Genotypic and phenotypic variability in temperate marine picophytoplankton related to vertical mixing

Summary

Phytoplankton irradiance exposure (intensity and spectral composition) is strongly influenced by physical processes in the ocean. Stratification traps phytoplankton in the upper water layer, thereby enhancing ultraviolet radiation (UVR: 280-400 nm) and excessive photosynthetically active radiation (PAR: 400-700 nm) exposure.

In contrast, deep vertical mixing leads to low mean irradiance levels. Although sunlight is required for photosynthesis, excess irradiance can cause adverse effects that range from reduced photosynthetic efficiency (photoinhibition) to viability loss. However, excess irradiance effects depend on photoacclimation, a process by which algae balance photosynthesis and photoprotection during irradiance changes and on nutrient availability. It is expected that climate change affects the onset and break-up of stratification in temperate and warm-temperate oceanic regions. Because phytoplankton productivity provides the basis of open ocean ecosystems and, moreover, a feedback for anthropogenic carbon emissions, it is essential to understand how stratification and mixing affects phytoplankton performance. This recently finished (2013) project was a combination of ecophysiological laboratory studies using prokaryotic and eukaryotic picophytoplankton isolates and two field campaigns in the North Atlantic Ocean. In order to start laboratory experiments, a picophytoplankton culture collection was started, including the key oceanic species Prochlorococcus spp. and Synechococcus spp. Experiments were conducted studying photoacclimation potential of five key picophytoplankton species, using our computer controlled dynamic irradiance set-up. In addition, photoacclimation and photoregulation of these key species were studied as a function of increased temperature and nutrient availability. This work has resulted in a PhD thesis (G. Kulk, thesis defence date September 6, 2013).

(NWO-ALW)