No abstract

Abstract. Microzooplankton grazing and algae growth responses to increasing pCO 2 levels (350, 700 and 1050 µatm) were investigated in nitrate and phosphate fertilized mesocosms during the PeECE III experiment 2005. Grazing and growth rates were estimated by the dilution technique combined with taxon specific HPLC pigment analysis. Microzooplankton composition was determined by light microscopy. Despite a range of up to 3 times the present CO 2 levels, there were no clear differences in any measured parameter between the different CO 2 treatments. During days 3-9 of the experiment the algae community standing stock, measured as chlorophyll a (Chl-a), showed the highest instantaneous grow rates (k=0.37-0.99 d −1 ) and increased from ca. 2-3 to 6-12 µg l −1 , in all mesocosms. Afterwards the phytoplankton standing stock decreased in all mesocosms until the end of the experiment. The microzooplankton standing stock, that was mainly constituted by dinoflagellates and ciliates, varied between 23 and 130 µg C l −1 (corresponding to 1.9 and 10.8 µmol C l −1 ), peaking on day 13-15, apparently responding to the phytoplankton development. Instantaneous Chl-a growth rates were generally higher than the grazing rates, indicating only a limited overall effect of microzooplankton grazing on the most dominant phytoplankton. Diatoms and prymnesiophytes were significantly grazed (12-43% of the standing stock d −1 ) only in the prebloom phase when they were in low numbers, and in the post-bloom phase when they were already affected by low Correspondence to: K. Suffrian

Copepods dominate the biomass of marine zooplankton and through their prey selection they act as top-down regulators of planktonic communities. We investigated feeding preference of copepods in the presence of the diatom Skeletonema marinoi at different time points throughout the development of a bloom and a culture. Quantitative PCR gut content assessment revealed that the food uptake of the copepod Calanus spp. on mixed diets and on artificially induced mesocosm blooms was selective. Uptake of S. marinoi was highest during the post-bloom phase in the mesocosms even if the abundance of this alga was already low. In laboratory assays, copepods showed a greater preference for S. marinoi in the late stationary phase than for cultures of the same strain under exponentially growing culture conditions. The copepods thus discriminate between different growth phases of a single algal species in both laboratory and field settings. In parallel, we monitored cellular metabolites of the diatom using a metabolomic approach. Complex changes in the metabolic profile occur during development of a culture. Since no obvious effect of nutrient quality and cell size was involved, we suggest that changes in (info)chemicals within or surrounding S. marinoi regulate selective feeding by zooplankton.

Quantification of feeding rates and selectivity of zooplankton is vital for understanding the mechanisms structuring marine ecosystems. However, methodological limitations have made many of these studies difficult. Recently, molecular based methods have demonstrated that DNA from prey species can be used to identify zooplankton gut contents, and further, quantitative gut content estimates by quantitative PCR (qPCR) assays targeted to the 18S rRNA gene have been used to estimate feeding rates in appendicularians and copepods. However, while standard single primer based qPCR assays were quantitative for the filter feeding appendicularian Oikopleura dioica, feeding rates were consistently underestimated in the copepod Calanus finmarchicus. In this study, we test the hypothesis that prey DNA is rapidly digested after ingestion by copepods and describe a qPCR-based assay, differential length amplification qPCR (dla-qPCR), to account for DNA digestion. The assay utilizes multiple primer sets that amplify different sized fragments of the prey 18S rRNA gene and, based on the differential amplification of these fragments, the degree of digestion is estimated and corrected for. Application of this approach to C. finmarchicus fed Rhodomonas marina significantly improved quantitative feeding estimates compared to standard qPCR. The development of dla-qPCR represents a significant advancement towards a quantitative method for assessing in situ copepod feeding rates without involving cultivation-based manipulation.

. (2016) Metabarcoding and metabolome analyses of copepod grazing reveal feeding preference and linkage to metabolite classes in dynamic microbial plankton communities. Molecular Ecology, 25 (21). pp. 5585-5602. Permanent WRAP URL:http://wrap.warwick.ac.uk/85060 Copyright and reuse:The Warwick Research Archive Portal (WRAP) makes this work by researchers of the University of Warwick available open access under the following conditions. Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners. To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.Copies of full items can be used for personal research or study, educational, or not-for profit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. Publisher's statement:This is the pre-peer reviewed version of the following article: Ray, J. L., Althammer, J., Skaar, K. S., Simonelli, P., Larsen, A., Stoecker, D., Sazhin, A., Ijaz, U. Z., Quince, C., Nejstgaard, J. C., Frischer, M., Pohnert, G. and Troedsson, C. (2016), Metabarcoding and metabolome analyses of copepod grazing reveal feeding preference and linkage to metabolite classes in dynamic microbial plankton communities. Mol Ecol, 25: 5585-5602. doi:10.1111/mec.13844, which has been published in final form at http://dx.doi.org/10.1111/mec.13844 . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP url' above for details on accessing the published version and note that access may require a subscription. Current address: Jenabios GmbH, Orlaweg 2, 07743 Jena, Germany. 31 Abstract 32In order to characterize copepod feeding in relation to microbial plankton community dynamics, 33we combined metabarcoding and metabolome analyses during a 22-day seawater mesocosm 34 experiment. Nutrient amendment of mesocosms promoted the development of haptophyte- Introduction 52The trophic efficiency of the marine food web depends upon the pathway of carbon flow from 53 primary production to predatory fish -either through the classical food web (diatoms to 54 mesozooplankton), the microbial food web (flagellates/bacteria to ciliates to mesozooplankton) Nejstgaard et al. 1997; 2001b, and further discussion on methods in Nejstgaard et al. 2008). Amplicon library preparation 148The universal primers F-1183mod and R-1443mod (Table 1) (Table S1). Primer F- using distance matrices (PERMANOVA) was performed using the adonis function in "vegan". 214Constrained correspondence analysis (CCA) was performed using the cca f...