Alkaline phosphatase activity of phytoplankton in East China Sea coastal waters with frequent harmful algal bloom occurrences

摘要

ABSTRACT: Alkaline phosphatase activity (APA) was measured during 3 cruises in spring 2002, 2003 and 2005 using bulk and single-cell assays in coastal waters in the East China Sea which experience frequent harmful algal bloom occurrences. The bulk APA ranged from below the detection limit to 73.53 nmol l^–1 h^–1, with mean values of 15.73 ± 14.12, 23.77 ± 15.20 and 11.48 ± 12.44 nmol l^–1 h^–1 for 2002, 2003 and 2005, respectively. The cell-bound fraction (mainly phytoplankton) was the major contributor to APA, with averages of 74 and 80% during 2003 and 2005, respectively. During the spring of 2005, most of the dominant dinoflagellates had high percentages of enzyme-labeled fluorescence (ELF)-labeled cells, while only a few diatoms and chrysophytes were labeled with ELF. Among the dinoflagellates, Protoperidinium spp. and Karenia mikimotoi had the highest percentages of ELF-labeled cells (84 and 82%, respectively), whereas Gonyaulax spp. and Dinophysis spp. had the lowest percentages of labeled species (17 and 21%, respectively). An alkaline phosphatase (AP) kinetic experiment was performed during 2005, with a turnover time of 10 h and a maximum potential velocity of 206.1 nmol l^–1 h^–1. The present results showed that severe phosphorus (P) stress occurred during springs in the study area, in particular when Prorocentrum donghaiense bloomed during 2003. AP played an important role in hydrolyzing soluble nonreactive phosphorus. The dominant dinoflagellates, which suffered more severe P stress compared to the diatoms, were the major AP producers during the spring of 2005, and differences in physiological P status existed among different dinoflagellate species.