Suruga Bay Research Articles

A Preliminary Study of the Age and Growth Patterns of a Sea Toad, Chaunax abei Le Danois, 1978, in Suruga Bay, Japan

Chaunax abei Le Danois, 1978, is a bottom-dwelling species caught by bottom trawls in Suruga Bay. In the present study, we assessed the age and growth pattern of C. abei from Suruga Bay during the period of 2021–2022 for the first time. The total length (TL) of the population ranged from 37.4–268.8 mm (mean ± SD: 124.7 ± 3.64 mm), and the fish weight (W) between 1.11–491.75 g (mean ± SD: 58.40 ± 7.25 g). The length-weight relationship was estimated as 𝑊𝑊=(2.07 × 10−5)𝑇𝑇𝑇𝑇2.996 (r2 = 0.937). Age determination was based on annual growth ring counts of transverse sections of the sagittal otoliths and age ranged from 1 to 12 years, with the majority of fish aged 4 (32.79 %) years old. The von Bertalanffy growth function was used to model the growth, and the parameters were found as: TL∞ = 468.1 mm, K = 0.056 year-1, t0 = -0.402 year. This research provides the first results on the growth of C. abei and enriches the regional fisheries biology database. Furthermore, it presents the primary population data on the growth patterns of one of the chaunacid species.

Kurbağa balığında (Chaunax abei Le Danois, 1978) Suruga Körfezi’ndeki (Japonya) tek gözlülük (tek taraflı anoftalmi)

The first case of monocularism (unilateral anophthalmia) was observed in a single specimen of Chaunax abei (Le Danois, 1978) during the seasonal trawl sampling in Suruga Bay in 2021. This occurrence marks the first reported incident of such an abnormality within the Chaunacid species. The monocularism was evidenced by photographs, and descriptive statistics of morphometric characters were presented.

Biodegradability of oxidized films of polyhydroxyalkanoate copolymers containing 2-hydroxy-4-methylthiobutyrate unit in seawater

Polyhydroxyalkanoate (PHA) copolymers consisting of 3-hydroxybutyrate, 2-hydroxy-4-methylthiobutyrate (2H4MTB), and 2-hydroxy-4-methylvalerate were biosynthesized by recombinant Escherichia coli using L-methionine as the 2H4MTB precursor. The 2H4MTB unit contains a sulfide group in its side chain that can be oxidized to sulfoxide and sulfone groups by oxidants, thereby increasing the hydrophilicity of the polymer. The PHAs were biosynthesized at 3.9, 9.2, and 13.9 mol% 2H4MTB, and their polymer films were oxidized with hydrogen peroxide. The surface of the oxidized film was characterized using Fourier-transform infrared spectroscopy, Raman spectroscopy, and contact angle analysis. The oxidized films with 13.9 mol% 2H4MTB showed a 30° lower water contact angle than the non-oxidized films. To assess their marine biodegradability, the PHA films were immersed for 114 days in seawater continuously pumped from two depths (24 and 397 m) in Suruga Bay, Shizuoka, Japan. The weight loss of the films immersed in deep seawater was higher than that of those immersed in surface seawater. Additionally, there was a tendency for higher degradation of the oxidized films than that of the non-oxidized films, which was also confirmed by the biochemical oxygen demand test. In the surface morphology analysis by scanning electron microscopy, irregularities were observed in the degraded films, but their morphologies differed between the oxidized and non-oxidized films. Based on these observations, the biodegradation of the PHA films in seawater is discussed.

