Allelopathic Effects And Its Ecological Significance Of Karlodinium Veneficum On Co-occuring Phytoplankton

In recent years,harmful algal blooms events were still increased around the world,mixed nutritional dinoflagellates algal blooms was one important trend.The Karlodinum veneficum algal blooms events were also happened from time to time,killed a lot of fish and other aquatic organisms,caused serious economic losses.At present,the formation mechanism of the K.veneficum is not clear,and the effects on other phytoplankton are rarely reported.This study is under the laboratory conditions,investigated the allelopathy of K.veneficum on multiple phytoplankton species,and the mechanism of allelopathy was preliminary discussed.The main results are briefly highlighted as follows:(1)K.veneficum was able to inhibit the growth of co-occuring phytoplankton,including Akashiwo sanguniea,Prorocentrum micans,Scrippsiella trochoidea,Phaeocystis globosa,and Rhodomonas salina.And the inhibiting effects were positively correlated with the cell density of K.veneficum.However,the inhibition effect on phytoplankton growth was different.K.veneficum had no inhibiting effects on Prymnesium parvum.In addition,the co-culture algae strains showed the promotion,inhibition and no effect on the growth of K.veneficum.A.sanguniea,P.micans,S.trochoidea,P.globosa,and R.salina had a significant role in promoting the growth of K.veneficum.P.parvum had certain inhibition and P.micans was almost not promoted the growth of K.veneficum.(2)Four components of K.veneficum culture all inhibited the growth of R.salina.Specifically,the strongest effect was observed in the sonicated culture,followed by the whole-cell culture,the filtrate of sonicated culture,and the cell-free filtrate of whole-cell culture.Comparison of these four components on R.salina,these results showed the allelochemical from K.veneficum not only exist inside the cell,but released into the ambient medium,and it was not stable outside the cell.(3)The allelopathy of K.veneficum on co-occuring phytoplankton observed to be regulated by nutritional conditions.The allelopathy of K.veneficum was enhanced significantly via increasing nutrient concentrations.Meanwhile,different nitrogen and phosphorus ratios will influence the allelopathy,the allelopathy of K.veneficum at lower N/P ratio(10 : 1)and higher N/P ratio(30 : 1)was significantly stronger than those at normal N/P ratio(20 : 1),indicating N-deficient and P-deficient conditions could enhance the toxicity of K.veneficum.The results of the study showed that K.veneficum may be obtained the important nutrients sources to promote the population growth from phytoplankton cells.Heterotrophy could be an important competing strategy for K.veneficum and thus plays an important role in the formation and maintenance of K.veneficum blooms.