High tolerance to fluctuating salinity allows Sargassum thunbergii germlings to survive and grow in artificial habitat of full immersion in intertidal zone

Abstract In this study, a four-way factorial experimental design (three temperatures, four salinities, two frequencies and three durations of osmotic stress) was used to test the tolerance of Sargassum thunbergii germlings shortly released from fertile thalli to osmotic stress. Results showed that the growth and survival of germlings were significantly affected by salinity and duration of osmotic stress, rather than by osmotic frequency. In addition to the main effects, all two-way, three-way and four-way interactions between the four stresses on the growth were significant. Germlings showed quick growth with relative growth rate (RGR, % day −1 ) over 16% when cultured at 32 psu combined with 30 °C. Although growths of germlings subjected to hypo-osmotic and hyper-osmotic conditions were significantly inhibited, RGRs over 12% were obtained except for those at 35 °C with the RGRs below 10%. In comparison to growth, survival was more tolerant to osmotic stress. Germlings showed high survivals over 60% when exposed to most osmotic stresses, by the end of experiment. Only under extreme conditions (12 psu for 4 h or 8 h at 35 °C) were the survivals reduced to below 10%. Although the effects of osmotic stress on the growth and survival were significant, germlings exhibited quick growth and high survival under most conditions. And those extreme conditions which had great destructive effect on germlings barely exist in field. Therefore, the construction of artificial tanks is feasible for the restoration of S. thunbergii beds in the intertidal zone.