Plankton and Benthos Research
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Original Papers
  • Minoru Ijichi, Gyo Itani, Hiroshi Ueda
    Type: Original Paper
    Volume 12 (2017) Issue 3 Pages 145-150
    Released: August 24, 2017
    JOURNALS FREE ACCESS
    The life cycle and precopulatory mate guarding behavior of the poecilostomatoid copepod Goidelia japonica associated with the spoon worm Urechis unicinctus (Echiura) are described based on specimens from 19 worms collected from western Japan. A total of 676 copepods were collected from the host’s rectum (494 copepods) and body surface (182 copepods). Copepod numbers were significantly correlated with host weight. Copepods in the rectum consisted almost completely of copepodids (35%) and adult males (65%), with only one non-ovigerous adult female recorded. In contrast, those on the body surface were all adult males (24%) or females (76%), of which 58% were ovigerous. No nauplii or CI occurred. In the rectum, 36% of the adult males guarded 67% of the copepodids, consisting of CII–CV. From these results, their life cycle is considered as follows: nauplii and CI live as plankton; just before or after molting to CII, they enter the host’s rectum and females are probably soon guarded by males; they grow up to CV there; CV females guarded by males move to the body surface just before the final molt; on the body surface females molt to adults and spawn eggs. Guarding the first symbiotic stage (CII) is a unique precopulatory behavior for symbiotic poecilostomatoid copepods. This can be explained from the viewpoint of evolutionary resolution of the intersexual conflict and advantage for early copepodids in precopula.
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  • Yusuke Yamana, Hisanori Kohtsuka
    Type: Original Paper
    Volume 12 (2017) Issue 3 Pages 151-163
    Released: August 24, 2017
    JOURNALS FREE ACCESS
    A new dendrochirotid sea cucumber collected in the intertidal zone of western Japan, Lipotrapeza littoralis sp. nov., is described. This species has a medium body size (approximately 30–80 mm), brownish body color, 20 tentacles arranged in a double circle (15+5), a long calcareous ring, ten anal papillae and five anal scales, and numerous pedicels covering the entire body at an even density. For comparison, we also examined the syntype specimens of Lipotrapeza japonica Heding and Panning, 1954 and provide illustrations of the general appearance of its body, calcareous ring, and ossicles. The calcareous rings of both species are very similar in appearance, but the new species is readily distinguishable from L. japonica by the number of anal papillae. The appearance of the rosette ossicles also differs in the two species.
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  • Ken-Ichiro Ishii, Ryoma Kamikawa
    Type: Original Paper
    Volume 12 (2017) Issue 3 Pages 164-170
    Released: August 24, 2017
    JOURNALS FREE ACCESS
    The non-photosynthetic diatoms Nitzschia spp. are known to have evolved from photosynthetic species to heterotrophic species by the loss of photosynthesis. We investigated their ability to tolerate wide ranges of temperatures and salinities. Nitzschia spp. were capable of surviving or thriving even at 5°C and 35°C. In addition, these diatoms were also capable of surviving at salinities of 0.5 and 12.0, while thriving at those from 1.0 to 9.0. Such tolerance to a wide range of temperatures and salinities would allow these non-photosynthetic diatoms to thrive in mangrove estuaries, where environmental conditions often drastically fluctuate. Our experiments revealed that the growth rates of the non-photosynthetic diatoms were larger than those estimated based on cell volumes and temperature, suggesting that these non-photosynthetic diatoms may be an important group of organisms contributing to material circulation by growing heterotrophically in mangrove estuaries.
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  • Hiroshi Ueda, Sakiko Orui Sakaguchi, Machiko Yamada
    Type: Original Paper
    Volume 12 (2017) Issue 3 Pages 171-178
    Released: August 24, 2017
    JOURNALS FREE ACCESS
    The estuarine planktonic calanoid copepod Eurytemora americana is described for the first time from Japan based on specimens from Dokai Bay, a small inlet of northern Kyushu in 1975, when the species was exclusively dominant in the innermost bay. This is the southernmost record of the species in the Northern Hemisphere. Morphological descriptions are provided, especially on characters different from or overlooked in previous descriptions. Compared with the recent description of the species from Korea, a distinct morphology is found in the spinule number on the male fifth leg, suggesting inter-population variation and therefore no gene flow between the Japanese and Korean populations. Eurytemora americana in Dokai Bay is regarded as an invasive alien species introduced via ship ballast water. Despite the dominance in 1975, the copepod was not collected from brackish waters in the innermost part of the bay in 2008. Global warming in spring and/or winter periods after the 1970s is a possible reason for the disappearance of this cold water species.
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  • Maritza Mendoza, Sarah K. Henkel
    Type: Original Paper
    Volume 12 (2017) Issue 3 Pages 179-189
    Released: August 24, 2017
    JOURNALS FREE ACCESS
    There has been increased enthusiasm to mitigate the negative effects of fossil fuel consumption through the use of cleaner sources of energy, like marine renewable energy (MRE). Concerns about MRE deployments have motivated research on the ecological effects of these new man-made structures in marine environments. We assessed the extent to which soft-sediment habitats are influenced by the presence of artificial structures deployed in Yaquina Bay, Oregon, USA. Grain size analyses confirmed artificial structures altered the sediment distribution around them with larger grain sizes detected closer to the structures. Infaunal abundances were higher closer to the artificial structures; however, these differences did not result in statistically significant effects on diversity or richness in relation to distance from the structures, nor were they sufficient to cause statistically significant changes in infaunal communities as compared to reference areas. This study provided additional evidence that artificial structures alter their physical environment, but in our study detected differences were less than those observed between the two different regions of the estuary and any effects on infauna were localized and smaller than differences between different regions of the estuary. Conducting these studies in an Oregon estuary provided a good proxy for estimating potential effects of in-stream tidal energy deployments in the Pacific Northwest while also demonstrating the importance of site-specific research.
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  • Yasuyo Tsuji, Shigeru Montani
    Type: Original Paper
    Volume 12 (2017) Issue 3 Pages 190-200
    Released: August 24, 2017
    JOURNALS FREE ACCESS
    Estuarine material circulation depends on the presence of both phytoplankton and suspended microphytobenthos in the water column. However, the spatial distribution of suspended microphytobenthos and phytoplankton in estuaries is poorly understood. In this study, the abundance of suspended microphytobenthos and phytoplankton in the water column was determined along the salinity gradient in Lake Furen, Japan, from April to October 2015.
    Throughout the study period, surface and bottom salinity changed horizontally from <10 to >30. Phytoplankton was the main contributor to spatial increases in total cell abundance in mesohaline water as a result of the lake’s hydrographic characteristics and water quality. The suspended microphytobenthos cell abundance in the surface and bottom water decreased with increasing salinity and was affected by the depth gradient. Suspended microphytobenthos cell abundances increased with depth (∼10 and 20% of total cell abundance in the surface and bottom water, respectively), which indicated that they were derived from microphytobenthos on the seafloor. The dominant suspended microphytobenthos taxa (Cocconeis spp. and Melosira varians) were mainly distributed in oligo- and mesohaline water, with peaks in mesohaline bottom water. In contrast, the dominant phytoplankton taxa (Skeletonema spp., Heterocapsa triquetra, and Prorocentrum spp.) were abundant at different salinity levels. The spatial distribution of dominant benthic and planktonic species in the water column was influenced by their tolerance to salinity. Our results suggest that suspended microphytobenthos contribute to microalgal communities in estuaries, especially those in bottom waters. Quantification of phytoplankton and suspended microphytobenthos will allow a better understanding of the effects of their spatial distribution on estuarine material circulation.
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