Otsuchi Bay Research Articles

Effect of disturbances on heart rate of captive loggerhead turtles

Diving animals are subject to disturbances within their underwater habitat, such as interactions with fisheries, vessel traffc and increased noise in the ocean. Research on the effect of disturbances on marine mammals and birds suggest stress related to disturbances can result in either increased or decreased heart rates. However, how disturbances affect endangered or threatened marine turtles is largely unknown. Relying on behavioral data is insuffcient because animals may respond physiologically to a stressful event but demonstrate no change in behavior. To assess how marine turtles respond to disturbances, we examined the heart rate of subadult loggerhead turtles (43.5 ± 9.1 kg) that were incidentally captured by set nets in or near Otsuchi Bay, Japan. Heart rate was measured in turtles at rest in shallow tanks (n=4), resting out of water (n=4), actively feeding (n=4) and during transport in a car (n =3) using self-contained ECG data loggers. Heart rate during car transport was significantly higher than all other categories (F = 80.9, p< 0.001). Mean heart rate during transport was at least 15 beats min−1 higher than any other category, even though turtles were typically calm during transport. The mean time for heart rate to recover to resting in water heart rate was 58 minutes; however, heart rate recovery varied widely and was likely dependent on post-transport activity. While previous research showed heart rate during routine activities in loggerhead turtles was driven by activity level, these results suggest that, during stressful events, heart rate can increase dramatically even though behaviorally, turtles appear quiescent. National Science Foundation, IOS-1121324. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Simultaneous determination of picomolar level of dissolved silver with other key trace metals in seawater samples using solid phase extraction and isotope dilution methods

Simultaneous determination of dissolved silver (dAg) with other key GEOTRACES trace metals is difficult because dAg in seawater tends to form negatively charged chloride species that result in only 75% recovery efficiency with commonly used NOBIAS PA-1 chelating resins. In this study, we developed a method using solid phase extraction coupled with isotope dilution that enables full quantification (97.9 ± 2.1%) of dAg along with other major trace metals including cadmium (Cd), copper (Cu), manganese (Mn), nickel (Ni), and lead (Pb) (recovery efficiency = 100% to 102%) in seawater samples. Seawater samples were first spiked with Ag-109 and allowed to reach isotopic equilibrium before extraction using NOBIAS PA-1 chelating resin. Then, dAg isotope ratios (Ag-109/Ag-107) before and after solid phase extraction were determined and used to quantify dAg. Determination of dAg with dissolved Cd, Cu. Mn, Ni, and Pb in reference seawater material CASS-6 resulted in deviations of between 1.0% and 8.8% from the consensus values, which are well within the standard error of measurement. We then successfully determined the concentrations of dissolved Cd (0.05–0.2 nM), Cu (0.5–13 nM), Mn (10–140 nM), Ni (2–12 nM), Pb (5–110 nM), and Ag (10–40 pM) in Otsuchi Bay, Japan and its surrounding rivers. Evaluation of the behavior of dAg under a salinity gradient using estuarine samples collected from Samunsam River, Malaysia shows increasing dAg concentration with salinity (R2 = 0.68), which suggests release of sedimental Ag under high ambient chloride concentrations. Our new method enables rapid and simultaneous measurements of dAg with other key GEOTRACES trace metals in a single analysis, which is expected to expedite analysis and increase availability of oceanic dAg data globally.

Distributions of humic substances in an estuarine region (Otsuchi Bay, Japan) determined using electrochemical and optical methods

Humic substances are major components of the dissolved organic carbon pool in aquatic environments that can bind to trace metals like copper and iron as organic ligands. The unique chromophoric and fluorescence properties of humic substances enabled measurements using conventional optical methods but recently a new electrochemical method using cathodic stripping voltammetry has emerged. In this study, we employed both methods to measure humic substances and elucidate their distribution patterns in Otsuchi Bay in Japan. The electroactive humic substances (eHS) detected using the electrochemical method were higher in the rivers (range 0.24 to 4.3 mg L−1) than in the coastal bay (range 0.08 to 0.69 mg L−1). Both methods revealed significantly higher humic concentrations in the surrounding rivers than in Otsuchi Bay, indicating that riverine sources are an important source of humic substances to Otsuchi Bay, consistent with previous observations in riverine systems globally. eHS correlated well with optical indices of dissolved organic matter (DOM) including humic and marine humic-like fluorescent DOM and chromophoric DOM. Furthermore, comparison with data from the literature suggests that about 20% of the weaker Cu-binding organic ligand pool in Otsuchi Bay may consist of eHS. As Cu-binding organic ligands, eHS may be important in buffering temporal or seasonal increases in Cu fluxes in estuarine regions, with possible implications for nutrient bioavailability and toxicity for primary producers.

