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Nine antialgal active compounds, (i.e. trehalose (1), twenty-two methyl carbonate (2), (-)-dihydromenisdaurilide (3), 3,7,11,15-tetramethyl-2-hexadecen-1-ol (4), isophytol (5), 8-hexadecenol (6), 17-hydroxyheptadecanoic acid (7), trans-asarone (8) and 2-amino-3-mercaptopropanoic acid (9)) were isolated from Ulva pertusa for the first time by sephadex LH-20 column chromatography, silica gel column chromatography and repeated preparative TLC. Except for compound 4, all compounds represented novel isolated molecules from marine macroalgae. Further, antialgal activities of these compounds against Amphidinium carterae, Heterosigma akashiwo, Karenia mikimitoi, Phaeocystis globosa, Prorocentrum donghaiense and Skeletonema costatum were investigated for the first time. Results showed these nine compounds have selectivity antialgal effects on all test red tide microalgae, and antialgal activities against red tide microalgae obviously enhanced with the increase of concentration of antialgal compounds. Based on this, EC50–96 h values of these nine compounds for six red tide microalgae were obtained for the first time. By analyzing and comparing EC50–96 h values, it has been determined that seven compounds (1, 3, 4, 6, 7, 8 and 9) showed the superior application potential than potassium dichromate or gossonorol and other six compounds as a characteristic antialgal agent against Heterosigma akashiwo, Karenia mikimitoi and Prorocentrum donghaiense. Overall this study has suggested that green algae Ulva pertusa is a new source of bioactive compounds with antialgal activity.

Seven antialgal compounds (1–7) were successfully isolated from the red alga Gracilaria lemaneiformis through a combination of silica gel column chromatography and repeated preparative thin-layer chromatography. On the basis of the spectral data, the compounds were identified as gossonorol (1), 7,10-epoxy-ar-bisabol-11-ol (2), glycerol monopalmitate (3), stigmasterol (4), 15-hydroxymethyl-2, 6, 10, 18, 22, 26, 30-heptamethyl-14-methylene-17-hentriacontene (5), 4-hydroxyphenethyl alcohol (6), and margaric acid (7). These seven compounds were isolated from G. lemaneiformis for the first time, while the compounds 4, 6, and 7 were isolated from marine macroalgae for the first time. Furthermore, a quantitative relationship between the inhibition of algal growth and the concentration of each antialgal compound was determined and important parameters for future practical HAB control, e.g., EC50-96h, were also obtained. The results indicated that isolated compounds 1–7 possess selective antialgal activity against the growth of several red tide microalgae (including Amphidinium carterae, Heterosigma akashiwo, Karenia mikimitoi, Phaeocystis globsa, Prorocentrum donghaiense, and Skeletonema costatum). Their antialgal activity against test red tide microalgae has not been previously reported. Furthermore, the EC50-96h of one or more of the compounds towards the tested red microalgae was not only significantly less than 10 μg/mL but also was smaller than that of the characteristic antialgal agent potassium dichromate. The study demonstrates that compounds 1–7 possess significant application potential as antialgal agents against several harmful red tide microalgae.

Biofouling is a particular problem in the pearl oyster culture. It may reduce the growth and survival rates of the cultured species. Foulers are often themselves filter feeders, and are therefore potential competitors for food resource with the cultured species. Fouling organisms may also reduce the oxygen supply. A study was conducted to measure the impact of foulers on feeding, oxygen consumption, and waste excretion. POM, ammonia, phosphate and oxygen concentration were measured in various treatments (cultured species，foulers). This study showed that fouling organisms had significant effect on food uptake, oxygen consumption and waste excretion. The clearance rate, ammonia and phosphate release rate, oxygen consumption rate of the fouled pearl oyster were greater than those of the clean pearl oysters. Other foulers that settled on cages or buoys also contributed much to phytoplankton depletion, oxygen consumption and concentration increase of ammonia and phosphate in water. Therefore, this study showed us that foulers were important competitors in the pearl oyster cultivation of Daya Bay in November 2005. Published