Jun Nishikawa

Fukushima-derived radionuclides in the ocean and biota off Japan

The Tōhoku earthquake and tsunami of March 11, 2011, resulted in unprecedented radioactivity releases from the Fukushima Dai-ichi nuclear power plants to the Northwest Pacific Ocean. Results are presented here from an international study of radionuclide contaminants in surface and subsurface waters, as well as in zooplankton and fish, off Japan in June 2011. A major finding is detection of Fukushima-derived 134Cs and 137Cs throughout waters 30–600 km offshore, with the highest activities associated with near-shore eddies and the Kuroshio Current acting as a southern boundary for transport. Fukushima-derived Cs isotopes were also detected in zooplankton and mesopelagic fish, and unique to this study we also find 110mAg in zooplankton. Vertical profiles are used to calculate a total inventory of ∼2 PBq 137Cs in an ocean area of 150,000 km2. Our results can only be understood in the context of our drifter data and an oceanographic model that shows rapid advection of contaminants further out in the Pacific. Importantly, our data are consistent with higher estimates of the magnitude of Fukushima fallout and direct releases [Stohl et al. (2011) Atmos Chem Phys Discuss 11:28319–28394; Bailly du Bois et al. (2011) J Environ Radioact, 10.1016/j.jenvrad.2011.11.015]. We address risks to public health and marine biota by showing that though Cs isotopes are elevated 10–1,000× over prior levels in waters off Japan, radiation risks due to these radionuclides are below those generally considered harmful to marine animals and human consumers, and even below those from naturally occurring radionuclides.

Distribution of salps near the South Shetland Islands during austral summer, 1990–1991 with special reference to krill distribution

Distribution and biomass of salps and Antarctic krill (Euphausia superba) were investigated near the South Shetland Islands during austral summer 1990–1991. Salp biomass ranged between 0 and 556 mgC·m−3 and was greatest at a station in the Bransfield Strait in late December 1990. Salp biomass was lower than that of E. superba. Two species of salps; Salpa thompsoni and Ihlea racovitzai were found, and the former was dominant numerically. Spatial distribution and generation composition of these two species was different. Spatial distributions of salps and E. superba did not overlap particularly so the January–February period. While E. superba was found mainly in the coastal area which showed high-chlorophyll a values, salps exhibited high biomass in the oceanic area with low chlorophyll a concentrations. Predation by salps on small krill and the competitive removal of food by them, are discussed as potential reasons for the relatively low abundance of E. superba at the stations where salps were present in great numbers.

Cellulose in the house of the appendicularianOikopleura rufescens

SummaryBy electron diffraction analysis, highly crystalline cellulose Iβ was found in the house (a special structure in which the tunicate lives) of the appendicularianOikopleura rufescens. Cellulose microfibrils 20 nm in width were observed in a random array or highly organized with rectangular spacing of 2 to 10 (im in the house. The bundled cellulose microfibrils formed in the inlet filters, which are highly ordered meshwork structures. This paper provides the first account of the existence of cellulose in the house of an appendicularian. Our findings showed that the house and tunic are homologous tissues among the tunicates, and that the common ancestor of the tunicates (ascidians, thaliaceans, and appendicularians) already possessed cellulose-biosynthetic ability.

Abundance and grazing impacts of krill, salps and copepods along the 140°E meridian in the Southern Ocean during summer

Abstract Abundance and grazing impacts of krill, salps and herbivorous copepods were investigated in Antarctic waters along the 140°E meridian, south of Australia, during the summers of 2002 and 2003. North of the Southern Boundary of the Antarctic Circumpolar Current (SB-ACC), macrozooplankton comprised species of Salpa thompsoni and large herbivorous copepods, while the area south of the SB-ACC was numerically dominated by Euphausia superba or E. crystallorophias. North of the SB-ACC, the estimate of grazing impact revealed that krill, salps and copepods, Calanoides acutus, Calanus propinquus, Rhincalanus gigas and Metridia gerlachei, are able to remove a maximum of 37% of the total phytoplankton standing stock in early to midsummer, but grazing is negligible in late summer. The high grazing impact is attributed to the relatively high zooplankton abundance and low phytoplankton abundance. South of the SB-ACC, overall daily grazing impact of the three zooplankton groups was low and did not exceed 6% of the total phytoplankton standing stock throughout the investigation period. Present results indicate that the contribution of krill, salps and copepods varies seasonally as well as regionally across the SB-ACC. It seems that the carbon transport from surface to deep water by macro- and mesozooplankton in summer in this area is relatively large north of the SB-ACC but small south of the SB-ACC.

