10 pages, 5 figures, 2 tables, supplementary information http://dx.doi.org/10.1038/srep14962.--This study is a contribution of the Marine Zooplankton Ecology Group (2014SGR-498) at the Institut de Ciències del Mar-CSIC, Planktonic copepods are a key group in the marine pelagic ecosystem, linking primary production with upper trophic levels. Their abundance and population dynamics are constrained by the life history tradeoffs associated with resource availability, reproduction and predation pressure. The tradeoffs associated with the ageing process and its underlying biological mechanisms are, however, poorly known. Our study shows that ageing in copepods involves a deterioration of their vital rates and a rise in mortality associated with an increase in oxidative damage (lipid peroxidation); the activity of the cell-repair enzymatic machinery also increases with age. This increase in oxidative damage is associated with an increase in the relative content of the fatty acid 22:6(n-3), an essential component of cell membranes that increases their susceptibility to peroxidation. Moreover, we show that caloric (food) restriction in marine copepods reduces their age-specific mortality rates, and extends the lifespan of females and their reproductive period. Given the overall low production of the oceans, this can be a strategy, at least in certain copepod species, to enhance their chances to reproduce in a nutritionally dilute, temporally and spatially patchy environment, This research was funded by projects CTM2011-23480 and CGL2014-59227-R of the Spanish Ministry of Economy and Competitiveness (cofinanced with FEDER funds, EU), Peer Reviewed

11 pages, 5 figures, 5 tables, 1 appendix supplementary data https://dx.doi.org/10.1016/j.scitotenv.2016.03.234.-- This work is a contribution to the consolidated research group 2014 SGR 498 of the Generalitat de Catalunya, We analyzed the concentrations of trace metals/metalloids (TMs) in the water, sediment and plankton of two semi-enclosed marine coastal inlets located north of Jurong Island and separated by a causeway (SW Singapore; May 2012-April 2013). The west side of the causeway (west station) has residence times of approximately one year, and the east side of the causeway (east station) has residence times of one month. The concentrations of most of the TMs in water and sediment were higher in the west than in the east station. In the water column, most of the TMs were homogeneously distributed or had higher concentrations at the surface. Preliminary evidence suggests that the TMs are primarily derived from aerosol depositions from oil combustion and industry. Analyses of TMs in seston (>. 0.7 μm; mostly phytoplankton) and zooplankton (>. 100 μm) revealed that the seston from the west station had higher concentrations of most TMs; however, the concentrations of TMs in zooplankton were similar at the two stations. Despite the high levels of TMs in water, sediment and seston, the bioaccumulation detected in zooplankton was moderate, suggesting either the presence of effective detoxification mechanisms or/and the inefficient transfer of TMs from primary producers to higher trophic levels as a result of the complexity of marine planktonic food webs. In summary, the TM concentrations in water and seston are not reliable indicators of the bioaccumulation at higher trophic levels of the food web, This work was funded through grant MadeInPlankton from Singapore National Parks Board - Singapore (NParks) and DHI-NTU Research Centre and Education Hub, Ung EliteForsk grants 10-093759 and 10-094773 from the Danish Ministry for Independent Research to GD, and Projects PROTOS (CTM2009-08783), TOPCOP (CTM2011-23480) and FERMI (CGL2014-59227-R) from the Spanish Ministry of Economy and Competitiveness to AC, Peer Reviewed

