Primary production and community structure of coastal phytoplankton in the Adriatic Sea: insights on taxon-specific productivity

We examined the relationship between phytoplankton primary production, biomass and community structure in a 2-year in situ survey in a predominantly bottom-up limited coastal sea (Gulf of Trieste, Adriatic Sea). Our results suggest that nutrient supply primarily shapes the phytoplankton community structure, which in turn governs the magnitude of primary production through the relative contribution of different phytoplankton groups and their group-specific chl anormalized primary production. Non-metric multidimensional scaling analysis with superposed thin plate regression splines was used to relate chl a-normalized primary production with each phytoplankton group, of which cyanobacteria were associated with the highest and diatoms with the lowest chl a-normalized primary production (>5 and 1–2 mg C [mg chl a]−1 h−1, respectively). However, both groups were associated with periods of high primary production, highlighting the taxonomic differences in phytoplankton functional traits. Annual primary production for the years 2010 and 2011, characterized by different nutrient availability especially during summer, was estimated at 87.4 and 60.2 g C m−2, respectively. Hence, even short-lived freshwater pulses during the annual irradiance maximum, sustaining a diatom-dominated assemblage rich in biomass, can substantially increase the annual primary production.