Evaluation of the bioactivities of water-soluble extracts from twelve deep-sea jellyfish species

Many polypeptides isolated from shallow water cnidarian species have been utilized as valuable biochemical tools in both basic and applied biological sciences. Deepwater cnidarian species might be another potential resource for novel biochemical tools. However, because of limited access to cnidarian samples from deep-sea environments, bioactive polypeptides have never before been reported from this group. In this study, we collected twelve deep-sea jellyfish species (nine hydrozoans and three scyphozoans) using a plankton net that was specially designed for collecting deep-sea organisms, and prepared water-soluble extracts, presumably containing polypeptides, of these jellyfishes. The extracts were subjected to cytotoxicity, hemolytic activity, and crustacean lethal toxicity tests. In the cytotoxicity test, six out of the nine tested hydrozoan species showed activity. In the hemolytic activity test, only three hydrozoans showed activity and none of the scyphozoan jellyfishes showed activity. In the crustacean lethality test, two hydrozoan jellyfishes and all three of the tested scyphozoan jellyfishes showed lethal activity. These results revealed a high incidence of water-soluble bioactive substances occurring in these deep-sea jellyfishes. Furthermore, all the heat-treated and the methanol-treated crude jellyfish extracts lost their bioactivities. Thus, it is likely that the bioactive compounds in the water-soluble extracts were unstable polypeptides (proteins). This is the first published report on bioactivities in extracts from deep-sea jellyfishes.

The untethered remotely operated vehicle PICASSO-1 and its deployment from chartered dive vessels for deep sea surveys off Okinawa, Japan, and Osprey Reef, Coral Sea, Australia

The untethered remotely operated vehicle (uROV) PICASSO-1, which is controlled in real time from a surface support vessel via a F0.9 mm fiber optic cable, is capable of dives to 1,000-m depth at a duration of up to 6 h and yet is deployable from ships of sizes as low as 17 tonnes. The vehicle was developed at the Japan Agency for Marine-Earth Science and Technology, has carried out 63 dives to date, and is now operable by a team of four biologists and one technician. PICASSO-1 can collect video (HDTV × 1, NTSC × 3) and environmental information (depth, temperature, salinity, dissolved oxygen concentration, fluorescence [chlorophyll a proxy], turbidity) concurrently, and this is output with vehicle heading, camera zoom, and other vital statistics via Ethernet. Acoustically obtained vehicle position information, deck and control room video, and sound data streams are also output via Ethernet, and the whole dive is recorded in a synchronous fashion on a logging/playback system that enables dives to be re-enacted in their entirety to facilitate analyses back in the laboratory. Operations have been successfully carried out overseas using a chartered dive boat, and the system represents a leap forward for exploration of the oceans to significant depths but at relatively low cost and with no loss in data quality.

Biomass, Abundance, and Vertical Distribution of Micronekton and Large Gelatinous Zooplankton in the Subarctic Pacific and the Bering Sea during the Summer of 1997

The biomass, abundance, and vertical distribution of micronekton, including enidarians, mysids, euphausiids, decapods, thaliaceans, and fishes, were studied on the basis of samples collected with an 8-m2 opening-closing rectangular midwater trawl (RMT-8, mesh size: 4.5 mm) at three stations in the subarctic Pacific (the western subarctic gyre, the central Subarctic, and the Gulf of Alaska) and one station in the oceanic Bering Sea. The total biomass in the 0–1000 m water column ranged from 2.9 to 5.1 gDW m−2. Except for primary consumers that showed highly variable biomass (thaliaceans and euphausiids), biomass was highest in the oceanic Bering Sea followed by the central (boundary between eastern and western gyres), western gyre, and eastern Gulf of Alaska. The biomass compositions by higher taxa were basically similar between regions: fishes were most dominant, followed by enidarians at all stations, except for the marked predominance of thaliaceans in the Gulf of Alaska. High biomasses of gelatinous animals (31% of overall dry weight), occasionally comparable to those of fishes and crustaceans, suggest their potential importance in the subarctic Pacific. Characteristics in vertical patterns of micronekton biomass common in all stations were: (1) a mesopelagic peak around 500–600 m both day and night, (2) a layer of low biomass in the cold intermediate water and/or in the upper mesopelagic zone, (3) a nighttime shift of biomass to upper layers, and (4) an highly variable biomass of epipelagic/interzonal migrants (euphausiids and thaliaceans).

