Zooplankton are major consumers of phytoplankton primary production in marine ecosystems. As such, they represent a critical link for energy and matter transfer between phytoplankton and bacterioplankton to higher trophic levels and play an important role in global biogeochemical cycles. In this Review, we discuss key responses of zooplankton to ocean warming, including shifts in phenology, range, and body size, and assess the implications to the biological carbon pump and interactions with higher trophic levels. Our synthesis highlights key knowledge gaps and geographic gaps in monitoring coverage that need to be urgently addressed. We also discuss an integrated sampling approach that combines traditional and novel techniques to improve zooplankton observation for the benefit of monitoring zooplankton populations and modelling future scenarios under global changes.

12 pages, 4 tables, 4 figuresGrazing by microzooplankton is typically assessed by dilution experiments of the whole natural community. However, in many ecosystems these experiments actually include not only micrograzers but also nanograzers. We discerned the relevance of micro- and nanograzers under contrasting trophic situations in the coastal NW Mediterranean throughout a seasonal cycle. We measured the grazing upon total, 10 μm chlorophyll a in 11 standard dilution experiments. We also conducted simultaneous dilution experiments with the 100% of the primary production consumed daily in July and August (the average impact for the whole study period was 58%). Grazing impact on >10 μm cells was very low, only significant in 5 out of 11 experiments (average impact of 23% of the >10 μm primary production consumed daily, range 23 to 71%). When the entire microbial community was size-fractioned by 10 μm, the potential impact of 10 μm organisms) weakly control the primary producers during the cold season (winter and most of the autumn), switch to nano-sized heterotrophic prey during spring, partially suppressing the impact of this group on phytoplankton, and finally are replaced by nanograzers during the warmer months (end of the summer period), heavily impacting the dominant small primary producers.This work was funded by grant CTM2004-02575/MAR from the Ministry of Education and Science of Spain, PhD fellowship to R.A. and V.S. from the same ministry, and an I3P contract to L.Y. from the CSIC. We thank 3 reviewers and R.W. Sanders for their very helpful and constructive commentsPeer reviewe

A simple method for the assay of aminoacyl-tRNA synthetases (AARS) activity was modified for application in planktonic crustaceans as an index of somatic growth. The cladoceran Daphnia magna was cultured in the laboratory and its AARS activity measured without substrate addition. The relationship between the enzyme activities of animals of similar age and individual biomass growing at different rates was tested. A significant relationship was found between AARS activity and somatic growth in terms of both protein and dry weight.