Adaptation of Synechococcus in situ determined by variability in intracellular phycoerythrin-543 at a coastal station off the Southern California coast, USA

Abstract

Concentrations of extracted phycobiliproteins were measured a t a station off the Southern California coast, USA, from November 1985 to March 1986. The main pigment found was phycoerythrin-543 (PE) from Synechococcus spp. as described by Alberte et al. (1984). Concentrations of PE in water column, between 3 and 40 m, varied between 0.01 and 1 60 pg 1-' Maximum values were found between 3 and 22 m. In situ concentrations of PE were posit~vely correlated with cell numbers of Synechococcusspp., which ranged from 1.4 to 116 X 106 cells I-', and showed maximal values between 3 and 13 m. Because no other types of PE were detected, all PE measured was considered to come from Synechococcus-type cells. Cellular concentrations of PE varied between 2.1 and 40.3 X 10-' pg PE cell-', with an average value of 10 5?4.1 X IO-' vg PE cell-' above the 1 % isolume for PAR (Photosynthetically Available Radiation). Pigment per cell increased consistently with depth dunng autumn and spring and had low and relatively constant values in the winter. High PE:cell (>20 X lO-' pg PE cell-') was observed only below the 1 % isolume for PAR. For all samples, cellular concentration of PE was inversely correlated with incident PAR and was positively correlated to dissolved inorganic nitrogen (nitrate) concentration. Cyanobactena were not a dominant component of phytoplankton standing stock during this study, contributing an estimated 4 to 15 O/O of total chlorophyll in the water column, but had high specific growth rates, with maximal values of >0.75 d-' close to the surface. Absorption of light at 540 nm, as measured by in vivo absorption spectra of phytoplankton, was not correlated with PE concentration in the water column.