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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. Source


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. Source


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. Source


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. Source


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. Source

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