Plankton and Benthos Research
Online ISSN : 1882-627X
Print ISSN : 1880-8247
ISSN-L : 1880-8247
Volume 19, Issue 1
Displaying 1-6 of 6 articles from this issue
Original Papers
  • Takeshi Sonoda, Susumu Chiba, Tomoyasu Yamazaki, Takahiro Nobetsu, Hid ...
    2024 Volume 19 Issue 1 Pages 1-16
    Published: February 28, 2024
    Released on J-STAGE: February 28, 2024
    JOURNAL FREE ACCESS
    Supplementary material

    The Shiretoko Peninsula, located at the southernmost point of the Sea of Okhotsk, was registered as a World Natural Heritage in 2005 in recognition of its rich biodiversity and an example of the interaction between marine and terrestrial ecosystems. However, there is insufficient information on its marine biota, which is an essential component of this ecosystem. This study was conducted from 2006 to 2019 to clarify the macroinvertebrate fauna along the shores of the Shiretoko Peninsula. A total of 299 species from 11 phyla were identified, including 118 mollusks, 107 crustaceans, 34 annelids, 24 echinoderms, and 16 species from other taxa, including two species recorded in Japan for the first time [Oregonia kurilensis (Decapoda: Brachyura) and Henricia alexeyi (Asteroidea: Echinasteridae)]. In addition, five species, including one new species of Isopoda, have been firstly reported from Japan based on the material collected by this project. Faunal similarity and biogeographical features differ between the Sea of Okhotsk side and the Nemuro Strait side of the peninsula, probably because of the effects of warm and cold currents, coastal topography, and drift ice pressure on the shore in winter. The macroinvertebrate fauna of the Shiretoko Peninsula is located at the boundary of different marine biogeographic provinces and is organized by environmental factors unique to the Sea of Okhotsk. Therefore, it is important to monitor the marine biota around the peninsula shores as these species act as bioindicators of environmental changes.

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  • Hiroshi Ueda, Kanako Sakaki, Hideyuki Kamakura
    2024 Volume 19 Issue 1 Pages 17-25
    Published: February 28, 2024
    Released on J-STAGE: February 28, 2024
    JOURNAL FREE ACCESS

    In 2001, many planktonic larvae of the lancelet Branchiostoma japonicum were found in the western Seto Inland Sea. To know their subsequent state, the benthic population at a small sandbank, named Ohzu, located there was surveyed with a grab sampler in total 26 times from November 2001 to November 2005. The mean population abundance at six stations was around 100 ind. m−2 until July 2002, and abruptly increased to 1041 ind. m−2 until November 2002 by a mass recruitment. Thereafter, the abundance decreased with fluctuations to around 200 ind. m−2 in November 2005. The 2002-year class continued to be the strongest year class until at least 2005. Planktonic larvae collected in July 2005 at 4-km intervals along an 80-km line showed strongly patchy aggregations with scales ranging 4 to 12 km. Their patchy aggregation probably resulted from a spawning habit known for lancelets, which spawn within a short time at night and synchronously a few times in summer. The mass recruitment in 2002 and the large interannual fluctuation of the benthic population were most likely caused by the accidental settlement of patchy larval aggregation. Populations at Ohzu and a site (Kaihara) about 6.5 km apart in June 2006 showed a similar age structure having the strongest age class is still regarded as the 2002-year class, suggesting that the two sites were settled by the same larval patch or different patches with different fertilization dates.

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  • Toru Kobari, Taiga Honma, Masafumi Kodama, Akinobu Kodama, Toshiteru W ...
    2024 Volume 19 Issue 1 Pages 26-36
    Published: February 28, 2024
    Released on J-STAGE: February 28, 2024
    JOURNAL FREE ACCESS
    Supplementary material

    The Tsushima Strait and the neighboring waters has been known as major spawning and nursery grounds for migratory fishes due to the high standing stocks of the plankton community in spring to summer. In the present study, spatial and temporal variations in taxonomic composition, standing stocks and productivity of the mesozooplankton community were investigated in the southwestern Japan Sea to explore their variations during the productive seasons. Both spatial and temporal fluctuations were significant for mesozooplankton standing stocks while only temporal variability affected their productivity. The mesozooplankton community was split into one coastal group, represented by cladocerans and noctilucids throughout the seasons, and five pelagic groups, predominated by calanoids, cyclopoids and copepod nauplii, with temporal replacement during spring to summer. The coastal community group contained the additional standing stocks of cladocerans and noctilucids along with the predominant copepods from the other groups and thus resulted in the spatial difference in mesozooplankton standing stocks between coastal and pelagic sites. Three pelagic community groups were characterized by the abundant appearance of noctilucids and clustered toward the pelagic stations neighboring the coastal community group. Generalized linear models demonstrated that salinity was a significant explanatory variable for standing stocks of mesozooplankton and coastal taxonomic groups (i.e., cladocerans and noctilucids). These findings suggest that the spatial and temporal variations in mesozooplankton standing stocks are a mixture of the pelagic community groups with the coastal community group advected toward the pelagic sites.