Two New Genera and Species of the Parasitic Copepod Family Chondracanthidae Milne Edwards, 1840 (Copepoda: Cyclopoida) from Deep-Sea Fishes Off Suruga Bay, Japan

PurposeThe present paper describes two new genera and species of the parasitic copepod family Chondracanthidae Milne Edwards, 1840 based on specimens collected from two species of deep-sea fishes at a depth of 212 m off Suruga Bay, Japan. Avatar nishidaigen. et sp. nov. is described from the host fish Chaunax abei Le Danois, 1978 (Chaunacidae). Kokeshioides surugaensisgen. et sp. nov. is described from the host fish Setarches longimanus (Alcock, 1894) (Setarchidae).MethodsFresh specimens of chondracanthids were collected from the buccal cavity of two species of deep-sea fishes (fish hosts were frozen), Chaunax abei Le Danois, 1978 (Lophiiformes: Chaunacidae) and Setarches longimanus (Alcock, 1894) (Perciformes: Setarchidae), caught at a depth of 212 m in Suruga Bay, Japan (34° 37′48.87″ N, 138° 43′2.958″ E). Both the species are described and illustrated based on ovigerous females.ResultsThe genus Avatargen. nov. can readily be distinguished from all other chondracanthid genera by the following combination of features: cephalothorax slightly wider than long with anterior pair of large and posterior pair of small lateral lobes, and two pairs of ventro-lateral processes; the very posteriormost part of the first pedigerous somite contributes to the neck; cylindrical trunk with two pairs of blunt proximal fusiform processes; antennule with small knob terminally; antenna bearing distal endopodal segment; labrum protruding ventrally; two pairs of biramous legs each with 2-segmented rami. Kokeshioidesgen. nov. has the following combinations of features that distinguish it from other chondracanthid genera: body flattened, without lateral processes; cephalothorax much wider than long, with paired anterolateral and posterolateral lobes, folded ventrally; the very posteriormost part of the first pedigerous somite contributes to the neck; mandible elongate; legs unique, heavily sclerotized, represented by two pairs of acutely pointed processes.ConclusionWith the addition of two new genera presently reported, the family Chondracanthidae currently includes 52 valid genera. Among the described genera Avatargen. nov. seems to be very primitive, while Kokeshioidesgen. nov. is highly advanced. The deduced evolutionary history of chondracanthid genera is also discussed.

Regime shift in the northernmost coral ecosystem: decline of the threatened coral Acropora pruinosa due to grazing by Diadema setosum

Once thriving in Suruga Bay, Japan, the threatened coral species, Acropora pruinosa, faced drastic declines due to climate change and sea urchin grazing. Fourteen-years of observation (2009–2023) showed near extinction, highlighting the urgent need for conservation of corals, even in temperate zones, to preserve biodiversity.

Reproductive biology and sperm storage characters in two bobtail squid species (Cephalopoda: Sepiolidae)

Abstract Bobtail squids (Family Sepiolidae) have a variety of sperm storage patterns, but their reproductive biology has not been studied in many species, especially those in Japanese waters. Two species, Austrorossia bipapillata (Subfamily Rossiinae) and Sepiolina nipponensis (Subfamily Heteroteuthinae) inhabit Suruga Bay in Japan. These were sampled approximately bimonthly by trawling at around 500 m between the end of September, 2020 and May, 2022. They were measured for body size (dorsal mantle length) and weighed for gonadosomatic index (GSI) calculation, and their sperm storage mechanism was investigated. The reproductive season occurs from May to October in A. bipapillata and from December to February in S. nipponensis. In both species, spermatangia were deposited inside the mantle cavity as implanted spermatangia. In A. bipapillata, 5.7 ± 6.5 spermatangia were deeply implanted in the opening of the oviduct, and in S. nipponensis 62.7 ± 61.5 spermatangia were attached to the left gill and surface of the connective-tissue capsule enclosing the digestive gland. The GSI was lower and there were fewer spermatophores stored in the spermatophoric sac of A. bipapillata males compared to S. nipponensis, leading us to suggest that it is exposed to weaker sperm competition than S. nipponensis, irrespective of similar sperm storage mechanism in the two species.

A new genus and new species of palaemonid shrimp (Decapoda: Caridea), associated with the deep-sea crinoid Metacrinus rotundus (Echinodermata: Isocrinidae), from Suruga Bay, Japan.

