Long-term monitoring of water quality and phytoplankton was conducted at 19 sampling stations in Harima-Nada, eastern Seto Inland Sea, Japan for 35 years from 1973 to 2007. There were two significant long-term changes, an increase in winter water temperatures of 0.042°C year −1 , and a decrease in dissolved inorganic nitrogen (DIN) from about 10 μM in the 1970s to~5 μM in the late 1990s due to the reduction in nutrient inputs. DIN concentrations and total phytoplankton cell density were both higher during the 1970s to the early 1980s and then exhibited a significant decrease in the mid 1980s and remained relatively constant thereafter. Diatoms were the dominant phytoplankton group (>90%) over the 35-year period, and there was a dramatic shift from Skeletonema dominance (~70%) to Chaetoceros in the mid 1980s. This shift in diatom species may be attributed to differences in the life cycle of Skeletonema and Chaetoceros and the response to the decrease in DIN concentration.

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Forty-five elements were determined in mantle muscle and liver of juvenile Japanese common squid, Todarodes pacificus, collected from three locations in and near Japanese coasts, using a high-resolution inductively coupled plasma mass spectrometer (HR-ICP-MS) and an inductively coupled plasma atomic emission spectroscope (ICP-AES). Multivariate statistical techniques were applied to discriminate populations of squids from these three locations by treating absolute and relative concentrations of trace elements. Significant differences were found in the concentrations of elements, particularly for some alkaline and alkaline earth elements in the muscle and liver and for some 3d transition elements in the liver of three groups of squids. Squids from the Pacific Ocean could be distinguished from those of the Sea of Japan by discriminant function analysis of elemental concentrations. Based on the analysis, the squids collected from the Nemuro Strait in Japan were predicted to belong to those from the Sea of Japan. Elemental concentrations and discriminant function analysis can be used to identify subpopulations and migratory routes of squids.