Search

The lateral transport of nutrient‐rich water masses from coastal areas to offshore areas is an important factor controlling the primary production of phytoplankton in offshore regions. If the coastal low‐salinity waters have high nutrient levels, lateral transport can be traced via salinity observations. However, if high level of nutrients in the waters are not coupled with low salinity, for example, input from coastal sediments, water transport cannot be traced via salinity observations. In this study, visible fluorescent organic matter (FOMvis) was monitored by an in situ sensor as a tracer for sediment‐affected water masses from coastal areas. The FOMvis distribution in the upper 500 m water layer in offshore Japan along the 143°E transect was generally controlled by the distributions of subtropical water (i.e., Kuroshio water and Tsugaru warm current water) and subarctic water (i.e., Oyashio water). However, anomalously high levels of FOMvis were observed at depths of 20–60 m at an observational station, which could not be explained by physical mixing. This likely originated from the lateral transport of water masses from coastal areas. In and around Sendai Bay, where observations were carried out as an example of the Japanese coast, high levels of FOMvis were observed, accompanied by negative N*, an indicator of denitrification, and phosphate and silicic acid inputs from anoxic sediments. These observational results imply that FOMvis observation via in situ sensors can be useful for tracing the input of nutrient‐rich sediment‐affected water masses from coastal areas to offshore oceans. Plain Language Summary: Phytoplankton activities in offshore oceans are often controlled by the supply of nutrients. Since the coastal oceans are generally characterized by high levels of nutrients, lateral transport of nutrients from the coastal ocean to the offshore ocean is likely an important nutrient source for phytoplankton, particularly in the boundary region. Rivers and sediments supply nutrients to coastal oceans. Nutrient transport accompanied by river water can be traced by salinity observations using conductivity sensors. However, the transport of sediment‐derived nutrients is difficult to trace via sensor‐based observations. The visible fluorescence of nonliving organic matter (traditionally defined as humic‐like fluorescence) has been suggested to be useful for tracing river water as well as coastal sediment‐affected water in marine environments. Here, we observed the simultaneous presence of sediment‐derived nutrients and visible fluorescent organic matter, which was detected by a sensor in the subsurface layer in the coastal area, that is, in and around Sendai Bay, Japan. A relatively high level of fluorescent organic matter was also observed in the Kuroshio‐Oyashio transition zone. These observational results indicate that fluorescent organic matter as detected by in situ sensors can be useful for tracing inputs of coastal sediment‐derived nutrients to offshore oceans. Key Points: A portion of the fluorescent organic matter in the Kuroshio‐Oyashio transition zone could be laterally transported from coastal areasHigh levels of fluorescent organic matter in subsurface layers in coastal regions are linked with sediment‐derived nutrientsSensor‐based observation of fluorescent organic matter can be used to effectively trace the export of coastal sediment‐derived nutrients [ABSTRACT FROM AUTHOR]

The determination of the causes for the changes in marine environment in areas with similar oceanic climate forcing on most suitable sites for scallop aquaculture can help to ensure long-term sustainability of the coastal ecosystem. This study assessed aquaculture suitability sites using dominant indicators of marine ecological dynamics on Japanese scallop culture in Funka and Mutsu Bays, Japan as comparative examples. Data sources comprised of Moderate Resolution Imaging Spectroradiometer ( MODIS), four dimensional-variational (4D- VAR) data assimilation system, Advanced Land Observing Satellite ( ALOS), in situ and buoy measurements. The suitable sites were ranked on a scale of 1 (least suitable) to 8 (most suitable). In the most suitable sites in aquaculture operational areas, Funka Bay had a high proportion (51.1%) than Mutsu Bay (13.7%) for the best performed model. Peaks of aquaculture suitability scores were attributed to potential effects of currents. Extreme sea temperatures (>24°C) in summer 2010 were associated with low performance of the 2010 model in Mutsu Bay and mortality of scallops based on sea temperature-depth visualizations. Future global warming effects are likely to decrease the most suitable culture sites in Funka Bay and loss of similar areas in Mutsu Bay. Thus, change in marine environment influences scallop culture development. Such concepts could form scientific basis for aquaculture planning on designated system of larval distribution and stock management of cultured species to minimize mortality and economic losses. [ABSTRACT FROM AUTHOR]

