present studies largely ignore the effect of prey presence on the grazer's volume and are usually based on short-term responses to temperature, This research was funded by Grant PID2020-118645RB-I00 by Ministerio de Ciencia e Innovación (MCIN)/AEI/10.13039/501100011033. With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S). The open access publication fee was covered by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI), Peer reviewed

12 pages, 5 figues, supplementary data https://doi.org/10.1093/ismejo/wrae130.-- Data availability: The raw data and the secondary derived data have been placed in the Zenodo repository within the project “The distinctive chemotactic responses of three marine herbivore protists to DMSP and related compounds” in the following link:
https://zenodo.org/communities/imedea_icm/records?q=&l=list&p=1&s=10&sort=newest
The codes are accessible in Github in the following links and connected to the Zenodo databases:
R scripts: https://github.com/medea95/Chemotaxis_experiments_R_scripts
Python scripts: https://github.com/medea95/Chemotaxis_experiments_Python_scripts
The cultures are in the ICM culture collection from which they can be ordered using the following link: https://www.icm.csic.es/ca/servei/cultius-de-plancton, Marine planktonic predator–prey interactions occur in microscale seascapes, where diffusing chemicals may act either as chemotactic cues that enhance or arrest predation, or as elemental resources that are complementary to prey ingestion. The phytoplankton osmolyte dimethylsulfoniopropionate (DMSP) and its degradation products dimethylsulfide (DMS) and acrylate are pervasive compounds with high chemotactic potential, but there is a longstanding controversy over whether they act as grazing enhancers or deterrents. Here, we investigated the chemotactic responses of three herbivorous dinoflagellates to point-sourced, microscale gradients of dissolved DMSP, DMS, and acrylate. We found no evidence for acrylate being a chemotactic repellent and observed a weak attractor role of DMS. DMSP behaved as a strong chemoattractor whose potential for grazing facilitation through effects on swimming patterns and aggregation depends on the grazer’s feeding mode and ability to incorporate DMSP. Our study reveals that predation models will fail to predict grazing impacts unless they incorporate chemotaxis-driven searching and finding of prey, This research was mainly funded by the European Research Council Advanced Grant (ERC-2018-ADG-834162) to R.S., under the EU’s Horizon 2020 research and innovation programme. Further funding was provided by Grants PID2020-118645RB-I00 to A.C. and TED2021-132886B-I00 to I.T., both funded by the Ministerio de Ciencia e Innovación (MCIN)/AEI/10.13039/501100011033, the latter with funds of the “EU NextGenerationEU/PRTR”. M.Z. and I.T. also acknowledge funding from the EU’s H2020 programme under the Marie Skłodowska-Curie grant agreement No 955910. The ICM-CSIC and the IMEDEA (UIB-CSIC) are supported by “Severo Ochoa Centre of Excellence” (CEX2019-000928-S) and “Maria de Maeztu Centre of Excellence” (CEX2021-001198) accreditations, respectively, from the Spanish government, Peer reviewed

14 pages, 5 figures, supplementary material https://www.frontiersin.org/articles/10.3389/fevo.2024.1505037/full#supplementary-material.-- Data availability statement: The original contributions presented in the study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding author, In recent decades, there has been a growing recognition that mixotrophy, the ability to utilize both phototrophy and phagotrophy, is more common among plankton than previously assumed. Even though mixotrophs can become highly abundant, especially under nutrient limitation, and significantly alter nutrient cycling and food-web dynamics due to their dual nutritional modes, a comprehensive synthesis from a stoichiometric perspective is still lacking. We conducted a systematic literature review in which we identified over 130 studies that directly relate nutrient ratios to mixotrophic protists at the organism to community scale. By conceptually linking mixotrophy with the concept of ecological stoichiometry, we provide insights into (1) the role of mixotrophic metabolism and nutrient limitation in regulating cellular homeostasis, (2) mixotroph abundance and community scale responses to nutrient limitation, and (3) the specific case of harmful algal bloom forming mixotrophs. On the organism scale, the existing literature points towards a stabilizing effect of mixotrophic metabolism on elemental composition, and the use of grazing as a compensation mechanism under stoichiometric imbalances in the water and prey. At the community scale, mixotrophs were found to increase in abundance relative to strict autotrophs and heterotrophs in nutrient-limited communities, and provide beneficial food for zooplankton grazers by maintaining relatively low and stable stoichiometry. Furthermore, global-scale models and studies of harmful algal blooms reveal the increasing importance of mixotrophs under climate change – highlighting the need for continued research addressing the interactions between mixotrophs and dynamic stoichiometry to understand the impacts of mixotrophs on global nutrient cycles, LS was supported by the grant “SeeWandel-Climate: Modelling the consequences of climate change and neobiota for Lake Constance” (Grant no. ABH025) within the framework of the Interreg VI programme “Alpenrhein-Bodensee-Hochrhein (Germany/Austria/Switzerland/Liechtenstein)” which funds are provided by the European Regional Development Fund as well as the Swiss cantons. ZSA was supported by the National Science Foundation Graduate Research Fellowship (Grant No. 2141064) and by the Simons Collaboration on Computational Biogeochemical Modeling of Marine Ecosystems/CBIOMES (Grant no. 549931). MG-M was supported by Grant PID2020-118645RB-I00 by MICIU/AEI/10.13039/501100011033 and by Grant (PRE2021-096866) funded by MCIN/AEI/10.13039/501100011033 and by the FSE+. AH was supported by the European Union HORIZON EUROPE program ACTNOW: Advancing understanding of Cumulative Impacts on European marine biodiversity, ecosystem functions and services for human wellbeing (Grant no. 101060072), With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

