Abstract
In order to clarify the variation of nutrients in the coastal area of southwestern Hokkaido, temperature, salinity, nutrient concentrations, and chl.a were measured for various waters from 2002 to February, 2005. Nutrients in sea surface water were low through a year except near the river mouth. Nutrients increased inwinter because of vertical mixing especially phosphate-P Nitrogen and silica supply depends greatly on the river discharge from March to May because of snow melting. Phytoplankton bloom was observed in spring from February to April and nutrients remarkably decreased during bloom. After bloom both nitrogen and phosphorus were depleted throughout the survey area until autumn fall season. Nitrogen was most important factor to limit primary production in the surface and production layer except summer.
