Effects of Nutrient Addition on Phytoplankton Growth in the Coastal Waters of Kagawa Prefecture, Eastern Seto Inland Sea, Japan

¹ Faculty of Food Biotechnology and Innovation, Assumption University of Thailand, Bangkok, Thailand
² Faculty of Agriculture, Kagawa University, Kagawa, Japan

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

This research explores the effects of nutrient addition on phytoplankton growth. In marine ecosystems, nutrients refer to dissolved inorganic nitrogen (DIN), phosphorus (DIP) and dissolved silica (DSi). These nutrients often directly limit the growth of phytoplankton—the main primary producer and the fundamental food source for higher trophic organisms in marine ecosystems. This study conducted nutrient addition experiments on phytoplankton growth in the Seto Inland Sea, an area currently facing oligotrophication due to rapid seawater quality improvement, which may be affecting phytoplankton species composition and contributing to a decrease in fisheries yields. Seawater was incubated in enrichment experiments over 48 hours for each nutrient, with chlorophyll a measured as an indicator of phytoplankton biomass. Results showed increased phytoplankton growth only in nitrogen-enriched (nitrate-enriched) samples, indicating that DIN was insufficient when compared to the other essential nutrients. This research indicates nitrogen as the limiting nutrient in the studied area.