Dynamics of microplastic transport and accumulation in a rural coastal area: Insights from the Otsuchi Bay, a small ria in Sanriku, Japan

Microplastic (MP) pollution in coastal areas has received increasing attention recently. However, studies focused on MP pollution in rural coastal areas remain limited compared to those in metropolitan coastal areas. This study observed MP particles accumulated on the seafloor of the Otsuchi Bay, a small ria bay located on the Pacific coast, Sanriku, Japan. The MP concentrations in the sediment ranged from 2.6 ± 0.3 to 13.6 ± 9.8 pcs g−1 dry weight (DW) and 2.6 ± 1.4 to 5.1 ± 1.2 pcs g−1 DW in March and September 2021, respectively. No significant difference in MP concentrations was detected between March and September. The MP concentration in the Otsuchi Bay was lower than that observed in other highly populated coastal areas but was relatively high considering the population size of the catchment area. MP particles smaller than 1000μm were the most prevalent, accounting for 96.3% of all MP samples. MP size at the bay head was smaller than that at the central bay for high-density MPs; however, the relationship was reversed for low-density MPs. Analysis of the MP distribution pattern using a two-dimensional numerical model suggests that the horizontal distribution of MPs in the Otsuchi Bay depends on the size and density of MP particles. It is also strongly influenced by both the tidal oscillating currents characteristic to the bay and vertical terminal velocity of MP particles. Sedimented MP distributions in a bay with a small catchment population with limited MP sources shed light on our understanding of MP transport dynamics.

Species‐specific patterns in spatio‐temporal dynamics of juvenile chum salmon and their zooplankton prey in Otsuchi Bay, Japan, revealed by simultaneous eDNA quantification of diverse taxa from the same water samples

AbstractTo understand the spatio‐temporal dynamics of juvenile chum salmon Oncorhynchus keta and their zooplankton prey, the neritic Pseudocalanus newmani, the oceanic Eucalanus bungii, and Themisto japonica, we developed species‐specific environmental DNA (eDNA) quantification methods. First, we confirmed that juvenile chum salmon collected in Otsuchi Bay preyed on the target zooplankton by the stomach contents analyses using the developed assays. Size‐fraction analyses of the water collected in the bay showed that P. newmani and E. bungii DNA were derived mostly from nauplii and early copepodids. We then investigated the distribution and abundance of zooplankton and juvenile chum salmon in Otsuchi Bay using eDNA analyses of the same water samples collected from January to June in 2018 and 2019. Chum salmon DNA was found in the bay from the end of January to mid‐June. P. newmani DNA appeared across the bay throughout the season and were most abundant from February to May, while the other two species DNA were only found in spots, in lower quantities, from March to May. The timings that the zooplankton DNA quantities became greater were corresponded well to that of the Oyashio water intrusion into the bay. In addition, the environmental data indicates that P. newmani was possibly transported also by the Coastal Oyashio water in 2019. The present study successfully revealed species‐specific patterns in the dynamics of zooplankton and chum salmon, reflecting their ecological characteristics and oceanographic conditions, and showed the effectiveness of simultaneous eDNA quantifications for diverse taxa from the same water samples.

