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

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 × 10 5 cells ml -1 and 4.8 × 10 5 cells ml -1 , respectively, when the 2 species coexist.KEY WORDS: Allelopathy · Bacillariophyceae · Skeletonema costatum · Raphidophyceae · Heterosigma akashiwo · Bi-algal culture · Growth inhibition Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 339: [83][84][85][86][87][88][89][90][91][92] 2007 Honjo (1994) and Smayda (1998) indicated that most pelagic blooms attributed to O. luteus were almost certainly those of H. akashiwo. Therefore, we will treat O. luteus described by Pratt (1966) and Honjo & Tabata (1985) as H. akashiwo.In in situ and in vitro experiments, high concentrations of Olisthodiscus luteus inhibit the growth of Skeletonema costatum, while lower concentrations stimulate the growth of S. costatum (Pratt 1966). Similarly, Honjo et al. (1978) reported that Heterosigma akashiwo and S. costatum alternated in forming red tide blooms in the fishing port of Hakozaki. They found that filtrate from dense cultures of H. akashiwo, reenriched with nutrients, suppressed the growth of S. costatum. Furthermore, Honjo & Tabata (1985) reported an apparent and reciprocal codominance between O. luteus and diatoms in a 70 m 3 outdoor tank with flowing coastal water.Unfortunately, none of the in vitro experiments mentioned above used axenic strains. In this study, we used axenic strains of Heterosigma akashiwo and Skeletonema costatum. First, we conducted bi-algal culture experiments with several combinations of initial cell densities of the 2 species. Second, we examined allelopathic interactions between H. akashiwo and S. costatum by way of both growth experiments using culture filtrates and of bi-algal culture experiments under noncontact conditions. Finally, we simulated the...

Extracellular polysaccharide-protein complexes of a harmful alga mediate the allelopathic control it exerts within the phytoplankton community

“…Thus, it is likely that the allelopathic effects of H. akashiwo were both species-specific and dependent upon the cell density of the target species. This supported the finding of a previous study (Yamasaki et al, 2007), and suggested that allelopathy drives the alternation of the two species in the field. Similarly, the diatom T. rotula was also strongly inhibited depending upon the concentration of protein dissolved in the filtrate of H. akashiwo (Figure 2, Supplementary Figure 2).…”

“…Similarly, APPCs were detected by a dot-blot analysis of axenic cultures of H. akashiwo at densities 1 Â 10 5 cells per ml (Supplementary Figure 3b), at which H. akashiwo can inhibit S. costatum growth in the laboratory experiments (Yamasaki et al, 2007); these findings supported the conclusion drawn from the field study (Figures 6b and c) that APPCs can affect the growth of other phytoplankton in the field. A comparison of dot-blots from 40 mg ml -1 culture filtrate and from the dense bloom sampled on 8 June (Figure 6d) showed a similar stain density in both, indicating a similar amount of allelopathic activity, which was sufficient to suppress S. costatum growth.…”

“…All strains were tested for bacterial contamination by the fluorochrome 4 0 ,6-diamidino-2-phenylindole staining method (Porter and Feig, 1980), and were verified as axenic. Cultures were maintained in 100-ml flasks containing 50 ml modified SWM-3 medium (Yamasaki et al, 2007) without the addition of calcium pantothenate, nicotinic acid, p-aminobenzonic acid, biotin, inositol, folic acid and thymine, at a salinity of 25 at 25 1C under 228 ( ± 5) mmol m -2 s -1 of cool-white fluorescent illumination on a 12:12 h light/dark cycle. In addition, the modified SWM-3 medium was autoclaved (at 121 1C for 15 min) and contained a Tris (hydroxymethyl) aminomethane buffer (Wako Pure Chemical Industries, Ltd.) to prevent pH change during culture.…”

“…Furthermore, Honjo and Tabata (1985) reported an apparent and reciprocal codominance between O. luteus and diatoms in a 70 m 3 outdoor tank with flowing coastal water. Recently, we investigated growth interactions between H. akashiwo and S. costatum using bi-algal cultures under axenic conditions, and our findings indicated that the growth of either species could be suppressed by the unidentified allelochemicals of the other, depending on cell densities (Yamasaki et al, 2007).…”

Dietary effects of the red-tide raphidophyte Heterosigma akashiwo on growth of juvenile Manila clams, Ruditapes philippinarum

“…Strains of H. akashiwo, C. neogracile, Nannochloropsis sp., and the haptophyte Pavlova lutheri (Droop) Green, 1975 were inoculated at a density of 5,000 cells mL 1 into 200-mL glass flasks (n=3) containing 150 mL modified SWM-3 medium (Yamasaki et al 2007). After incubation for 12 d at 25°C under 150 ( 10) μmol photons m 2 s 1 of cool-white fluorescent illumination on a 12 : 12 h light : dark cycle, 100 mL from each of the three replicate flasks was centrifuged at 700 g for 15 min, and the cell pellet from each sample was frozen at -30°C until used for total sugar and acidic sugar determination.…”