Contribution of Submarine Groundwater on the Water-Food Nexus in Coastal Ecosystems: Effects on Biodiversity and Fishery Production

Abstract:

Economic values of the ecosystem services of coastal ecosystems have been evaluated as among the highest of those the world’s ecosystems. Recently more attentions have been paid on the mechanisms how the freshwater contribute to the high productivity and species diversity of the coastal ecosystems. In the present study, results from physical and biological surveys conducted at four locations (Yuza, Otsuchi, Obama and Beppu) in Japan in order to examine effects of river water and submarine groundwater on productivity and species diversity of fishery resources are introduced. Fish sampling was conducted by the use of small seine net (2 x 1 mm, 2 mm mesh). Invertebrates (crustaceans and polychaetes, as prey for the fishes) were collected with a plankton net (0.3 x 0.4 m, 1 mm mesh) and a core sampler (10 x 10 cm circular cylinder). In addition, underwater camera recording was conducted by four digital cameras (1 min interval, for 3 hours) to analyze abundance and species composition of fishes around each sampling site. Relationships between physical parameters (water temperature, salinity and Rn concentration) and biological parameters (abundance, biomass and species diversity of fish, crustaceans and polychaetes) were investigated. Significant increase in abundance and number of species of fishes and some invertebrate species were observed in three of the four locations, indication submarine groundwater promote biological production and species diversity in coastal ecosystems. The mechanisms how the freshwater input from the land contributes to the high productivity and species diversity in the coastal ecosystems will be examined through wood web analysis (e.g. stomach contents and stable isotopes) in the ongoing study. Possible effects of climatic changes (including the global warming) through spatio-temporal variability in submarine groundwater discharge on the productivity and species diversity in coastal ecosystems are predicted based on the species interactions and optimum temperature for each species.