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Yamada M.,Fukuoka Women's University | Otsubo M.,Fukuoka Women's University | Tada K.,Kagawa University | Nakano Y.,University of Ryukyus | And 5 more authors.
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2017

The species composition of the genus Skeletonema (Bacillariophyceae) was investigated in five Japanese coastal waters by analyzing large subunit rDNA D1-D3 sequences and the fine morphological structures of vegetative and germinated cells. The predominant species were S. grevillei from Main Okinawa Island Midwaters in the subtropical zone and S. dohrnii from the Ariake Sound, Toyama Bay, and Onagawa Bay in the temperate zone, and Funka Bay in the subarctic zone. S. japonicum was found with S. dohrnii in the latter four bodies of water. During the warm season, S. costatum, which can acclimate to low salinity, was found predominantly in the Ariake Sound and Toyama Bay, where the salinity was low, despite the fact that S. costatum is able to germinate from sediments over the temperature range of 10-30°C. The absence of S. costatum vegetative cells in the winter was due to lower specific growth rates of S. costatum than those of S. dohrnii and S. japonicum. During warm periods, S. grevillei and S. pseudocostatum occurred as the dominant species in Onagawa Bay and Funka Bay respectively, where salinities were usually >30. The species composition and seasonal succession of Skeletonema were closely related to temperature and salinity. © 2017 The Japanese Society of Fisheries Science.


Qiu X.,Kyushu University | Yamasaki Y.,National Fisheries University | Shimasaki Y.,Kyushu University | Gunjikake H.,Kyushu University | And 7 more authors.
Thalassas | Year: 2011

We investigated growth interactions between the raphidophytes Chattonella antiqua (Hada) Ono and Heterosigma akashiwo (Hada) Hada ex Hara et Chihara using bi-algal cultures under axenic conditions. The growth of C. antiqua and H. akashiwo each tended to be strongly suppressed when the other species reached early stationary phase. A mathematical model was used to simulate the growth interactions of C. antiqua and H. akashiwo in bi-algal cultures. The model showed that C. antiqua outcompetes H. akashiwo over time in bi-algal cultures under all experimental conditions. Furthermore, despite re-enrichment with nutrients, the filtrate from dense cultures of C. antiqua reduced the maximum growth rate of H. akashiwo and filtrate from dense cultures of H. akashiwo reduced both the maximum growth rate and maximum yield of C. antiqua.


Qiu X.,Kyushu University | Yamasaki Y.,National Fisheries University | Shimasaki Y.,Kyushu University | Gunjikake H.,Kyushu University | And 8 more authors.
Marine Ecology Progress Series | Year: 2012

Growth interactions between the raphidophyte Heterosigma akashiwo and the dinoflagellate Akashiwo sanguinea were examined by using bi-algal culture experiments under axenic conditions. There was a lethal effect of H. akashiwo (initial cell density: 1 × 10 2 or 1 × 10 4 cells ml -1) on A. sanguinea at an initial cell density of 1 × 10 2 cells ml -1. Growth of both species was suppressed concurrently when initial cell densities of H. akashiwo and A. sanguinea were 1 × 10 2 and 2 × 10 3 cells ml -1, respectively. A mathematical model was used to simulate growth and interactions in bi-algal cultures. The model predicted that H. akashiwo would outcompete A. sanguinea over time. A cell-free enriched filtrate prepared from dense culture of H. akashiwo reduced both maximum growth rate and maximum yield of A. sanguinea. A filtrate of A. sanguinea prepared in the same manner only reduced maximum yield of H. akashiwo but did not affect its maximum growth rate. Growth of A. sanguinea in bi-algal cultures under contact conditions was significantly lower than that in mono-algal culture and in bi-algal cultures under noncontact conditions. Morphologically abnormal A. sanguinea cells occurred at high frequency only when A. sanguinea was cultured together with H. akashiwo under direct cell contact condition. Moreover, growth inhibition and formation of morphologically abnormal cells of A. sanguinea were induced in a concentration-dependent manner by allelochemicals (including allelochemical polysaccharide-protein complexes) produced by H. akashiwo. These results suggest that growth inhibition effects, via allelochemicals and direct cell contact by Heterosigma akashiwo, influence bloom formation of Akashiwo sanguinea in the field. © 2012 Inter-Research.


