BUSCADOR RECOLECTA

It is a contribution of the Marine Zooplankton Ecology Group (2017 SGR 87), Proper thermal adaptation is key to understanding how species respond to 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, comparing strains adapted at 16, 19 and 22 °C and those adapted at 16 °C and exposed for 3 days at 19 and 22 °C (acclimated treatments). Neither CNP contents nor the 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 from 16 to 19 °C; above 19 °C, however, the results were variable. Despite the disparity in the responses between species and physiological rates, in general, it seems that 19 °C-adapted organisms performed better than acclimated-only organisms. However, at 22 °C, most species were at the limit of their metabolisms and were unable to fully adapt. Nevertheless, adaptation to higher temperatures conferred some advantages prior to sudden increases in temperature (up to 25 °C) that simulated a heatwave episode. 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 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 Investigación (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), Para 4 especies: Volumen (µm3/depredador), Tasa crecimiento (µ 1/d), Tasa de ingestion (cells/ind/d), Eficiencia bruta de crecimiento (GGE, %), Peer reviewed

We aimed at studying the mechanisms underneath the ascending and descending sections of the thermal performance curves in marine protozoans. To do so, we exposed Gyrodinium dominans and two strains of Oxyrrhis marina from different origins to three temperatures representative of each section of the thermal response curve (12ºC, ascending section; 18ºC, top; 25ºC, descending section). 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 a triangular response with maximum values at the intermediate temperature. However, G. dominans showed similar growth rates at 12 and 18ºC, and even if showed a marked decrease in growth rates at 25ºC, this was not significant. Ingestion rates were higher at 18ºC for all the strains. The respiration rates of G. dominans were unaffected by temperature, but the respiration rates of both O. marina strains increased with temperature. The specific dynamic action 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 within strains of the same species. G. dominans maintained similar growth at all temperatures by balancing anabolism and catabolism functions. 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”. R.A.M. was funded by a PhD fellowship from the National Commission of Science (CONICYT), Ministry of Education, Chile. It is a contribution of the Marine Zooplankton Ecology Group (2017 SGR 87). With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Para 3 especies de protozoos marino: Tasa de respiración con y sin comida (µmol O2/ind/h), Tasa crecimiento (µ 1/d), Tasa de ingestion (cells/ind/d), Eficiencia bruta de crecimiento (GGE, %), Peer reviewed

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

The temperature-size rule hypothesized that there is a negative relationship between the size (volume) of an organism and the temperature. This applies to both unicellular and pluricellular organisms. Here, we question this hypothesis for the particular case of protozoans, because in these organisms the volume is directly related to the consumption of prey, and on most of the occasions the true volume of the cell is unknown. To prove our arguments, we designed a series of experiments with the heterotrophic dinoflagellate O. marina, including functional and numerical responses, time-dependent acclimation responses, and estimation of the protozoan volume during long periods of starvation. Our data showed that, in fact, the observed temperature-size rule in unicellular grazers results from anabolic and catabolic imbalances, and that the relationship between size and temperature weakens after proper thermal adaptation. We also showed that once prey are fully digested, the protozoan’ size is the same irrespectively of the temperature. Finally, we set the basis for proper acclimation during short-term temperature experiments, which specifies that at least 3 days should be allowed for proper temperature acclimation. We also suggest that, for trustable experiments, the grazer should be incubated at the target prey concentration for at least 24h before conducting the experiments. The ecological implications of a lack of correlation between microzooplankton size and temperature are also discussed, 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”. It is a contribution of the Marine Zooplankton Ecology Group (2017 SGR 87). With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Para Oxyrrhis marina: Tasas de ingestion a diferentes concentraciones de alimento (presa/ind/d), Tasa crecimiento (µ 1/d), Volumen (µm3); para la presa (Rhodomonas salina): volume (µm3), Peer reviewed

We exposed the calanoid copepod Paracartia grani, reared in the laboratory at 19°C, to warmer conditions (22°C and 25°C) for 11 generations and examined the direct effects of temperature on feeding, fecundity, development, population sex ratio and somatic traits (adult and egg sizes and adult carbon content), 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”. CJ was supported by Grant [PRE2018-084738] funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Rearing temperature, generation, prosome length, carbon content, ingestion rate, egg production rate, egg diameter, gross-growth efficiency, hatching success, Peer reviewed

