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14 pages, 5 figures, 2 tables, 2 dataset https://doi.org/10.20350/digitalCSIC/14028 and https://doi.org/10.20350/digitalCSIC/14029.--This study is a contribution of the Marine Zooplankton Ecology Group (2017SGR-87) at the Institut de Ciències del Mar (ICM-CSIC), We describe the ontogenetic variation in elemental and stoichiometric composition of two copepod species with very contrasted life history patterns, the calanoid Paracartia grani and the cyclopoid Oithona davisae. The first species is a broadcasting, highly productive copepod, whereas the latter is an egg-carrying copepod, much less productive. We reared cultures of both species under conditions of excess food and analyzed their C, N and P composition, and their molar ratios, along development. Both species differed on their specific P content, whereas the specific C and N content were similar. As expected, the specific P content of P. grani was higher, resulting in lower C:P and N:P ratios. Furthermore, we compared our elemental composition data with previously reported stage-specific (nauplii and adult female) maximum growth rates of these two species. We found that for O. davisae, the ontogenetic variation in specific P content agreed with the reported differences in growth rate along development; however, in the case of P. grani, in which juvenile and adult maximum growth rates are similar, the variations in specific P content along development did not reflect the growth rate pattern, Fondo Europeo de Desarrollo Regional (FEDER)/Ministerio de Ciencia, Innovación y Universidades-Agencia Estatal de Investigación [CTM2017–84288-R], With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

Memoria de tesis doctoral presentada por Manuel Olivares Requena para obtener el título de Doctor en Ciencias del Mar 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).-- 155 pages, figures, tables, annexes, [EN] Marine planktonic copepods play a key ecological role in pelagic food webs. The study of their patterns of activity is fundamental in order to better understand the processes involved in the transfer of energy from lower trophic levels to higher-level consumers in marineecosystems. This thesis is an attempt to deepen the knowledge of the factors that affect the activity patterns of marine copepods. Some of these aspects had not been addressed previously and others still requiredfurther investigation. In particular, this thesis primarily focuses on the study of daily and diel patterns of feeding of marine planktonic copepods, and the influence of factors like ontogeny, gender, food availability, predation threat, light conditions, mutigenerational rearing in the laboratory, and temperature. The experimental work carried out in this thesis mostly consisted of laboratory incubations using wild and laboratory-reared specimens of the calanoid copepods Centropages typicus and Paracartia grani. Among the main findings in this thesis are the stage- and gender-specific differences in the feeding patterns of marine planktonic copepods. Moreover, we analyzed the role of predation risk and that of other factors in the modulation of feeding rhythms, and also evaluated the physiological costs related to temperature fluctuations involved in diel vertical migration. The new insights obtained in this thesis will certainly increase our capability to estimate the grazing impact of copepod populations in plankton communities, and will allow us to obtain better estimates of energy transfer in marine pelagic food webs, [ES] Los copépodos planctónicos desempeñan un papel ecológico clave en las redes tróficas pelágicas marinas. El estudio de sus patrones de actividad es fundamental para comprender mejor los procesos involucrados en la transferencia de energía desde los niveles tróficos inferiores a los consumidores superiores en los ecosistemas marinos. Esta tesis es un intento de profundizar en el conocimiento sobre los factores que modulan los patrones de actividad de los copépodos marinos. Algunos de estos aspectos no se habían estudiado previamente y otros aún requerían más investigación. En particular, esta tesis se centra principalmente en el estudio de los patrones diarios de alimentación de los copépodos planctónicos marinos y la influencia de factores como la ontogenia, el género, la disponibilidad de alimento, la amenaza de depredación, las condiciones de luz, la crianza multigeneracional en el laboratorio y la temperatura. El trabajo experimental llevado a cabo en esta tesis ha consistido mayoritariamente en incubaciones de laboratorio utilizando especímenes salvajes y de laboratorio de los copépodos calanoideos Centropages typicus y Paracartia grani. Entre los principales hallazgos en esta tesis destacan las diferencias en los patrones de alimentación entre estadios de desarrollo y entre sexos de copépodos planctónicos marinos. También se analiza el papel del riesgo de depredación y el de otros factores en la modulación de los ritmos de alimentación y se evalúan los costes fisiológicos relacionados con las fluctuaciones de temperatura implicadas en la migración vertical diaria. Los nuevos conocimientos obtenidos en esta tesis aumentarán nuestra capacidad para estimar el impacto de la depredación de las poblaciones de copépodos en las comunidades de plancton y nos permitirán obtener mejores estimaciones de la transferencia energética en las redes tróficas pelágicas marinas, The present Ph. D. thesis was conducted in 2016-2020 at Institut de Ciències del Mar (ICM-CSIC) under the supervision of Dr. Enric Saiz Sendrós and Dr. Albert Calbet Fabregat within the frame of the projects FERMI (CGL2014-59227-R) and ZOOTHERM (CTM2017-84288-R). [...] The Ph. D. student Manuel Olivares was supported financially by an FPU grant (FPU15/01747) from the Spanish Ministry of Education, Culture and Sport, Peer reviewed

