Experimental Study On The Interaction Between Epizoic Diatoms And Pseudodiaptomus Annandalei

Diatom is the main food source for zooplankton copepods and its interaction with copepods mainly reflects in the nutritional relationship.However,there is fewer researches on the epibiotic diatoms lived on the surface of copepods,or so-called epizoic diatoms.In fact,the phenomena that epizoic diatoms attach to the surface of copepods are common in nature.It has been widely reported and there may be a complex ecological relationship between them.Exploring the relationship and potential attachment mechanism between epizoic diatom and copepods can be contributed to reveal the new relationship between copepods and diatoms.It has an important theoretical and practical significance for marine biology and ecology research.Three epizoic diatoms,Falcula hyalina,Haslea xiamensis and Synedra tabulata isolated from the body surface of Pseudodiaptomus annandalei were used in this study.We explored the effects of Pseudodiaptomus annandalei on biochemical compositions of different epizoic diatoms as well as the survival of Pseudodiaptomus annandalei.The results are listed as follow:1.Pseudodiaptomus annandalei enhanced the cell density and the Chi a content of epizoic diatoms.Under pure-culture condition,the max cell density of Falcula hyalina,Haslea xiamensis and Synedra tabulata were(1.295±0.120)×106,(1.5±0)×105 and(7.47±0.153)×104 cells/mL respectively,the Chi a contents were 343.04±13.3,421.1±18.6 and 329.42±28.42 ?g/L respectively,while under co-culture condition,the max cell density rised to(1.595±0.092)×106,(2.03±0.252)×105 and(8.10±0.153)×104 cells/mL,and the Chi a contents rised to 471.98±3.03,470.7±9.85 and 388.26±1.69?g/L respectively.It showed that Pseudodiaptomus annandalei had a positive impact on photosynthesis of epizoic diatoms.The value of F,,/Fm of Falcula hyalina rised from 0.68±0.010 to 0.71±0.006 remarkably,the potential light conversion efficiency of it was affected most by Pseudodiaptomus annandalei.2.The influence of Pseudodiaptomus annandalei on biochemical compositions is species specific.Under pure-culture condition,the content of polysaccharides and proteins in colloidal exopolymeric substance of Falcula hyalina was 0.101±0.007 and 0.016±0.0006 mg/mL,it rised to 0.142±0.002 and 0.021±0.0033 mg/mL respectively under co-culture condition,while in Haslea xiamensis,it rised from 0.137±0.004 and 0.027±0.005 mg/mL to 0.182±0.007 and 0.030±0 mg/mL.The results showed that Pseudodiaptomus anandalei enhanced the content of polysaccharides and proteins in colloidal exopolymeric substance of Falcula hyalina and Haslea xiamensis.In addition,the intracellular proteins content of Synedra tabulata remarkably increased.Affected by Pseudodiaptomus annandalei,it rised from 6.624±0.228 to 8.509±0.553 ?g/mL.Pseudodiaptomus annandalei had the maximum influence on attachment of Falcula hyalina,the following was Haslea xiamensis,and the minimum was Synedra tabulata because the uronic acid content of Falcula hyalina increased remarkably from 0.021±0.0004 to 0.028±0.0004 ?g/mL under co-culture condition.3.Three epizoic diatoms could be food sources for Pseudodiaptomus annandalei,since the survival of copepod was higher.The release of nitrate and phosphate from Pseudodiaptomus annandalei provided nutrition for the growth of epizoic diatoms.Since the nitrate nitrogen content of Falcula hyalina and Haslea xiamensis in culture medium was 0.391±0.060 and 2.109±0.117 mg/L,and it rised to 3.036±0.402 and 5.073±0.064 mg/L under co-culture condition.Besides,the phosphate content in the culture medium of Haslea xiamensis was significantly higher in later logarithmic growth period.It indicated that bottom-up effect by nutrition from Pseudodiaptomus annandalei excretion was greater than top-down effect by predation.4.Pseudodiaptomus annandalei could promote the growth of epizoic diatoms by releasing nutrients.The free epizoic diatoms could also be used as the food source for Pseudodiaptomus annandalei to some extent during the culture process.It might be a symbiotic relationship between them and there was interspecific difference in this relationship.Pseudodiaptomus annandalei had greatest effects on Falcula hyalina,the following was Haslea xiamensis and the minimal was Synedra tabulata.The uronic acid in the attached exopolymeric substance might be an important factor affecting the attachment of epizoic diatoms on Pseudodiaptomus annandalei.The copepods might affect the symbiotic model by the secretion of uronic acid.