AME prepress abstract  -  DOI: https://doi.org/10.3354/ame01860

Effect of salinity on interspecific competition between the dinoflagellate Alexandrium catenella and the raphidophyte Heterosigma akashiwo

Yasuhiro Yamasaki*, Masaki Fujita, Shuichi Kawano, Toshinori Baba

*Email: yamasaky@fish-u.ac.jp

ABSTRACT: We investigated the effect of salinity on interspecific competition between the dinoflagellate Alexandrium catenella and the raphidophyte Heterosigma akashiwo using bi-algal cultures under several culture conditions. When initial cell densities of A. catenella and H. akashiwo were both 1 × 102 cells ml–1 at a salinity of 30, the growth of H. akashiwo was strongly suppressed by A. catenella, and no intact H. akashiwo cells were observed. In contrast, the growth of A. catenella was suppressed when initial cell densities of A. catenella and H. akashiwo were 1 × 102 and 1 × 104 cells ml–1, respectively. Interestingly, the growth of A. catenella was notably suppressed in bi-algal cultures at a salinity of 20 when initial cell densities of A. catenella and H. akashiwo were both 1 × 102 cells ml–1. In addition, growth of H. akashiwo in bi-algal cultures with A. catenella under cell-contact conditions was significantly inhibited, whereas growth of H. akashiwo was not inhibited by A. catenella in non-contact culture conditions. Furthermore, live-cell-mediated hemolytic activity of A. catenella was detected, but no hemolytic activity was detected in A. catenella culture filtrate. In contrast, growth of A. catenella was significantly inhibited by 50 to 100 µg ml–1 of a crude extract, including allelochemicals, from H. akashiwo culture filtrate. Therefore, salinity and interspecific interactions via allelopathy and/or cell contact might be important factors determining the growth dynamics of A. catenella and H. akashiwo in the field.