Complex factors contribute to the chemical composition of clastic sediments traveling from rivers to the ocean along island arcs: A case study of the Otsuchi area, Northeast Japan

AbstractThe chemical composition of coastal sediments and river sediments is influenced by the geological constitution of provenance and fractionation of clastic particles during sedimentary processes. The intricate nature of the geology in active subduction zones has complicated the comprehension of detrital sediments. More geochemical case studies in such areas are necessary to enhance the understanding of the coastal detrital sediments. This study presents the results of a geochemical and particle size analysis of sediment samples from the Sanriku coastal area of Northeast Japan, including inside and outside of Otsuchi Bay and the three rivers that flow into the bay. Otsuchi Bay area is known to have been severely affected by the 2011 off the Pacific coast of the Tohoku Earthquake and tsunami, and tsunami deposits on its seabed have been reported. The present geochemical analysis indicates that the sediments along those three rivers are well explained by the mixing of rocks occurring in their respective provenance. The chemical composition and particle size distribution of the sediments within Otsuchi Bay suggested the removal of coarse‐grained quartz. They increased the abundance of fine‐grained mafic minerals from Unosumai River having the largest catchment area among the three rivers. During shell debris in the seabed sediment outside of the bay made interpretation of the results was difficult; the sediments collected closer to the bay mouth contained more coarse‐grained material with a composition closer to granitoid and sandstone in the provenance. In contrast, offshore sediments consisted of finer grains with a composition closer to mudstone. Notably, the sediments within Otsuchi Bay did not exhibit the characteristic compositional fractionation or particle size distribution associated with tsunami deposits. These findings underscore the importance of considering the geological diversity of provenances and the particle size distribution of minerals in understanding coastal sediments in subduction zones, including tsunami deposits.

Deep-sea bottom-water environment change caused by sediment resuspension on the continental slope off Sanriku, Japan, before and after the 2011 Tohoku Earthquake

The 2011 off the Pacific coast of Tohoku Earthquake occurred off southern Sanriku, Japan, on March 11 and generated strong shaking and huge tsunami along the entire eastern coast of Tohoku. The mainshock and numerous large aftershocks caused mass-wasting sedimentation events on the continental shelf, slope, and trench bottom. To investigate the impacts of the 2011 Tohoku Earthquake on the deep-sea bottom-water environment off Sanriku, we conducted shipboard surveys up to ~ 2000 dbar during 2011–2018 and long-term monitoring of the seafloor on the continental slope using a deep-sea station (~ 1000 dbar) off Otsuchi Bay during 2012–2018. The high turbidity (maximum ~ 6%) was observed for the bottom water deeper than 500 dbar on the continental slope of the entire area off Sanriku during 2012–2018. This high turbidity was caused by sporadic sediment resuspension induced by frequent large aftershocks. Furthermore, dissolved oxygen concentrations in the bottom layer from 1000 to 1500 dbar dropped significantly by about 10% after the earthquake, while nutrients and dissolved inorganic carbon showed no significant changes but exhibited wide variations. The high turbidity was associated with the increase in the concentrations of phosphate, dissolved inorganic carbon, and methane, as well as the decrease in those of dissolved oxygen and nitrate. This suggests that remineralization of suspended organic matter resulting from the respiration and denitrification of microbial communities after the earthquake caused the chemical properties of the deep-sea bottom-water. The deep-sea bottom-water environment change was maintained by sporadic sediment resuspension due to continued large aftershocks and was likely caused by variations in dissolved inorganic carbon and phosphate. There are two peaks in the concentration and carbon isotope ratio of methane on the deeper slope from 1000 to 2000 dbar near the hypocenter, which were advected along isopycnal surfaces of 27.38σθ (1000 dbar) and 27.56σθ (1500 dbar). The source of the shallower peak of chemical input is considered to be the sediment resuspension from the shallow sediment on the continental slope induced by the mainshock and large aftershocks.Graphical abstract

A new species of Caprella (Crustacea: Amphipoda: Caprellidae) from Gippsland Lakes, Australia, with a redescription of Caprella acanthogaster Mayer, 1890 from northern Japan

Caprella acanthogaster Mayer, 1890 sensu lato (Crustacea: Amphipoda: Caprellidae) has previously been recorded from temperate and cold waters of Far East Asia and Australia. A detailed morphological comparison of specimens collected from Gippsland Lakes (Victoria, Australia) and Otsuchi Bay (Tohoku District, Japan) revealed that C. acanthogaster sensu lato from these regions comprises two separate species. Caprella acanthogaster Mayer, 1890 sensu stricto is confirmed to be distributed in northern Japan. Caprella tamboensis sp. nov. is present in Victoria and Tasmania, Australia, and most noticeably differs from C. acanthogaster sensu stricto in having a relatively short triangular projection on the palm of propodus of gnathopod 2 and a relatively longer peduncle article 2 of antenna 1 (being longer than article 3).

