Red tides in Masan Bay, Korea in 2004–2005: I. Daily variations in the abundance of red-tide organisms and environmental factors

Abstract

To investigate red tides in Masan Bay, Korea, in which red tides have frequently occurred, we measured the abundance of red-tide organisms at a fixed station daily from June 2004 to May 2005. We daily measured physical, chemical, and biological properties. During the study period, 36 red-tide events occurred. Of these, 7 events were overwhelmingly dominated by cryptophytes, 5 by phototrophic dinoflagellates, 2 by diatoms, 2 by raphidophytes, 1 by a mixotrophic ciliate, and the rest by mixtures of several taxonomic groups. The durations of the red-tide events ranged from 1 to 40 days and total duration was 195 days. Most of the red tides occurred between June and September 2004 and between January and March 2005. The maximum abundance and biomass of total phototrophic dinoflagellates were 27,183cellsml−1 and 3516ngCml−1, respectively, while those of total diatoms were 71,538cellsml−1 and 10,981ngCml−1, respectively. Furthermore, the maximum abundance and biomass of total raphidophytes were 90,010cellsml−1 and 10,177ngCml−1. The biomass of total phototrophic dinoflagellates had significant positive correlations with salinity, pH, dissolved oxygen, euglenophytes, raphidophytes, cyanobacteria, and heterotrophic bacteria, but negative correlations with temperature, nitrite plus nitrate and phosphate concentrations. In addition, the biomass of raphidophytes had a significant positive correlation with temperature, pH, and heterotrophic bacteria, but a negative correlation with salinity and the phosphate concentration. This evidence suggests that red-tide dynamics dominated by these phototrophic dinoflagellates and raphidophytes may be mainly affected by potential prey concentrations rather than inorganic nutrient concentrations. Daily sampling is necessary to explore red-tide dynamics in Masan Bay because the generation time of the causative species is ∼0.5–3 days.