WP8 Impact on trophic interactions Two main foci: 1)The: C:N:P stoichiometry - food quality - TEP production – bacterial DOC consumption – algal/bacterial nutrient competition –– set of interactions. 2)Grazing vs viral lysis. Particularly for Ehux.

Idealized food web model Thingstad et al., J.Mar.Syst Higher pCO 2 increases the C:N (and C:P? ratio) What are the food web consequences of this? Does it matter whether bacteria are C or N(P,Fe) limited? Is the phyoplankton community structure important for the competitive balance between phytoplankton and bacteria (flagellates, Phaeocystis, small vs large diatoms…)?

Biodiversity aspect: Coexistence on one resource maintained by size- selective predation Thingstad et al., J.Mar.Syst. 2007

Same principle at higher level of resolution: Coexistence maintained by species-specific viral lysis Flag- ellate #1 Flag- ellate #2 Ehux Ciliates Virus #1 Virus #2 EhV Size-class (small flagellates) abundance controlled by size-selective predation. Species abundance controlled by lytic viruses. Fate of coccoliths different depending on whether predation or lysis is dominating? ”Up” the food chain ”Down” to DOM

WP 8 partner involved 1.1 LOV 2 UiB3 IFM 13 NIOZ 24 SOTON Impact on trophic interactions Task number Quantify the effects of acidification on predator-mediated mortality of autotrophic and heterotrophic microorganisms in the pelagic mesocosms studies Focus 1 & Focus 2 T8.1 XXXX Quantify the consequences of changes in prey quality (e.g. C:nutrient ratios as expected in task 8.1) for herbivorous predators in microcosms Focus 1 T8.2 XXX Quantify the consequences of changes in the bioavailability of algal exudates (as expected in task 8.1), also including indirect effects due to TEP enhanced cell aggregation, for predatory control by grazing and viral lysis in microcosms Focus 1 & Focus 2 T8.3 XX Determine the quantitative importance of coccoliths in reducing mortality due to predation and viral infection Focus 2 T8.4 XX XX

Task 8.1 Quantify the effects of acidification on predator-mediated mortality of autotrophic and heterotrophic microorganisms in the pelagic mesocosms studies Month: LOV Impact on grazing & viral lysis UiB IFM Impact of mesozoopl on phyto & micro NIOZ Estimate viral lysis & microzoopalnkton grazing SOTON Microcosms and mesocosms, time not specified D8.4 Datasets on predatory effects from pelagic mesocosm experiments (month 42; O, PP) Participate in mesocosms

Task 8.2 Quantify the consequences of changes in prey quality (e.g. C:nutrient ratios as expected in task 8.1) for herbivorous predators in microcosms LOV UiB IFM Food quality effects on development/ egg production NIOZ SOTON Mesocosms; 5 CO 2 -levels gradient design D8.3 Dataset on food quality effects on predators in pelagic microcosms (month 36; O, PP)

Task 8.3 Quantify the consequences of changes in the bioavailability of algal exudates (as expected in task 8.1), also including indirect effects due to TEP enhanced cell aggregation, for predatory control by grazing and viral lysis in microcosms LOVEffects on TEP formation & aggregation UiBFood web consequences of increased C:nutrient stoichiometry IPY meso- cosm Ny Ålesun d EPOC A mesoco sm NÅ MERCL IM cruise Svalbard IFM NIOZ SOT ON Microcosms D8.2 Dataset on ocean acidification effects on algal exudation and its consequences (month 36; O, PP)

Task 8.4 Determine the quantitative importance of coccoliths in reducing mortality due to predation and viral infection LOV UiB IFM NIOZ Lytic virus growth cycle studies SOTO N effect on omega calcite and on the proteomics signatures of coccolithophores. Also: molecular PhD student Lab experiments D8.1 Tipping point/risk assessment of ocean acidification effects on viral infection and predation on calcifying algae. Linking observations of calcification and performance (WP4 and WP6) to trophic interactions (WP8) (month 36; R, PU) Microcosms; pCO2, light and trace metal controlled, time not specified

Deliverable (without associated task) D 8.5 Improved model description(s) relating direct OA effects on organisms to properties of the lower pelagic food web linking WP8 to WP9 (month 36; O, PP) UiB will, in project MERCLIM (R.Bellerby), have a PhD student looking at how to incorporate microbiology into the Barents Sea model of D. Slagstad

Associated projects: SOTON : PhD student: in silico assessment of putative coccolithophore calcification genes, monitor the expression of selected candidate genes under low and high CO2 conditions representative of the modern ocean and future climate scenarios, and use confocal microscopy to assess sub- cellular localization of gene products. UiB: Acidification and viruses. PhD student Cátia Carreira (Vigo). 6 months exchange stipend from Norwegian Research Council. UIB: MERCLIM (R.Bellerby); Norwegian Research Council. Arctic ecosystem studies. UiB : PAME-Nor. Microbial consumption of DOC in Arctic waters.

DELIVERABLES WP 8 partner involved 1.1 LOV 2 UiB 3 IFM 13 NIOZ 24 SOTON Impact on trophic interactions Deliverable number Tipping point/risk assessment of ocean acidification effects on viral infection and predation on calcifying algae. Linking observations of calcification and performance (WP4 and WP6) to trophic interactions (WP8) (month 36; R, PU) D8.1 XX XX Dataset on ocean acidification effects on algal exudation and its consequences (month 36; O, PP) D8.2 XX Dataset on food quality effects on predators in pelagic microcosms (month 36; O, PP) D8.3 XXX Datasets on predatory effects from pelagic mesocosm experiments (month 42; O, PP) D8.4 XXXX Improved model description(s) relating direct OA effects on organisms to properties of the lower pelagic food web linking WP8 to WP9 (month 36; O, PP) D8.5 XXXXX