Straightforward upriver migration to spawning sites by chum salmon Oncorhynchus keta homing to coastal short rivers in the Sanriku region.

In chum salmon (Oncorhynchus keta) homed to the Sanriku region, Japan, most of the fish are matured in bays and spawn near river mouths in coastal short rivers; therefore, their upriver migration is extremely short, but their behavioural characteristics have remained unknown. Upriver migration in the Otsuchi River, a typical coastal river, was evaluated from behavioural and physiological aspects. Homing salmon tracked in Otsuchi Bay held in the inner bay for less than 1 day to more than 10 days before river entry. The varied holding duration was negatively correlated with plasma 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) concentration, an indicator of maturation. After river entry, however, most fish were captured in weirs near the river mouths within 2 days regardless of the DHP concentration. Of the 34 fish released in the river, on the contrary, eighteen and five fish were seen next day in the main spawning sites located at c. 1.5 km upstream and in the branch creek, respectively, and 85% of the fish held position there until their death. The mean survival time of released fish was 5.8 days. Plasma DHP level suggested that preparations for spawning were already completed at the timing of the release. Taken together, homing salmon completed spawning preparation in the bay, and then they moved to their spawning sites immediately after river entry and spawned there during their short remaining life. This upriver migration contrasts with those of other populations, such as early migrants and long river migrants, whose maturation is completed during upriver migration.

Disturbed virus-bacteria dynamics in Otsuchi Bay (Japan) after the mega-earthquake and tsunami in March 2011

On 11 March 2011, a mega-earthquake followed by a huge tsunami hit a large area of the Pacific coast of Tohoku, Japan, and caused widespread disturbances in marine ecosystems; however, the impacts on virus-bacteria systems have not yet been elucidated. To investigate whether virus-bacteria interactions were affected by the earthquake and tsunami, we analyzed time series data of viral and bacterial abundances in Otsuchi Bay. Data were collected every 2 mo, from July 2011 to September 2015. Bacterial abundance exhibited a recurrent seasonal cycle with high abundance during the warm season. The seasonal trend of viruses generally followed that of the bacteria, yielding an average virus to bacteria ratio (VBR) of 10.8 ± 3.6 (mean ± SD; n = 432). A notable exception was found at the first 2 sampling times (July and September 2011) when the VBR was consistently low, with an average value of 5.9 ± 1.2 (n = 32). The average VBR during these time periods was substantially lower than the VBR observed in the same season of subsequent years. An analysis of the subset of data collected in the warm season of 2011 and 2012 revealed that the viral abundance and VBR were negatively correlated with turbidity. These results support the hypothesis that viruses were scavenged by non-host particles from the resuspended sediments and damaged catchment. The earthquake and tsunami thus exerted a prolonged impact, over several months, on the virus-bacteria dynamics in Otsuchi Bay.

Topographic features and sedimentary structures around off Otsuchi Bay

Topographic features and sedimentary structures around off Otsuchi Bay

Dive into the sea: first molecular phylogenetic evidence of host expansion from terrestrial/freshwater to marine organisms in Mermithidae (Nematoda: Mermithida).

We report the first mermithid nematode found to be parasitic in a marine tanaidacean crustacean. Ten host tanaidaceans were collected from a depth of 52 m in Otsuchi Bay, Iwate, Japan, north-western Pacific, and identified as a species in the tanaidid genus Zeuxo Templeton, 1840. Nematodes occurred in the host's body cavity; in one case, at least two individuals inhabited a single host. We provide a brief description and illustrations of the morphology of the nematode. In a phylogenetic reconstruction based on the 18S ribosomal RNA gene, the nematode nested in a clade otherwise containing mermithids from terrestrial or freshwater hosts, showing an expansion in host utilization in Mermithidae Braun, 1883 from terrestrial/freshwater hosts to a marine organism.

