Suruga Bay Research Articles

Seasonal abundance of marine cladocerans in the offshore waters of Suruga Bay, Japan

Seasonal abundance of marine cladocerans in the offshore waters of Suruga Bay, Japan

Occurrence and levels of polybrominated diphenyl ethers (PBDEs) in deep-sea sharks from Suruga Bay, Japan

Few studies have investigated the prevalence of polybrominated diphenyl ethers (PBDEs) in deep-sea sharks. In this study, the levels and profiles of PBDEs were determined in liver samples of eight different species of deep-sea sharks collected in Suruga Bay, Japan. Widespread contamination of PBDEs in the deep-sea environment was reconfirmed in this study as these persistent organic pollutants (POPs) were detected in all specimens analyzed. Mean ΣPBDE levels in the deep-sea sharks ranged from 7 to 517 ng/g of lipid weight. The distribution patterns of BDE homologues were similar in all species where tetra-BDEs provided the dominant contribution to total PBDEs (46%). PBDEs levels were similar to, or higher than, those seen in other deep-sea sharks from different regions. The levels of PBDEs were likely to reflect their feeding preferences as higher PBDE levels were seen in species with higher trophic positions.

New Species of Lower-Shelf to Upper-Slope Ctenostome Bryozoans from Pacific Japan, with a Family Range Extension.

Ctenostome bryozoans were collected from depths of 150-300 m in Suruga Bay, the Kumano Sea, and off Sendai Bay on the Pacific coast of Japan. Among these samples were five new species, three of which were epibiotic on other animals. Alcyonidium clavum n. sp., found encrusting cirri of the stalked crinoid Metacrinus rotundus, was previously reported in Japan as Alcyonidium mamillatum, but differs from the latter in lacking rings on the peristome. Triticella parvacrista n. sp. and Triticella cunabula n. sp. were epibiotic on the isopod Bathynomus doederleini and the pycnogonid Ascorhynchus japonicum, respectively. This is the first record of the genus Triticella from Japanese waters. These species differ from previously described species in autozooidal morphology, particularly the dimensions of the autozooidal dilatation, in the presence or absence of the frenaculum, and in the septate junction between the dilatation and pedicel. Bockiella arcatumida n. sp., found as erect colonies on pebbles and hydroids collected off Sendai Bay, differs from previously known species in the size and arrangement of the kenozoids in the branch. Metalcyonidium morum n. sp., collected southwest of the Izu Peninsula, occurred as small colonies having a peduncle of short kenozooids. This is the first record from the northwestern Pacific for both the genus Metalcyonidium and the family Clavoporidae. Metalcyonidium morum n. sp differs from Metalcyonidium gautieri, the only other species known in the genus, in having the capitulum divided into two parts, and in the length of the kenozooids comprising the peduncle.

First Record of Elasmobranch Hosts for the Gnathiid Isopod Crustacean Thaumastognathia: Description of Thaumastognathia bicorniger sp. nov.

Gnathiid larvae (Crustacea; Isopoda; Gnathiidae) infesting elasmobranch and holocephalan fishes from mainly bathyal depths off Suruga Bay, off Kume-jima Island, and five sites from off Tokyo Bay to Shimoda City, Japan were examined. A total of 1460 gnathiid larvae were sampled from 87 host individuals belonging to seven families and 10 species. The morphology of these larvae was distinguishable from other gnathiid species by the head appendages. These larvae presented two pigmentation patterns, stripes or spots, on their dorsal thoraxes in live specimens. Furthermore, they were determined as the second and third stage praniza larvae on the basis of allometric variance of maximum head and abdomen widths. A third stage praniza with stripe pigmentation metamorphosed into an adult male and could be identified as a new species of the genus Thaumastognathia Monod, 1926. The duration between detachment from the host and metamorphosis into male adult required 204 days. This paper describes Thaumastognathia bicorniger sp. nov. on the basis of P3/stripe larvae and the male adult. This report is the first record of the larva and host information for a species of Thaumastognathia.