Climate changes affect coastal environments and aquaculture, threatening food security and economic growth. Japanese scallop (Mizuhopecten yessoensis) culture is economically important for the coastal communities of Dalian, China, and Funka Bay, Japan. In this study, we combined satellite remote-sensing data,in situobservations, and a suitable aquaculture site selection model to explore the interactions between marine environments and climate variability over a recent 10-year period (2003–2012). Our selection of appropriate zones in these two Far Eastern regions and our analyses of climatic event (Arctic Oscillation (AO), winter East Asian monsoon (EAM), and El Niño/La Niña Southern Oscillation (ENSO)) and meteorological (precipitation, temperature, and wind) data allowed us to determine the impacts of climate change on regional coastal environments and prospects for scallop aquaculture. These analyses showed that AO and EAM strongly influenced the aquaculture areas on the Dalian coast through their effects on temperature during winter. We also determined that wind was the main driving force behind regional environmental changes during spring. Conversely, ocean conditions and suitable areas in Funka Bay changed rapidly relative to oceanic and atmospheric circulation. In Funka Bay, areas appropriate for scallop aquaculture and variations in chlorophyll-aconcentration (which reflect the availability of algal food for scallops) were strongly correlated with ENSO, precipitation, and air temperature. These correlations demonstrate the influence of oceanic and atmospheric parameters on the productivity of scallop aquaculture in Funka Bay.Adaptation to oceanic and atmospheric changes should be considered when developing plans and management strategies for coastal scallop aquaculture in northeast Asia. [ABSTRACT FROM AUTHOR]

Abstract: Inter-annual variability in the magnitude and timing of the spring bloom was investigated for the Oyashio region (40 °-48 °N, 143 °E-152 °E) using 10 years (from 1998 to 2007) of satellite ocean-color data. Geostrophic currents were examined using satellite altimeter data. Early spring blooms (>1.5mgm−3) occurred in early April 2001 and late March 2002. The 2001 bloom continued for one month. Late blooms occurred from mid-May 1999, early June 2004 and late April 2006, continuing for about 1 month, 8 days and 16 days, respectively. A strong bloom (4.7mgm−3) also occurred in mid-April 1998; however, it terminated in early May. We classified the Oyashio region based on the pattern of temporal variation of Chl-a concentration from March to June. The spatio-temporal variability in Chl-a concentration during spring was different among years. The area where Chl-a concentration was highest in April was more extensive in 2001, 2002 and 2006 than usual. In 1999, the area where Chl-a concentration was highest in May was the widest among the 10 years. Mesoscale eddies and currents with high velocity were frequently observed in the area of high Chl-a concentration east of Hokkaido, propagating Coastal Oyashio Water of low salinity and low density into the oceanic region. That strengthened stratification in the surface layer. We suggest that this seaward transfer of coastal water could be one of the important factors for phytoplankton distribution in two ways: (1) horizontal advection of water with high Chl-a concentration and (2) enhancement of stratification in the oceanic region. [Copyright &y& Elsevier]

Arctic ecosystems are altered profoundly by climate changes. However, the responses of Arctic marine and terrestrial ecosystems as well as their biodiversity to global warming remain largely unknown. This article provides comprehensive insights into the results and major findings from the Arctic Challenge for Sustainability (ArCS) Project – an Arctic region research program initiated in Japan, which aims to address and advance our understanding of these uncertainties. Marine ecosystem studies have identified several biogeochemical processes that are associated with sea ice decline and northward transport and shift of marine species across multiple trophic levels over the Bering and Chukchi Sea shelves. Studies of the terrestrial ecosystem have identified factors that are important for the understanding of terrestrial biodiversity and ecosystems, including Arctic lakes, under the presence of global warming. Novel fungal species from the Arctic terrestrial ecosystem have also been isolated and described. Overall, these results could contribute to the conservation and sustainable management of the Arctic ecosystem services. • Most publications from the ArCS project were reviewed. • Biogeochemical process assciated with sea ice decline and northward shift of marine species were revealed. • Novel fungal species in the terrestrial ecosystem and notable contributions of biological interaction to ecosystem changes were discovered. [ABSTRACT FROM AUTHOR]

