Akashiwo Research Institute of Kagawa Prefecture

Takamatsu-shi, Japan

Akashiwo Research Institute of Kagawa Prefecture

Takamatsu-shi, Japan
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Escalera L.,Spanish Institute of Oceanography | Reguera B.,Spanish Institute of Oceanography | Takishita K.,Japan Agency for Marine - Earth Science and Technology | Yoshimatsu S.,Akashiwo Research Institute of Kagawa Prefecture | Koike K.,Hiroshima University
Protist | Year: 2011

Photosynthetic dinoflagellates possess a great diversity of plastids that have been acquired through successful serial endosymbiosis. The peridinin-containing plastid in dinoflagellates is canonical, but many other types are known within this group. Within the Dinophysiales, several species of Dinophysis contain plastids, derived from cryptophytes or haptophytes. In this work, the presence of numerous intracellular cyanobacteria-like microorganisms compartmentalized by a separate membrane is reported for the first time within the benthic dinophysoid dinoflagellate Sinophysis canaliculata Quod et al., a species from a genus morphologically close to Dinophysis. Although the contribution of these cyanobacterial endosymbionts to S. canaliculata is still unknown, this finding suggests a possible undergoing primary endosymbiosis in a dinoflagellate. © 2010 Elsevier GmbH.

Tada K.,Kagawa University | Oyama K.,Kagawa Prefectural Fisheries Experimental Station | Shiratsuchi K.,Kagawa University | Masui T.,Kagawa Prefectural Fisheries Experimental Station | And 2 more authors.
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2015

The cause of a significant Coscinodiscus wailesii bloom that occurred in October 2013 at the eastern part of the Seto Inland Sea was investigated. C. wailesii is a harmful species that causes serious damage to Nori (Pyropia) culture. This bloom had seldom been observed since 1990, which was thought to be the result of the gradual decrease in nutrient concentrations in this area after 1970 and in particular, a decrease in dissolved inorganic nitrogen concentrationafter 1990. However, a large C. wailesii bloom occurred in October 2013, just after vertical mixing of the water column. At that time, nutrient concentrations of bottom water suddenly decreased, but those of surfacewater did not increase. This was probably due to the consumption of nutrients by the C. wailesii bloom. In September 2013, one month prior to its bloom, both rainfall and solar irradiance were particularly high.Moreover, the euphoticzone depth was notably deeper. It was thought that the large C. wailesii bloom was due to the combination of sufficient nutrient supply, sufficient light irradiation and deeper euphotic zone in the vertical mixing period. Ourresults suggested that the recurrence of these factors could cause C. wailesii bloom to occur again even under a low nutrient situation.

Yamaguchi H.,Kagawa University | Hirade N.,Kagawa University | Higashizono K.,Kagawa University | Tada K.,Kagawa University | And 3 more authors.
Journal of Sea Research | Year: 2015

The Bisan Strait is a vertically well-mixed, shallow area (mean depth 13.9m) in the Seto Inland Sea. The strait has the lowest Secchi transparency (mean 4.5m) within the Inland Sea because of active sediment re-suspension. Therefore, in comparison with adjacent areas, phytoplankton production in the strait may be strongly affected by light availability in addition to nutrient availability. In this study, we examined environmental variables, photosynthesis-irradiance (P-I) curves and phytoplankton production in the Bisan Strait over 1year. There were temporal variations in the light-saturated photosynthesis rate (PBm) and initial slope of P-I curve (αB), with maxima in autumn and minima in spring. Most of the variability in PBm and αB was explained by variations in nutrient concentrations (dissolved inorganic nitrogen) and water temperature. Meanwhile, phytoplankton production reached a peak in summer and a nadir in spring, but an autumn peak in production was not observed. Diagnostic analysis suggested that, for almost all of the year, nutrients were more important for phytoplankton growth than light limitation. However, light limitation became more important in autumn when underwater irradiance reached low levels. Therefore, the lack of an autumn peak in production is likely to be related to light limitation. We suggest that low light availability during the autumn depresses the annual rate of phytoplankton production in the Bisan Strait, in comparison with adjacent areas where seasonal stratification is established and phytoplankton blooms frequently occur in early autumn. © 2015 Elsevier B.V.