Account of the recent decline of the sakura-ebi fishery in Suruga Bay, Japan:Verifying the cause

Account of the recent decline of the sakura-ebi fishery in Suruga Bay, Japan:Verifying the cause

Growth and reproduction of the mole crab Hippa truncatifrons in Suruga Bay, central Japan

Growth and reproduction of the mole crab Hippa truncatifrons in Suruga Bay, central Japan

New Records of Azooxanthellate Scleractinian Corals (Cnidaria: Anthozoa) from Sagami Bay and Suruga Bay, Japan.

Sagami Bay and Suruga Bay harbor a rich marine biodiversity; however, their outer-shelf scleractinian coral fauna has not been characterized to date. Scleractinian corals were collected by dredge sampling of the Japanese Association for Marine Biology (JAMBIO) Coastal Organisms Joint Surveys in 2015 to elucidate the diversity of azooxanthellate scleractinian corals from the outer shelf zones of Sagami Bay and Suruga Bay. In this study, a total of 1291 azooxanthellate scleractinian specimens were collected, corresponding to 23 genera and 18 species, five of which are new records for Sagami Bay and eight are new records for Suruga Bay. Moreover, in all localities, except sampling locality (SL) 8, more than 70% of the specimens showed asexual reproduction. This finding suggests that asexual reproduction may play an important role in increasing the coral population size in soft-substrate environments of the outer shelf.

Surface-Layer Circulations in Suruga Bay Induced by Intrusions of Kuroshio Branch Water

The water mass structure in Suruga Bay is strongly influenced by open-ocean water. In particular, it is suggested that intermittent intrusions of the Kuroshio water generate characteristic circulations in the surface layer of the bay. In this study, we investigated the processes of the intrusions of open-ocean water into the bay and related generation of bay-scale cyclonic and anti-cyclonic circulation patterns. In doing so, we used an ocean simulation product with observational data constraint on meso and larger scales and with a resolution fine enough to resolve the smaller-scale intrusion structure. Cyclonic and anti-cyclonic circulation patterns as suggested by previous observational studies were detected as positive and negative first leading empirical orthogonal function (EOF) modes of the velocity field in Suruga Bay. The time scale of occurrences of these patterns was estimated as about 1 month, which was consistent with short-term Kuroshio fluctuations as reported in previous studies. Conditions favorable for generating these patterns were analyzed for three typical Kuroshio path periods individually. As suggested by previous studies, relatively strong northward flow to the west of Zeni-su generally promoted the open-ocean water intrusions into the eastern bay mouth, leading the cyclonic circulation in Suruga Bay. Our results showed that the correlation of this relation was significant for each Kuroshio path period. The open-ocean water intrusion increased the surface-layer temperature in Suruga Bay by about 0.7°C on average. On the other hand, the anti-cyclonic circulation pattern in Suruga Bay tended to be generated with relatively weak northward flow to the west of Zeni-su during the large meander Kuroshio path period, whereas this relation was rather weak during other periods. These results were mostly supported by available observations and would be useful for integrating our understanding of the influences of the western boundary current fluctuations on the circulation and temperature variations in proximal bays.

Improved geometry of the subducting Philippine Sea plate beneath the Suruga Trough

The Philippine Sea (PHS) plate subducts beneath the Eurasian plate at the Suruga Trough where megathrust earthquakes have repeatedly occurred. We used data from permanent seismic stations on land and temporary seismic stations beneath Suruga Bay to resolve the seismic velocity structure from the surface to 40–60 km depth beneath the Tokai region. The Median Tectonic line runs through the Tokai region and forms a boundary between high-V and low-V zones. We constrained the configuration of the subducting PHS plate using results from seismic tomography, hypocentral distribution of microseismicity, and low-angle thrust-type earthquakes. The oceanic crust of the PHS plate is characterized by low-V and high-Vp/Vs values. Events with thrust-type focal mechanisms are expected at the plate boundary. We constructed the geometry of the surface of the subducting PHS plate using this information. This geometry is also consistent with the results of receiver functions. The surface of the PHS plate is slightly (approximately 6–10 km) shallower than estimated from previous studies, especially in the zone extending from the Suruga Trough to a depth of 20 km. The data combination of permanent land and temporary OBS station with rays crossing the plate boundary clarify the plate configuration at the shallow subduction zone.

