Latitudinal changes of copepod egg production rates in Atlantic waters: Temperature and food availability as the main driving factors

Planktonic copepod abundance and egg production rates were determined in relation to temperature and chlorophyll concentration across a latitudinal transect in the Atlantic Ocean, ranging from 52"s to 24ON. Copepod distribution followed a pattern similar to that of chlorophyll a, with higher values at the southern latitudes. In contrast, egg production rates were significantly higher in the Atlantic intertropical zone, in the vicinity of the Equator. Copepod abundance was determined mainly by phytoplankton concentration, while rate processes (egg production rates) depended on chlorophyll a concentration and temperature. We propose multiple regression models including these 2 factors that explain up to 70% of the carbon specific egg production rates. The accuracy of these models versus previous ones including only temperature is also discussedhis study was financially supported by grant AMB94-0739 from the Spanish Interministerial Com- mission of Science and Technology (CICYT) to S A. and grants PN92-46651369 and EX96-46651369 from the Spanish Ministry of Universities and Research to A.C. IPeer reviewe

Copepod feeding in the ocean: Scaling patterns, composition of their diet and the bias of estimates due to microzooplankton grazing during incubations

16 pages, 9 figures, 1 table, electronic supplementary material in https://doi.org/10.1007/s10750-010-0421-6Here, we report insights from the compilation and analysis of data on marine calanoid copepod feeding rates in the ocean. Our study shows that food availability and body weight are major factors shaping copepod feeding rates in the field, with a relatively minor role of temperature. Although the maximal feeding rates of copepods that are observed in the field agree with the well-known 3/4 of body size scaling rule for animals, copepod feeding in the oceans is typically limited and departs from this rule. Ciliates and dinoflagellates appear to be highly relevant in the composition of copepod diets, and this represents an indirect increase in the flux of primary production that is likely to reach the upper trophic levels; this contribution is higher in the less productive systems and may help to explain accounts of proportionally higher standing stocks of copepods supported per unit of primary producer biomass in oligotrophic environments. Contrary to common belief, diatoms emerge from our dataset as small contributors to the diet of copepods, except in some very productive ecosystems. We have also evaluated the bias in the estimation of copepod grazing rates due to within-bottle trophic cascade effects caused by the removal of microheterotrophs by copepods. This release of microzooplankton grazing pressure accounts for a relevant, but moderate, increase in copepod grazing estimates (ca. 20-30%); this bias has an effect on both the carbon flux budgets through copepods and on our view of their diet composition. However, caution is recommended against the indiscriminate use of corrections because they may turn out to be overestimates of the bias. We advise that both uncorrected and corrected grazing rates should be provided in future studies, as they probably correspond to the lower and upper boundaries of the true grazing rates. © 2010 Springer Science+Business Media B.V.This study was supported by project OITHONA (CTM2007-60052) from the Spanish Ministry of Education and SciencePeer Reviewe

Caveats on the use of rotenone to estimate mixotrophic grazing in the oceans

11 pages, 5 figures, 2 tablesPhagotrophic mixotrophs (mixoplankton) are now widely recognised as important members of food webs, but their role in the functioning of food webs is not yet fully understood. This is due to the lack of a well-established technique to estimate mixotrophic grazing. An immediate step in this direction would be the development of a method that separates mixotrophic from heterotrophic grazing that can be routinely incorporated into the common techniques used to measure microplankton herbivory (e.g., the dilution technique). This idea was explored by the addition of rotenone, an inhibitor of the respiratory electron chain that has been widely used to selectively eliminate metazoans, both in the field and in the laboratory. Accordingly, rotenone was added to auto-, mixo-, and heterotrophic protist cultures in increasing concentrations (ca. 24 h). The results showed that mixotrophs survived better than heterotrophs at low concentrations of rotenone. Nevertheless, their predation was more affected, rendering rotenone unusable as a heterotrophic grazing deterrent. Additionally, it was found that rotenone had a differential effect depending on the growth phase of an autotrophic culture. Altogether, these results suggest that previous uses of rotenone in the field may have disrupted the planktonic food webThis project is a contribution of the Marine Zooplankton Ecology Group from the Generalitat de Catalunya (2017 SGR 87) and has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 766327With the funding support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), of the Spanish Research Agency (AEI

Metabolic rates and carbon budget of early developmental stages of the marine cyclopoid copepod Oithona davisae

