Use of intracellular amino acid analysis as an indicator of the physiological status of natural dinoflagellate populations

Abstract

The physiological status of 2 dinoflagellate populations in Bantry Bay, Ireland, was examined by use of amino acid analys~s. Observations were made durlng two 24 h periods. In one, during an upwelling event, the phytoplankton population was of low density (ca 1 yg chl a I ' ) and dominated mainly by Ceratium, Prorocentrum and Scrippsiella species. In the second (1 wk later), following relaxation of the upwelling and an incursion of surface water from the adjacent open coastal region, the phytoplankton community was dominated by Ceratium spp. and Gyrodiniurn aureolum with chl a concentrations up to 10 times higher. During the first sampling period, there was evidence of slight N-stress at the surface; the ratio of intracellular glutamine/glutamate (Gln/Glu) was 0.35, increasing with ammonium spiking There was evidence of C-stress at the chl maximum, where Gln/Glu was high (1.2) and decreased on exposure to increased irradiance. During the second samphng period, Gln/Glu was low (0.1) suggesting a poor N-status. However, there was little or even a negative response of Gln/Glu to ammonium splking; glutamate responded to the spiklng rather than glutamine. The general composition of the intracellular amino acid pool was similar to that at the first period, with high proportions of N-rich amino acids such as arginine. This second population appeared to be physiologically damaged in some way; this would not appear to have been simply a result of N-stress, but perhaps reflected the consequences of the associated advective process and exposure of the algae to high photon flux densities. The concentration of dissolved free a m n o acids (DFAA) during the second period was up to 4 times higher than at the first, but still dominated by serine and glycine. DFAA appeared to relate more to the presence of zooplankton than to the phytoplankton.