13 pages, 8 figures, 3 tables, 1 appendix supplementary data https://dx.doi.org/10.1016/j.marenvres.2016.06.005.-- This work is a contribution to the consolidated research group 2014 SGR 498 of the Generalitat de Catalunya, We studied the plankton dynamics of two semi-enclosed marine coastal inlets of the north of Jurong Island separated by a causeway (SW Singapore; May 2012–April 2013). The west side of the causeway (west station) has residence times of ca. one year and is markedly eutrophic. The east side (east station) has residence times of one month and presents lower nutrient concentrations throughout the year. The higher nutrient concentrations at the west station did not translate into significantly higher concentrations of chlorophyll a, with the exception of some peaks at the end of the South West Monsoon. Microzooplankton were more abundant at the west station. The west station exhibited more variable abundances of copepods during the year than did the east station, which showed a more stable pattern and higher diversity. Despite the higher nutrient concentrations at the west station (never limiting phytoplankton growth), the instantaneous phytoplankton growth rates there were generally lower than at the east station. The phytoplankton communities at the west station were top-down controlled, largely by microzooplankton grazing, whereas those of the east station alternated between top-down and bottom-up control, with mesozooplankton being the major grazers. Overall, the trophic transfer efficiency from nutrients to mesozooplankton in the eutrophic west station was less efficient than in the east station, but this was mostly because a poor use of inorganic nutrients by phytoplankton rather than an inefficient trophic transfer of carbon. Some hypotheses explaining this result are discussed, This work was funded through grant MadeInPlankton from Singapore National Parks Board – Singapore (NParks) and from DHI-NTU Research Centre and Education Hub Ung EliteForsk Grants10-093759 and 10-094773 from the Danish Ministry for Independent Research to GD, and Projects PROTOS (CTM2009-08783), TOPCOP (CTM2011-23480) and FERMI (CGL2014-59227-R) from the Spanish Ministry of Economy and Competitiveness to AC., Peer Reviewed

Special issue Current trends in protistology – results from the VII ECOP - ISOP Joint Meeting 2015.-- 25 pages, 6 figures, 1 table, Functional ecology is a subdiscipline that aims to enable a mechanistic understanding of patterns and processes from the organismic to the ecosystem level. This paper addresses some main aspects of the process-oriented current knowledge on phagotrophic, i.e. heterotrophic and mixotrophic, protists in aquatic food webs. This is not an exhaustive review; rather, we focus on conceptual issues, in particular on the numerical and functional response of these organisms. We discuss the evolution of concepts and define parameters to evaluate predator–prey dynamics ranging from Lotka–Volterra to the Independent Response Model. Since protists have extremely versatile feeding modes, we explore if there are systematic differences related to their taxonomic affiliation and life strategies. We differentiate between intrinsic factors (nutritional history, acclimatisation) and extrinsic factors (temperature, food, turbulence) affecting feeding, growth, and survival of protist populations. We briefly consider intraspecific variability of some key parameters and constraints inherent in laboratory microcosm experiments. We then upscale the significance of phagotrophic protists in food webs to the ocean level. Finally, we discuss limitations of the mechanistic understanding of protist functional ecology resulting from principal unpredictability of nonlinear dynamics. We conclude by defining open questions and identifying perspectives for future research on functional ecology of aquatic phagotrophic protists, HA was supported by grants from the German Research Foundation (DFG; AR 288/16) and from the Federal Ministry for Education and Research (BMBF: 03G0237B; 02WRM1364D). Project FERMI (CGL2014-59227-R) was awarded to AC from the Spanish Ministry of Economy and Competitiveness. RA was supported by the the European Union's Horizon 2020 research and innovation programme (Marie Sklodowska-Curie grant agreement No 658882). PJH was supported by the Danish Council for independent Reseach, project DDF-4181-00484. TW was financially supported by the Austrian Science Fund (FWF, projects P20118-B17 and P20360-B17). DJSM received no support for his efforts on this study, other than his salary provided by the University of Liverpool, Peer Reviewed

