Specific absorption coefficient and phytoplankton community structure in the southern region of the California Current during January 2002

Abstract

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 Nina 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.