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To improve the quality of Sargassum fusiforme seedlings, suitable strains of juveniles regenerated from holdfasts need to be bred. In this study, effects of different temperatures (16, 20, and 24 °C) and irradiances (100, 120, and 160 µmol photons·m−2·s−1) on the growth of juveniles (new individuals) from the holdfasts of S. fusiforme were investigated to provide strategies for the cultivation of vegetative propagation seedlings of S. fusiforme. The results demonstrated that during cultivation at 24 °C, the regenerated juveniles rotted after twenty-one days, and their relative growth rate, photosynthetic activity and pigment content decreased substantially. The low temperature of 16 °C also decreased their photosynthetic activity and growth considerably. At a high irradiance of 160 µmol photons·m−2·s−1, the growth rate and photosynthetic activity decreased. Under conditions of 20 °C and 120 µmol photons·m−2·s−1, juveniles showed higher photosynthetic activity and nitrate uptake rates, which increased the growth of the juveniles and lateral branches and promoted the accumulation of photosynthetic pigment. Therefore, culture conditions of 20 °C and 120 µmol photons·m−2·s−1 can be applied for early indoor cultivation of regenerated juveniles of S. fusiforme. This study provided technical support for solving the problem of single provenance of S. fusiforme seedlings. [ABSTRACT FROM AUTHOR]

Sargassum fusiforme is often adversely affected by epiphytic algae during its cultivation. However, the biological differences between S. fusiforme and the epiphytic algae have not yet been elucidated detrimental to the management of S. fusiforme culture. In this study, we sampled S. fusiforme and main epiphytic algae Ulva lactuca in a marine culture cycle and compared their biological characteristics. It indicated that, except during low‐temperature months (January and March), the photosynthetic electron activity of U. lactuca were generally higher than S. fusiforme. The nitrogen uptake rates of S. fusiforme and U. lactuca were all significantly higher in the earlier growth stage than other stages. In most cases, the nitrogen uptake and utilization of U. lactuca was higher than those of S. fusiforme. Although S. fusiforme absorbed more trace elements, U. lactuca had relatively strong photosynthesis and nutrient absorption performance; thus, the latter accumulated more soluble carbohydrate and protein and may have stress effect on S. fusiforme. This study will be helpful for understanding the differences in the biological characteristics of economic seaweed and its epiphytic macroalgae and provides a reference for the friendly management and healthy development of seaweed cultivation. [ABSTRACT FROM AUTHOR]

Mariculture of the economically important seaweed will likely be affected by the combined conditions of ocean acidification that resulting from increasing CO2 rising and decreased light levels, especially under high culture intensity and high biomass accumulation. To examine this coupling effect on the photosynthetic performance of Sargassum fusiforme seedlings, we cultured seedlings of this alga under different light and CO2 levels. Under low light conditions, elevated CO2 significantly decreased the photosynthesis of S. fusiforme seedlings, including a decreased photosynthetic electron transport rate. Seedlings grown under the low light intensity exhibited higher photosynthetic rates and compensation irradiance, and displayed higher photosynthetic pigment contents and light absorption than seedlings grown under high light intensity, providing strong evidence of photosynthetic acclimation to low light. However, the captured light and energy were insufficient to support photosynthesis in acidified seawater regardless of increased dissolved inorganic carbon, resulting in declined carbohydrate and biomass accumulation. This indicated that S. fusiforme photosynthesis was more sensitive to acidified seawater in its early growth stage, and strongly affected by light intensity. Future research should evaluate the practical manipulation of biomass accumulation and mariculture densities during the early culture period at the CO2 level predicted for the end of the century. [ABSTRACT FROM AUTHOR]