Baseline soundscapes of deep‐sea habitats reveal heterogeneity among ecosystems and sensitivity to anthropogenic impacts

AbstractUnderwater soundscapes, though invisible, are crucial in shaping the biodiversity of marine ecosystems by acting as habitat‐specific settlement cues for larvae. The deep sea has received little attention in soundscape research, but it is being targeted for mineral extraction to feed the ever‐growing needs of our society. Anthropogenic impacts on soundscapes influence the resilience of key shallow‐water habitats, and the same likely applies to the deep. Japan is a forerunner in deep‐sea mining, but virtually no deep soundscape baselines exist for Japanese waters. Here, we report baseline soundscapes from four deep‐sea locations in Japan, including the Suiyo Seamount hydrothermal vent, the abyssal plain around the Minamitorishima Island home to manganese nodule fields and muds rich in rare‐earth elements, twilight depths off Sanriku, as well as a typical bathyal system in Suruga Bay. Long‐duration audio recordings were visualized and factorized by an unsupervised machine learning model, revealing differing characteristics among the habitats. Two locations near the coast are highly influenced by shipping noise. The Suiyo vent is characterized by low‐frequency sounds from venting, and the abyssal Minamitorishima is quiet with a flat spectral shape. Noise from observation platforms is likely sufficient to alter soundscape characteristics, especially in offshore locations, suggesting offshore mining‐targeted areas are susceptible to impacts from anthropogenic noise. We argue that the monitoring of soundscapes is an indispensable component for assessing potential mining impacts on deep‐sea ecosystems. Our results establish reference points for future soundscape monitoring and assessment in Japanese waters as well as similar ecosystems globally.

Seasonal and vertical variations in phytoplankton photosynthetic parameters and primary production in Suruga Bay, Japan

Seasonal and vertical variations in phytoplankton photosynthetic parameters and primary production in Suruga Bay, Japan

Carotenoid Nostoxanthin Production by Sphingomonas sp. SG73 Isolated from Deep Sea Sediment.

Carotenoids are used commercially for dietary supplements, cosmetics, and pharmaceuticals because of their antioxidant activity. In this study, colored microorganisms were isolated from deep sea sediment that had been collected from Suruga Bay, Shizuoka, Japan. One strain was found to be a pure yellow carotenoid producer, and the strain was identified as Sphingomonas sp. (Proteobacteria) by 16S rRNA gene sequence analysis; members of this genus are commonly isolated from air, the human body, and marine environments. The carotenoid was identified as nostoxanthin ((2,3,2′,3′)-β,β-carotene-2,3,2′,3′-tetrol) by mass spectrometry (MS), MS/MS, and ultraviolet-visible absorption spectroscopy (UV-Vis). Nostoxanthin is a poly-hydroxy yellow carotenoid isolated from some photosynthetic bacteria, including some species of Cyanobacteria. The strain Sphingomonas sp. SG73 produced highly pure nostoxanthin of approximately 97% (area%) of the total carotenoid production, and the strain was halophilic and tolerant to 1.5-fold higher salt concentration as compared with seawater. When grown in 1.8% artificial sea salt, nostoxanthin production increased by 2.5-fold as compared with production without artificial sea salt. These results indicate that Sphingomonas sp. SG73 is an efficient producer of nostoxanthin, and the strain is ideal for carotenoid production using marine water because of its compatibility with sea salt.

Governing in an uncertain time: the case of Sakura shrimp fishery, Japan

Known as the “Jewel of Suruga Bay,” Sakura shrimp has long been an important fishery that supports the economy of the local communities in Suruga Bay, Shizuoka, Japan. The fishery experienced an unprecedented decline in 2018, with the catch volume falling to 312 mt, which is about one-fourth of the average catch from 2010 to 2017. This has led to the questioning of the pooling system, considered an effective management system in the long history of the fishery. Other natural and anthropogenic factors have also been discussed as possible causes of the resource decline. Through a pre- and post-crisis analysis, this paper examines the complex issues and challenges facing the Sakura shrimp fishery, focusing specifically on the performance of the governance system, given its structure and functions. Drawing on informal discussion with key stakeholders involved in the fishery and field observation, the paper discusses the nature of the problem and proposes transdisciplinarity as a new lens for governing the shrimp fishery in a time of uncertainty.

