Investigation of the Inhibitory Effects of Mangrove Leaves and Analysis of Their Active Components on Phaeocystis globosa during Different Stages of Leaf Age.

The presence of harmful algal blooms (HABs) can cause significant problems to the quality of the water, the marine ecosystems, and the human health, and economy worldwide. Biological remediation can inhibit harmful algal growth efficiently in an environmental-friendly manner. Therefore, the research conducted on biological remediation with regard to the inhibition of HABs is becoming a major focus in marine ecology. To date, no study has been reported with regard to the red tides occurring in mangrove wetlands. Therefore, the present study used two mangrove species, namely and and one harmful algae species as experimental organisms. The present study determined the inhibitory effects and algae physiology of specific aqueous extracts from mangrove leaves on the viability of harmful algae, and analyzed the main chemical composition of the aqueous extracts by ultra-performance liquid chromatography coupled to high resolution mass spectrometry (UPLC-QTOF-MS). The results indicated that the aqueous extracts from different leaf ages of and leaves exhibited apparent inhibitory effects on the growth of . The inhibitory effects of and leaves aqueous extracts on the growth of were in the following order: senescent > mature > young leaves. The levels of the parameters superoxide dismutase (SOD) activity, glutathione (GSH), and malondialdehyde (MDA)content in following treatment with and leaves aqueous extracts were increased as follows: senescent > mature > young leaves. Simultaneously, the intensity of the ion peaks of the specific secondary metabolites assigned (No.: 4 Rt: 2.83 min), (No.: 7 Rt: 3.14 min), (No.: 8 Rt: 3.24 min), (No.: 9 Rt: 3.82min) and (No.: 10 Rt: 4.10 min) were increased. These metabolites were found in the aqueous extracts from leaves. The intensities of the ion peaks of the secondary metabolites , in the aqueous extracts from the leaves were also increased. The majority of the substances that inhibited the algae found in the mangrove plants were secondary metabolites. Therefore, we considered that the norsesquiterpenes compounds , , , and and a phenolic glycoside compound were the active constituents in the aqueous extracts of the mangrove leaves responsible for the inhibition of algae growth. This evidence provided theoretical guidance for the development of biological methods to control red tides and for the further use of substances with antiproliferative activity against algae.