Differential dissolved oxygen consumption during the decomposition of seven bloom-forming phytoplankton

Abstract Decomposition of bloom-forming organisms often causes coastal hypoxia. To predict hypoxia, the density of a bloom-forming species, its decline rate, and oxygen consumption rate during decomposition should be determined. To determine these parameters, the density of morphologically intact and partially decomposed (PD) cells, and dissolved oxygen (DO) concentrations during a five-day incubation in darkness were measured. Using these data, the decline rate of cell density (k decline ) and oxygen consumption rate per decomposed cell (OC decomposed cell ) of seven bloom-forming species, including diatoms Skeletonema dohrnii , Thalassiosira minuscula and Chaetoceros peruvianus , dinoflagellates Margalefidinium polykrikoides and Tripos furca , and nanoflagellates Teleaulax amphioxeia and Heterosigma akashiwo were calculated. Among the species, Te . amphioxeia had the highest k decline , 0.66 d − 1 , and M . polykrikoides had the highest OC decomposed cell , 69 pmol O 2 cell −1 d − 1 . k decline were species-specific and showed no correlation with cell carbon biomass, whereas OC decomposed cell showed positive correlation with cell carbon biomass. When DO during decomposition of the species were estimated based on k decline value of (1) intact cells only, (2) intact plus PD 0.5 cells, and (3) intact plus PD 1 cells, the estimates using intact plus PD 0.5 cells for dinoflagellates and intact plus PD 1 cells for the others were closest to the measured DO. Furthermore, the Q 10 coefficient calculated from the k decline for S . dohrnii determined at 15 and 25 °C was 3.1. The present study provides a foundation for understanding phytoplankton bloom dynamics and hypoxia formation at a species level.