Qiu X.,Kyushu University | Yamasaki Y.,National Fisheries University | Shimasaki Y.,Kyushu University | Gunjikake H.,Kyushu University | And 6 more authors.
Harmful Algae | Year: 2011

We investigated the growth interactions between the raphidophyte Chattonella antiqua and the dinoflagellate Akashiwo sanguinea by using bi-algal cultures under axenic conditions. When initial cell densities of C. antiqua and A. sanguinea both were 1×102 cells ml-1, C. antiqua grew faster and its growth inhibitory effect on A. sanguinea was stronger than that of A. sanguinea on C. antiqua. In other combinations of inoculation densities, the species that was inoculated at lower cell density (1×102 cells ml-1) stopped growing soon after the start of the experiments, and cell density of this species gradually decreased after the other species reached early stationary phase. The mathematical model used to simulate the growth and interactions between the two species predicts that C. antiqua and A. sanguinea will approach an unstable equilibrium point of about 2.16×104 cells ml-1 (C. antiqua) and 1.46×104 cells ml-1 (A. sanguinea). Thus, one of the species always inhibits the growth of the other and their initial cell densities are critical in determining the successful species in growth competition. When one of these two species was inoculated at the cell density of 2×103 cells ml-1 in bi-algal culture experiments under noncontact and contact conditions, its growth inhibitory effect toward the other species was greater under contact conditions than under noncontact conditions. Furthermore, enriched filtrate from dense culture of C. antiqua resulted in both reduced maximum yield and maximum growth rate of A. sanguinea, whereas that of A. sanguinea resulted only in reduced maximum yield of C. antiqua but did not affect its growth rate. © 2011 Elsevier B.V.


Shikata T.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Matsubara T.,Saga Prefectural Ariake Fisheries Research and Development Center | Yoshida M.,Kagawa Prefectural Government | Sakamoto S.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Yamaguchi M.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Fisheries Science | Year: 2015

Winter blooms of the diatom Asteroplanus karianus cause bleaching of cultivated Pyropia. We examined the effects of temperature, salinity, and photosynthetic photon flux density (PPFD) on the growth of A.karianus, using culture strains from the Ariake Sea. The maximum growth rate occurred at 20 °C and a salinity of 20, and growth rates at 15–25 °C and salinities of 15–33 were >70 % of this maximum. However, A. karianus could not survive at 30 °C. The threshold PPFD for growth was approximately 1 μmol photons m−2 s−1; this value was lower than that for other coastal diatoms. The half-saturation PPFD was 41.3 μmol photons m−2 s−1 at 15 °C and 30.5 μmol photons m−2 s−1 at 25 °C. The photosynthetic activity (Fv/Fm) of A. karianus was saturated at 50 μmol photons m−2 s−1, which is similar to or lower than surface PPFDs on cloudy days. We found that A. karianus is eurythermal and euryhaline and can photosynthesize and grow in very low light but not at high temperature. These physiological characteristics may partly explain why this diatom blooms in winter, when temperature and PPFD are at their lowest during the year in the Ariake Sea. © 2015, Japanese Society of Fisheries Science.


Yagi Y.,Kochi University | Yagi Y.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Kinoshita I.,Kochi University | Fujita S.,Nishinihon Institute of Technology Ltd. | And 2 more authors.
Environmental Biology of Fishes | Year: 2011

To examine the importance of the upper estuarine areas of Ariake Bay as a nursery ground for fish, assemblages of larvae and juveniles were compared among various aquatic habitats. The upper estuaries of the bay (the Rokkaku and Hayatsue estuaries) are brackish, highly turbid waters with high tidal velocities, and differ substantially from the Isahaya area, which has been separated from the bay by a man-made dike, to the middle estuary (the Kikuchi estuary). Abundances of larvae and juveniles were higher in the estuaries than in the open bay and Isahaya areas. Abundant species in the upper estuaries were similar to each other, but differed from those of the middle estuary. This was primarily due to larvae and juveniles of fishes that occurred almost entirely in the upper estuaries, such as Acanthogobius hasta, Boleophthalmus pectinirostris, Coilia nasus, Cynoglossus abbreviatus, Nibea albiflora, Odontamblyopus lacepedii, Trachidermus fasciatus and Tridentiger barbatus. These results suggest that the upper estuaries play an important role as nursery grounds for fishes. © 2011 Springer Science+Business Media B.V.


Katano T.,Saga University | Yoshino K.,Saga University | Matsubara T.,Saga Prefectural Ariake Fisheries Research and Development Center | Hayami Y.,Saga University
Journal of Oceanography | Year: 2012

