Spring phytoplankton community response to an episodic windstorm event in oligotrophic waters offshore of East Sea in 2016

Abstract

Prior to and following an episodic windstorm event. we investigated the phytoplankton distribution and its relationship to environmental factors at 40 stations in oligotrophic waters offshore from the Ulleungdo and Dokdo islands in East Sea. In addition, in order to investigate the growth response of the phytoplankton assemblage and its nutrient consumption, we conducted nutrient addition bioassay experiments (control, +N, +P, and +NP, in both the presence and absence of added Fe) using surface seawater collected from stations 36 and 40, which are in the vicinity of the Dokdo. Field measurements showed that the surface water temperature ranged from 13.33°C to 16.l8°C and the salinity ranged from 34.03 to 34.55. The nitrate+nitrite, phosphate, and silicate concentrations varied from 0.07 to 2.22 &micro M, 0.01 &micro M to 0.19 &micro M and 0.76 to 6.93 &micro M, respectively. The Chl―a concentration varied from 0.36 to 15.97 &micro g L (average 2.66 士 3.26 &micro M), but was significantly higher in Zone III―a (Dokdo) than in Zone I―b (between Ulljin and Ulleungdo, prior to the wind storm), Zone 1-a(between Ulljin and Ulleungdo, following the wind storm), and Zone II―a(Ulleungdo) (F=17.438, p<0.001 ANOVA). Diatoms and Raphidophyta were the dominant phytoplankton types. Following episodic windstorm events the abundance of the raphidophyte Heterosigma akashiwo was maintained at high levels in the offshore oligotr. In addition, in order to investigate the growth response of the phytoplankton assemblage and its nutrient consumption, we conducted nutrient addition bioassay experiments (control, +N, +P, and +NP, in both the presence and absence of added Fe) using surface seawater collected from stations 36 and 40, which are in the vicinity of the Dokdo. Field measurements showed that the surface water temperature ranged from 13.33°C to 16.l8°C and the salinity ranged from 34.03 to 34.55. The nitrate+nitrite, phosphate, and silicate concentrations varied from 0.07 to 2.22 &micro M, 0.01 &micro M to 0.19 &micro M and 0.76 to 6.93 &micro M, respectively. The Chl―a concentration varied from 0.36 to 15.97 &micro g L (average 2.66 士 3.26 &micro M), but was significantly higher in Zone III―a (Dokdo) than in Zone I―b (between Ulljin and Ulleungdo, prior to the wind storm), Zone 1-a(between Ulljin and Ulleungdo, following the wind storm), and Zone II―a(Ulleungdo) (F=17.438, p<0.001 ANOVA). Diatoms and Raphidophyta were the dominant phytoplankton types. Following episodic windstorm events the abundance of the raphidophyte Heterosigma akashiwo was maintained at high levels in the offshore oligotr