Presentation Information
[AOS27-P02]Rapid Report on Four-Season Observations in Orido Bay: A Former Underwater Log Storage Site
*Yuka SHINOZAKI1, Marina ORITA1, Takashi KOBAYASHI1, Masaki HISADA1 (1.NTT, Inc.)
Keywords:
Orido Bay,moored observations,water quality,sediment quality,four-season observations,ecosystem modeling
We aim to develop an ocean ecosystem forecasting technology [1] that uses ecosystem models built from observational data to predict spatiotemporal ecosystem variability while reflecting interdependencies among species. To obtain the data required to build a coupled ecosystem model (hydrodynamic + biogeochemical), we conducted multi-season observations in Orido Bay (Shizuoka, Japan). In this former surface log-storage basin, environmental improvement is desired.
Observations consisted of (i) continuous monitoring using moored buoys and (ii) ship-based spot observations. Observation sites (Fig. 1) were: Site O (opposite bank of the Tomoe River mouth), Site N (breakwater opening in the northern bay), eastern sites M/J/F, and western sites L/K/D. The northern and western parts are separated by breakwaters and connected only via the eastern part.
Continuous monitoring was conducted during 21 Nov 2024–21 Jan 2025 (autumn–winter) and 16 Jun 2025–20 Aug 2025 (spring–summer). ICT buoys were deployed at Sites O and N in both periods. In spring–summer, bottom-moored systems for near-bottom monitoring were additionally deployed at Sites L and M. In autumn–winter, ICT buoys carried electromagnetic current meters at the surface and mid-depth (Currents) and a chlorophyll fluorescence/turbidity sensor at mid-depth (Chl/Turb). In spring–summer, the ICT buoy at Site O carried Currents + Chl/Turb + CTD (conductivity–temperature–depth) at the surface and Currents + CTD near the bottom; at Site N, Currents + Chl/Turb were installed at the surface and Currents + CTD near the bottom. Bottom-moored systems at Sites L and M were equipped with a dissolved oxygen (DO) sensor, a CTD, and a Chl/Turb sensor.
Spot observations included: water sampling for water quality (WQ) and zooplankton (Zoo), vertical profiling with a multi-parameter water-quality sonde (AAQ-VP), environmental DNA (eDNA), sediment sampling for sediment properties (Sed), benthic fauna (Benthos), biological observations by divers and/or an underwater ROV (Bio Obs.), and phytoplankton (Phyto). WQ/Zoo/AAQ-VP were conducted in Nov/Jan/May/Aug; eDNA in Nov/May/Aug; Sed in Nov/Jul; Benthos in Jul; Bio Obs. and Phyto in Nov/May/Aug (Fig. 2).
Key findings are as follows. Limited seawater exchange was observed, and concomitantly, environmental conditions gradually deteriorated across multiple indicators from the northern part (Site N) through the eastern part (Sites M/J/F) to the western part (Sites L/K/D). The western part showed localized hypoxia in summer. Near-bottom environments were characterized by black, sludge-like mud rich in organic matter and nutrients, presumably related to historical log-storage activities, with a sulfurous odor detectable even on deck, indicating generally harsh conditions for aquatic organisms. In contrast, along revetments and piles, sessile organisms such as barnacles, oysters, ascidians, and mussels were observed with high coverage, and fish were confirmed swimming around them, suggesting that an ecosystem has been established by organisms adapted to the local environment. In addition, the year-round occurrence of warm-current-associated fish species (e.g., Scatophagus argus and Platax teira) suggests influences of Kuroshio-derived warm waters and/or ongoing water temperature rise.
We are currently conducting detailed analyses of these observational results and are constructing an Orido Bay ecosystem model. Using this model, we plan to evaluate potential environmental improvement measures.
