Effects of watershed land use on coastal marine environments: A multiscale exploratory analysis with multiple biogeochemical indicators in fringing coral reefs of Okinawa Island.

Abstract

The analytical spatial scale and selection of biogeochemical indicators affect interpretations of land-use impacts on coastal marine environments. In this study, nine biogeochemical indicators were sampled from 36 locations of coral reefs fringing a subtropical island, and their relationships with watershed land use were assessed by spatial autoregressive models with spatial weight matrixes based on distance thresholds of a few to 30km. POM-relevant indicators were associated with agricultural and urban lands of watersheds within relatively small ranges (6-14km), while the concentrations of inorganic nutrients were associated with watersheds within 20km or more. The macroalgal δ15N showed a strong relationship with agricultural lands of watersheds within 7km and urban/forest lands of watersheds within 24km. These results demonstrate significant effects of land use on the coral reef ecosystems of the island, and the importance of appropriate combinations of analytical scales and biogeochemical indicators.