Seasonal phytoplankton growth and distribution pattern by environmental factor changes in inner and outer bay of Ulsan, Korea

Abstract

To assess the relationship between environmental factors and seasonal phytoplankton community structure, we investigated abiotic and biotic factors in Ulsan Bay, Korea. We divided the bay into two areas based on geographical characteristics and compared the difference in each factor between inner bay and outer bay with t-test statistics. As a result, temperature in the outer bay was higher than that of the inner bay during winter and autumn. However, opposite trend was observed during spring and summer. Salinity was significantly lower in the inner bay than that of the outer bay in winter, spring, and summer (p < 0.01). However, the salinity was not significant different between the inner bay and the outer bay in the autumn (p > 0.05). In particular, high nutrient concentration was observed in most stations during winter season due to vertical well mixing. The nutrient concentration was significantly higher in surface layers of inner bay after rainfall, particularly in the summer. The relative contribution of < 20 &micro m (nano and pico) size phytoplankton was increased in all seasons with continuously low nutrients from the offshore water due to their adaption to low nutrient without other large competitors. Interestingly, high population of Eutreptiella gymnastica was kept in the inner bay during the spring and summer associated with high DIN after river discharge following rainfall, suggesting that DIN supply mig and compared the difference in each factor between inner bay and outer bay with t-test statistics. As a result, temperature in the outer bay was higher than that of the inner bay during winter and autumn. However, opposite trend was observed during spring and summer. Salinity was significantly lower in the inner bay than that of the outer bay in winter, spring, and summer (p < 0.01). However, the salinity was not significant different between the inner bay and the outer bay in the autumn (p > 0.05). In particular, high nutrient concentration was observed in most stations during winter season due to vertical well mixing. The nutrient concentration was significantly higher in surface layers of inner bay after rainfall, particularly in the summer. The relative contribution of < 20 &micro m (nano and pico) size phytoplankton was increased in all seasons with continuously low nutrients from the offshore water due to their adaption to low nutrient without other large competitors. Interestingly, high population of Eutreptiella gymnastica was kept in the inner bay during the spring and summer associated with high DIN after river discharge following rainfall, suggesting that DIN supply mig