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18 pages, 9 figures, 4 tables, The cyclopoid copepod Oithona similis is one of the most abundant copepods in the oceans and has a potentially important role in pelagic food webs. However, there is a lack of knowledge on aspects of its biology and function in planktonic communities. In the present study, we aimed to assess and compare the species’ trophic role in Greenlandic coastal waters during the winter-spring transition, with a focus on its winter behaviour, when large calanoids are not present in the surface layer. Two locations were studied: waters offshore from Godthåbsfjord (Nuuk) in winter, and Qeqertarsuaq (Disko Bay) in spring (bloom and post-bloom period). The potential prey of adult females of O. similis was quantified, and grazing experiments were conducted to determine the feeding rates of adult females on phytoplankton and protozooplankton >10 µm. The abundance, stage composition, and egg production of O. similis was also investigated. Ciliates were the preferred prey for O. similis, which confirms its importance as a link between the microbial food web and higher trophic levels. We observed high egg production rates and efficiencies of O. similis in winter, confirming that it is active and successfully reproductive in food-limited winter conditions. Our results stress that O. similis is a key component of Arctic and subarctic marine communities throughout the year, We thank the Greenland Institute of Natural Resources in Nuuk for excellent laboratory facilities, K. Arendt for helping with laboratory logistics, and F. Heinrich for helping on board the boat ‘Erisaalik’ during the samplings in Godthåbsfjord. We also thank the Arctic station in Qeqertarsuaq (University of Copenhagen) for providing an excellent working platform and ship time, and the crew of the RV ‘Porsild’ for enthusiastic help during sampling. We also thank N. Lundholm for her advice on diatom and protozooplankton identification. This research was funded by the Greenland Climate Research Centre through the project 6505 to T.G.N. and the European Commission FP7 EURO-BASIN (grant agreement: 264 933). The Spanish Ministry of Economy and Competitiveness supported this work through the projects CTM2007-60052, CTM2010-10036-E, and CTM2011-23480 to E.S. (2009SGR-1283) and a PhD fellowship (BES-2008-004231) and mobility grant to S.Z.T. We thank J. Turner for English editing and 2 anonymous reviewers for their positive comments on the manuscript

The effects of temperature and food availability on feeding and egg production of the Arctic copepod Calanus hyperboreus were investigated in Disko Bay, western Greenland, from winter to spring 2009. The abundance of females in the near bottom layer and the egg production of C. hyperboreus prior to the spring bloom document that reproduction relies on lipid stores. The maximum in situ egg production (± SE) of 54 ± 8 eggs female −1 d −1 was recorded in mid-February at chlorophyll a concentrations below 0.1 µg l −1 , whereas no egg production was observed in mid-April when the spring bloom developed. After reproduction, the females migrated to the surface layer to exploit the bloom and refill their lipid stores. In 2 laboratory experiments, initiated before and during the spring bloom, mature females were kept with and without food at 5 different temperatures ranging from 0 to 10°C and the fecal pellet and egg production were monitored. Food had a clear effect on fecal pellet production but no effect on egg production, while temperature did not have an effect on egg or fecal pellet production in any of the experiments. Analyses of carbon and lipid content of the females before and after the experiments did not reflect any effect of food or temperature in the pre-bloom experiment, whereas in the bloom experiment a clear positive effect of food was detected in female biochemical profiles. The lack of a temperature response suggests a future warmer ocean could be unfavorable for C. hyperboreus compared to smaller Calanus spp. which are reported to exploit minor temperature elevations for increased egg production.

