Specific absorption coefficient and phytoplankton community structure in the southern region of the California Current during January 2002
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Measurements of the specific absorption coefficients of phytoplankton (a*ph) are currently required to estimate primary productivity at regional to global scales using satellite imagery. The variability in a*ph and phytoplankton size fraction was determined during January 2002 in the southern region of the California Current. Median values of a*ph at 440 nm and 674 nm were 0.061 and 0.028 m2 (mg Chl-a)−1 and significant variability was found between inshore and offshore stations. A decrease of a*ph is associated with increased phytoplankton abundance and larger species. The a*ph tends to be high when the photoprotector zeaxanthin is present in elevated concentrations and phytoplankton abundance lower. The nano-microphytoplankton (>5 µm) community consisted of 28 diatom and 15 dinoflagellate genera with mean abundance values of 2.8 and 1.6 × 103 cells l−1, respectively. The picophytoplankton (<5 µm) community consisted of Prochlorococcus sp. (mean 8.2 × 106 cells l−1) and Synechococcus sp. (mean 19.5 × 106 cells l−1), as well as a mixture of picoeukaryotes (mean 8.6 × 106 cells l−1). The contributions of nano-microphytoplankton and picophytoplankton to the total biomass (µg C l−1) were 46% and 54%, respectively. This study showed that picophytoplankton cells increased 2.5 times up during January 2002 compared with the previous year. It was concluded that the waning of La Niña conditions had a clear effect on the pelagic ecosystem in January 2002 and that the higher microphytoplankton abundance in the California Current was dominated by local and regional seasonal processes.
KeywordsSpecific absorption phytoplankton flow cytometry HPLC-pigments California Current
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