We studied the role of sophorolipid in inhibiting harmful algae bloom(HAB).Different sophorolipid concentrations were tested on marine microalgae,zooplankton,fish,and bivalve(Mytilus edulis) in laboratory.The result shows that sophorolipid could inhibit the growth of algal species selectively.Among three algae species selected,Platymonas helgolandica var.tsingtaoensis was promoted with increasing sophorolipid concentration;Isochrysis galbana was inhibited seven days later in sophorolipid concentration below 40 mg/L;and Nitzschia closterium f.minutissima was inhibited obviously in only a high sophorolipid concentration over 20 mg/L.Therefore,sophorolipid in a low concentration at <20 mg/L could remove certain harmful algae species effectively without harming other non-harmful microalgae.For other animals,sophorolipid could inhibit the growth of ciliate Strombidium sp.by 50% at 20 mg/L sophorolipid concentration after 96 h.The concentration in 96-h LC50 for Calanus sinicus,Neomysis awatschensis,Lateolabrax japonicus,and Paralichthys olivaceus was 15,150,60,and 110 mg/L,respectively.The 24 h LC50 value for Artemia salina was 600 mg/L.The relative clearance rate of mussel Mytilus edulis decreased to 80%,40%,and 20% of the control group after being exposed to 20,50,and 100 mg/L sophorolipid for 24 h.Therefore,the toxicity for mitigation of harmful algae bloom at previously recommended concentration of 5-20 mg/L sophorolipid is low for most tested organisms in this reaserch.
We used long term monitoring data to evaluate changes in abundance and species dominance of small-jellyfish (collected with zooplankton net whose bell diameter was less than 5 cm) between 1991 and 2009 in the Jiaozhou Bay, China. Zooplankton samples were vertically towed with conical plankton net from near-bottom to surface, identified microscopically, and mapped in time-space using Grapher 7.0 and Surfer 8.0. Results show that the abundance of small-jellyfish throughout the bay had been increasing during 2001-2009 on average of 15.2 ind./m 3 , almost 5 times higher than that between 1991 and 2000. The occurrence of peak abundance shifted from spring to summer after 2000, and two peaks appeared in spring and summer, respectively, after 2005. Both the abundance and the frequency of blooms of small-jellyfish increased after 2000 in the bay. In addition, the biodiversity of jellyfish has increased significantly in recent years with a change in dominant species. Several new dominant species appeared after 2000, including Rathkae octopunctata in winter, Phialidium hemisphaericum in spring, summer, and autumn, Phialucium carolinae in spring, and Pleurobrachia globosa in summer and autumn, while some previous dominant species throughout the 1990s (Eirene ceylonensis, Zanclea costata, Lovenella assimilis, and Muggiaea atlantica) were no longer dominant after 2000. The abundance of small-jellyfish was positively correlated with the density of dinoflagellates, and the abundance of zooplankton. We believe that the changes in smalljellyfish abundance and species composition were the result of eutrophication, aquaculture and coastal construction activities around the bay. Concurrently, seawater warming and salinity decrease in recent decades promoted the growth and reproduction of small-jellyfish in the bay.
