Flushing rate and salinity may control the blooms of the toxic dinoflagellate Alexandrium tamarense in a river/estuary in Osaka Bay, Japan |
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| Authors: | Keigo Yamamoto Hirotaka Tsujimura Masaki Nakajima Paul J Harrison |
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| Institution: | 1. Marine Fisheries Research Center, Research Institute of Environment, Agriculture and Fisheries, Osaka Prefecture, Misaki, Sennan, Osaka, 599-0311, Japan
2. Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada
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| Abstract: | The first observation of a red tide of the toxic dinoflagellate Alexandrium tamarense in the Yodo River estuary, Osaka Bay, Japan was in the spring of 2007. To clarify which environmental factors controlled the abundance of A. tamarense, field surveys were conducted in 2008 and 2009. In 2008, the increase of A. tamarense occurred from early to mid-March and temperatures ranged from 9 to 13 °C. In contrast, in 2009, the increase was 1 month later, from early to mid-April and therefore temperatures were higher. In both years, A. tamarense was most abundant when salinities were relatively high (15–25), river discharge was low, and the water column was stable. There were no cells during periods of low salinity (<10), high discharge. In 2008, possibly silicate and phosphate were limiting during the simultaneous diatom and A. tamarense bloom in early March with silicate restricting the further growth of diatoms. In this estuarine basin, freshwater discharge from the weir increased the flow rate at stations downstream of the weir and deterred bloom formation by A. tamarense. Conversely, the lack of discharge increased the salinity and stability of the water column and decreased in the flow rate in the river/estuary. This process promoted the initiation of the bloom of A. tamarense and the subsequent accumulation of paralytic shellfish toxin in the brackish water clam Corbicula japonica. It is recommended that a constant discharge from the weir is maintained in order to prevent blooms of A. tamarense and subsequent paralytic shellfish poisoning (PSP) incidents in this area. |
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