The temperature-size rule states that as the temperature increases, the body size of organisms decreases. This rule has been observed in a wide range of organisms, including marine phytoplankton and it is particularly important to model and predict the effects of global warming on the structure and functioning of marine ecosystems. This is so because the size of marine phytoplankton is a critical trait that determines their ecological and biogeochemical roles in marine ecosystems. The size of marine phytoplankton is also affected by resource availability, which relates to growth rates. Here, we compare the effects of a long-term exposure to several temperatures on the cell size of three marine microalgae during their growth curves. The species chosen were the cryptophyte Rhodomonas salina, the dinoflagellate Heterocapsa niei, and the diatom Conticribra (previously Thalassiosira) weissflogii. All algae conformed the temperature-size rule during all the phases of the growth curve. However, the size variations of the microalgae in each of the phases were species-specific. R. salina and H. niei showed higher volumes in the exponential growth phase than during the decline of growth and early stationary phases. Contrarily, the diatom showed smaller volumes during the exponential phase of growth than during the other phases. Overall, the effects of growth rate on cell size exceeded those of temperature for the expected ocean warming by the end of the century. These results also partially support the higher relevance of resource supply than temperature in explaining the variability of phytoplankton size structure in marine ecosystems, 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”. With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Para las tres microalgas, Rhodomonas salina, Heterocapsa niei, Conticribra weissflogii, abundancias, y volumen a diferentes temperaturas, Peer reviewed

We have studied the response of the marine calanoid copepod Paracartia grani to dietary elemental imbalances, This research was supported by Grant [PID2020-118645RB-I00] funded by MCIN/AEI/10.13039/501100011033, Elemental content, C:N ratios, C:P ratios, N:P ratios, copepod ingestion rate, copepod egg production rate, hatching success, gross-growth efficiency of egg production, egg size, nauplius body size, threshold elemental ratios for C:N and C:P, 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

The study of a species' thermal tolerance and vital rate responses provides useful metrics to characterize its vulnerability to ocean warming. Under prolonged thermal stress, plastic and adaptive processes can adjust the physiology of organisms. Yet it is uncertain whether the species can expand their upper thermal limits to cope with rapid and extreme changes in environmental temperature. In this study, we reared the marine copepod Paracartia grani at control (19°C) and warmer conditions (25°C) for >18 generations and assessed their survival and fecundity under short-term exposure to a range of temperatures (11-34°C). After multigenerational warming, the upper tolerance to acute exposure (24 hours) increased by 1-1.3°C, although this enhancement decreased to 0.3-0.8°C after longer thermal stress (7 days). Warm-reared copepods were smaller and produced significantly fewer offspring at the optimum temperature. No shift in the thermal breadth of the reproductive response was observed. Yet the fecundity rates of the warm-reared copepods in the upper thermal range were up to 21-fold higher than the control. Our results show that chronic warming improved tolerance to stress temperatures and fecundity of P. grani, therefore enhancing its chances to persist under extreme heat events, 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”. “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”, Rearing temperature, generation, exposure temperature, survival 24h, survival 7d, egg production rate, fitness index, egg diameter, female prosome length, 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

ASLO Aquatic Sciences Meeting, Resilience and Recovery in Aquatic Systems, 4-9 June 2023, Palma de Mallorca, Spain.-- 1 page, figures, Marine sciences and the effects of climate change in the oceans are usually not a substantial part, if any, of school curricula. The result of such a deficiency in knowledge will be a new generation of adults with little comprehension of the importance of the ocean. To fill this gap, we as scientists should do our best to communicate and educate. Stories for children and comics are valuable tools to reach this goal are. I present a story in which Fred the copepod explains, in an educational and entertaining way, what copepods are, what they do in the sea, and the problems he experiences during his life. He introduces concepts such as predation, reproduction, vertical migration, and pollution and presents other components of plankton, such as microplankton and meroplankton. The ultimate goal is to make children and adults aware of the fragility and importance of plankton and the need to take care of the sea. The original book has two levels of reading: one designed for children from 6 years old and another for adults who want to know more about marine plankton. This dual way of providing information will reach a much larger audience. If you want to have access to this additional content, you can use the QR code at the bottom of the poster, This poster was funded by Grant PID2020-118645RB-I00 by To learn more MCIN/AEI/10.13039/501100011033

