Effect of pH and salinity on the removal of phytal animals during summer cultivation of Sargassum fusiforme and Sargassum fulvellum in Korea

The brown seaweeds, Sargassum fusiforme and Sargassum fulvellum are edible and highly valued in Korea. During the summer season, phytal animals graze heavily on young algal blades and holdfasts of these two species and substantially reduce harvestable biomass. Acid and salinity treatments are used to efficiently control infestations by phytal animals in other cultivated algae (e.g., Pyropia), but their effects on the removal of phytal animals in Sargassum cultivation are unknown. Here we investigated the effects of pH (range 2 ~ 13) and salinity (range 0 ~ 44 psu) on the removal of two major phytal animals, Caprella scaura and Gammaropsis utinomi, associated with S. fusiforme and S. fulvellum. We also examined the optimum quantum yield (F v/F m) of algae in the same experimental conditions to quantify the tolerance of algae to acid and salinity treatments. The two animal species experienced more than 80 % mortality at pH lower that pH 4 and the extreams of salinity (0 ~ 10 and 44 psu) after a 5-min of immersion. The quantum yield of S. fulvellum was not significantly different from controls (ambient pH and salinity) within the pH 4–10 range and within the 7–40 psu salinity range. Similarly, the quantum yield of S. fusiforme was not significantly different from controls within the pH 3–11 range and the 0–44 psu salinity range. Therefore, if pH and salinity conditions outside these ranges were used in commercial Sargassum culture, the removal of the two animal species would be higher, but quantum yield of algae would be substantially reduced. These results indicate that pH and salinity treatments could be used effectively to remove the phytal organisms without significantly affecting optimum quantum yield in S. fusiforme and S. fulvellum.