Temperature, salinity, nutrients (nitrate, nitrite, silicate, and phosphate), and chlorophyll-a concentrations were collected and utilized as environmental parameters at the same depth as the POM samples. Water samples were obtained using Niskin bottles mounted on a rosette or a bucket to measure nutrient, chlorophyll-a, and POM concentrations. The nutrient and chlorophyll-a concentrations were analyzed following Kodama et al. (2015). The detection limits of the nutrient concentrations were 0.01–<0.05 µM for nitrite and phosphate, 0.01–<0.1 µM for nitrate, and 0.05–<0.3 µM for silicate, estimated using the standard deviations of blank values. The temperature and salinity at the 0-m depth were defined as the values observed by the CTD sensors at 1-m depth because salinity at the 0 m depth sometimes exhibited “unreliable” values. To treat the common-logarithm transformed values, the nutrient concentrations of < 0.01 µM (below the detection limit) were set as 0.01 µM.