Population dynamics of the harmful diatom Eucampia zodiacus Ehrenberg causing bleachings of Porphyra thalli in aquaculture in Harima-Nada,the Seto Inland Sea,Japan |
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| Institution: | 1. Fisheries Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Minami-Futami 22-2, Futami, Akashi, Hyogo 674-0093, Japan;2. Kakogawa Agriculture, Forestry and Fisheries Office, Tenjingi 97-1, Jikemachi, Kakogawa-cho, Kakogawa, Hyogo 675-8566, Japan;3. Laboratory of Marine Environmental Microbiology, Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan;1. Department of Earth and Marine Science, Jeju National University, Ara 1 Dong, Jejusi 690-756, Republic of Korea;2. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA;1. Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany;2. National Oceanic and Atmospheric Administration, National Ocean Service, National Centers for Coastal Oceans Science, Center for Fisheries and Habitat Research, 101 Pivers Island Road, Beaufort, North Carolina 28516, United States;3. Stazione Zoologica Anton Dohrn, Villa Comunale, 80121 Napoli, Italy;4. Plant Functional Biology and Climate Change Cluster, University of Technology Sydney, Sydney, PO Box 123 Broadway, NSW 2007, Australia;5. Woods Hole Oceanographic Institution, MS # 32, 266 Woods Hole Road, Woods Hole, Massachusetts 02543, United States |
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| Abstract: | The diatom Eucampia zodiacus Ehrenberg is one of the harmful diatom species which indirectly cause bleachings of Nori (Porphyra thalli) in aquaculture through competitive utilizing of nutrients (especially nitrogen) and resultant nutrient depletion in water columns during the bloom events. The seasonal changes in environmental factors, cell density and cell size of E. zodiacus were investigated for 4 years (April 2002–December 2005) to understand the population ecology of this diatom in Harima-Nada, the eastern part of the Seto Inland Sea, Japan. Vegetative cells of E. zodiacus were usually detected year-round. Total cell densities of E. zodiacus annually peaked from mid-February to early April, and high cell densities were observed in the whole water columns during the bloom-period. Nutrient concentrations decreased with the increase of cell density of E. zodiacus, and low nutrients concentrations continued throughout the E. zodiacus bloom-period. The average cell size (length of apical axis) of E. zodiacus populations ranged from 10.8 μm to 81.2 μm, and the restoration of cell size occurred once in autumn every year just after reaching the minimum cell size. In addition, its great seasonal regularity was confirmed by the decrease and restoration of its cell size through 4-year study period. Temperature and nutrients were suitable in autumn for the growth of E. zodiacus, its blooms never occur in that season. These results strongly suggest that E. zodiacus did not have a resting stage, and it spends autumn for size restoration and starts to bloom thereafter in Harima-Nada in winter and spring, causing fishery damage to Nori aquaculture by resulting nutrient deprivation. |
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