10 pages, 5 figures, 1 table, supplementary data https://doi.org/10.1016/j.marenvres.2024.106827.-- Data availability: Data will be uploaded to Digital.CSIC repository upon acceptance https://doi.org/10.20350/digitalCSIC/17567, We investigated the impact of sublethal thermal stress on physiological rates of the copepod Paracartia grani, and explored the influence of previous thermal history on this response. The copepods, originally reared at 19 °C, were raised for 23 generations at 22 °C and 25 °C, and posteriorly exposed for 7-d to stress temperature (28 °C). The copepod acclimation capacity was assessed by comparing metabolic balance at 28 °C against their respective rearing temperatures. There was an inverse relationship between rearing temperature and body size and carbon content for the reared copepod lines. Weight-specific rates, except respiration, increased with rearing temperature, whereas per capita rate differences were levelled, partly due to differences in copepod size. Heat stress impact, as weight-specific rate fold-change, appeared inversely related to rearing temperature. Carbon gains were overall sufficient and slightly in excess to account for carbon losses. Gross-growth efficiency across warming scenarios was conserved, emphasizing resilience to environmental change. Our findings underscore the importance of considering the species' thermal history when predicting the response of copepod populations to climate change associated phenomena such as gradual slow ocean warming or heatwave events, This research was funded by Grants CTM2017-84288-R, PID2020-118645RB-I00 and PID2023-150548NB-I00 by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” and ERDF/EU. C. J. was supported by Grant [PRE2018-084738] funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. The open-access publication fee was covered by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI), With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

14 pages, 4 figures, 2 tables, supporting information https://doi.org/10.1002/lno.70264.-- Data Availability Statement: The data that support the findings of this study are openly available in Digital.CSIC repository at https://doi.org/10.20350/digitalCSIC/17501, The impact of climate change stressors on marine copepods, key organisms at the base of ocean food webs, remains understudied. This study examined how warming affects their functional and numerical responses, critical life history traits linked to fitness. We conducted laboratory experiments on the calanoid species Paracartia grani, exposing it to a +6°C increase at two temporal scales, short term (4 d) and long term (21 generations; ca. 1 yr), and compared with the control at 19°C. We observed distinct patterns between warming treatments. Short-term warming increased intake rates and satiation levels, causing a mismatch between the functional and the numerical responses. Additionally, egg size and phosphorus body content declined, collectively resulting in reduced reproductive efficiency at high food concentrations. Long-term warming shifted satiation to higher food concentrations, possibly due to decreased foraging capacity (i.e., maximum clearance rate) in the smaller, warm-reared copepods; in turn, maximum feeding rates indicated physiological compensation, and reproductive efficiency showed no consistent pattern. High food availability altered the copepod elemental content, which appeared to be linked to reproductive effort. Short-term warming raised C : P and N : P ratios, while C : N ratios remained stable across all treatments. Our findings reveal how warming and resource availability interact to shape copepod performance and elemental fluxes, and highlight the importance of incorporating time-scale dependent thermal effects into ecosystem models for better forecasting in a context of climate change, The open-access publication fee was covered by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). [...] This study acknowledges the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928.S), and the research group “Plankton Ecology and Ocean Health” (2021 SGR 0047).[...] This research was funded by Grants PID2020-118645RB-I00 and PID2023-150548NB-I00 by MICIU/AEI/10.13039/501100011033 and by “ERDF/EU.” Carlos de Juan was supported by Grant PRE2018-084738 funded by MICIU/AEI/10.13039/501100011033 and by “ESF Investing in your future”, Peer reviewed

Marine planktonic predator-prey interactions occur in microscale seascapes, where diffusing chemicals may act either as chemotactic cues that enhance or arrest predation, or as elemental resources that are complementary to prey ingestion. The phytoplankton osmolyte dimethylsulfoniopropionate (DMSP) and its degradation products dimethylsulfide (DMS) and acrylate are pervasive compounds with high chemotactic potential, but there is a longstanding controversy over whether they act as grazing enhancers or deterrents. Here, we investigated the chemotactic responses of three herbivorous dinoflagellates to point-sourced, microscale gradients of dissolved DMSP, DMS, and acrylate. We found no evidence for acrylate being a chemotactic repellent and observed a weak attractor role of DMS. DMSP behaved as a strong chemoattractor whose potential for grazing facilitation through effects on swimming patterns and aggregation depends on the grazer's feeding mode and ability to incorporate DMSP. Our study reveals that predation models will fail to predict grazing impacts unless they incorporate chemotaxis-driven searching and finding of prey.