Our project will study the mid-trophic levels (zooplankton and micronekton) of the large pelagic ecosystems of the Pacific where more than 50% of the global tuna catches are produced. Zooplankton and micronekton are components linking the physical/chemical factors, which influence their distribution and abundance, with the megafauna (e.g. tuna, marine mammals, seabirds) which are their predators. The aim of our project is to fill the important gap in knowledge on the large pelagic ecosystems of the Pacific. Our goal is to bring scientific knowledge for a sustainable management of the pelagic resources by understanding the functioning of the pelagic ecosystems (from physics to intermediate levels) and by collecting observations to validate and improve ecosystem models used to analyse the tuna resources (SEAPODYM).

We propose a series of multidisciplinary cruise to collect seawater physical and chemical data as well as data on zooplankton and micronekton. The first cruise WARMALIS1 was conducted along the south-north transect WARMALIS1 between 20°S and 4°N along the longitude 163°E. The following cruises will cover another north-south transect (150°W) and one east-west transect (5°S) crossing the large pelagic ecosystems of the western and central Pacific in rich and poor areas in terms of tuna catches. To characterise physico-chemical conditions and primary production, we will measure temperature, salinity, oxygen, fluorescence, light, currents, nutrients, photosynthetic pigments, phytoplankton abundance, primary production, phytoplanktonic communities. Secondary production (zooplankton, micronekton) will be measured with acoustic (TAPS, S-ADCP, EK60) and net sampling of zooplankton and micronekton. A standardised sampling strategy has been established to collect micronekton (same depths and time at each station) to properly compare the various ecosystems crossed and avoid differences linked to day or night sampling or at different depths. Depth and time of the day are primordial parameters influencing micronekton biomass and diversity. Specialists in dynamic, acoustic, biogeochemistry, oceanography, biology and fisheries coming from different research institutions will collect, analyse and model observations on the mid-trophic levels. This cruise will be complemented by physical, chemical and biogeochemical modelling and by modelling of the pelagic ecosystem to include physico-chemical data, plankton and micronekton. Moreover, those observation data of micronecton will be analysed to validate the SEAPODYM ecosystem model with the objective of assimilating the observations to improve the model.