Special volume: Planet Ocean. Scientia Marina 80(Suppl.1) 2016.-- 9 pages, 7 figures, 3 tables, [EN] The temporal and spatial changes of zooplankton and chlorophyll a concentration were studied during the warm stratification period (early June) at three stations whose traits corresponded to the coastal, frontal, and offshore-dome water conditions described for the Catalan Sea. We sampled the stations for 12 days at a frequency ranging from less than 10 to 102 h, with a spatial resolution ranging from 10 to 104 m. The objective was to determine the variability of mesozooplankton and phytoplankton (chlorophyll a) biomass, and average individual size (mass) across a coast-offshore transect in relation to the stratification conditions prevailing in the NW Mediterranean during summer. The vertical distribution of phytoplankton biomass displayed a clear deep maximum at 60 m depth except at the coastal station. This maximum exists during most of the year and is especially important during the density stratification period. It was accompanied during daylight hours by a coherent zooplankton maximum. At sunset mesozooplankton ascended and dispersed, with larger organisms from deeper layers joining the migrating community and increasing the average individual mass. The highest variability of mesozooplankton biomass, individual mass and chlorophyll a concentration occurred at the front station due to the coupling between the vertical migration of zooplankton and the particular characteristics of the front. According to the data shown, the highest variability was observed at the lowest scales, [ES] Durante el periodo de estratificación térmica (principios de junio) se estudiaron los cambios temporales y espaciales de concentración de zooplancton y clorofila a en tres estaciones cuyos rasgos corresponden a las condiciones de aguas costeras, frontal y domo central descritas para el Mar Catalán. Muestreamos las estaciones a lo largo de 12 días con una frecuencia que varió entre <10 h y 102 h, y con una resolución espacial entre 10 y 104 m. El objetivo fue determinar la variabilidad de la biomasa del fitoplancton (clorofila a) y del mesozooplancton, así como de su tamaño individual promedio a lo largo de un transecto costa-mar abierto en relación con las condiciones de estratificación térmica típicas del Mediterráneo del Noroccidental desde finales de primavera a finales de verano. La distribución vertical de la biomasa de fitoplancton mostró la existencia de un máximo profundo a 60 m de profundidad, excepto en la estación costera. Aunque cierta heterogeneidad vertical en la biomasa de fitoplancton suele observarse durante la mayor parte del año, es especialmente importante durante el período de estratificación de densidad. El máximo de fitoplancton estuvo acompañado durante las horas de luz por un máximo de zooplancton, que en la crepúsculo ascendía y se dispersaba, y al que se unían organismos de mayor tamaño procedentes de zonas más profundas, contribuyendo a aumentar la masa individual promedio. La mayor variabilidad de biomasa mesozooplanctónica, de la masa individual y de la concentración de clorofila a se observó en la estación frontal debido al acoplamiento entre la migración vertical del zooplancton y las características particulares del frente. Según los datos presentados la mayor variabilidad fue observada en las escalas espaciales y temporales más bajas, The VARIMED-95 cruise took place in the frame-work of the Spanish research project AMB94-1019 from the Ministry of Science to M. Alcaraz. Financial support was also provided by the projects MAR98-0854 and CTM2006-12344-c02 to M.A., TOPCOP-CTM2011-23480 to E. Saiz and FERMI (CGL2014-59227-R) to AC and ES, Peer Reviewed

20 pages, 6 figures, 4 tables, supporting information https://doi.org/10.1371/journal.pone.0172902.s001, data availability https://doi.pangaea.de/10.1594/PANGAEA.872504, Laboratory feeding experiments were conducted to study the functional response and prey size spectrum of the young naupliar stages of the calanoid copepod Paracartia grani Sars. Experiments were conducted on a range of microalgal prey of varying sizes and motility patterns. Significant feeding was found in all prey of a size range of 4.5-19.8 μm, with Holling type III functional responses observed for most prey types. The highest clearance rates occurred when nauplii fed on the dinoflagellate Heterocapsa sp. and the diatom Thalassiosira weissflogii (respectively, 0.61 and 0.70 mL ind d), suggesting an optimal prey:predator ratio of 0.09. Additional experiments were conducted to examine the effects of the presence of alternative prey (either Heterocapsa sp. or Gymnodinium litoralis) on the functional response to the haptophyte Isochrysis galbana. In the bialgal mixtures, clearance and ingestion rates of I. galbana along the range of the functional response were significantly reduced as a result of selectivity towards the larger, alternative prey. Paradoxically, relatively large prey trigger a perception response in the nauplii, but most likely such prey cannot be completely ingested and a certain degree of sloppy feeding may occur. Our results are further evidence of the complex prey-specific feeding interactions that are likely to occur in natural assemblages with several available prey types, LH was funded by the Walter and Andrée de Nottbeck Foundation (http://www.nottbeck.org/en) and University of Helsinki (https://www.helsinki.fi/en). ES was funded by projects CTM2011-23480 and CGL2014-59227-R of the Ministerio de Economía, Industria y Competitividad (http://www.mineco.gob.es/portal/site/mineco/) (cofinanced with FEDER funds, EU) (http://ec.europa.eu/regional_policy/es/funding/erdf/)., Peer Reviewed

