Using a temperature-based GIS model to identify potential habitat for Zostera japonica in Humboldt Bay, CA

A geographic information system allows for the ability to predict potential distributions of spreading non-native species by identifying suitable, unoccupied habitat. Zostera japonica (Asch. and Grabn.), a non-native seagrass from the subtropical western Pacific, has expanded its distribution in the NE Pacific since its introduction in the mid-1900s. Humboldt Bay in northern California and the nearby Eel River estuary now represent the southern extent of its non-native range. In this study, in situ intertidal temperature data were used to predict optimal Z. japonica habitat in Humboldt Bay. Kriging analysis was used to produce an interpolated temperature map of the Humboldt Bay intertidal mudflat during the 2010 growth season, and the scenario of a warmer growth season was examined. Optimal habitat was identified by the amount of time a given section of mudflat spends within a temperature range that is optimal for Z. japonica growth (20oC – 30oC). The spatial extent of native eelgrass (Zostera marina, Linnaeus) habitat was used to exclude areas of intertidal that, due to interspecific competition, would not provide suitable Z. japonica habitat. The model identifies large areas of upper-intertidal mudflat as optimal potential Z. japonica habitat, especially in northern Humboldt Bay where Z. japonica has been spreading since 2001, and describes southern Humboldt Bay, where the non-native is absent, as less optimal than northern Humboldt Bay. Additionally, the warmer scenario predicts a substantial increase in optimal Z. japonica habitat in South Bay's upper intertidal and an increase in relative habitat suitability in unvegetated North Bay mudflat as compared to the cooler scenario. The predictions generated by this model have important implications for resource managers monitoring spread and attempting local eradication of this species.