Metacrimenes fenestra, a new palaemonid genus and species is described on the basis of an ovigerous female and one juvenile specimen from Suruga Bay, central Japan. The specimens were associated with the stalked crinoid Metacrinus rotundus Carpenter, 1885, collected at a depth of 131200 m. Photographs taken in situ indicate that the shrimp lives ectosymbiotically on its crinoid host. The greatly reduced bud-like exopod on the third maxilliped links the new genus to Mesopontonia Bruce, 1967 (Indo-West Pacific) and Waldola Holthuis, 1951 (East Pacific), in which the exopod is absent, but the presence of antennal spine on the carapace and the non-elongate, symmetrical second pereopods immediately distinguish Metacrimenes n. gen. from these genera. Molecular phylogenetic analysis using a dataset concatenating two mitochondrial markers (16S rRNA and COI genes) clusters the new genus with Paraclimenes gorgonicola (Bruce, 1967), two species of Mesopontonia and Brucecaris tenuis (Bruce, 1969). However, in Paraclimenes Bruce, 1995 and Brucecaris Marin & Chan, 2006, the third maxilliped exopod is normally developed, flagellum-like. Other differentiating characters between the new taxon and the presumably allied taxa are discussed.

Refraction Seismic Survey in Suruga Bay Using OBSs and Air-gun Sources: Increased Subsurface Velocity Structure Observed at the Northern Part of the Senoumi Bank

Refraction Seismic Survey in Suruga Bay Using OBSs and Air-gun Sources: Increased Subsurface Velocity Structure Observed at the Northern Part of the Senoumi Bank

Isolation and characterization of polyhydroxyalkanoate-degrading bacteria in seawater at two different depths from Suruga Bay.

Polyhydroxyalkanoate (PHA) is a highly biodegradable microbial polyester, even in marine environments. In this study, we incorporated an enrichment culture-like approach in the process of isolating marine PHA-degrading bacteria. The resulting 91 isolates were suggested to fall into five genera (Alloalcanivorax, Alteromonas, Arenicella, Microbacterium, and Pseudoalteromonas) based on 16S rRNA analysis, including two novel genera (Arenicella and Microbacterium) as marine PHA-degrading bacteria. Microbacterium schleiferi (DSM 20489) and Alteromonas macleodii (NBRC 102226), the type strains closest to the several isolates, have an extracellular poly(3-hydroxybutyrate) [P(3HB)] depolymerase homolog that does not fit a marine-type domain composition. However, A. macleodii exhibited no PHA degradation ability, unlike M. schleiferi. This result demonstrates that the isolated Alteromonas spp. are different species from A. macleodii. P(3HB) depolymerase homologs in the genus Alteromonas should be scrutinized in the future, particularly about which ones work as the depolymerase.

Ocean Bottom Seismometers in Suruga Bay reveal a shear zone inside the Philippine Sea plate slab

Suruga Bay lies along the Tokai segment of the Nankai-trough, which last ruptured in the 1854 M8.4 Ansei-Tokai Earthquake, making it a potential locus for the next major earthquake on the Nankai-trough. Moderate size earthquakes have occurred in the Suruga Trough axial region (M6.5 in 2009 and M6.2 in 2011) that resulted in a prominent excitation of seismicity. Unfortunately, our ability to accurately locate these events is hampered by a sparse routine seismic observation network around the bay. In order to improve location accuracy, a total of 2 sets of 7 OBSs were deployed inside Suruga Bay, 6 from the spring of 2017, and an additional OBS from spring 2019. By combining the data from our OBS stations with that of existing land-based stations surrounding Suruga Bay, we were able to accurately relocate the observed seismic activity inside the Philippine Sea plate (PHS). Our combined processing revealed a 25° northwest-dipping 2–5 km wide zone on which the regional seismic activity occurs. Overall, seismic activity is observed to be 5–10 km shallower than previously determined from routine network data alone. A striking feature of the analyzed activity is the presence of a prominent strike-slip component in the focal mechanisms, which exhibit P-axes almost exclusively oriented towards the north. Furthermore, taking into consideration the apparent difference in the direction of the P-axis of the stress field to the calculated sense of movement of Izu peninsula by GNSS data, and the ongoing internal deformation observed by geodetic and geological data, we propose the existence of a shear zone inside the subducting PHS starting from the southern tip of Izu Peninsula and extending across the bay under Shizuoka city. This zone of strain partitioning acts as a buffer between the northward-colliding Izu Peninsula and the northwest-directed subduction of the PHS observed by GNSS.