ASLO Aquatic Sciences Meeting, Resilience and Recovery in Aquatic Systems, 4-9 June 2023, Palma de Mallorca, Spain.-- 1 page, figures, Temperature is one of the most prominent climate-change variables affecting marine zooplankton activity and distribution. The impact of warming on zooplankton depends not only on physiological sensitivity, but also on the temporal scale of exposure and the species acclimation capacity. Warming events of a few days or weeks of duration will mainly impact at the intragenerational level, while longer-term warming will reflect on multigenerational responses. In this study, we compare the effects of +3 and +6ºC thermal stress on the vital rates of the copepod <em>Paracartia grani</em> at short (2 and 7 days, acclimation response) and long (>10 generations, multigenerational response) time scales. <em>P. grani</em> showed high phenotypic plasticity after 2-d exposure, increasing feeding and egg production rates. This acute response, however, declined quickly and after 7 days of exposure the enhancement of physiological rates was still positive but of lesser magnitude (Q₁₀ <2). Multigenerational rearing at the tested temperatures resulted in a further reduction of the copepod response to temperature and the apparent loss of thermal effects, implying further adaptive compensation processes. The metabolic costs of the thermal responses, estimated as the copepod gross-growth efficiency, did not appear to be influenced by temperature, suggesting the species has high thermal tolerance, 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.”