10 pages, 4 figures, 2 tables, In this study, we aim at disentangling the causes and consequences of diel feeding rhythms in marine microzooplankton. We focused on the diel feeding activity of two heterotrophic dinoflagellate species, Gyrodinium dominans (one laboratory strain) and Oxyrrhis marina (laboratory cultivated and wild strains). We observed higher ingestion during the day in both dinoflagellate species. Feeding rhythms appeared to be independent of circadian changes in prey biochemical composition. Grazers fed with prey under stationary phase, with equivalent stoichiometric composition between day and night, showed 5 (G. dominans) and 10 (O. marina) times higher ingestion rates during the day. Previous grazer feeding history (starved vs well-fed) did not affect the feeding rhythm. However, prey concentration altered the rhythm; food limiting conditions reduced the amplitude of the rhythms. Our results establish a resource dependence of diel periodicity in microzooplankton grazing, which can have unanticipated consequences for standard field dilution grazing experiments, This study was funded by project FERMI (CGL2014-59227-R; MINECO/FEDER, UE). Anna Arias was funded with a FPI fellowship (BES-2015-074092) from the MINECO of Spain, Peer Reviewed

This study is a contribution of the Marine Zooplankton Ecology Group (2014SGR-498) at the Institut de Ciències del Mar-CSIC.-- 11 pages, 5 figures, Planktonic copepods are a very successful group in marine pelagic environments, with a key role in biogeochemical cycles. Among them, the genus Oithona is one of the more abundant and ubiquitous. We report here on the effects of caloric (food) restriction on the ageing patterns of the copepod Oithona davisae. The response of O. davisae to caloric restriction was sex dependent: under food limitation, females have lower age-specific mortality rates and longer lifespans and reproductive periods; male mortality rates and life expectancy were not affected. Males are more active swimmers than females, and given their higher energetic demands presumably generate reactive oxygen species at higher rates. That was confirmed by starvation experiments, which showed that O. davisae males burn through body reserves much faster, resulting in shorter life expectancy. Compared with common, coastal calanoid copepods, the effects of caloric restriction on O. davisae appeared less prominent. We think this difference in the magnitude of the responses is a consequence of the distinct life-history traits associated with the genus Oithona (ambush feeder, egg-carrier), with much lower overall levels of metabolism and reproductive effort, This research was funded by projects CTM2011-23480 and CGL2014-59227-R of the Spanish Ministry of Economy, Industry and Competitiveness (co-financed with FEDER funds, EU), Peer Reviewed

11 pages, 5 figures, 3 tables, We report the effects of small-scale turbulence at realistic intensity (ε = 1.1 × 10 cm s) on the growth and grazing rates of three marine heterotrophic dinoflagellates (Peridiniella danica, Gyrodinium dominans and Oxyrrhis marina) and one ciliate (Mesodinium pulex). All the dinoflagellates showed a reduction of volume-based growth rates, whereas M. pulex did not. P. danica was the most affected by small-scale turbulence, followed by G. dominans, and O. marina. Turbulence slightly increased O. marina ingestion rates, but this increase was not statistically significant. G. dominans and M. pulex ingestion rates were modestly lower under turbulence, and P. danica completely ceased feeding in turbulent treatments. Gross growth efficiencies of G. dominans and O. marina were negatively affected by turbulence, whereas they remained unaltered for M. pulex. P. danica feeding and growth rates in the presence of turbulence were close to zero. Overall, there was a negative relationship between the effects of turbulence on ingestion rates and the time needed to process a prey item. Neglecting the effects of turbulence in microzooplankton grazing estimates in the field could produce biased approximations of their impacts on primary producers, Projects PROTOS (CTM2009-08783) and FERMI (CGL2014-59227-R) from the Spanish Ministry of Economy, Industry and Competitiveness (co-financed with FEDER funds from the EU). R.A.M. was funded by a PhD fellowship from the National Commission of Science (CONICYT), Ministry of Education, Chile, Peer Reviewed

