Evaluation of seafloor environmental characteristics of harvesting ground of a kelp Saccharina longissima using GIS in the Pacific coastal area of eastern Hokkaido, Japan

Abstract

The characteristics of the seafloor environment of the harvesting grounds of the kelp, Saccharina longissima, were evaluated by spatial analysis using a geographic information system (GIS) in the Pacific coastal area of eastern Hokkaido. The kelp harvesting grounds were formed in water depths ranging from 1.2 m to 9.6 m, slopes ranging from 0° to 16.3°, bottom substrate (coarseness score) ranging from 1.82 to 3.00, bottom current velocities ranging from 0.7 cm/s to 116.4 cm/s, and a maximum slope of 37.6°. These values include the viable environmental conditions for the kelp. The kelp growth parameters estimated from kelp measurement data before the harvesting season were positively related to the bottom current velocity. This suggests that the bottom current velocity has a significant effect on kelp growth. The 58 harvesting grounds were classified into two categories based on their growth: those with high kelp growth and those with low kelp growth. Based on a decision tree model, the differences between the two harvesting ground categories were explained by the bottom current velocity, maximum slope, and bottom substrate. In addition, their specific environmental conditions were also quantified. The quantified environmental conditions were also used to create a potential map for the kelp growth in the harvesting grounds. This study provides an understanding of the environmental characteristics of the kelp harvesting grounds, as well as a procedure for mapping the kelp growth potential, thus contributing to the sustainable use of the kelp resources through kelp harvesting ground management and maintenance.