Organic acid treatment for removal of epiphytic Ulva L. attached to Sargassum fusiforme seedlings.

The attachment of epiphytes to Sargassum fusiforme seedings has become a serious problem in S. fusiforme aquaculture. In this study, we investigated the effect of citric acid on the attachment of Ulva lactuca to S. fusiforme seedlings. Seedlings of S. fusiforme were treated with different concentrations of citric acid (0.05 mol·L−1, 0.08 mol·L−1, 0.15 mol·L−1) for different times (1, 3 and 5 min) and the death rate of the attached U. lactuca was measured. Citric acid treatment caused the death of U. lactuca , with the death rate increasing gradually with increasing concentrations of citric acid and treatment time. However, treatment with a high concentration of 0.15 mol·L−1 citric acid for 5 min impaired electron transfer of the S. fusiforme seedlings, decreasing photosynthesis and causing irreversible damage to the seedlings, and eventually resulting in the rotting and subsequent death of the seedlings. Treatment of the S. fusiforme seedlings with 0.08 mol·L−1 citric acid for 3 min was an optimal condition for the complete removal of epiphytic U. lactuca. Furthermore, subsequent culture of the treated seedlings by this optimal condition in the presence of 1.5 mg/L α-naphthaleneacetic acid during the recovery process was conducive to the normal growth of the S. fusiforme seedlings. • The citric acid was used to treat Ulva lactuca on Sargassum fusiforme seedlings. • 0.08 mol·L−1 citric acid for 3 min was optimal to treat the epiphytic U. lactuca on Sargassum fusiforme seedlings. • The physiological status of the seedling could be restored to the pre-treatment level with the addition of 1.5 mg·L−1 α-naphthaleneacetic acid. [ABSTRACT FROM AUTHOR]