Downstream Migration and Spatial Distribution of Juvenile Chum Salmon in the Otsuchi Bay, the Sanriku Coast of Iwate, Japan

Downstream Migration and Spatial Distribution of Juvenile Chum Salmon in the Otsuchi Bay, the Sanriku Coast of Iwate, Japan

Influence of normal tide and the Great Tsunami as recorded through hourly-resolution micro-analysis of a mussel shell

We report here hourly variations of Mg/Ca, Sr/Ca, and Ba/Ca ratios in a Mediterranean mussel shell (Mytilus galloprovincialis) collected at the Otsuchi bay, on the Pacific coast of northeastern Japan. This bivalve was living in the intertidal zone, where such organisms are known to form a daily or bidaily growth line comprised of abundant organic matter. Mg/Ca ratios of the inner surface of the outer shell layer, corresponding to the most recent date, show cyclic changes at 25–90 μm intervals, while no interpretable variations are observed in Sr/Ca and Ba/Ca ratios. High Mg/Ca ratios were probably established by (1) cessation of the external supply of Ca and organic layer forming when the shell is closed at low tide, and (2) the strong binding of Mg to the organic layer, but not of Sr and Ba. Immediately following the great tsunami induced by the 2011 Tohoku earthquake, Mg/Ca enrichment occurred, up to 10 times that of normal low tide, while apparent Ba/Ca enrichment was observed for only a few days following the event, therefore serving a proxy of the past tsunami. Following the tsunami, periodic peaks and troughs in Mg/Ca continued, perhaps due to a biological memory effect as an endogenous clock.

Relationships between maturational status and migration behavior of homing chum salmon Oncorhynchus keta in inner bays of the Sanriku coast

The correlations among gonad maturity and various homing behaviors of chum salmon, Oncorhynchus keta, were evaluated using acoustic tracking of tagged fish in Otsuchi Bay, Japan. There was a negative correlation between the time duration from release of tagged fish until river entry and the plasma 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) levels, an indicator of final maturation. Females with high DHP entered the rivers soon after the release, whereas females with low DHP (<10 ng/ml) took a few days to more than one week until river entry. Similar correlation was also found in males. A pattern of river entry correlated with maturational conditions was also observed in fish entering the rivers of neighboring bays. DHP concentrations of fish caught in the rivers were consistently higher. On the other hand, more than half of released salmon departed from the bay regardless of their plasma DHP level, suggesting that maturational status does not force homing adults to enter the most available nearest rivers. Fish entering the rivers experienced ambient temperatures less than 8 °C, which is approximately 5 °C lower than that of the bay. These results indicate that homing salmon hold their position in the bay until just before spawning, which may be attributable to low temperature avoidance. This characteristic type of river entry may be suitable to geographical features and thermal regimes of this region.

Draft Genome Sequence of the Aerobic Anoxygenic Phototrophic Bacterium Roseobacter sp. Strain OBYS 0001, Isolated from Coastal Seawater in Otsuchi Bay, Japan.

ABSTRACTHere, we report the draft genome sequence of the aerobic anoxygenic phototrophic bacterium Roseobacter sp. strain OBYS 0001, isolated from coastal seawater in Ostuchi Bay, Japan. This genome sequence could be useful for our understanding of the variation in photosynthesis-related genes among aerobic anoxygenic phototrophs.

Degradation of ester linkages in rice straw components by Sphingobium species recovered from the sea bottom using a non-secretory tannase-family α/β hydrolase.

Microbial decomposition of allochthonous plant components imported into the aquatic environment is one of the vital steps of the carbon cycle on earth. To expand the knowledge of the biodegradation of complex plant materials in aquatic environments, we recovered a sunken wood from the bottom of Otsuchi Bay, situated in northeastern Japan in 2012. We isolated Sphingobium with high ferulic acid esterase activity. The strain, designated as OW59, grew on various aromatic compounds and sugars, occurring naturally in terrestrial plants. A genomic study of the strain suggested its role in degrading hemicelluloses. We identified a gene encoding a non-secretory tannase-family α/β hydrolase, which exhibited ferulic acid esterase activity. This enzyme shares the consensus catalytic triad (Ser-His-Asp) within the tannase family block X in the ESTHER database. The molecules, which had the same calculated elemental compositions, were produced consistently in both the enzymatic and microbial degradation of rice straw crude extracts. The non-secretory tannase-family α/β hydrolase activity may confer an important phenotypic feature on the strain to accelerate plant biomass degradation. Our study provides insights into the underlying biodegradation process of terrestrial plant polymers in aquatic environments.

