The Yellow Sea green tide: A risk of macroalgae invasion.

Large scale green tides have bloomed successively in the Yellow Sea since 2007. The floating ecotype of Ulva prolifera, which is responsible for the environmental disaster, drifted a long distance during the blooming time and was exotic to the coastal area. The Yellow Sea green tide can be a potential source to incur bio-invasion. In this study, the distribution pattern and propagule pressure of the floating ecotype was investigated along the Qingdao coastline, which was seriously impacted by the green tide. Two out of 661 attached Ulva specimens collected in different seasons were identified as the floating ecotype by molecular markers, indicating that a few individuals of the floating ecotype had settled down, and their attached population could have spontaneously established. In seawater and sediments, the proportion of the floating ecotype in Ulva propagules reached up to 32% and 69% respectively when the floating algae was accumulating on seashore, which was a great propagule pressure to the local ecosystem. Results of the field test indicated that the available resources and the competition between the floating ecotype and the local Ulva species might be the main restrictions for settlement. Though the current scale of the established population is still small, the risk of biological invasion by the floating ecotype exists and it deserves more attention.

Increased potential for wound activated production of Prostaglandin E2 and related toxic compounds in non-native populations of Gracilaria vermiculophylla.

The capacity of the East Asian seaweed Gracilaria vermiculophylla ("Ogonori") for production of prostaglandin E2 from arachidonic acid occasionally causes food poisoning after ingestion. During the last two decades the alga has been introduced to Europe and North America. Non-native populations have been shown to be generally less palatable to marine herbivores than native populations. We hypothesized that the difference in palatability among populations could be due to differences in the algal content of prostaglandins. We therefore compared the capacity for wound-activated production of prostaglandins and other eicosatetraenoid oxylipins among five native populations in East Asia and seven non-native populations in Europe and NW Mexico, using a targeted metabolomics approach. In two independent experiments non-native populations exhibited a significant tendency to produce more eicosatetraenoids than native populations after acclimation to identical conditions and subsequent artificial wounding. Fourteen out of 15 eicosatetraenoids that were detected in experiment I and all 19 eicosatetraenoids that were detected in experiment II reached higher mean concentrations in non-native than in native specimens. Wounding of non-native specimens resulted on average in 390% more 15-keto-PGE2, in 90% more PGE2, in 37% more PGA2 and in 96% more 7,8-di-hydroxy-eicosatetraenoic acid than wounding of native specimens. Not only PGE2, but also PGA2 and dihydroxylated eicosatetraenoic acid are known to deter various biological enemies of G. vermiculophylla that cause tissue or cell wounding, and in the present study the latter two compounds also repelled the mesograzer Littorina brevicula. Non-native populations of G. vermiculophylla are thus more defended against herbivory than native populations. This increased capacity for activated chemical defense may have contributed to their invasion success and at the same time it poses an elevated risk for human food safety.