16S rRNA Gene Amplicon Sequencing of the Gut Microbiota of Chimaera phantasma (Silver Chimaera) Captured off Koshimoda in Suruga Bay, Japan

The intestinal microbiota of Chimaera phantasma (silver chimera) (two females and one male) collected off Koshimoda in Suruga Bay in April to May 2022 were comprehensively analyzed. Bacteria belonging to the phylum Proteobacteria were the dominant species. Occupancy rates of other bacterial phyla differed greatly among the samples.

Newly designed glass apparatus to conduct stepwise dissolution experiment for radiocarbon using fish otoliths

Isotopes and trace elements extracted from fish otoliths have been widely used to understand different fish habitats. Otoliths can track the life-long histories of fish habitats and can supplement the information that is often difficult to reconstruct using tagging methods. Due to the advancement of radiocarbon measurement techniques, small quantities can be prepared for this purpose, and radiocarbon can be used to understand the migration history by referring to the variations of radiocarbon in the surface ocean. One major drawback of otolith isotope methods is the length of time it takes to collect samples by milling before each sample can be measured by accelerator mass spectrometry. Sequential acid digestion systems can potentially offer a solution whereby each dissolution step can provide information of otolith growth. Here we designed a glass apparatus that can be used for this purpose. We tested the otoliths from the western Pacific roughy (Hoplostethus japonicus) caught in Suruga Bay off the coast of Japan to see if their otoliths can provide reliable information in reconstructing their life history. The results show radiocarbon concentrations in the otoliths gradually decreased, indicating the habitat depth of analyzed individuals gradually shifted from deep to shallow water demonstrating the promise of this method to understand fish habitats. This is consistent with expected behavior considering the oceanography of the region. Thus, stepwise dissolution using a newly designed glass apparatus, proposed here, can aid marine fish ecological studies using otoliths.

Steady-state density-driven flow and transport: Pseudo-transient parameter continuation

Density-driven flow and transport is one of the dominant physical processes in coastal aquifer systems. To better manage water resources in coastal areas, the interactions need to be understood between freshwater and denser seawater. Numerical models often suffer from excessive computational cost to simulate the equilibrium steady state due to the nonlinear nature of the governing equations to describe density-driven flow. This study suggests a pseudo-transient parameter continuation (PTPC) approach which combines two general solution strategies for nonlinear steady-state equations: the pseudo-transient continuation (PTC) and parameter continuation (PC) methods. The new method gradually adjusts the maximum density (or parameter continuation) in the transient simulation framework (or pseudo-transient). The PTPC method is generally supposed to converge as in PTC and as efficiently as PC when the scheduling for parameter adjustment is set to be optimal. Through a proof-of-concept example, it is illustrated that the solution path to the steady state in PTPC is in between the paths from the PTC and PC approaches, depending on the level of aggressiveness of the parameter adjustment scheduling. As yet being empirical, the PTPC approach is promising and can be applicable to efficiently solve other steady-state nonlinear equations. The method was successfully applied to characterize and better understand the groundwater flow system in the Suruga Bay area, Japan.

Cladoceran communities in offshore Suruga Bay, Japan: How are they formed?

Cladoceran communities in offshore Suruga Bay, Japan: How are they formed?