The Japanese scallop (Mizuhopecten yessoensis) is an important commercial species in the Dalian coastal area. The present study employed a suitable aquaculture site-selection model (SASSM) and used satellite remote-sensing data to analyze the spatiotemporal distribution of suitable areas for Japanese scallop aquaculture in the Dalian coastal area from 2003 to 2012. The study area was divided into four marine zones. The results demonstrated that the suitability scores of scallop aquaculture areas were high in May and low in February. The Changhai County (Zone II) and Lushunkou areas (Zone III) exhibited high potential for Japanese scallop aquaculture development. The results of the suitability models were consistent with the existing scallop aquaculture in the study area. These zones, combined with climatic events [the winter East Asian Monsoon (EAM) and El Niño/La Niña–Southern Oscillation (ENSO) events], were used to examine the impact of climate variability on scallop aquaculture. Results suggest that the suitability scores in Zone III were more sensitive to changes in environmental factors (e.g., sea surface temperature, chlorophyll-a, and suspended sediment) and climate changes, whereas the correlations among these factors were not significant in Zone II. Adaptation to these changes should be considered when developing plans and management strategies for scallop aquaculture. [ABSTRACT FROM AUTHOR]

Abstract: River plumes have important effects on marine ecosystems. Variation in the extent and dispersal of river plumes is often associated with river discharge, wind characteristics and ocean circulation. The objectives of this study were to identify the Tokachi River plume by satellite, determine its relationship with river discharge and clarify its temporal and spatial dynamics. SeaWiFS multispectral satellite data (normalized water-leaving radiance: nL w) with 1.1km spatial resolution were used to determine the spatial and temporal variability of the plume during 1998–2002. Supervised maximum likelihood classification using six channels of nL w at 412, 443, 490, 510, 555 and 670nm with each band''s spectral signature statistic was used to define classes of surface water and to estimate the plume area. Supervised maximum likelihood classification separated three to four classes of coastal water based on optical characteristics as a result of wind stress events. The satellite-observed plume area was correlated with the amount of river discharge from April to October. The plume distribution patterns were influenced by wind direction and magnitude, the occurrences of a near-shore eddy field and surface currents. Empirical orthogonal function (EOF) was used to express the spatial and temporal variability of the plume using anomalies of nL w(555) monthly averaged images. The first mode (44% of variance) showed the turbid plume distribution resulting from re-suspension by strong wind mixing along the coast during winter. This mode also showed the plume was distributed along-shelf direction in spring to early autumn. The second mode (17% of variance) showed spring pattern across-shelf direction. EOF analysis also explained the interannual variability of the plume signature, which might have been affected by the flow of the Oyashio Current and the occurrence of a near-shore eddy field. [Copyright &y& Elsevier]

After the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP), Japan, in March 2011, 137 Cs in demersal fish had, between 2011 and 2015, a prolonged ecological half-life when compared to pelagic fish. Using stable isotope mixing models combined with gut content analysis and 137 Cs activity concentrations, this study investigated the hypothesis that an unexplored food web structure could be a contributing factor explaining the ecological half-life of 137 Cs in benthic flatfish. Benthic invertebrates and demersal fish species sampled in 2015 still showed 137 Cs activity concentrations higher than pre-accident. The mixing models of stable N and C isotopes and gut content analysis identified deposit, suspension and filter feeders to be the main flatfish food items in the benthos. There was a significant correlation between 137 Cs activity concentrations in specific flatfish species and benthos, and between 137 Cs activity concentrations in benthos and surface sediment. The results of this study partially explained the 137 Cs activity concentrations found in the analysed demersal fish, suggesting that the benthos can be a continuous source of 137 Cs for the demersal fish during this period of time. Extending monitoring programmes to include invertebrates that are not food species for humans would greatly improve our ability to understand the role of trophic transfer pathways and take appropriate management actions., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)