We utilized the varying fatty acid composition of phytoplankton to create 19 different food treatments based on different ratios of 5 potentially important fatty acids and offered these to the copepod Temora longicornis. Egg production and hatching was monitored and related to ingested carbon, dietary fatty acids and the utilization of maternal fatty acid reserves. Egg production rates depended on ingested carbon and the fatty acid 20:5n-3 from the diet and from the female reserves. Hatching success showed a significant dependence on the ingested and maternal fatty acids 22:6n-3, 18:5n-3 and 18:3n-3. Production of nauplii as a combination of egg production and hatching was highly dependent on the fatty acid 22:6n-3 and carbon ingestion. The study confirms the importance of n-3 polyunsaturated fatty acids for copepod reproduction and indicates that the female differen- tially utilizes its fatty acid reserves depending on dietary fatty acid availability during reproduction and that egg production and hatching are dependent on different dietary fatty acids.

A unialgal diet of a non-neurotoxic strain of the dinoflagellate Alexandrium tamarense strongly modified egg production and hatching success in the copepod Temora stylifera, even though grazing rates were relatively constant over time. Both exponential and stationary cultures of A. tamarense reduced egg production and hatching success, but the effect of stationary cultures on hatching success was dramatic, with egg viability dropping to 0% after 24 h of feeding. HPLC analy- ses revealed that the A. tamarense clone was non-neurotoxic, with a mean toxin content of about 0.005 fmol per cell, indicating that adverse effects were not due to saxitoxins or neosaxitoxins. 1 H-NMR analyses also revealed that diatom-derived PUSCAs (polyunsaturated short-chain alde- hydes) were not responsible for reduced hatching rates, since these compounds were absent in A. tamarense as compared to the diatom Skeletonema costatum. Extracts of A. tamarense and the diatom-derived PUSCA 2-trans-4-trans-decadienal were also assessed in terms of biological effects on sea urchin embryo cell divisions. A. tamarense did not show anti-mitotic properties, as extracts did not block first-cell cleavage compared to decadienal. However, A. tamarense extracts did block fer- tilization success when sea urchin oocytes were first incubated for 30 min in extracts and then fertil- ized, as opposed to S. costatum extracts, which did not affect normal elevation of the fertilization membrane. This is the first report that dinoflagellates produce antiproliferative compounds, other than PUSCAs, that can potentially reduce copepod egg production and hatching success.

11 pages, 8 figures, 6 tables, Egg production rates of the copepods Centropages typicus, Clausocalanus lividus and Temora stylifera were determined in the temperate oligotrophic western Mediterranean during late spring and early summer. Egg production appeared to be severely limited and related to the concentration of >5 μm chlorophyll. Although phytoplankton can partially explain the observed gradient in egg production from coastal waters towards the open sea, it is not sufficient to explain the recorded egg production rates, and other non-pigmented items (microzooplankton) must be important components of the copepod diet. Copepod growth rates appeared uncoupled to the pattern in copepod abundance from coastal to oceanic waters, suggesting the role of other factors such as predation or advection in determining their distribution

International audience; A detailed individual-based model of egg production of Calanus finmarchicus is proposed. Female growth and egg production are represented by 8 state variables (gut content, nutrient pool, structural body, oil sac, and 4 stages of oocyte maturation) which are regulated by physiological processes. Clutch size is set constant under continuous food conditions, but the spawning interval changes with food availability and temperature depending on the rate of oocyte maturation. Smaller clutches can occur when eggs are released under bad external conditions. Thus changing conditions can produce different clutch size distributions. For model validation, egg production experiments were conducted under different constant and fluctuating food concentrations and compared with model simulations. In the experiments, egg production was strongly affected by food fluctuation. In experiments with alternating feeding and starvation cycles integrated egg production was affected by mean food concentration during the experiment rather than by the frequency of the cycles. The model reproduces correctly the egg production rates and final body carbon of females kept in the different food regimes. It provides a dynamical explanation of physiological responses of the individual under short-term food variation. When food becomes unavailable, the most advanced oocytes are released and egg production continues until the nutrient pool decreases below a minimal critical value. Thereafter, no eggs are laid. When food reappears, somatic growth resumes until structural body weight is restored, then oogenesis is fuelled. Experimental results were simulated correctly without using matter from the lipid pool