A New Method for Investigating Relationships Between Distribution of Sessile Organisms and Multiple Terrain Variables by Photogrammetry of Subtidal Bedrocks

Previous studies of habitat suitability of sessile organisms on subtidal rocky substrata have been focused only one or two terrain attributes. In this study, we propose a new method to construct a centimeter resolution seafloor topographic model by using underwater photogrammetry to obtain multiple terrain variables and to investigate relationships between the distribution of sessile organisms and multiple terrain variables. Point cloud models of five square sections (11.3–25.5 m2) of the bedrock surface of Otsuchi Bay were reconstructed with a 0.05 m resolution. Using the 0.01 m resolution point cloud models, five terrain variables were calculated on each face of the mesh models: height above seafloor, topological position index, slope, aspect, and ruggedness. The presence/absence data of four species of sessile organisms (ascidian Halocynthia roretzi, barnacle Balanus trigonus, polychaete Paradexiospira nakamurai, and articulated coralline algae Pachyarthron cretaceum) were located on the mesh models. H. roretzi and B. trigonus were more abundant on vertical and high faces above the seafloor, and P. nakamurai were more abundant at high faces above the surroundings. In high position where the current velocity increases, the three sessile animals may have an advantage for their suspension feeding. In contrast, P. cretaceum, unlike the other three sessile animal species, occurred at various heights and on gentle slope faces suitable for photosynthesis.

Wide-range detection of Cu-binding organic ligands in seawater using reverse titration

The toxicity and bioavailability of Cu in seawater were estimated using its chemical speciation. In this study, the concentrations and conditional stability constants (K'CuL) of Cu complexes with Cu-binding organic ligands (L) in seawater were determined using the reverse titration–competitive ligand exchange–adsorptive cathodic stripping voltammetry method. The concentrations of strong and weak ligands (L1 and L2, respectively) were determined using reverse titration via the addition of Cu to seawater samples to achieve ligand saturation. Our results revealed that the reverse titration method can be successfully used for the detection of high concentrations of L2. Using the reverse titration method, we detected L2 concentrations that exceeded 80 and 120 nM in seawater samples from the subtropical western North Pacific Ocean and Otsuchi Bay Japan, respectively. The K′CuL1 and K′CuL2 values obtained using the reverse titration method were comparable with those obtained using the forward titration method. Therefore, the reverse titration method can be used to determine the chemical speciation of Cu in the ocean and coastal regions as supplement to the more conventional forward titration method.

Aggregation of adult abalone Haliotis discus hannai during the spawning season, and its associations with seasonal and interannual changes in the macroalgal community

Clarification of the biological and/or physical factors determining the location requirements for spawning aggregations is necessary for understanding the population dynamics of free-spawning marine animals. We monitored the density of adult abalone Haliotis discus hannai on 2 types of artificial reefs with different heights (tall and short blocks) and the surrounding seabed area in Otsuchi Bay, northeast Japan, from February 2016 to December 2019. In addition, the number of neighboring adults located within a 50 cm radius from each individual was counted from March 2017 to December 2019. Algal succession in the 3 types of location (tall and small blocks, seabed) was monitored and compared with temporal fluctuations in adult abalone density. Our results show that the fluctuations in density were different among the 3 locations, especially during the spawning season (August-October). On tall blocks, clear increases in adult abalone density and number of neighboring adults were confirmed during the spawning seasons in 2016 and 2019. In contrast, there was no clear increase in the adult density on small blocks and surrounding bottom areas. Aggregations on the tall blocks clearly differed among the 4 years, and the difference was considered to be influenced by differences in the macroalgal species and coverage during the spawning season. This is the first study to report that a difference in phenology among algal species is a key factor in the formation of spawning aggregations of a free-spawning marine animal.