The effects of algal blooms on seaweeds have been rarely studied, although harmful algal blooms (HABs) are now normally regarded as worldwide incidents. In the present study, the effects of dense Karenia mikimotoi cells on the growth and photosynthesis of Hizikia fusiformis , a common and commercially cultivated macroalga in coastal waters of the East China Sea (ECS), were studied to understand the possible consequences when the mariculture encountered a dense harmful algal bloom. Furthermore, the counteraction of the latter on the growth and photosynthetic activities of K. mikimotoi was determined to evaluate the contribution of H. fusiformis commercial cultivation to environmental improvements. The results showed that the chlorophyll a (Chl a ) contents, maximal photochemical efficiency ( F v / F m ) and relative electron transfer rate (rETR) of gas vesicles (specialized leaves), adult and young receptacles of H. fusiformis were all significantly ( P < 0.05) inhibited compared with the mono-cultured ones. When compared with mono-cultured H. fusiformis (without K. mikimotoi ), the Chl a contents in gas vesicles, adult and young receptacles decreased by 20.6%, 17.6% and 33.2% within 2 weeks. Correspondingly, the F v / F m decreased by 7.9%, 37.4% and 43.7%; the apparent photosynthetic efficiency ( α ) decreased by 9.4%, 47.1% and 48.3%; and rETR decreased by 19.5%, 52.6% and 68.2%, respectively. The Chl a concentration of the mono-cultured K. mikimotoi (without H. fusiformis ) increased to 2247.97 μg l −1 from 958.11 μg l −1 within 14 d. Those of the co-cultivated ones (with H. fusiformis ), however, increased to 1591.31 μg l −1 on the 8th day and then decreased rapidly to 254.99 (±37.73) μg l −1 after the next 6 days. Furthermore, compared with the mono-cultured K. mikimotoi cells, the F v / F m , α and rETR max of co-cultivated ones decreased by 9.4%, 36.3% and 30.6%, respectively. The results indicated that the mature sporophytes of H. fusiformis were resistant to dense K. mikimotoi blooms and this resistance was organ-dependent as: gas vesicle > adult receptacles > young receptacles. On the other hand, commercial mariculture of H. fusiformis demonstrated the potential of preventing the occurrence of algal blooms. [ABSTRACT FROM AUTHOR]

The increase in atmospheric CO 2 and acid rain precipitation are serious global environmental problems that have had worldwide consequences, including the damage of biodiversity in intertidal zones. The decline in species richness in the intertidal zone of Wenzhou, China, is a typical example. In this study, we investigated the effects of CO 2 -enriched seawater, CO 2 -enriched air and acid rain on a dominant species, Corallina sp., and an inferior species, Ulva conglobata , in the intertidal zone of Wenzhou. The responses of Corallina sp. and U. conglobata to high-CO 2 seawater are similar, demonstrating that both of them are tolerant of seawater acidification induced by aerating CO 2 -enriched air. The PSII activities of Corallina sp. declined markedly when exposed to CO 2 -free air, while they increased significantly with high-CO 2 air. An increase of non-photochemical quenching (NPQ) was induced by CO 2 -free air, but it declined remarkably with CO 2 -enriched air, suggesting that Corallina sp. can use atmospheric CO 2 as carbon source for photosynthesis. Corallina sp. survived extremely low pH conditions (pH 3) and could regulate the pH of their ambient seawater through the dissolution of CaCO 3 , while the photosynthetic properties of U. conglobata decreased drastically and even the thalli were damaged irreversibly under low pH conditions (pH 3). These results suggest that Corallina sp. is much more tolerant of extremely low pH than U. conglobata . Based on these results, we suggest that it is not the increase of atmospheric CO 2 but acid rain at least in part contributed to the damage of the biodiversity in the intertidal zone, with the result that these areas are now mainly dominated by Corallina sp. [ABSTRACT FROM AUTHOR]