Occurrence mode of Holocene tsunami overwash controlled by the geomorphic development along the eastern Nankai Trough, central Japan

Re-analysis of the lithological, paleontological, and geochemical data of three lagoonal sediment cores reveal the tsunami overwash history from 8000 to 6500 cal BP along the northern Suruga Bay coast, facing the eastern Nankai Trough. The coring sites are located in a transcect 0.8, 1.5, and 1.7 km inland, respectively, from the coastline at the time the overwash events occurred. The washover sand beds are distinguished from the lagoonal muds by the presence of quartz and mica, which are abundant on the outer (marine) side of the lagoon, as well as marine shell fossils. The increased C/S ratio often associated with sand beds, reflects input of open seawater to the reductive lagoon, and supports this interpretation. A maximum of eight tsunami deposits were identified between ∼7800 and 6500 cal BP, many of which can be correlated between the three cores. The magnitude of tsunami overwash implied by the thickness and grain size of tsunami deposits, and increase of C/S ratio following their deposition is relatively large at ∼7500-7200 cal BP during the post-glacial sea level rise and decreases with time during the subsequent high sea level stand. This occurrence mode (timing and scale of formation) of tsunami washover is explained by temporal changes in coastal geomorphology, rather than differences in the magnitude of individual tsunamis. Around 7500-7200 cal BP, sea level rise equilibrated with or exceeded the growth of the bay mouth barrier, and tsunamis could easily cross the small barrier and enter the lagoon, leaving behind thick and coarse-grained deposits. As the barrier becomes larger during the subsequent sea-level highstand, only the highest-amplitude waves exceeded the height of the barrier. By ∼6500 years ago, the barrier was high enough to prevent tsunamis from entering the lagoon. Similarly, the occurrence mode of tsunami deposits reported along the coast of Suruga Bay and Enshu-nada over the past 6000 years can be explained in relation to the growth of coastal barriers.

Influence of suspended inorganic particles (kaolinite) on eggs and larvae of the pelagic shrimp Lucensosergia lucens

The pelagic shrimp Lucensosergia lucens is a commercially important species in Japan, predominantly harvested in Suruga Bay. It has been suggested that a marked decrease in the wild population over recent years is associated with an increased concentration of suspended particles. We tested the hypothesis that suspended inorganic particles (kaolinite) negatively affect the hatching ratio of fertilized eggs, and the survival, growth, and metamorphosis of nauplius and elaphocaris larvae. The relative hatching ratio of eggs decreased from 100 to 57.7% at 139 mg L−1 of kaolinite particles. Similarly, the relative survival ratio of nauplius larvae progressively decreased from 100% in filtered seawater to 73.6% after 72 h of exposure to 139 mg L−1 of kaolinite particles. Consequently, the survival ratio of elaphocaris larvae was greatly reduced at high particle concentrations. Exponential growth in the standard lengths of elaphocaris larvae occurred at particle concentrations < 6.9 mg L−1, but growth was inhibited at kaolinite concentrations > 20 mg L−1.

Diurnal Coastal Trapped Waves and Associated Deep‐Ocean Mixing Near the Head of Suruga Trough

AbstractCoastal submarine canyons are expected to be sites of enhanced turbulent mixing which create productive fishing areas in coastal waters. Recent studies suggested the potential role of diurnal coastal trapped waves (CTWs) in inducing significant turbulent mixing in coastal submarine canyons poleward of 30° where the diurnal tide becomes subinertial. Nevertheless, the detailed physical processes responsible for the generation and dissipation of CTWs in such submarine canyons have hardly been investigated so far. In the present study, to investigate the turbulent mixing processes associated with diurnal CTWs in submarine canyons, we carry out high‐resolution (Δx, Δy = 1/240°) non‐hydrostatic three‐dimensional numerical experiments focusing on Suruga Bay located at the north end of Suruga Trough, Japan. The numerical experiments show that diurnal (subinertial) tidal currents over the Izu Ridge generate CTWs which propagate cyclonically along the coast of Suruga Bay. In the middle of Suruga Bay, bottom‐intensified flow due to the diurnal CTWs interacts with rough seafloor topography to excite upward propagating internal lee waves, which create mixing hotspots extending high above the seafloor. The resulting diurnal (subinertial) tidal energy dissipation in Suruga Bay is found to be much larger than that associated with semidiurnal (superinertial) internal tides. Furthermore, it is found that baroclinic energy flux based on a simple barotropic‐baroclinic decomposition severely underestimates the wave energy flux in areas with high CTW activity. These results strongly indicate that the existence of CTWs might be a key factor to clarify the dissipation/mixing processes in submarine canyons.