Corrigendum Adaptive feeding behavior and functional responses in zooplankton https://doi.org/10.1002/lno.10804, 14 pages, 5 figures, 2 tables, supporting information https://doi.org/10.1002/lno.10632, Zooplankton may modify their feeding behavior in response to prey availability and presence of predators with implications to populations of both predators and prey. Optimal foraging theory predicts that such responses result in a type II functional response for passive foragers and a type III response for active foragers, with the latter response having a stabilizing effect on prey populations. Here, we test the theoretical predictions and the underlying mechanisms in pelagic copepods that are actively feeding (feeding‐current feeders), passively feeding (ambushers), or that can switch between the two feeding modes. In all cases, individual behaviors are consistent with the resulting functional response. Passive ambushing copepods have invariant foraging behavior and a type II functional response, as predicted. When foraging actively, the species with switching capability change its functional response from type II to III and modify its foraging effort in response to prey density and predation risk, also as predicted by theory. The obligate active feeders, however, follow a type II response inconsistent with the theoretical prediction. A survey of the literature similarly finds consistent type II response in ambush feeding copepods, but variable (II or III) responses in active feeders. We examine reasons for why observed behaviors at times deviate from predictions, and discuss the population dynamics and food web implications of the two types of functional responses and their underlying mechanisms, The Centre for Ocean Life is supported by the Villum Foundation. ES was funded by grant CGL2014-59227-R (MINECO/FEDER, UE), and P.T. by a sabbatical grant from University of Gothenburg, Peer Reviewed

9 pages, 5 figures, 2 tables, The dilution technique is the most widely used method to estimate microzooplankton herbivory in aquatic systems. This technique relies on the assumption that during the incubation phytoplankton growth is independent of the dilution factor; otherwise, biased estimates of microzooplankton grazing are obtained. To fulfil the requirement, nutrients should be routinely added to the dilution set. Here, we question the extent to which the assumption of equal phytoplankton growth along the dilution series might be actually met in the published experiments, even when nutrients are added. We also provide evidence that the violation of such assumption results in severely inflated estimates of microzooplankton grazing. Finally, we propose a simple procedure, based on the Redfield relationship, to overcome the problem and guarantee accurate results of dilution grazing experiments, This research was funded by project “Daily feeding rhythms in marine microzooplankton” FERMI (CGL2014-59227-R) of the Spanish Ministry of Economy, Industry and Competitiveness (co-financed with FEDER funds, EU), Peer Reviewed

The ubiquitous, biogenic trace gas dimethylsulfide (DMS) represents the largest natural source of atmospheric sulfur. Given DMS involvement in cloud formation and climate, understanding and parameterizing the oceanic DMS source and cycling processes is a necessary challenge. We report DMS cycling rates from microzooplankton dilution grazing experiments conducted monthly during 1 year in coastal northwestern Mediterranean waters. Concentrations of DMS, its algal precursor dimethylsulfoniopropionate (DMSPt) and chlorophyll a (Chla) ranged 0.9–11 nmol L−1, 10–71 nmol L−1, and 0.2–1.5 µg L−1, respectively. By comparing the growth and stock production rates of the DMSP-producing algae to those of total phytoplankton, we estimated that 3 ± 4% (range 0.4–12%) of the carbon primary production was invested in DMSP biosynthesis. Microzooplankton grazing rates on DMSP-producing phytoplankton (0.46–1.45 day−1) were generally higher than those on the bulk assemblage (0.08–0.99 day−1), except in midsummer months. This could have been due to the smaller size of most DMSP producers. There was no indication of micrograzer selection against DMSP-containing phytoplankton, since they were not grazed at lower rates than the bulk phytoplankton assemblage. A proportion of 6–20% of the grazed DMSP was converted into DMS, and this grazing-derived production accounted for 32–96% of dark gross DMS production by the total community. Bacteria consumed daily ≤ 14–100% of the gross DMS production, which resulted in biological DMS turnover times of 1 to ≥ 10 days. Throughout the year, grazing-mediated DMS production explained 73% of the variance in the DMS concentration, implying that microzooplankton grazing plays a major role in controlling DMS concentration in surface waters across a broad range of environmental and productivity conditions in the Mediterranean Sea. These findings should help improve the representation of herbivore grazing in prognostic models to predict the distribution and dynamics of the global DMS emission and its feedback response to changing climate, This work was supported by the Spanish Ministries of Science through the projects MICROROL (CTM2004-02575/MAR to A.C.), SUMMER (CTM2008-03309 to R.S.), BIOGAPS (CTM2016-81008-R to R.S.) and FERMI (CGL2014-59227-R to A.C. and E.S.), and PhD fellowships to V.S. and R.A., Peer Reviewed

