Plankton and Benthos Research
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Volume 10 , Issue 4
Showing 1-7 articles out of 7 articles from the selected issue
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Original Papers
  • Ilka Straehler-Pohl, Sho Toshino
    Type: Original Paper
    Volume 10 (2015) Issue 4 Pages 167-177
    Released: January 16, 2016
    JOURNALS FREE ACCESS
    The name Carybdea morandinii Straehler-Pohl & Jarms, 2011 was applied to unknown cubopolyps found on dead coral rock at the Hagenbeck Zoo, Hamburg, Germany, during 1999, and a description was given of its early life history. Although included in Carybdeidae Lesson, 1843, its familial affinities remained uncertain. In 2006, a population of unidentified cubopolyps was discovered on the walls of a saltwater tank at the Umikirara Aquarium, Nagasaki, Japan. In addition, an immature cubomedusa and polyps were collected at Ginowan and Ishigaki, Okinawa, Japan, in 2002 and 2012. Genetic analysis established that these polyps and the medusa belonged to the same species as the polyps found in Nagasaki. Comparisons of the anatomy and asexual propagation methods of Japanese polyps, and their newly detached medusae, with early life stages of cubozoans cultured in Germany, revealed that the Japanese populations were likely conspecific with Carybdea morandinii. Subsequent genetic analysis confirmed this identification. Morphology of Japanese medusae revealed that they were referable to the family Alatinidae Gershwin, 2005, and within that family to the genus Alatina Gershwin, 2005, rather than to the family Carybdeidae.
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  • Hiromi Kasai, Kazumasa Hirakawa
    Type: Original Paper
    Volume 10 (2015) Issue 4 Pages 178-186
    Released: January 16, 2016
    JOURNALS FREE ACCESS
    Oceanographic surveys were performed in the coastal and offshore regions of the southwestern Okhotsk Sea off Hokkaido, Japan during the sea ice-free period (i.e., April to December), and 39 on-deck incubations for primary production were conducted using a simulated in situ method with 13C tracer. Temperature and salinity at the sea surface differed significantly between the coastal and offshore regions, whereas the concentrations of chlorophyll a (Chla) and nitrates did not. Seasonal changes in vertical profiles and standing stocks of Chla within the euphotic layer (21–70 m depth) in the coastal region differed from those in the offshore region, showing a subsurface Chla maximum during summer and autumn. The vertical profiles of primary production and Chla-specific primary production (PB) indicate that PB is dependent on PAR (photosynthetically available radiation) and that peak primary production seems to be observed around the depth of the subsurface Chla maximum. No regional differences in PB or primary production were observed. PB in the surface layer exhibited clear seasonality. However, the monthly mean of primary production integrated within the euphotic layer over both regions was relatively stable from 400–600 mgC m−2 day−1 from April to November. In conclusion, the primary productivity in the southwestern Okhotsk Sea is stably high from spring to autumn, although the phytoplankton bloom in early spring immediately after the sea ice break was likely missed.
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  • Hiroaki Tsutsumi, Atsushi Takamatsu, Sayaka Nagata, Ryo Orita, Akira U ...
    Type: Original Paper
    Volume 10 (2015) Issue 4 Pages 187-201
    Released: January 16, 2016
    JOURNALS FREE ACCESS
    In the inner part of Ariake Bay, located on the west coast of Kyushu, in western Japan, red tides have occurred with more frequency since the second half of the 1990s. Hypoxic waters have occurred during the summer months since the 2000s, despite the fact that nutrient loading from the land to the bay has not increased over the last five decades. We monitored water conditions at nine stations in the inner part of the bay, conducted benthic environmental surveys, and quantitative samplings of macro-benthic communities at the innermost four stations between 2002 and 2008. Each summer, the water was well-stratified due to the development of a halocline and a thermocline. The DO of the water below the pycnocline fell to hypoxic conditions. At the innermost three stations in the bay, the mud content and organic matter content of the sediment increased significantly, and the carbon stable isotope ratios of the organic matter contained in the sediment ranged between −21.3±0.5‰ and −20.7±0.5‰ of δ13C. These facts indicated that the organic matter was derived photosynthetically from marine phytoplankton. The increase in the mud content of the sediment indicates a deceleration in the tidal current. This may be a key event that induces a series of environmental changes and disturbances, including the stratification of the water, the more frequent occurrence of red tides, the progress of the organic enrichment of the sediment, and the occurrence of hypoxic water during the summer.
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  • Shoichi Shimoyama, Toshihiko Ichihara, Kaori Tsukano, Minami Kabashima ...