During the artificial cultivation of Sargassum fusiforme , a variety strains were inadvertently crossed during the cultivation cycle, making it difficult to preserve the superior strains that were previously bred, leading to reduced economic benefits. The use of holdfasts of S. fusiforme was found to have considerable potential for sub-culturing selected superior strains. In this study, we conducted experiments to investigate the effects of different temperatures (i.e., 16, 20, and 24 °C) and irradiances (i.e., 140, 105, and 70 μmol photons·m−2·s−1) on juveniles (i.e., new individuals) regeneration from S. fusiforme holdfasts and their growth. The results showed that photosynthetic activity and the absorption and utilization of nitrate by juveniles could be promoted through regulating temperature and irradiance, resulting in improved relative growth and regeneration rates. In the first six days, the regeneration rate was highest when cultured at 24 °C. After six days, the regeneration rate gradually increased at 20 °C and 140 μmol photons·m−2·s−1. Furthermore, the growth rate of regenerated juveniles, photosynthetic activity and nitrogen absorption rates were also significantly higher than those observed for all other treatments. However, at 24 °C, the efficiency of photosynthesis and nitrate absorption of the juveniles decreased, inhibiting their growth, resulting in rotting after twenty-four days. Therefore, for the large-scale breeding S. fusiforme , the method of adjusting the temperature in the different stages of the culturing process can be used to optimize the indoor vegetative propagation process of regeneration from the holdfasts. This method could solve the underlying problem of maintaining superior strains which resulted from the breeding programme of S. fusiforme. • Juvenile regeneration from S. fusiforme holdfast was influenced by temperature and irradiance. • Conditions of 20 °C and 140 μmol photons·m−2·s−1 was beneficial to the regeneration of juveniles and their growth. • Conditions of 24 °C and 140 μmol photons·m−2·s−1 was the optimal condition for regeneration but not for juvenile growth. • Adjusting the temperature in different stages of culture can optimize the indoor regeneration from the holdfasts. [ABSTRACT FROM AUTHOR]

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]

During the growth period of economically cultured Sargassum fusiforme , offshore eutrophication and ammonium release from sediments, both induced by high temperatures, significantly affect the photosynthesis and growth of this seaweed. In the present study, S. fusiforme seedlings were treated with various ammonium-nitrogen (NH 4 +-N) gradients and light intensities to evaluate the effects of these treatments on algal photosynthesis and NH 4 +-N accumulation. The results showed that a certain concentration of NH 4 +-N (300 μmol L−1) increased the photosynthetic electron transport rate (rETR) and maximum photosynthetic rates (Pm) of the S. fusiforme seedlings, but a high NH 4 +-N (900 μmol L−1) reduced the light-saturated rETR , the maximum quantum yield, and Pm. Although the seedlings maintained high NH 4 +-N uptake rates under high ammonium concentration, the glutamate synthase and glutamine synthetase activities were adversely affected, indicating that the absorption and assimilation of NH 4 +-N were not synchronous. Under low light conditions, high ammonium concentrations significantly inhibited the electron transfer and photosynthetic rates of the seedlings and negatively impacted the photosynthetic pigment synthesis and photosynthetic product accumulation. Sargassum fusiforme seedlings displayed a degree of photosynthetic tolerance to the increased ammonium concentrations. However, excessively high ammonium concentrations caused stress to the S. fusiforme seedlings, and this could inhibit algal growth and even cause death by inhibition of the photosynthetic process. These results indicated the concentration effects of ammonium eutrophication on the marine cultivation of S. fusiforme. It also showed that ammonium tolerance of S. fusiforme could be enhanced by improving the light conditions under high ammonium concentrations. • Certain concentration of NH 4 +-N (300 μmol∙L-1) increased photosynthesis of S. fusiforme seedling. • S. fusiforme seedling had photosynthetic tolerance to increased ammonium concentrations. • However, excessively high ammonium (900 μmol∙L-1) stressed seedling growth by inhibition of its photosynthetic process. • Low light intensified the inhibition of high ammonium on seedling photosynthesis and photosynthetic product accumulation. [ABSTRACT FROM AUTHOR]