BUSCADOR RECOLECTA

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

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

The feeding activity of copepods is crucial for the structure and functioning of marine ecosystems. Quantification of feeding rates of different copepod life stages across a range of prey densities (functional response) is essential knowledge for improvement of plankton dynamic models. In this study, we conducted experiments to compare the feeding functional responses of nauplii, copepodites, and adults of the marine copepod Paracartia grani (formerly Acartia grani) when grazing on the flagellate Rhodomonas salina. We found that all copepod stages followed a sigmoid curve in their functional responses (Holling Type III model), indicating a metabolic threshold constraining foraging effort at low prey densities. Maximum clearance rates of nauplii and copepodites increased with body mass with a power scaling factor of 1, but maximum clearance rates of adults did not follow the pattern observed for juvenile stages, likely because of the relatively small prey size used in the experiments. Copepod maximum ingestion rates, however, showed allometric scaling along ontogeny that was closer to the typical 0.75 power law and seemed to not be so dependent on prey size. The insights obtained from our study highlight stage-specific differences in copepod feeding activity, and can help improve our capability to estimate the energy flow through copepods in marine food webs, This study was framed within the project FERMI (CGL2014-59227-R, MINECO/AEI/FEDER, UE). 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, clearance rate, ingestion rate, Peer reviewed

Marine planktonic copepods frequently exhibit diel feeding cycles coupled with vertical migrations. However, copepod feeding rhythms can be influenced by factors others than different food availability between layers. In this study, we determined the changes in the diel feeding behaviour of two marine copepod species (Centropages typicus and Paracartia grani) through multigenerational laboratory rearing, ontogeny, and upon the exposure to predator chemical cues. The wild females of both C. typicus and P. grani showed marked feeding rhythms with higher ingestion rates at night. The diel rhythms of C. typicus were maintained in the first laboratory-reared generation (F1), suggesting maternal effects, but disappeared in the following generations. The P. grani females of a long-term culture (> 10 years) also showed no differences in their day–night feeding activity. Ontogenetic variations were detected in the F1 generation of C. typicus: feeding rhythms were absent in naupliar stages, but adults fed more intensely at night. In the case of the cultured P. grani, in general none of the stages showed feeding rhythms. Laboratory-reared C. typicus (8–11 generations) did not recover back the natural cyclic feeding when exposed to jellyfish and fish exudates, indicating that either predation risk does not significantly affect their diel feeding activity or predator-induced responses in marine copepods might not involve chemical signalling. Our study confirms that feeding-related functional traits of marine copepods can experience quick multigenerational changes in the laboratory; consequently, cultured copepods might not be good models for studies involving their diel feeding behaviour, This study was framed within the Project FERMI (CGL2014-59227-R, MINECO/AEI/FEDER, UE). Manuel Olivares is supported financially by a 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 generation, copepod stage, day/night, presence/absence of predator exudates, predator species, predator species AphiaID, prey concentration, prey size, number of copepods per bottle, copepod size, incubation time, clearance rate, ingestion rate, Peer reviewed

Predators can induce changes in the diel activity patterns of marine copepods. Besides vertical migration, diel feeding rhythms have been suggested as an antipredator phenotypic response. We conducted experiments to assess the non-lethal direct effects of the predator Meganyctiphanes norvegica (northern krill) on the diel feeding patterns of the calanoid copepod Centropages typicus. We also analysed the influence of seasonal photoperiod and prey availability on the intensity of copepod feeding rhythms. We did not detect any large effect of krill presence on the diel feeding behaviour of copepods, either in day-night differences or total daily ingestions. Seasonal photoperiod and prey availability, however, significantly affected the magnitude of copepod feeding cycles, with larger diel differences in shorter days and at lower prey concentrations. Therefore, the role of non-lethal direct effects of predators on the diel feeding activity of marine copepods remain debatable and might not be as relevant as in freshwater zooplankton, The research leading to these results received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730984, ASSEMBLE Plus project. 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 was framed within the project FERMI (CGL2014–59227-R, MINECO/AEI/FEDER, UE), and M.O. 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, predator species, predator species AphiaID, day/night, predator/no predator, prey concentration, prey size, number of copepods per bottle, copepod size, number of predators per bottle, predator size, incubation time, number of copepod faecal pellets, faecal pellet volume, 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