Nutritional composition and total collagen content of three commercially important edible jellyfish.

The study aimed to evaluate nutraceutical potential of three commercially significant edible jellyfish species (Acromitus hardenbergi, Rhopilema hispidum and Rhopilema esculentum). The bell and oral arms of these jellyfishes were analyzed for their proximate composition, calorific value, collagen content, amino acid profile, chemical score and elemental constituent. In general, all jellyfish possessed low calorific values (1.0-4.9 kcal/g D.W.) and negligible fat contents (0.4-1.8 g/100 g D.W.), while protein (20.0-53.9 g/100 g D.W.) and minerals (15.9-57.2g/100g D.W.) were found to be the richest components. Total collagen content of edible jellyfish varied from 122.64 to 693.92 mg/g D.W., accounting for approximately half its total protein content. The dominant amino acids in both bell and oral arms of all jellyfish studied includes glycine, glutamate, threonine, proline, aspartate and arginine, while the major elements were sodium, potassium, chlorine, magnesium, sulfur, zinc and silicon. Among the jellyfish, A. hardenbergi exhibited significantly higher total amino acids, chemical scores and collagen content (p<0.05) compared to R. hispidum and R. esculentum. Having good protein quality and low calories, edible jellyfish is an appealing source of nutritive ingredients for the development of oral formulations, nutricosmetics and functional food.

In-situ Observations of Symbionts on Medusae Occurring in Japan, Thailand, Indonesia and Malaysia

During an ecological investigation on symbionts of medusae in Eastern and Southeastern Asian waters, seven species of hydro- and scypho-medusae were found to harbor a wide variety of invertebrates and fi shes: the isopod Idotea metallica and the nudibranch Fiona pinnata on the chondrophoran Vellela vellela; the actiniarian Peachia quinquecapitata on the leptomedusa Aequorea coerulescens; the butterfi sh Psenopsis anomala and the hyperiid amphipod Hyperia galba associated with the semaestome Chrysaora melanaster; H. galba on the semaestome Aurelia limbata; metacercariae of three species found in the mesogloea of a semaestome, Aurelia sp.; the ophiuroid Ophiocnemis marmorata, the caridean shrimp Latreutes spp., and the shrimp scad Alepes djedaba on the rhizostome Rhopilema hispidum; the swimming crab Charybdis feriata and A. djedaba on the rhizostome Versuriga anadyomene. Juveniles of benthic organisms such as crabs and ophiuroids seem to become hitchhikers for dispersal, while juvenile fi sh utilize medusae as refugia against predation. Since the previous and present studies have shown that edible rhizostomes are associated with many kinds of symbionts, fi sheries for these jellyfi shes possibly hinder the recruitment of symbionts such as decapods, ophiuroids and fi sh.

Still alive? Fine structure of the barrels made by Phronima (Crustacea: Amphipoda)

Amphipods of the genus Phronima are known to make a barrel-shaped house from the gelatinous matrix of pelagic tunicates or siphonophores. Among the seven barrels examined here, one barrel of Phronima curvipes was supposed to be made from a swimming bell of a siphonophore based on its morphology, while the other six barrels made by P. sedentaria were immunochemically and/or morphologically identified as tunicates (i.e. Thetys vagina , other salps and pyrosomas). Histological observation showed that the phronimids had completely eaten the animal tissues other than the gelatinous matrix (i.e. tunic or mesoglea). Tunic cells were found in the tunicate barrel and some were probably tunic phagocytes that appeared to be alive and functional. In the tunicate barrels, cuticular layers of the tunic were found on both the outer and inner side of the barrel wall. Tunic cuticle would be regenerated on the inner side after the epidermis was grazed by the phronimids. The cuticular layers would protect the tunic matrix from the invasion of microorganisms. In the barrel supposed to originate from Thetys vagina , there are minute protrusions on the tunic cuticle as found in the intact tunic of this species. In the barrel from a siphonophore, neither cells nor cuticle regeneration were found. No bacteria were observed in the barrel, suggesting that the barrel has some antibiotic system.