Eutrophication trends in the coastal region of the Great Tokyo area based on long-term trends of Secchi depth.

Background: The coastal ocean's environment has changed owing to human activity, with eutrophication becoming a global concern. However, oligotrophication occurs locally and decreases fish production. Historically, the Secchi depth has been used as an index of primary productivity.

Empirical estimation of marine phytoplankton assemblages in coastal and offshore areas using an in situ multi-wavelength excitation fluorometer.

Phytoplankton assemblages are essential for understanding the quality of primary production in marine ecosystems. Here, we describe the development of a methodology for monitoring marine phytoplankton assemblages using an in situ multi-wavelength excitation fluorometer (MEX). The MEX recorded the fluorescence excited with nine light-emitting diodes, temperature, and sensor depth.

Longitudinal and Vertical Variations of Dissolved Labile Phosphoric Monoesters and Diesters in the Subtropical North Pacific.

The labile fraction of dissolved organic phosphorus (DOP) - predominantly consisting of phosphoric esters - is an important microbial P source in the subtropical oligotrophic ocean. However, unlike phosphate, knowledge for labile DOP is still limited due to the scarcity of broad and intensive observations. In this study, we examined the concentrations and size-fractionated hydrolysis rates of labile phosphoric monoesters and diesters along a >10,000 km longitudinal transect in the North Pacific (23°N; upper 200-m layer).