MEPS 339:83-92 (2007)  -  doi:10.3354/meps339083

Allelopathic interactions between the bacillariophyte Skeletonema costatum and the raphidophyte Heterosigma akashiwo

Yasuhiro Yamasaki1,*, Sou Nagasoe1,2, Tadashi Matsubara1, Tomoyuki Shikata1, Yohei Shimasaki1, Yuji Oshima1, Tsuneo Honjo1

1Laboratory of Marine Environmental Science, Division of Marine Biological Chemistry, Department of Bioscience and Biotechnology, Faculty of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
2Present address: Harmful Algal Bloom Division, National Research Institute of Fisheries and Environment of Inlannd Sea, 2-17-5 Maruishi, Hatsukaichi, Hiroshima 739-0452, Japan

ABSTRACT: We investigated growth interactions between Skeletonema costatum (Greville) Cleve and Heterosigma akashiwo (Hada) Hada ex Hara et Chihara using bi-algal cultures under axenic conditions. When inoculated at high cell densities, growth of both species was coincidentally suppressed. In other combinations of inoculation density, the species first reaching stationary phase substantially reduced maximum cell densities of the other species. When cultured together under conditions without cell contact, growth of S. costatum and H. akashiwo were both suppressed. Furthermore, despite re-enrichment with nutrients, filtrates from dense cultures of S. costatum and H. akashiwo reciprocally reduced their maximum cell densities. In additional experiments, growth of Chaetoceros muelleri was also suppressed with filtrates from the above cultures, but growth of Prorocentrum minimum was not. Therefore, growth interactions between these species strongly suggest the involvement of allelopathic substances secreted by both species. Finally, growth and interaction of S. costatum and H. akashiwo in bi-algal cultures were simulated using a mathematical model. This model indicated that S. costatum and H. akashiwo steadily approach a stable equilibrium point of about 3.4 × 105 cells ml–1 and 4.8 × 105 cells ml–1, respectively, when the 2 species coexist.

KEY WORDS: Allelopathy · Bacillariophyceae · Skeletonema costatum · Raphidophyceae · Heterosigma akashiwo · Bi-algal culture · Growth inhibition

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