19 pages, 11 figures, 5 tables, supplementary information https://doi.org/10.1038/s41598-019-38507-9, Oligotrophic and productive areas of the ocean differ in plankton community composition and biomass transfer efficiency. Here, we describe the plankton community along a latitudinal transect in the tropical and subtropical Atlantic Ocean. Prochlorococcus dominated the autotrophic community at the surface and mixed layer of oligotrophic stations, replaced by phototrophic picoeukaryotes and Synechococcus in productive waters. Depth-integrated biomass of microzooplankton was higher than mesozooplankton at oligotrophic stations, showing similar biomasses in productive waters. Dinoflagellates dominated in oligotrophic waters but ciliates dominated upwelling regions. In oligotrophic areas, microzooplankton consumed ca. 80% of the production, but ca. 66% in upwelling zones. Differences in microzooplankton and phytoplankton communities explain microzooplankton diel feeding rhythms: higher grazing rates during daylight in oligotrophic areas and diffuse grazing patterns in productive waters. Oligotrophic areas were more efficient at recycling and using nutrients through phytoplankton, while the energy transfer efficiency from nutrients to mesozooplankton appeared more efficient in productive waters. Our results support the classic paradigm of a shorter food web, and more efficient energy transfer towards upper food web levels in productive regions, but a microbially dominated, and very efficient, food web in oligotrophic regions. Remarkably, both models of food web exist under very high microzooplankton herbivory, This research was funded by projects Migrants and Active Flux in the Atlantic Ocean (MAFIA, CTM2012-39587-C04-01) to S.H.L. and Daily feeding rhythms in marine microzooplankton (FERMI, CGL2014-59227-R; MINECO/FEDER, UE) to A.C. L.A. was funded with a doctoral fellowship (BES-2013-063148) from the MINECO of Spain, Peer Reviewed

9 pages, 3 figures, 1 table, Temporal programs synchronised with the daily cycle are of adaptive importance for organisms exposed to periodic fluctuations. This study deepens into several aspects of the exogenous and endogenous nature of microbial grazers. We investigated the diel rhythms of cell division and feeding activity of four marine protists under different light regimes. In particular, we tested if the feeding cycle of protistan grazers could be mediated by a light-aided enhancement of prey digestion, and also explored the consequences of cell division on diel feeding rhythms. Cell division occurred at night for the heterotrophic dinoflagellates Gyrodinium dominans and Oxyrrhis marina. In contrast, the mixotrophic dinoflagellate Karlodinium armiger and the ciliate Strombidium sp. mostly divided during the day. Additionally, a significant diurnal feeding rhythm was observed in all species. When exposed to continuous darkness, nearly all species maintained the cell division rhythm, but lost the feeding cycle within several hours/days (with the exception of O. marina that kept the rhythm for 9.5 days). Additional feeding experiments under continuous light also showed the same pattern. We conclude that the feeding rhythms of protistan grazers are generally regulated not by cell division nor by the enhancement of digestion by light. Our study, moreover, indicates that the cell division cycle is under endogenous control, whereas an external trigger is required to maintain the feeding rhythm, at least for most of the species studied here, This work is supported by the FERMI project (CGL2014-59227-R; MINECO/AEI/FEDER, UE) and is a contribution of the Marine Zooplankton Ecology Group (2017 SGR 87). AA was funded with a FPI fellowship (BES-2015-074092) from the MINECO of Spain, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

