Algal-bacterial interactions and aggregation: Implications for the plankton succession in neritic seas of the temperate zone in the course of climate change

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It is to be expected and partially already noticeable that, due to climate change and increasing temperatures, the development of phytoplankton blooms in neritic regions of the temperate zone undergoes changes. This is true for aggregation of diatoms in the course of the bloom development. Interactions with heterotrophic bacteria play an important role in aggregation processes, as has been found most recently. We hypothesize that with increasing temperatures in particular in spring aggregation and subsequent sedimentation will be enhanced such that fewer resources are available to the Zooplankton. This hypothesis will be tested with axenic and non-axenic cultures of four diatoms, which will be inoculated with bacterial pure cultures and defined mixed cultures and with bacterioplankton of the North Sea. Therefore, the excretion of transparent expopolymer particles and of dissolved organic material and its bacterial utilization and aggregation will be investigated in these cultures growing in rolling tanks as a function of the temperature between 4 and 20 °C. Further the aggregation potential of natural North Sea phytoplankton will be assessed as a function of temperature.