Memoria de tesis doctoral presentada por Carlos de Juan Carbonell para obtener el título de Doctor en Ciéncies Marines por la Universitat de Barcelona (UB), realizada bajo la dirección del Dr. Enric Saiz Sendrós y del Dr. Albert Calbet Fabregat del Institut de Ciències del Mar (ICM-CSIC).-- 183 pages, [EN] Ectothermic animals are highly sensitive to changes in the environmental temperature. As ocean temperatures rise, a major concern is the potential impact of warming on copepods, which are crucial contributors to marine food webs. However, our understanding of how copepods respond to chronic temperature changes and the underlying physiological mechanisms is limited due to a scarcity of long-term studies. This thesis presents a series of experiments investigating the direct effects of temperature on copepod phenotypic traits across multiple generations. We specifically focused on the calanoid copepod Paracartia grani, exposed at long-term to warmer conditions (+3°C and +6°C). We explored the implications of chronic thermal stress for production, energetics, life-history as well as the copepod’s resilience to extreme events and low food availability.
The results showed that higher rearing temperatures accelerated copepod hatching and development rates, resulting in a reduction of the adult body size and elemental content (carbon, nitrogen and phosphorous). Initially, temperature increased the copepod main physiological rates (ingestion, respiration and reproduction), but these effects were compensated within a few generations under warmer conditions, with no relevant costs on multiple life-history traits, including the efficiency of food utilized for reproduction, energetics, nauplii hatching success or the sex ratio. Adult body stoichiometric ratios (C:N, C:P, and N:P) were either altered across generations. P. grani exhibited a broad thermal tolerance range (11-32ºC), and long-term warming (+6ºC) even expanded their tolerance to acute high temperatures (>30ºC). However, prolonged exposure to these temperatures reduced its survival after a week, diminishing the advantage gained from warm rearing. At these extreme temperatures, reproduction was reduced but sustained, thereby expanding the fitness of copepods reared under warming conditions. The thermal resilience of this species to extreme temperatures was highlighted when subjected to sub-lethal thermal stress (28ºC), which did not affect the metabolic balance of copepods regardless of the rearing temperatures (19, 22 and 25ºC). As a main trade-off, following chronic warming the food uptake under low food conditions of the prey Rhodomonas salina was highly reduced, potentially indicating a decline in feeding efficiency and subsequent reduction in reproductive activity.
Overall, the research carried out in this thesis suggests that P. grani has a large capability to adapt to temperature increases, maintaining key activities, like grazing and production. Nevertheless, an increase in thermal anomalies, low food availability, or the combination of both factors may limit their capacity to persist in their local environment. Given that the thermal effects on development were not compensated at long-term, size reductions in copepods might be a major consequence of ocean warming, with important ramifications for marine food webs and biogeochemical cycles. [...], [ES] Los animales ectotermos son altamente sensibles a cambios de la temperatura ambiental. Ante el aumento de las temperaturas del océano, una de las principales cuestiones es su impacto en los copépodos, los cuales desempeñan un papel crucial a las redes tróficas pelágicas marinas. Sin embargo, debido a la escasez de estudios que aborden los efectos térmicos a largo plazo, nuestro conocimiento sobre su posible respuesta y de los procesos fisiológicos subyacentes es limitado. Esta tesis presenta una serie de estudios experimentales que investigan los efectos directos de la temperatura sobre los rasgos fenotípicos de los copépodos a lo largo de múltiples generaciones. Específicamente, se centra en el copépodo calanoide Paracartia grani, expuesto a largo plazo a temperaturas elevadas (+3 y +6ºC). Se exploran las implicaciones del estrés térmico para la producción, balance energético, historia vital, así como la resiliencia de los copépodos a eventos de calor extremo y a la baja disponibilidad de alimento.
Los resultados muestran que una mayor temperatura de cultivo acelera las tasas de eclosión y desarrollo de los copépodos, lo que resulta en una reducción del tamaño corporal de los adultos y del contenido elemental (carbono, nitrógeno y fósforo). Inicialmente, la temperatura aumentó las principales tasas fisiológicas de los copépodos (ingestión, respiración y reproducción) pero estos efectos se compensaron en unas pocas generaciones de exposición, sin que se produjeran costes relevantes en múltiples rasgos de su ciclo biológico, como la eficiencia de la utilización de alimento en la reproducción, el balance energético, la tasa de eclosión o la proporción de sexos. La relaciones estequiométricas de los adultos (C:N, C:P y N:P), tampoco fueron alteradas después de múltiples generaciones. P. grani mostró tolerancia a un amplio rango de temperaturas (11-32ºC) y después del calentamiento a largo plazo (+6ºC) incluso amplió su tolerancia a temperaturas extremas (>30ºC). Sin embargo, una exposición prolongada redujo su supervivencia después de una semana, disminuyendo la ventaja adquirida. A estas temperaturas extremas, la reproducción se redujo significativamente, pero manteniéndose y ampliando así la aptitud de los copépodos cultivados a mayores temperaturas. Asimismo, un estrés térmico subletal (28ºC) no afectó al equilibrio metabólico de los copépodos cultivados a diferentes temperaturas (19, 22 y 25ºC). Como principal desventaja, tras el calentamiento crónico la tasa de ingestión en bajas concentraciones de comida de la presa Rhodomonas salina se redujo significativamente, lo que podría indicar una reducción de la eficiencia de alimentación; y, consecuentemente, disminuyó su actividad reproductora.