Recent Shoreline Changes Due to High-Angle Wave Instability along the East Coast of Lingayen Gulf in the Philippines

A small perturbation on the shoreline may develop under high-angle wave conditions, resulting in the formation of sand spits along the shoreline. Serizawa et al. explained the development of sand spits caused by the instability mechanism using the BG model (a model for predicting 3-D beach changes based on Bagnold’s concept). However, examples of the development of sand spits caused by this mechanism in the field are limited in number. Lingayen Gulf in the Philippines has a large aspect ratio, so shoreline instability occurs along the coastline, significantly affecting the shore protection along the coast. In this study, the shoreline instability along the river delta coasts around the Balili and Aringay Rivers flowing into Lingayen Gulf and a sand spit were investigated using satellite images together with field observation. The shoreline changes observed south of the Aringay River mouth were compared with those observed in a previous study on the development of a sand spit by San-nami et al. The rate of longshore sand transport to form a sand spit at Santo Tomas in Lingayen Gulf was estimated to be approximately 1.3 × 105 m3/yr, which is in good agreement with the value measured on the Shimizu coast in Suruga Bay, with a comparable aspect ratio of 1.2 relative to 1.3 in Lingayen Gulf. It was concluded that shoreline undulations have evolved downcoast of two river deltas owing to high-angle wave instability along the east coast of Lingayen Gulf and the formation of a sand spit has occurred. A soft measure, such as sand bypassing, would be better to be adopted along the coasts in Lingayen Gulf instead of hard measures against erosion, to prevent rapid expansion of an artificial, protected coastline.

First record of swimming speed of the Pacific sleeper shark Somniosus pacificus using a baited camera array

AbstractThe Pacific sleeper shark Somniosus pacificus is one of the largest predators in deep Suruga Bay, Japan. A single individual of the sleeper shark (female, ~300 cm in total length) was observed with two baited camera systems deployed simultaneously on the deep seafloor in the bay. The first arrival was recorded 43 min after the deployment of camera #1 on 21 July 2016 at a depth of 609 m. The shark had several remarkable features, including the snout tangled in a broken fishing line, two torn anteriormost left-gill septums, and a parasitic copepod attached to each eye. The same individual appeared at camera #2, which was deployed at a depth of 603 m, ~37 min after it disappeared from camera #1 view. Finally, the same shark returned to camera #1 ~31 min after leaving camera #2. The distance between the two cameras was 436 m, and the average groundspeed and waterspeed of the shark were 0.21 and 0.25 m s−1, respectively, which were comparable with those of the Greenland shark Somniosus microcephalus (0.22–0.34 m s−1) exhibiting the slowest comparative swimming speed among fish species adjusted for size. The ambient water temperature of the Pacific sleeper shark was 5.3 °C, which is considerably higher than that of the Greenland shark (~2 °C). Such a low swimming speed might be explained by the ‘visual interactions hypothesis’, but it is not a consequence of the negative effects of cold water on their locomotor organs.

Discovery of a colossal slickhead (Alepocephaliformes: Alepocephalidae): an active-swimming top predator in the deep waters of Suruga Bay, Japan

A novel species of the family Alepocephalidae (slickheads), Narcetes shonanmaruae, is described based on four specimens collected at depths greater than 2171 m in Suruga Bay, Japan. Compared to other alepocephalids, this species is colossal (reaching ca. 140 cm in total length and 25 kg in body weight) and possesses a unique combination of morphological characters comprising anal fin entirely behind the dorsal fin, multiserial teeth on jaws, more scale rows than congeners, precaudal vertebrae less than 30, seven branchiostegal rays, two epurals, and head smaller than those of relatives. Mitogenomic analyses also support the novelty of this large deep-sea slickhead. Although most slickheads are benthopelagic or mesopelagic feeders of gelatinous zooplankton, behavioural observations and dietary analyses indicate that the new species is piscivorous. In addition, a stable nitrogen isotope analysis of specific amino acids showed that N. shonanmaruae occupies one of the highest trophic positions reported from marine environments to date. Video footage recorded using a baited camera deployed at a depth of 2572 m in Suruga Bay revealed the active swimming behaviour of this slickhead. The scavenging ability and broad gape of N. shonanmaruae might be correlated with its colossal body size and relatively high trophic position.