Detection of the Largest Deep-Sea-Endemic Teleost Fish at Depths of Over 2,000 m Through a Combination of eDNA Metabarcoding and Baited Camera Observations

The Yokozuna Slickhead Narcetes shonanmaruae is a recently described deep-sea fish species and an active-swimming, relatively large top predator in Suruga Bay, Japan. Its only known habitat is the deepest part of the bay (&amp;gt;2,000 m); six individuals have been collected thus far (up to 138 cm in total length). During our monitoring survey of faunal diversity on seamounts within marine protected areas in Japanese waters, environmental DNA (eDNA) metabarcoding revealed the Yokozuna Slickhead 12S ribosomal RNA gene sequence on/around three seamounts belonging to the Nishi-Shichito Ridge (at depths of around 2,000 m) located 400–600 km south of the known locality. A baited camera system deployed at the foot of one of the three seamounts at a depth of 2,091 m captured a Yokozuna Slickhead individual that was over 250 cm in total length, threatening Pacific Grenadiers Coryphaenoides acrolepis around the bait and attacking the bait cage. A combination of eDNA metabarcoding and baited camera observation represents a powerful tool for the detection of rare predatory fish species and the study of their ecology even in the deep sea, thus helping to better understand vulnerable marine ecosystems and reveal the impact of the rapidly changing global ocean.

A new snailfish of the genus Careproctus (Cottoidei: Liparidae) from the Pacific coast of southern Japan

A new snailfish, Careproctus tomiyamai, is described on the basis of four specimens collected from Suruga Bay, Tosa Bay, and the Hyuga-nada Sea, southern Japan (600–808 m depth). It is distinguished from all currently recognized congeners by the following combination of characters: total vertebrae 56–58; dorsal-fin rays 51 or 52; anal-fin rays 44–46; pectoral-fin rays 30–32; pyloric caeca 9–13; body slender, maximum depth 15.6–22.8% standard length (SL); teeth on both jaws strongly trilobed; pectoral fin shallowly notched, longest lower lobe ray 9.8–14.3% SL [46.0–60.4% head length (HL)]; proximal pectoral radials 4 (3 + 1), upper portion of 1st and 3rd radials, and lower portion of 2nd radial notched; fenestrae in pectoral girdle 2, between scapula and 1st proximal radial, and 2nd and 3rd proximal radials; pelvic disk oval, wider than long, length 3.4–4.3% SL (14.2–19.3% HL), moderately to deeply cupped; peritoneum black in preserved specimens.

Single-cell genotyping of phytoplankton from ocean water by gel-based cell manipulation.

A comprehensive understanding of phytoplankton diversity is valuable for assessing an environment of interest as phytoplankton are primary producers in various aquatic food webs. Microscopic analyses are useful for diversity assessment based on characteristic cell morphologies. However, phylogenetic classification based solely on morphology requires an extremely high level of expertise. The genetic approach is another option for evaluating phytoplankton diversity; however, it cannot reveal morphological information. To integrate these two approaches, an original technology was developed, that is referred to as microcavity array (MCA)/gel-based cell manipulation (GCM). The model experiments using monocultures of various phytoplankton indicated that the efficiencies of cell recovery and isolation of single-cell plankton were dependent on cell size and shape. Cells with widths larger than the cavity width showed high level of recovery and isolation efficiency. Subsequent whole-genome amplification (WGA) of isolated single-cell plankton provided a sufficient amount (≈30μg) of WGA products for genetic analyses. Furthermore, it is showed that MCA/GCM could directly analyze phytoplankton in ocean water obtained from Suruga Bay, Japan, without any cumbersome pretreatment. These results indicate that MCA/GCM technology is a powerful tool for elucidating the phytoplankton diversity in marine environment.