Sampling at the western English Channel observatory dates back approximately 100 years, with a more complete sampling programme since 1988. The data set in this study was collected over a five year period between 2001 and 2005. The variables measured allow for a more complete understanding of the ecosystem, this is the only study to have reported the photo-physiology measurements over such time scales. The western English Channel is situated in a boundary zone between the oceanic waters of the Northern Atlantic and the coastal waters of the English Channel. This study has provided substantial evidence that the phytoplankton functional type (PFT) succession is governed by the environmental drivers (irradiance, surface water temperature and nutrient availability) and as the environmental conditions vary each year so does the phytoplankton seasonal succession. The relationships between the phytoplankton pigment assemblage, with particular interest to the ratios of chlorophyll a, photo-synthetic and photo-protective carotenoids to total pigment concentration, are investigated. The chlorophyll a to Total pigment ratio (Chla/TP) is reported to increase in conditions conducive for growth and decrease when conditions are less favourable, this is related to both PFTs synthesising Chla preferentially in periods of growth and a shift in the community structure. The photo-physiology of the PFT community indicated relatively high values of Fv/Fm throughout the whole time series, adding further evidence of community shifts where PFTs adapted to the particular conditions. The σpsII was shown to be one of the mechanisms by which PFTs adapt to the environmental conditions. σpsII is high in low light regimes and is reduced when irradiance levels are high. The optical absorption by phytoplankton is shown to correlate with the pigment ratio (Chla/TP) and to a lesser extent σpsII. No consistent correlations between the Fv/Fm and the optical absorption could be identified.

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