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A new species of Leptostraca, Sarsinebalia agoensis sp. nov., from Ago Bay, Japan is described from specimens found at a depth of 120 m. The new species differs from other known Sarsinebalia species as follows: the compound eye has three distal lobes; the anterior margin of the first antennal segment has one distal process covered with setae; and the lateral margin of pleopod 1 exopod bears 5–6 simple, robust spines. A taxonomic key to all species of Sarsinebalia is also provided.

A new species of Leptostraca, Nebalia tagiri sp. nov. is described and illustrated. This species was sampled from 200 m depth at a hydrothermal field in Wakamiko Caldera of Kagoshima Bay, Japan. Nebalia tagiri sp. nov. is different from known Nebalia species as follows: rostral length 2.4 times as long as width; article 4 of antennule with 3–5 robust distal spines; antennular scale approximately twice as long as wide; article 3 of antenna with eight spines and nine spine-like setae along proximal half, two thin setae and six spine-like setae on external lateral face, six spines and four simple setae on distal margin; article 1 of second maxilla longer than article 2; article 2 of mandibular palp with two thin setae; exopod of pleopod 1 with 21 spines along lateral margin; furcal rami longer than combined length of pleonite 7 and telson; rounded denticles of pleonite 6 and 7; anal-plates ‘shoulder’ not distinct. Furthermore, this specimen is the first genus Nebalia found in the hydrothermal vent. The distribution and ecology of this new species is also discussed and a key to all species of Nebalia is provided.

Species composition, diversity and biomass of jellyfish (Cnidaria and Ctenophora), with their spatiotemporal distributions, were analyzed in the upper 1500 m of the Oyashio front, the Transition zone and the Kuroshio extension, off Tohoku, northeastern Japan, between May 2005 and March 2006. Species composition and abundance differed remarkably between the shallower layer and the deeper layer at the boundary of 300-500 m depth, where water density was within the range of the North Pacific Intermediate Water. In the deeper layer, diversity reached its peak with the appearance of 27 taxa common in all the regions throughout the year, though abundance was low. Pantachogon haeckeli and Crossota rufobrunnea were dominant in the deeper layer. The possibility of diel vertical migration was suggested in two midwater species: Euphysa japonica and Atolla vanhoeffeni. In the Oyashio waters, jellyfish abundance was much higher than in the Transition waters and Kuroshio-derived waters, but with low diversity, dominated by large numbers of Aglantha digitale and Dimophyes arctica. High values of diversity were found in the Kuroshio-derived waters with various tropical and warm-water species, especially calycophoran siphonophores being present. In the Transition waters, diversity was relatively high, with co-occurrence of warm-water species and cold-water species. Jellyfish biomass tended to be high in the midwater zone due to the occurrence of large species, particularly Scyphozoa. Carbon-based jellyfish biomass calibrated with other studies exceeded that of other organism groups. [ABSTRACT FROM AUTHOR]

The nitrogen (δ15N) and carbon stable isotope (δ13C) values of six species of euphausiids predominant in the northwestern (NW) Pacific Ocean were investigated to elucidate speciesspecific feeding habits and seasonal and regional differences. The order of annual mean δ15N values was: Tessarabrachion oculatum Hansen, 1911 (11.2 ± 0.8‰) > Thysanoessa longipes Brandt, 1851 (10.4 ± 0.4‰) > Thysanoessa inspinata Nemoto, 1963 (9.3 ± 0.8‰) > Nematoscelis difficilis Hansen, 1911 (8.2 ± 1.4‰) > Euphausia pacifica Hansen, 1911 (7.7 ± 0.5‰) > Euphausia gibboides Ortmann, 1893 (6.9 ± 0.9‰). The trophic levels of four species based on δ15N values were estimated as 3.6, 3.2, 2.9, and 2.5 for T. oculatum, T. longipes, T. inspinata, and E. pacifica, respectively, in the Oyashio region in June 2011. The seasonal differences in δ15N values of these species were relatively small, which suggests euphausiids play the same role in the food web throughout the year. Carapace lengths were negatively correlated with δ15N values of five species except T. longipes. Regional differences in stable isotope ratios that might reflect regional differences in the primary producer signature were observed: higher δ13C values and lower δ15N values in the Oyashio-Kuroshio mixed water region compared to those in the Oyashio region. The biplot of δ13C and δ15N annual mean values with zooplankton in the NW Pacific shows that euphausiids have a wide range of δ15N values, suggesting they play diverse roles in the pelagic food web in the region. [ABSTRACT FROM AUTHOR]

Abstract  We investigated the chromophoric dissolved organic matter (CDOM) of river water in the Sakawa River and of surface water in the vicinity of the river’s mouth in Sagami Bay, Japan, during the period from July 2003 to July 2004. Absorption by CDOM was modeled as a logarithmic function. As a qualitative index of CDOM, the slope (S) of this function was estimated for a wavelength range from 280 to 500 nm. As a quantitative index of CDOM, the integration of absorption was determined between 280 and 500 nm (Σ 280 500 a CDOM). High seasonal variability of S values was observed at the marine station. The S values at the upstream stations were related to chlorophyll a concentrations but not to bacterial abundance, whereas the integrated values at upstream stations were correlated with precipitation. Seasonal variability in the integrated values was low at the downstream stations, where the effect of effluent from nonpoint sources and sewage treatment plants was strong. Anthropogenic CDOM at the downstream stations appeared to be degraded by microbial utilization and photodegradation, whereas terrestrially derived CDOM at the upstream stations was less degraded. These qualitative differences in CDOM and the marked effect of dilution by seawater near the Sakawa River mouth suggest that the dynamics of CDOM in riverine and coastal environments should be studied with careful consideration of both spatial and temporal variations, particularly in small estuaries. [ABSTRACT FROM AUTHOR]

Abstract??The seasonal abundance of the dominant dinoflagellate,Ceratium fusus, was investigated from January 2000 to December 2003 in a coastal region of Sagami Bay, Japan. The growth of this species was also examined under laboratory conditions. In Sagami Bay,C. fususincreased significantly from April to September, and decreased from November to February, though it was found at all times through out the observation period.C. fususincreased markedly in September 2001 and August 2003 after heavy rainfalls that produced pycnoclines. Rapid growth was observed over a salinity range of 24 to 30, with the highest specific rate of 0.59 d?1measured under the following conditions: salinity 27, temperature 24?C, photon irradiance 600?mol m?2s?1. The growth rate ofC. fususincreased with increasing irradiance from 58 to 216?mol m?2s?1, plateauing between 216 and 796?mol m?2s?1under all temperature and salinity treatments (except at a temperature of 12?C). Both field and laboratory experiments indicated thatC. fusushas the ability to grow under wide ranges of water temperatures (14?28?C), salinities (20?34), and photon irradiance (50?800?mol m?2s?1); it is also able to grow at low nutrient concentrations. This physiological flexibility ensures that populations persist when bloom conditions come to an end. [ABSTRACT FROM AUTHOR]