A novel cross-disciplinary approach to solve an old enigma: the food-web transfer of the mass-blooming phytoplankter Phaeocystis.

-Big blooms of the phytoplankton species Phaeocystis pouchetii are commonly observed along the Norwegian coast and into the Barent Sea every spring during or right after, the seasonally occurring diatom bloom. The species is therefore (potentially) an important carbon source for zooplankton which in turn is food for larger animals. Phaeocystis may, however, be able to defend itself against grazing by establishing big colonies (so that the grazers find them too big to eat), or by excreting substances that have an antipredator effect (e.g. PUA = polyunsaturated aldehydes). Therefore one has wondered, and by means of traditional grazing methodology, tried to estimate how much of the biomass that actually is transferred to higher levels within the food web. Our recently developed molecular methods enable specific quantification of zooplankton feeding on Phaeocystis and have given us hopes that we may improve such estimates. The main aim of the current project was thus to investigate feeding by the dominating micro- and mesozooplankton in Norwegian waters using a combination of molecular and classical approaches. During the first year of the project we performed a mesocosm experiment and manipulated the plankton community in big seawater enclosures (mesocosms) in order to promote blooms of diatoms and/or Phaeocystis so that we could study grazing activity during these blooms. We investigated the microbial community (abundance and composition), nutrient conditions, chemical profiles and found that during both types of blooms the concentrations of PUAs were elevated, and the probable reason for the observed underestimation of grazing rates. We have published a paper in which we describe the situation and suggest methodology to reduce the underestimation (Stoecker et al. 2015). By 454-sequencing and quantitative PCR have we also produced data that enables us to tell what the dominating zooplankton actually ate and how large portion of the Phaeocystis cells they ate (Ray et al. under revision). During the second year of the project fourteen of us (from Norway, Sweden, Denmark, Germany, Russia and the US) went to the Barents Sea with FF Håkon Mosby in order to find natural blooms of Phaeocystis and just as for the mesocosm studied grazing in various parts of the food web. We found new and older blooms of Phaeocystis in the Barents Sea, Porsangerfjorden and Ulsfjorden and determined concentrations s of nutrients, virus, bacteria, phytoplankton and zooplankton. We also collected data for DNA, amino acid, and stable isotope signatures in the water and in the zooplankton guts. We measured bacterial production, grazing rates for various grazers and metabolic profiles from water and grazers. We recently submitted one paper from this study to L&O Method in which we show that the chemical composition of the water masses differs with age of the bloom and how this affect grazing measurements. Also in this paper we suggest how to improve the current methodology. We are still working to combine the combine the knowledge of metabolic profiles and molecular data at the various sites in order to analyze the efficiency of zooplankton grazing on Phaoecystis under different natural conditions. Several of the project participants participated on the Aquatic Mesocosm Research Symposium, October 16-19 2012 Heraklion, Greece in order to present results from the mesocosm experiment. In 2014 we participated with several contributions based on results from the project at the på IMBER Open Science Conference "Future Ocean" 23-27 juni i Bergen. Bernadette Pree won the prize for "The best student Oral Presentation" with her contribution "Phaeocystis pouchetii bloom from the perspective of heterotrophic bacteria". She was subsequently invited to publish it in IMBER Newsletter No. 27, sept 2014. Three participants Pree (UiB, Norway), Kuhlisch (Jena University, Germany) and Wolfram (Jena University, Germany) are in the process of finishing up their PhD thesis, and is due at the end of 2015, mid 2016 and end of 2016, respectively. Results from PHAEONIGMA are important part of all three thesis.

Phaeocystis spp. are key primary producers in the world oceans, and seasonally constitute the majority of total pelagic biomass at higher latitudes. The trophodynamics of these algae are therefore of key importance for understanding some of the largest ec osystems on Earth. Despite decades of investigations the quantitative knowledge about these algae as food for zooplankton and subsequent productivity of higher trophic levels is limited and contradictory. Recent results suggests that this is due to large errors in laboratory estimates, methodological difficulties, and lack of knowledge about the influence of chemical signaling including anti-predational metabolites in situ. However, our recently developed molecular methods enable specific quantification o f copepods and other zooplankton feeding on Phaeocystis in situ. Based on these, we propose to investigate feeding by the dominating micro- and mesozooplankton in Norwegian waters using a combination of molecular, specific stable isotope analysis and clas sical approaches. The dynamics of metabolites hypothesized to regulate the feeding on Phaeocystis (chemical signaling) will be simultaneously analyzed using cutting-edge metabolomic approaches. The project is based on a close cooperation by an established group of international leaders in their respective fields, and will develop Norwegian research skills and expertise through focus on training of young scientists in state-of-the-art methodology. To achieve a lasting effort towards gender equality we will promote female candidates combined with national and international network building. We have ambitious publication plans and anticipate considerable national and international interest. This project aims to establish advanced methodologies in quantitativ e aquatic ecology, and has a significant potential to increase the quantitative understanding of Phaeocystis in the global cycling of climate gases and transfer of energy to higher trophic levels, such as fisheries.