[A-OS13] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

[AOS13-09] Interannual variations of the lower-trophic level ecosystem in the Harima-Nada, eastern Seto Inland Sea, Japan simulated by a plankton functional type model.

*Naoki Yoshie¹, Ayaka Hiramine¹ (1.Center for Marine Environmental Studies, Ehime University)

Keywords:nutrient, phytoplankton, zooplankton, ecosystem model, coastal ocean

In recent years, the effects of considerable decline of nutrient concentration with the strong and long-term regulation of nutrient discharge on the lower-trophic level ecosystem have received a lot of attention in the Harima-nada, eastern Seto Inland Sea, Japan. To investigate these effects, we conducted the numerical simulations using a plankton functional type model from 2000 to 2013 with the several different boundary conditions, which included decreasing of nutrient concentration with the discharge regulation and increasing of water temperature with the climate change. The model successfully reproduced the observed quite strange interannual variations, which were almost constant biomass of total phytoplankton in spite of the considerable decline of nutrient concentration, and also reproduced significant decrease in biomass of meso-zooplankton such as copepod. This is because the decrease in large-sized phytoplankton such as diatom due to both the decline of nutrient and increase of water temperature was canceled out by the increase in small-sized phytoplankton associated with the increase of water temperature. The decrease of diatom with both the decline of nutrient and increase of water temperature caused the decrease of copepod, which was extremely important feed for anchovy and sand eel in this region. It might be a reason for significant reduce of fish resources in the Harima-Nada.