Acknowledgments: We would like to express our sincere gratitude to Shizuoka Prefecture, Shizuoka City, ITEC CORPORATION, Shimizu Fisheries Cooperative Association, Yamamoto Tsuribune-ten, Yugen Kaisha Fujiya Tsuribune-ten, Yugen Kaisha Harakin Tsuribune, and all stakeholders related to Orido Bay for their generous support and cooperation in conducting the observations.
Reference
[1] Marine-ecosystem future-forecasting technology for biodiversity conservation, NTT R&D Website, https://www.rd.ntt/e/se/technology/biodiversity.html
Observations consisted of (i) continuous monitoring using moored buoys and (ii) ship-based spot observations. Observation sites (Fig. 1) were: Site O (opposite bank of the Tomoe River mouth), Site N (breakwater opening in the northern bay), eastern sites M/J/F, and western sites L/K/D. The northern and western parts are separated by breakwaters and connected only via the eastern part.
Continuous monitoring was conducted during 21 Nov 2024–21 Jan 2025 (autumn–winter) and 16 Jun 2025–20 Aug 2025 (spring–summer). ICT buoys were deployed at Sites O and N in both periods. In spring–summer, bottom-moored systems for near-bottom monitoring were additionally deployed at Sites L and M. In autumn–winter, ICT buoys carried electromagnetic current meters at the surface and mid-depth (Currents) and a chlorophyll fluorescence/turbidity sensor at mid-depth (Chl/Turb). In spring–summer, the ICT buoy at Site O carried Currents + Chl/Turb + CTD (conductivity–temperature–depth) at the surface and Currents + CTD near the bottom; at Site N, Currents + Chl/Turb were installed at the surface and Currents + CTD near the bottom. Bottom-moored systems at Sites L and M were equipped with a dissolved oxygen (DO) sensor, a CTD, and a Chl/Turb sensor.
Spot observations included: water sampling for water quality (WQ) and zooplankton (Zoo), vertical profiling with a multi-parameter water-quality sonde (AAQ-VP), environmental DNA (eDNA), sediment sampling for sediment properties (Sed), benthic fauna (Benthos), biological observations by divers and/or an underwater ROV (Bio Obs.), and phytoplankton (Phyto). WQ/Zoo/AAQ-VP were conducted in Nov/Jan/May/Aug; eDNA in Nov/May/Aug; Sed in Nov/Jul; Benthos in Jul; Bio Obs. and Phyto in Nov/May/Aug (Fig. 2).
Key findings are as follows. Limited seawater exchange was observed, and concomitantly, environmental conditions gradually deteriorated across multiple indicators from the northern part (Site N) through the eastern part (Sites M/J/F) to the western part (Sites L/K/D). The western part showed localized hypoxia in summer. Near-bottom environments were characterized by black, sludge-like mud rich in organic matter and nutrients, presumably related to historical log-storage activities, with a sulfurous odor detectable even on deck, indicating generally harsh conditions for aquatic organisms. In contrast, along revetments and piles, sessile organisms such as barnacles, oysters, ascidians, and mussels were observed with high coverage, and fish were confirmed swimming around them, suggesting that an ecosystem has been established by organisms adapted to the local environment. In addition, the year-round occurrence of warm-current-associated fish species (e.g., Scatophagus argus and Platax teira) suggests influences of Kuroshio-derived warm waters and/or ongoing water temperature rise.
We are currently conducting detailed analyses of these observational results and are constructing an Orido Bay ecosystem model. Using this model, we plan to evaluate potential environmental improvement measures.
Acknowledgments: We would like to express our sincere gratitude to Shizuoka Prefecture, Shizuoka City, ITEC CORPORATION, Shimizu Fisheries Cooperative Association, Yamamoto Tsuribune-ten, Yugen Kaisha Fujiya Tsuribune-ten, Yugen Kaisha Harakin Tsuribune, and all stakeholders related to Orido Bay for their generous support and cooperation in conducting the observations.
Reference
[1] Marine-ecosystem future-forecasting technology for biodiversity conservation, NTT R&D Website, https://www.rd.ntt/e/se/technology/biodiversity.html