Effect of silicate and inorganic carbon availability on the growth and competition of a diatom and two red tide dinoflagellates

Abstract

:The influence of silicate and inorganic carbon availability on the growth of three common algal species, namely, the diatom Skeletonema costatum (Coscinodiscophyceae) and the dinoflagellates Prorocentrum minimum and Alexandrium tamarense (Dinophyceae), was studied. Competition experiments using these three species were performed under different conditions to determine the dominance of red tide algal species in certain marine environments. Skeletonema costatum outgrew the two dinoflagellates in the silicate-replete medium as a result of its high growth rate. However, the cell density of S. costatum decreased with reduced silicate and changed inorganic carbon availabilities. Skeletonema costatum stopped growing when the inorganic carbon concentration was doubled at a constant pH of 7.7, which may have resulted from the enhanced growth of the two dinoflagellates. Prorocentrum minimum and A. tamarense became dominant at constant pH 7.7 conditions. As a component of the CO2 concentrating mechanism (CCM), extracellular carbonic anhydrase (eCA) showed significantly lower activities in S. costatum under low-silicate and constant pH 7.7 conditions; whereas, the P. minimum eCA activity remained almost unaffected. Different eCA responses to reduced silicate and varied carbon sources suggested that the species differed in inorganic carbon acquisition. The results suggested that patterns of species dominance of bloom-forming microalgae may be related to silicate and inorganic carbon availabilities.