The raphidophyte Chattonella and the bacillariophyte Skeletonema are representative bloom-causing organisms in the Ariake Sea, Japan. Changes in their abundance were monitored to clarify the role of river discharge in the red tides caused by these organisms in the innermost area of the sea. In late June 2010, heavy rain occurred and subsequently river discharge increased. A Chattonella bloom occurred after heavy rain on July 5, although Chattonella abundance was very low (<1 cell ml -1) before the heavy rain (June 29). Maximum cell density reached 4. 2 × 10 3 cells ml -1 at the surface. Thus, the bloom developed as the river plume extended in the estuary. During the course of extension of the river plume, the Chattonella population rapidly developed using the nutrients supplied by the river. Just after the Chattonella bloom, heavy rain occurred again and a very large quantity of river water flowed into the estuary. Consequently, the salinity of the surface decreased to 5 in the study area on July 16. Chattonella did not migrate to the surface probably because of the overlying low-salinity water; Chattonella formed a thin layer (20-50 cm in thickness) at the depth where salinity was 10. However, a Skeletonema population developed at the surface. On July 20, Skeletonema density at the surface exceeded 10 5 cells ml -1. With the decline of the Skeletonema abundance due to the nutrient limitation, Chattonella again formed bloom probably using deep-nutrient pool by their vertical migration behavior. The present study clearly demonstrates that the Chattonella can form dense bloom after the heavy rain. The seed population awaiting the river discharge is probably essential to the rapid development of Chattonella in the estuary. © 2012 The Oceanographic Society of Japan and Springer.


Matsubara T.,Saga Prefectural Ariake Fisheries Research and Development Center | Yokoo K.,Saga Prefectural Ariake Fisheries Research and Development Center | Koga H.,Saga Prefectural Ariake Fisheries Research and Development Center
Bulletin of the Plankton Society of Japan | Year: 2011

In the Ariake Sea, off Saga Prefecture, Japan, a Chattonella red tide was first observed in 1984, and it has since been observed in 15 of the 26 years up to 2009. Recently, the detrimental effect on fisheries associated with harmful red tides in this area has become a matter of concern. This study examines the effectiveness of predicting the Chattonella red tide in the Ariake Sea off Saga Prefecture through discriminant analysis based on meteorological data for Saga City. Discriminant analysis using values of total precipitation for the first 10 days of July, average daily global radiation for the first 10 days of July and average daily global radiation for the third 10 days of May in Saga City from 1984 to 2009 could distinguish the years in which Chattonella red tides occurred in this area with about 90% accuracy. In addition, it was found that in this area, the Chattonella red tide tended to occur in years when the total precipitation on the first 10 days of July was low and average daily global radiation on the first 10 days of July and that on the third 10 days of May were high.


Yamaguchi H.,Kochi University | Minamida M.,Kochi University | Matsubara T.,Saga Prefectural Ariake Fisheries Research and Development Center | Okamura K.,Kochi University
Marine Ecology Progress Series | Year: 2014

In the Ariake Sea, Japan, the pennate diatom Asteroplanus karianus has formed massive blooms each winter since 2008. During the peak of the bloom, seaweeds of the genus Pyropia, which are cultivated to make nori products, are discolored due to nutrient deficiency. We investigated the nutrient dynamics associated with A. karianus blooms in the Ariake Sea and measured the uptake of nitrate and phosphate by an axenic strain of A. karianus. Dissolved inorganic nitrogen and dissolved inorganic phosphorus in the coastal waters were significantly lower in areas where A. karianus cells were proliferating (r ≤ -0.955, p < 0.01), and these nutrients were severely depleted during the period of blooming. In the laboratory, the maximum uptake rate and half-saturation constant of A. karianus cultures were 27.3 fmol N cell-1 h-1 and 7.44 μmol N l-1, respectively, for nitrate and 22.6 fmol P cell-1 h-1 and 3.61 μmol P l-1, respectively, for phosphate. This study demonstrates that A. karianus blooms significantly deplete nutrients in the water column. The winter blooms presumably deplete dissolved inorganic nitrogen and dissolved inorganic phosphorus from the water column and may indirectly cause Pyropia nutrient deficiency. © Inter-Research 2014.


Matsubara T.,Saga Prefectural Ariake Fisheries Research and Development Center | Yokoo K.,Saga Prefectural Ariake Fisheries Research and Development Center | Kawamura Y.,Saga Prefectural Ariake Fisheries Research and Development Center
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2014

Asteroplanus karianus is a harmful diatom and a causative organism in the bleaching of cultured nori (Pyropia). The relationship between the population dynamics of A. karianus and environmental factors was investigated in the Ariake Sea, off Saga Prefecture, Japan. Phytoplankton composition and relevant environmental variables were recorded from December 2007 to March 2012. In addition, the growth and germination of A. karianus under high water temperature and low water temperature conditions were studied in the laboratory. The field study indicated that A. karianus caused red tides only in winter. Nonetheless, laboratory studies indicated that the growth rate of A. karianus was higher under high water temperature conditions than low water temperature conditions. Conversely, the results suggested that the time required for germination of resting stage cells of A. karianus, in bottom sediment was shorter under low water temperature conditions.

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