12 pages, 6 figures, 3 tablesThe genus Oithona has been considered the most abundant and ubiquitous copepod in the world’s oceans. However, despite its importance, the metabolism of its developmental stages (nauplii and copepodites), crucial to explain their evolutionary success, is almost unknown. We determined respiration rates, ammonium and phosphate excretion rates, and the net growth efficiencies of early developmental stages of Oithona davisae as related to stage, body weight, temperature, and food availability. Respiration and excretion rates increased with increasing body weight and were positively related to temperature and food. Specific respiration rates of nauplii and copepodites varied from 0.11 to 0.55 d-1 depending on stage, body weight, temperature, and food availability. Metabolic C:N ratios were higher than 14, indicating lipid-oriented metabolism. Assimilation efficiencies and net growth efficiencies ranged from 65% to 86% and from 23% to 32%, respectively, depending on body weight, stage, and temperature. Assimilation efficiencies and net growth efficiencies estimated using the respiration rates of nauplii with food were 1.7 times higher and 0.6 times lower, respectively, than those calculated using respiration rates of nauplii without food. Therefore, the use of respiration rates measured in filtered seawater led to substantial bias on the estimations of zooplankton carbon budget. O. davisae developmental stages exhibited similar assimilation and growth efficiencies but lower carbon-specific respiratory losses than calanoid copepods. Hence, the low metabolic costs of Oithona compared with calanoids may be one reason for their success in marine ecosystemsThis work was funded by the Spanish Ministry of Science and Innovation (MICINN) through a Ph.D. fellowship to R.A. (BES-2005-7491) and the research projects CTM2004-02775 and Intramural-200630I226 to A.C., CTM2007-60052 to E.S., and CTM2006-12344 to M.A.Peer reviewe

Bridging the gap between marine biogeochemical and fisheries sciences; configuring the zooplankton link

Mitra, Aditee ... et. al.-- Special issue North Atlantic Ecosystems, the role of climate and anthropogenic forcing on their structure and function.-- 24 pages, 6 figures, 2 tablestrophic components interact. However, integrative end-to-end ecosystem studies (experimental and/or modelling) are rare. Experimental investigations often concentrate on a particular group or individual species within a trophic level, while tropho-dynamic field studies typically employ either a bottom-up approach concentrating on the phytoplankton community or a top-down approach concentrating on the fish community. Likewise the emphasis within modelling studies is usually placed upon phytoplankton- dominated biogeochemistry or on aspects of fisheries regulation. In consequence the roles of zooplankton communities (protists and metazoans) linking phytoplankton and fish communities are typically under-represented if not (especially in fisheries models) ignored. Where represented in ecosystem models, zooplankton are usually incorporated in an extremely simplistic fashion, using empirical descriptions merging various interacting physiological functions governing zooplankton growth and development, and thence ignoring physiological feedback mechanisms. Here we demonstrate, within a modelled plankton food-web system, how trophic dynamics are sensitive to small changes in parameter values describing zooplankton vital rates and thus the importance of using appropriate zooplankton descriptors. Through a comprehensive review, we reveal the mismatch between empirical understanding and modelling activities identifying important issues that warrant further experimental and modelling investigation. These include: food selectivity, kinetics of prey consumption and interactions with assimilation and growth, form of voided material, mortality rates at different age-stages relative to prior nutrient history. In particular there is a need for dynamic data series in which predator and prey of known nutrient history are studied interacting under varied pH and temperature regimes. © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY licenseAC is funded by the Ministry of Science and Innovation of Spain through project CTM2009-08783. AM was part funded by NERC UK project NE/K001345/1. KJF was funded by NERC UK through projects NE/H01750X/1 and NE/F003455/1. [...] This review was supported in part by project EURO-BASIN (Ref. 264933, 7FP, European Union), and by a Leverhulme International Network ‘‘Placing marine mixotrophs in context: modelling mixotrophy in a changing world’’Peer reviewe

The effect of short-term temperature exposure on vital physiological processes of mixoplankton and protozooplankton

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

Functional ecology of aquatic phagotrophic protists - Concepts, limitations, and perspectives

Special issue Current trends in protistology – results from the VII ECOP - ISOP Joint Meeting 2015.-- 25 pages, 6 figures, 1 tableFunctional 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 protistsHA 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 LiverpoolPeer Reviewe