    Type: Original Paper
    Volume 10 (2015) Issue 4 Pages 202-214
    Released: January 16, 2016
    JOURNALS FREE ACCESS
    Long plate-like sediment samples were collected using a Geoslicer technique at five different sites on the sandy tidal flats along the eastern coast of Ariake Bay, Kyushu, western Japan, where there are major harvesting sites of the edible clam Ruditapes philippinarum. The deposition process of the sediment and fossil contents of the shellfish in these Geosliced samples were examined, dating the deposition process of the sediment to at least 400 years ago with a trace of a giant tsunami that occurred in 1792, and radio-active matters (14C contained in the wood pieces, 210Pb and 137Cs), and describing the distribution of the fossil contents of the shellfish in the sediment samples. These results indicate that dense patches of R. philippinarum were established later than 180 to 190 years ago at the sampling sites, and it is very likely that this species was introduced to the sandy tidal flats in Ariake Bay in an anthropogenic way. This conclusion coincides with archaeological evidence collected from shell mounds established in the coastal areas of Ariake Bay during the Jomon and Tumulus Periods (13,000 BC to 600 AD). Ruditapes philippinarum was very rare among fossil shells collected from the shell mounds except one created at the mouth of the bay. This species does not favor the water conditions in the estuary where the salinity tends to be variable due to the inflow of freshwater from rivers. It seems that various kinds of human manipulation are essential for R. philippinarum to be maintained in large numbers on the tidal flats at the mouths of the rivers in the inner parts of Ariake Bay.
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Notes
  • Masaya Toyokawa, Naoki Fujii
    Type: Note
    Volume 10 (2015) Issue 4 Pages 215-219
    Released: January 16, 2016
    JOURNALS FREE ACCESS
    Two invasive hydromedusae Maeotias marginata and Blackfordia virginica, both distributed worldwide, were recorded for the first time in Japan, from the river-mouth of Ariake Bay. Maeotias marginata resembles superficially another limnomedusa, Eperetmus typus, but has more numerous tentacles than E. typus at the same level of the bell margin. Maeotias marginata is distinguished from another cosmopolitan freshwater limnomedusa, Craspedacusta sowerbyi, by the presence of numerous centripetal canals. Blackfordia virginica is distinguished from the Campanulariidae by the character that the endodermal core of tentacles extends inwards from the bell margin into the mesoglea. Both M. marginata and B. virginica have been known to occur in the bay by local fishermen for at least several decades. The introduction of edible bivalves from China and Korea, and transport in the ballast of freighters are considered as possible mechanisms for the introduction of these species.
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  • Shahnawaz Gul, Shahnaz Jahangir, Agustín Schiariti
    Type: Note
    Volume 10 (2015) Issue 4 Pages 220-224
    Released: January 16, 2016
    JOURNALS FREE ACCESS
    This study reports on the jellyfish (Cnidaria: Scyphozoa) fishery in Pakistan for the first time. Two jellyfish species: Catostylus perezi and Rhopilema hispidum, marketed with the trade names: banana and flower-jellyfish, respectively, are commercially exploited in Pakistan with the former being caught and exported in much higher relative quantities. C. perezi is fished in Balochistan, while R. hispidum is fished in Sindh province. Fishing seasons vary between February/March to July/August and 8–10 companies are regularly processing jellyfish, primarily using the oral arms, their fused-portion and scapulets, while umbrellas are typically not processed. The industry in the region has great potential because C. perezi occurs at high abundances in the northern Arabian Sea along the Balochistan coast of Pakistan.
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  • Kouki Fukuoka, Toru Shimoda, Kazuo Abe
    Type: Note
    Volume 10 (2015) Issue 4 Pages 225-232
    Released: January 16, 2016
    JOURNALS FREE ACCESS
    Mesozooplankton is an important component of coral reef ecosystems. This study investigated the community structure and abundance of copepods in the fore-reef environment around channel mouths and the adjacent offshore waters of Ishigaki Island in the summer. The fore-reef station group of copepods was significantly distinguishable from the offshore station group in terms of community structure. Unlike the fore-reef group, the offshore group showed high species diversity, low density of calanoids and was composed mainly of oceanic species. The fore-reef group was characterized by the littoral species Acartia fossae, Bestiolina similis, Oithona simplex, and Oithona dissimilis. High densities of these species were recorded near channel mouths. The pattern of tidal changes near the channel mouth accorded with the characteristics of the environment. The channel mouths might be preferred because they offer a food-rich environment for the coral reef species A. fossae, passive transportation by the ebb current for the estuarine species O. dissimilis, and reef system circulation for the euryhaline species B. similis and O. simplex. The species composition and densities of the calanoids in the fore-reef stations differed between the east and west sides of the channel mouths, suggesting tidal and topographical influences.
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