13 pages, 5 figures, 1 table.-- Dataset: https://doi.org/10.20350/digitalCSIC/13882, 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), and is a contribution of the Marine Zooplankton Ecology Group (2017 SGR 87). Manuel Olivares is supported financially by a FPU Grant (FPU15/01747) from the Spanish Ministry of Education, Culture and Sport, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

10 pages, 2 figures, 2 tables.-- Our data will be archived in a data repository after publication.-- Dataset https://doi.org/10.20350/digitalCSIC/13883, 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, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI), Peer reviewed

11 pages, 6 figures, 2 tables, Microzooplankton play a pivotal role in the energy transfer between lower and upper trophic levels in marine planktonic food webs. While laboratory data suggest that microzooplankton exhibit higher feeding rates during the daytime, evidence from the field is scarce and contradictory. In this study, we first characterized the nano- and microplanktonic communities of the Gullmar Fjord (Sweden) and its environmental conditions during July and August 2017. Then, we explored the grazing impact of microzooplankton on the phytoplankton community of this ecosystem and assessed their diel grazing activity using the dilution technique. Finally, we evaluated the impact of mesozooplankton at natural concentrations during the experiments. Microzooplankton removed 26% of the phytoplankton standing stock and 96% of the primary production daily, while mesozooplankton did not exert a significant impact on microplankton activity. We did not detect significant diel microzooplankton grazing rhythms during the first experimental period; however, during the second part of the study, after an upwelling event, grazing rates were significantly higher during the night. Therefore, the microzooplankton grazing rhythm in natural systems may vary according to the species composition and abundances of both microzooplankton and prey communities, This study was funded by The Royal Swedish Academy of Sciences (KVA Fund) and the FERMI project 526 (CGL2014-59227-R; MINECO/AEI/FEDER, UE), and it is a contribution of the Marine Zooplankton Ecology Group 527 (2017 SGR 87). AA was funded with an FPI fellowship (BES-2015-074092) from the MICINN of Spain, With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI)

9 pages, 4 figures, 3 tables, supplementary information https://doi.org/10.1007/s00248-020-01665-9, We have assessed the effect of copepod chemical cues on the diel feeding rhythms of heterotrophic and mixotrophic marine protists. All phagotrophic protists studied exhibited relatively high diurnal feeding rates. The magnitude of the diel feeding rhythm, expressed as the quotient of day and night ingestion rates, was inversely related to the time that phagotrophic protists were maintained in the laboratory in an environment without predators. In the case of the recently isolated ciliate Strombidium arenicola, the rhythm was lost after a few months. When challenged with chemical alarm signals (copepodamides) from the copepod Calanus finmarchicus at realistic concentrations (0.6–6 pM), S. arenicola partially re-established diurnal feeding. Conversely, the amplitude of the diel feeding rhythm for the ciliate Mesodinium rubrum was not affected by copepodamides, although the 24-h integrated food intake increased by approximately 23%. For the dinoflagellates Gyrodinium dominans and Karlodinium armiger, copepodamides significantly reduced the amplitude of their diel feeding rhythms; significant positive effects on total daily ingestion were only observed in G. dominans. Finally, the dinoflagellate Oxyrrhis marina, isolated >20 years ago, showed inconsistent responses to copepodamides, except for an average 6% increase in its total ingestion over 24 h. Our results demonstrate that the predation risk by copepods affects the diel feeding rhythm of marine protists and suggests a species-specific response to predation threats, This work was supported by the FERMI project (CGL2014-59227-R; MINECO/AEI/FEDER, UE) and is a contribution of the Marine Zooplankton Ecology Group (2017 SGR 87). AA was funded with an FPI fellowship (BES-2015-074092) from the MICINN of Spain, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Peer reviewed