16S rRNA Gene Amplicon Sequencing of Gut Microbiota in Three Species of Deep-Sea Fish in Suruga Bay, Japan.

We report here 16S rRNA gene amplicon sequence analysis of the gut microbiota in three species of deep-sea fish collected from Suruga Bay, Japan. Of the three species, two were dominated by the phylum Proteobacteria (genus Photobacterium), while one was dominated by the phyla Spirochaetes (genus Brevinema) and Tenericutes (unclassified Mycoplasmataceae).

Turbidity Current in the Northern Suruga Bay Recorded by Ocean Bottom Seismographs after Passing Typhoon No. 24 in 2018

Turbidity Current in the Northern Suruga Bay Recorded by Ocean Bottom Seismographs after Passing Typhoon No. 24 in 2018

Deep-sea water displacement from a turbidity current induced by the Super Typhoon Hagibis.

Turbidity currents are the main drivers behind the transportation of terrestrial sediments to the deep sea, and turbidite deposits from such currents have been widely used in geological studies. Nevertheless, the contribution of turbidity currents to vertical displacement of seawater has rarely been discussed. This is partly because until recently, deep-sea turbidity currents have rarely been observed due to their unpredictable nature, being usually triggered by meteorological or geological events such as typhoons and earthquakes. Here, we report a direct observation of a deep-sea turbidity current using the recently developed Edokko Mark 1 monitoring system deployed in 2019 at a depth of 1,370 m in Suruga Bay, central Japan. A turbidity current occurred two days after its probable cause, the Super Typhoon Hagibis (2019), passed through Suruga Bay causing devastating damage. Over aperiod of 40 hours, we observed increased turbidity with turbulent conditions confirmed by a video camera. The turbidity exhibited two sharp peaks around 3:00 and 11:00 on October 14 (Japan Standard Time). The temperature and salinity characteristics during these high turbidity events agreed with independent measurements for shallow water layers in Suruga Bay at the same time, strongly suggesting that the turbidity current caused vertical displacement in the bay’s water column by transporting warmer and shallower waters downslope of the canyon. Our results add to the previous few examples that show meteorological and geological events may have significant contributions in the transportation of shallower seawater to the deep sea. Recent technological developments pertaining to the Edokko Mark 1 and similar devices enable straightforward, long-term monitoring of the deep-seafloor and will contribute to the understanding of similar spontaneous events in the deep ocean.

Effect of diatom abundance and biogenic silica availability on the population growth of tintinnid ciliates at Suruga Bay

The effects of diatom abundance and biogenic silica (BSi) deposition on the population growth of tintinnid ciliates were investigated using incubations of sub-surface waters (10 m depth) of Suruga Bay, Japan in April and November 2018. Seawater for incubation was pre-filtered using a 200-µm mesh to remove mesozooplankton grazers. Initial concentrations of dissolved inorganic nitrogen were similar in both seasons, but silicic acid and phosphate were higher in April than in November. This allowed us to observe the growth of planktonic communities under varied silicic acid availability and explore the effects of BSi accumulation and food availability on the growth of tintinnids. Phytoplankton blooms dominated by diatoms formed in both, April and November incubations, but their biomass was higher in April than in November, demonstrating the effects of nutrients, particularly silicic acid, on diatom growth. The BSi concentration increased in both incubations but was higher in April than in November, confirming the effects of diatom abundance and size on BSi deposition. Tintinnid biomass also increased in both incubations but was higher in April than in November, showing that the biomass of tintinnid was affected by the BSi concentration. Species composition of diatoms affected the species composition of tintinnids by providing selected material for the construction of their lorica. Moreover, the results showed that the food supply mainly provided by pico-nanoflagellates via microbial loop and detritus may limit tintinnids’ population growth in natural planktonic ecosystems and this demonstrates tintinnids’ role as top predators in the microbial loop