14:30 〜 14:45
[AHW22-13] From mountain to deep sea: effects of riverine nutrient flux by Kanogawa River on coastal and deep-sea food webs in Suruga Bay
キーワード：diatom、food webs、land-ocean linkage、phytoplankton growth、riverine nutrients、satellite data
Terrestrially derived nutrients play an important role in maintaining biodiversity and ecosystem functioning in coastal ecosystems. Our previous studies have revealed that river and spring-fed waters from the quaternary volcanic area of the Kanogawa River watershed (e.g., Mt. Fuji area) contain high concentrations of basalt-derived minerals (P, Si, V, etc.) and such “volcanic nutrient inputs” provide important nutrient subsidies to phytoplankton communities in the coastal waters of Suruga Bay. Here we show by satellite image analyses and field surveys that the biogeochemical flux of volcanic nutrients by the Kanogawa River partly controls the growth and dynamics of diatom phytoplankton in surface waters, thereby supporting higher trophic-level consumers from upper to deep oceans in Suruga Bay.
We constructed the state-space model to describe the time-series data of satellite chlorophyll a (Chla) concentrations (obtained from MODIS-Aqua) during the 2003-2020 period, with the river-flow pattern being incorporated into the model as an explanatory factor. The model revealed that the changes in river flow in three major rivers (Fuji River, Abe River, and Kanogawa River) significantly influenced the spatiotemporal variation of Chla. Moreover, the detailed spatial data of satellite Chla concentrations (GCOM-C/SGLI) obtained for 37 flooding events during the 2018-2021 period showed that the apparent growth rate of phytoplankton off the north-east coast of Suruga Bay responded positively and non-linearly to the increase of flood magnitude of the Kanogawa River. The results suggest that riverine nutrient transport is important for phytoplankton growth in this study area.
Amplicon sequencing analyses targeting 16S and 18S rRNA genes showed that diatoms (Chaetoceros spp. and Skeletonema spp.) often predominated in planktonic communities off the Kanogawa River estuary, and the carotenoid fucoxanthin (i.e., a proxy for diatoms) was closely associated with Si supply by river waters. Furthermore, stable isotope mixing analysis (MixSIAR) revealed that the secondary productions of zooplankton (e.g., calanids), large arthropods (e.g., shrimps, crabs, etc.) and fish from surface to deep sea were mainly supported by large phytoplankton (> 100 µm in cell size), rather than small suspended particles (< 100 µm) or terrestrial organic matter. Quantitative fatty acid signature analysis (QFASA) also identified large phytoplankton (mainly diatoms) as the most important basal resource for coastal and deep-sea faunal communities. These results imply that volcanic mountains (e.g., Mt.Fuji) and deep-sea ecosystems are connected at least partly via riverine transport of dissolved Si and the resultant stimulation of diatom production and trophic transfer to higher consumers. Our results indicate that integrative watershed management along the land-to-river-to-ocean continuum is necessary to sustain biodiversity and the integrity of various ecosystem services offered from Suruga Bay.
We constructed the state-space model to describe the time-series data of satellite chlorophyll a (Chla) concentrations (obtained from MODIS-Aqua) during the 2003-2020 period, with the river-flow pattern being incorporated into the model as an explanatory factor. The model revealed that the changes in river flow in three major rivers (Fuji River, Abe River, and Kanogawa River) significantly influenced the spatiotemporal variation of Chla. Moreover, the detailed spatial data of satellite Chla concentrations (GCOM-C/SGLI) obtained for 37 flooding events during the 2018-2021 period showed that the apparent growth rate of phytoplankton off the north-east coast of Suruga Bay responded positively and non-linearly to the increase of flood magnitude of the Kanogawa River. The results suggest that riverine nutrient transport is important for phytoplankton growth in this study area.
Amplicon sequencing analyses targeting 16S and 18S rRNA genes showed that diatoms (Chaetoceros spp. and Skeletonema spp.) often predominated in planktonic communities off the Kanogawa River estuary, and the carotenoid fucoxanthin (i.e., a proxy for diatoms) was closely associated with Si supply by river waters. Furthermore, stable isotope mixing analysis (MixSIAR) revealed that the secondary productions of zooplankton (e.g., calanids), large arthropods (e.g., shrimps, crabs, etc.) and fish from surface to deep sea were mainly supported by large phytoplankton (> 100 µm in cell size), rather than small suspended particles (< 100 µm) or terrestrial organic matter. Quantitative fatty acid signature analysis (QFASA) also identified large phytoplankton (mainly diatoms) as the most important basal resource for coastal and deep-sea faunal communities. These results imply that volcanic mountains (e.g., Mt.Fuji) and deep-sea ecosystems are connected at least partly via riverine transport of dissolved Si and the resultant stimulation of diatom production and trophic transfer to higher consumers. Our results indicate that integrative watershed management along the land-to-river-to-ocean continuum is necessary to sustain biodiversity and the integrity of various ecosystem services offered from Suruga Bay.