En general, los resultados de esta tesis sugieren que P. grani posee la capacidad de adaptarse a un aumento gradual del calentamiento, manteniendo actividades clave, como la ingestión y la producción. Sin embargo, un aumento de las anomalías térmicas, una baja disponibilidad de alimento o la combinación de ambos factores pueden limitar su capacidad de persistir localmente. Dado que los efectos térmicos sobre el desarrollo no fueron compensados a largo plazo, la disminución de tamaño de los copépodos puede ser una de las mayores implicaciones del calentamiento del océano, con importantes ramificaciones en las redes tróficas y los ciclos biogeoquímicos marinos. [...], [CAT] L’activitat fisiològica dels animals ectoterms està estretament lligada a la temperatura ambiental. Per tant, davant l’escalfament de les temperatures de l’oceà, una de les principals preocupacions és el seu impacte en els copèpodes, els quals exerceixen un paper crucial a les xarxes tròfiques marines. Tot i això, a causa de l’escassetat d’estudis que aborden els efectes tèrmics a llarg termini, el nostre coneixement sobre la seva possible resposta i els processos fisiològics subjacents són encara limitats. Aquesta tesi presenta una sèrie d’estudis experimentals que investiguen els efectes directes de la temperatura sobre els trets fenotípics dels copèpodes al llarg de múltiples generacions. Específicament, ens centrem en el copèpode calanoide Paracartia grani, exposat a llarg termini a temperatures elevades (+3ºC i +6ºC). Explorem les implicacions de l’estrès tèrmic per a la producció, el balanç energètic, l’historia vital, així com la resiliència dels copèpodes a esdeveniments de calor extrems i a la baixa disponibilitat d’aliment.
Els resultats mostren que una major temperatura de cultiu accelera les taxes de reclutament i el desenvolupament dels copèpodes, cosa que resulta en una reducció de sa mida corporal dels adults i del seu contingut elemental (carboni, nitrogen, fòsfor). Inicialment, la temperatura va augmentar les principals taxes fisiològiques dels copèpodes (ingestió, respiració i reproducció), però aquests efectes es varen compensar en unes poques generacions d’exposició sense implicar costos rellevants en múltiple trets del seu cicle biològic, com l’eficiència de la utilització de l’aliment per la reproducció, l’èxit de reclutament de ses larves o la proporció de sexes. Tampoc no es van veure alterades les relacions estequiomètriques en els adults (C:N, C:P i N:P). P. grani va mostrar tolerància a un ampli rang de temperatures (11-32ºC) i el seu cultiu a temperatures més elevades (+6ºC) va ampliar la seva tolerància a temperatures extremes (>30ºC). Tot i això, una exposició perllongada va reduir la seva supervivència després d’una setmana, reduint l’avantatge adquirit. A aquestes temperatures extremes, la reproducció es va reduir però mantenint-se, ampliant així l’aptitud dels copèpodes cultivats a més temperatura. Així mateix, un estrès tèrmic subletal (28ºC) no va afectar l’equilibri metabòlic dels copèpodes en cap de les condicions de cultiu (19, 22 i 25ºC). Com a principal desavantatge, després de l’escalfament crònic la taxa d’ingestió en baixes concentracions de la presa Rhodomonas salina es va reduir significativament, lo que podria indicar una reducció de l’eficiència d’alimentació i, conseqüentment, una disminució de la seva activitat reproductora.
En general, els resultats d’aquesta tesi suggereixen que P. grani posseeix una gran capacitat d’adaptar-se a un augment gradual de la temperatura, mantenint activitats clau com la ingestió i la producció. Tot i això, un augment de les anomalies tèrmiques, una baixa disponibilitat d’aliment o la combinació de totes dues poden limitar la seva capacitat de persistir localment. Atès que els efectes sobre el desenvolupament no es compensen a llarg termini, la reducció de mida dels copèpodes pot suposar una de les implicacions més importants de l’escalfament de l’oceà, amb importants ramificacions a les xarxes tròfiques i als cicles biogeoquímics marins. [...], This PhD thesis was developed between September 2019 and March 2024 in the Institut de Ciències del Mar (ICM-CSIC; Barcelona, Spain) within the framework of ZOOTHERM (Thermal acclimation and adaptation in marine zooplankton; CTM2017-84288-R) and ZOOTENUT projects (Future climate change scenarios and marine zooplankton: Synergistic effects of temperature and nutrient deficiencies on long-term adapted populations; PID2020-118645RB-I00), funded by the Spanish Ministry of Science, Innovation and Universities (MCIN/AEI/10.13039/501100011033) and the European Regional Development Fund (ERDF): A way of making Europe. C. de Juan was supported by a predoctoral contract (FPI, PRE2018-084738) funded by the Spanish Ministry of Science, Innovation and Universities (MCIN/AEI/10.13039/501100011033) and the European Social Fund (ESF): Investing in your future. This thesis acknowledges the “Severo Ochoa Centre of Excellence” accreditation (CEX2019-000928.S) to the ICM-CSIC, Peer reviewed