Changes in the elemental composition and stoichiometric ratios of the marine calanoid copepod Paracartia grani along development, reared in the laboratory fed the cryptophyte Rhodomonas salina, This study was supported by [CTM2017–84288-R] funded by Fondo Europeo de Desarrollo Regional (FEDER)/Ministerio de Ciencia, Innovación y Universidades-Agencia Estatal de Investigación, Body length; C, N and P contents per individual; C:N molar ratio; C:P molar ratio; N:P molar ratio; Body volume; C, N and P contents per unit body volume, Peer reviewed

Changes in the elemental composition and stoichiometric ratios of the marine cyclopoid copepod Oithona davisae along development, reared in the laboratory fed the heterotrophic dinoflagellate Oxyrrhis marina, This study was supported by [CTM2017-84288-R] funded by Fondo Europeo de Desarrollo Regional (FEDER)/Ministerio de Ciencia, Innovación y Universidades-Agencia Estatal de Investigación, Body length; C, N and P contents per individual; C:N molar ratio; C:P molar ratio; N:P molar ratio; Body volume; C, N and P contents per unit body volume, Peer reviewed

10 pages, 1 figure, 3 tables.-- Data availability The datasets generated and/or analysed during the current study will be available in the Digital. CSIC repository after publication https://doi.org/10.20350/digitalCSIC/14138.-- This version of the article has been accepted for publication, after peer review and is subject to Springer Nature’s AM terms of use, but is not the Version of Record and does not reflect post-acceptance improvements, or any corrections. The Version of Record is available online at: https://doi.org/10.1007/s00027-021-00841-4, Diel vertical migration exposes zooplankton to fluctuating environmental conditions. In our study, we investigated the physiological costs of diel temperature fluctuations of vertical migration in the neritic marine copepod Centropages typicus, and checked whether the direct effects of fluctuating temperature on copepod performance may differ from those of average temperature conditions (Jensen’s inequality). We determined the rates of egestion, egg production, and respiration of copepods exposed to four temperature regimes including one treatment that simulated diel vertical migration (DVM, 10 h at 14 °C and 14 h at 19 °C) and three treatments with constant temperature (14, 17 and 19 °C). We found that the physiological performance of C. typicus was not significantly different between fluctuating (DVM) and average (17 °C) temperature conditions, thus indicating that differences between varying and average temperature effects might not emerge in migrant zooplankton exposed to thermal variations of moderate magnitude (5 ºC). The copepods exposed to fluctuating temperature mimicking vertical migration (DVM) showed better performance (e.g. higher egg production) than those exposed to constant depth conditions (14 °C); however, no significant differences were detected when compared to constant surface conditions (19 °C). Our study indicates that neritic marine copepods experiencing daily moderate temperature fluctuations through vertical migration may not suffer physiological costs due to temperature associated with this behaviour. In this sense, these animals might have physiological mechanisms to compensate diel temperature fluctuations, which would represent a particularly relevant preadaptation to cope with the increased thermal variability predicted in future climates, This study was framed within the project ZOOTHERM (CTM2017-84288-R, MICIU/AEI/FEDER, UE), and Manuel Olivares was supported financially by an FPU grant (FPU15/01747) from the Spanish Ministry of Education, Culture and Sport, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed

Diel vertical migration exposes zooplankton to fluctuating environmental conditions. In our study, we investigated the physiological costs of diel temperature fluctuations of vertical migration in the neritic marine copepod Centropages typicus, and checked whether the direct effects of fluctuating temperature on copepod performance may differ from those of average temperature conditions (Jensen’s inequality). We determined the rates of egestion, egg production, and respiration of copepods exposed to four temperature regimes including one treatment that simulated diel vertical migration (DVM, 10 h at 14 °C and 14 h at 19 °C) and three treatments with constant temperature (14, 17 and 19 °C). We found that the physiological
performance of C. typicus was not significantly different between fluctuating (DVM) and average (17 °C) temperature conditions, thus indicating that differences between varying and average temperature effects might not emerge in migrant zooplankton exposed to thermal variations of moderate magnitude (5 ºC). The copepods exposed to fluctuating temperature mimicking vertical migration (DVM) showed better performance (e.g. higher egg production) than those exposed to constant depth conditions (14 °C); however, no significant differences were detected when compared to constant surface conditions (19 °C). Our study indicates that neritic marine copepods experiencing daily moderate temperature fluctuations through vertical migration may not suffer physiological costs due to temperature associated with this behaviour. In this sense, these animals might have physiological mechanisms to compensate diel temperature fluctuations, which would represent a particularly relevant preadaptation to cope with the increased thermal variability predicted in future climates, This study was framed within the project ZOOTHERM (CTM2017-84288-R, MICIU/AEI/FEDER, UE), and Manuel Olivares was supported financially by an FPU grant (FPU15/01747) from the Spanish Ministry of Education, Culture and Sport, Number of experiment, date of experiment, temperature, bottle volume, prey species, prey species AphiaID, copepod species, copepod species AphiaID, copepod stage, prey concentration, prey size, number of copepods per bottle, copepod size, incubation time, egestion rate, egg production rate, respiration rate, Peer reviewed

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

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)

16 pages, 8 figures, supplementary data https://doi.org/10.1093/plankt/fbac017.-- Data archiving: DIGITAL.CSIC repository https://doi.org/10.20350/digitalCSIC/14664, We studied the phenotypic response to temperature of the marine copepod Paracartia grani at the organismal and cellular levels. First, the acute (2 days) survival, feeding and reproductive performances at 6–35°C were determined. Survival was very high up to ca. 30°C and then dropped, whereas feeding and fecundity peaked at 23–27°C. An acclimation response developed after longer exposures (7 days), resulting in a decline of the biological rate processes. As a consequence, Q10 coefficients dropped from 2.6 to 1.6, and from 2.7 to 1.7 for ingestion and egg production, respectively. Due to the similarity in feeding and egg production thermal responses, gross-growth efficiencies did not vary with temperature. Respiration rates were less sensitive (lower Q10) and showed an opposite pattern, probably influenced by starvation during the incubations. The acclimation response observed in the organismal rate processes was accompanied by changes in body stoichiometry and in the antioxidant defense and cell-repair mechanisms. Predictions of direct effects of temperature on copepod performance should consider the reduction of Q10 coefficients due to the acclimation response. Copepod population dynamic models often use high Q10 values and may overestimate thermal effects, This research was funded by Grant [CTM2017-84288-R] by Ministerio de Ciencia e Innovación (MCIN)/Agencia Estatal de Investigación (AEI/ 10.13039/501100011033) and by Fondo Europeo de Desarrollo Regional (FEDER, EU) “Una manera de hacer Europa”. 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

We have studied the phenotypic response, at the cellular and organismal levels, of the marine calanoid copepod Paracartia grani to short- and medium-term thermal stress, This research was supported by Grant [CTM2017-84288-R] funded by MCIN/ AEI /10.13039/501100011033/ and by FEDER Una manera de hacer Europa, Survival, body composition stoichiometry, enzymatic biomarkers, LPO levels, ingestion rates, fecal pellet production rates, egg production rates, gross-growth efficiencies, respiration rates, 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

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

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

12 pages, 5 figures, 2 tables, supplementary data https://doi.org/10.1093/plankt/fbad037.-- Data Availability: The dataset generated for this study is accessible through the Digital.CSIC repository https://doi.org/10.20350/digitalCSIC/15494, The study of a species’ thermal tolerance and vital rates 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 h) 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”. 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

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