Mechanisms underlying regime shifts to picophytoplankton dominance in coastal water bodies

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Human populations load aquatic ecosystems with nutrients, leading to new anthropogenically driven phytoplankton community assemblages, in some cases dominated by small cells. Management efforts often fail to restore such systems, due to resilience of the newly established phytoplankton communities. I hypothesize that small phytoplankton taxa are coming to dominate not only their expected current ultra-oligotrophic niches, but also some emerging eutrophied systems, with effects on food web and ecosystem functions. The focus is on the picocyanobacterium Cyanobium. It has photosystems specially adapted to coastal waters and a year-round dominance is already described for some systems. Since especially coastal waters show a very dynamic change of environmental factors, I will use multifactorial approaches. The aim is to analyse the effect of ecophysiologically relevant environmental changes on the growth and function of small phytoplankton species, which are emerging coastal dominants. Environmental combinations (light, temperature, nutrients) will be initially tested in a high-throughput approach based upon parallel well plates with automated growth analyses. Subsequently, key environmental combinations will be studied in larger turbidostat units to test physiomic responses of phytoplankton to fluctuating environments. To achieve these studies I will test new hybrid-turbidostats to maintain environmental regimes. Outflow from the turbidostats will then inoculate downstream sterile batch microcultures, for short term experiments on the effects of inherited protein legacies and resource allocations in cells coming from different initial acclimation states. The inclusion of multiple interacting variables with important, but non-model species, will be risky, but our system understanding lacks dynamic hyper-dimensional approaches. The results will help formulate a new theoretical understanding of phytoplankton community successions in the Anthropocene.