Kuno S.,Kyoto University | Kamikawa R.,Kyoto University | Kamikawa R.,University of Tsukuba | Yoshimatsu S.,Akashiwo Research Institute of Kagawa Prefecture | And 3 more authors.
Phycological Research | Year: 2010

The genetic diversity of the ciguatera fish poisoning-related dinoflagellate distributed in Japanese coastal areas was investigated. The entire sequence of the 5.8S rRNA gene and two internal transcribed (ITS) regions were determined, which included putative pseudogenes, from 19 strains of dinoflagellates assigned to the genus Gambierdiscus Adachi et Fukuyo collected from Japanese subtropical and temperate coastal areas. The sequences obtained from the 19 strains were divided into two types based on sequence similarity. Here we designate the two types as type 1 and type 2. For the relationship between the genotypes and origins of the strains used, the strains collected from subtropical areas possessed the type 1 sequence; whereas those from temperate areas possessed the type 2. This observation led us to question former reputations that Gambierdiscus cells observed in Japanese temperate areas are immigrants from Japanese subtropical areas. Subsequently, we sequenced a part of the 18S rRNA gene from two strains from subtropical areas and two from temperate areas. Unfortunately, phylogenetic analysis including the sequences obtained from various gonyaulacales dinoflagellates failed to determine the species phylogenetically closely related to and possible origin(s) of the Gambierdiscus sp. from the Japanese coastal areas. © 2010 Japanese Society of Phycology.

Koike K.,Hiroshima University | Akai N.,Kagawa Prefectural Fisheries Experimental Station | Liao L.M.,Hiroshima University | Ikeda S.,Hiroshima University | Yoshimatsu S.,Akashiwo Research Institute of Kagawa Prefecture
Parasitology International | Year: 2013

A green spotted Japanese sillago (Sillago japonica) was caught by a fisherman and brought to the laboratory for pathological inspection. The green spots were abundant on the lateral line and more extensively so within the mouth cavity. In both sites, green spots were embedded within the fish flesh and formed 2-3. mm dome-shaped colonies. SEM revealed these colonies to harbor numerous unknown cells with small, surface warts (ornamentations). Molecular analysis showed the cells were Desmodesmus (D. komarekii), a common freshwater coccoid green alga found in ponds and rivers worldwide. It is uncertain how the host fish came to be infected with the alga which was not merely attached externally but embedded within the flesh and inside the mouth cavity. This is the first case of parasitic form of coccoid green algae in marine fish and provides new insights into the variable nature of green algae. © 2013 Elsevier Ireland Ltd.

Masuda I.,Kyoto University | Masuda I.,University of Tokyo | Kamikawa R.,Kyoto University | Kamikawa R.,University of Tsukuba | And 5 more authors.
Harmful Algae | Year: 2011

Chattonella marina (Subrahmanyan) Hara et Chihara var. marina and Heterosigma akashiwo Hada (Hada) are members of raphidophycean algae responsible for large-scale red tides resulting in mass mortality of cultured fishes. For accurate monitoring and controlling the ecological dynamics of these harmful algae, sensitive genetic markers are indispensable. Since mitochondrial (mt) DNA sequences have been used for biogeographical and population studies of various eukaryotic species, we expect that mt genomes of C. marina and H. akashiwo may contain useful sequence information that can be used to examine their ecological dynamics. The present study characterizes the complete mt genomes of C. marina var. marina and H. akashiwo. The mt genomes of C. marina var. marina and H. akashiwo are 44,772. bp and 38,690. bp in length, respectively. Curiously, C. marina and H. akashiwo mt genomes have independently experienced partial genome duplication. For in-depth investigation of the evolution of the partially duplicated regions in the C. marina mt genome, we further determined the corresponding region in the mt genomes of eight additional Chattonella strains sampled from C. marina and close relatives. Our sequence comparison revealed that the duplicated regions accumulated multiple deletions as well as substitutions and repeats. Significantly, the nine Chattonella strains can be distinguished from each other based on the characteristics of these regions. © 2010 Elsevier B.V.

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