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  • Koichi Yano, Yoshiki Takayama, Shinji Shimode, Mitsuhiro Toratani, Hir ...
    2024 Volume 19 Issue 1 Pages 37-50
    Published: February 28, 2024
    Released on J-STAGE: February 28, 2024
    JOURNAL FREE ACCESS

    In mid-May 2020, a coccolithophore bloom of Gephyrocapsa oceanica Kamptner, 1943 was observed in Sagami Bay, Japan, possibly for the first time in 25 years. This species is a common yet elusive taxon in the waters around Japan, but there has only been one report of a bloom observation in Sagami Bay in 1995. The G. oceanica bloom in 2020 was observed by the combined approach of the JAXA ocean color remote sensing satellite “Shikisai” and field surveys. The true-color RGB images from the satellite showed the initial bloom in Tokyo Bay appears to have advected into Sagami Bay on May 5. On May 15, ad hoc field sampling was conducted based on visual confirmation from the shore. Nitrate, nitrite and phosphate concentrations at the sea surface were 3.28 µM, 0.11 µM and 0.29 µM, respectively, and higher than the median of May from 1997 to 2019. Chlorophyll a concentration was 2.23 µg L−1 at the sea surface, and cell density was 5.3 × 103 cells mL−1. The large bloom appears to have reached the western shorelines of the bay, and dispersed counterclockwise within the bay. The bloom reached an estimated 1119.02 km2 surface expression on May 17, and completely disappeared by May 24. Further, the median value of 19′-hexanoyloxyfucoxanthin (a signature pigment of haptophytes, including coccolithophores) concentration has been increasing from 2017 to 2020, and the coastal area of Sagami Bay may have changed to a region favorable for haptophytes.

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  • Eijiroh Nishi, Shinri Tomioka, Naoto Jimi, Yoshihiro Fujiwara, Elena K ...
    2024 Volume 19 Issue 1 Pages 51-59
    Published: February 28, 2024
    Released on J-STAGE: February 28, 2024
    JOURNAL FREE ACCESS

    We describe here a new species of Amphictene (Annelida, Polychaeta, Pectinariidae) from a depth of 1160 m off Kushiro, East Hokkaido, Japan. Amphictene hokkaido sp. nov. is characterized by the presence of following characters: a pair of ventral lappets in segment 1; ventro-median lobes in segments 2–4; anterior conical or rounded lappets on ventro-lateral lobe of segment 2; dorso-lateral pads in segments 3 and 4; 17 segments with chaetae on notopodia, 13 segments with uncini on neuropodia; notopodia in segment 21 with notopodial lappets beneath chaetal tuft; neuropodial uncini with 4–5 main teeth and subrostral process on basal prow; 7–9 pairs of scaphal hooks; scaphe with anterior median lobe and four pairs of lateral lobes; anal lobe with an anal cirrus and a row of postero-ventral minute cirri. We provide a diagnostic key to species of the genus.

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Note
  • Kohei Hamamoto, Akira Iguchi, Kodai Gibu, Hiroyuki Ozawa, Yoshihisa Fu ...
    2024 Volume 19 Issue 1 Pages 60-65
    Published: February 28, 2024
    Released on J-STAGE: February 28, 2024
    JOURNAL FREE ACCESS

    The giant mangrove whelk Terebralia palustris is known to have wide distribution ranging from east coast of African Continent to Western Pacific region. Up to date, the population reported from Miyako Island, Japan has been recognized as northernmost population of this species. However, we have found a new population from Zamami Island, Kerama Islands, Japan, and thus report here. The population was found in a muddy wetland with vegetation of sparse Rhizophora stylosa and abundant Phragmites sp. throughout the habitat. The population consists of both fully-developed (with thick edge of shell-opening) and still growing (without thick edge) individuals sympatrically, thus assumed to comprise at least two generations. Whereas, mean population density was 5.3 inds/m2 and the total number of individuals found in the entire-habitat survey was 102, those are both substantially smaller number when compared to other habitats in Ryukyu Islands. In population genetic analysis, both haplotype and nucleotide diversity indices were low. Also, haplotype network and maximum likelihood phylogenetic analysis showed that there is no distinct genetic isolation between Zamami and other areas in southern Ryukyu Islands. The dissimilar habitat from previous reports, low population density and small body size may imply that this population is newly recruited (naturally or artificially), or under strong environmental stress at an edge of its distribution, however, it is still unclear about the origin of this population form our data. To monitor the demography of this population, following observation to reveal growth and reproductive cycle is needed in the future.

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