Current status of green tide exposed to different nitrogen sources in Jeju Island, Korea

Abstract

In recent decades, massive algal bloom caused by Ulva spp. have become global phenomenon. It might be attributed to costal eutrophication caused by over-enrichment nutrient loads. Jeju Island is strongly affected by several nutrient sources such as groundwater, fish farm effluents and wastewater with high nitrogen concentrations. Massive green tides along the entire coast of Jeju Island have been found all year round in the early 2000s. In this study, to elucidate current status of green tide caused Ulva spp., area of green tide and biomass variation of Ulva spp. was investigated at seven sites exposed to different nutrient sources such as fish farm effluents, ground water and waste water. Water temperature, underwater light irradiance, salinity, pH and water column nutrients (NH4+, NO3-+NO2-, PO43-) concentrations were also measured bimonthly. U. ohnoi and U. pertusa were chiefly observed very every sampling occasion. Biomass of Ulva spp. was higher in sites affected various nutrient sources, than other study sites which is ambient nutrient sites. Biomass of Ulva species gradually increased with water temperature. Total area covered by Ulva mat was approximately 45,000m2 in July. Our results imply that green tide in Jeju Island may be affected by various environmental conditions, but a continuous investigation is needed to establish more detail information for green tides by multiple nutrient source.