| The feeding selectivity of bivalves directly affects the biomass and community structure of phytoplankton in natural environment.Studying the feeding selectivity of different phytoplankton assemblages by bivalves is of great significance for evaluating the impacts of bivalves on phytoplankton community and food web structure and function in coastal waters,and can also provide basic data and scientific guidance for the planning and management of bivalve culture.In previous studies,researchers studied the feeding selectivity of particulate matter by bivalves in natural water,but the results were inconsistent,and had geographical specificity.In this study,the feeding selectivity of different phytoplankton assemblages by bivalves was investigated from different angles by using the method of filtration experiment and field investigation.Both the microscopic observation and HPLC analyses were used in this study.The experiment was divided into three stages:(1)In September 2018,mussel filtration experiments were conducted in Sanggou Bay(Yellow Sea)to study the selective clearance efficiency of Mytilus coruscus on phytoplankton in water,and investigate the difference of phytoplankton community structure in stomach of M.coruscus and water;(2)From November 2018 to October 2019,seawater samples,wild Crassostrea gigas and Mytilus edulis were collected once a month in the offshore reef area of Qingdao(Yellow Sea)to study the differences in phytoplankton composition between stomach of bivalves and seawater in natural sea areas;(3)In May 2019,seawater samples and various cultured bivalves(Mytilus edulis,Crassostrea gigas,Argopecten irradians,Azumapecten farreri,and Mizuhopecten yessoensis)were collected from the bivalve culture area of Qinhuangdao(Bohai Sea),and the phytoplankton composition in stomach of bivalves and seawater were analyzed.The main results are shown as follows:Mussel filtration experiments in Sanggou Bay:(1)By comparing the phytoplankton composition in natural seawater and filtered seawater,we found that the mussel preferentially ingested cryptophytes and dinoflagellates,but picophytoplankton(prasinophytes and cyanobacteria)could be less retained by mussel.Mussel showed different selectivity to different diatom species,and the selectivity of mussel to Chaetoceros spp.and Skeletonema spp.were generally lower.(2)The stomach samples analysis showed that cryptophytes were not found in the stomach samples by microscopy,whereas the diagnostic pigment(alloxanthin)of cryptophytes were present in stomach samples,indicating that cryptophytes were ingested and readily digested by mussel.The proportion of Chaetoceros spp.and Skeletonema spp.in the stomach samples was significantly lower than that in the water,but mussel showed a higher selectivity to Pinnularia spp.and Cocconeis spp.,indicating that there was a great difference in diatom species entering the digestive gland of bivalves.The investigation on feeding behaviour of wild bivalves in the offshore reef area of Qingdao:(1)Microscopic results showed that oysters and mussels ingested mainly on diatoms and dinoflagellates,and the feeding selectivity of dinoflagellates and chrysophytes by bivalves were higher than diatoms.For specific algae,both bivalves preferentially avoided ingested Skeletonema spp.,Chaetoceros spp.,Leptocylindrus spp.,Asterionella spp.,Guinaridia spp.and Pseudo-nitzschia spp.Both bivalves preferentially ingested Coscinodiscus spp.,Paralia spp.,Prorocentrum spp.,Dinophysis spp.,Protoperidinium spp.,and Dictyocha spp.(2)HPLC pigment analysis showed that the main pigments accumulated in the stomach of both bivalves were Fuco and Peri,which proved that both bivalves mainly ingested diatoms and dinoflagellates.And the feeding selectivity of bivalves to dinoflagellates was higher than diatoms.The concentrations of Pras and Zea in the stomach samples was very low,indicating that the prasinophytes and cyanobacteria(pico-,< 2 ?m)could be less retained by both wild bivalves.The investigation on feeding behaviour of cultured bivalves in Qinhuangdao area:(1)Microscopic results showed that the five bivalves ingested mainly on diatoms and dinoflagellates,and the feeding selectivity of dinoflagellates by bivalves was higher than diatoms.Five bivalves preferentially avoided ingested Skeletonema spp.,and the feeding selectivity of Chaetoceros spp.and Nitzschia spp.by bivalves were low.Bivalves preferentially ingested Licmophora spp.,Pleurosigma spp.,Pinnularia spp.,Coscinodiscus spp.,Paralia spp.,Scrippsiella spp.,Dinophysis spp.,and Protoperidinium spp.Different bivalves showed similar feeding selectivity to different phytoplankton.(2)HPLC pigment analysis showed that the main pigments accumulated in the stomach of five bivalves were Fuco and Peri,which proved that five bivalves mainly ingested diatoms and dinoflagellates,but the feeding selectivity of dinoflagellates by bivalves was higher than diatoms.The concentrations of Pras and Zea in the stomach samples was very low,indicating that prasinophytes was not the main food source for five bivalves in Qinhuangdao area.Summarize the results of the above three experiments,we found that:(1)bivalves in different habitats preferentially ingested dinoflagellates,but the feeding selectivity of chained diatom Skeletonema spp.and Chaetoceros spp.by bivalves were low;(2)Coscinodiscus spp.,Paralia spp.,Prorocentrum spp.,Dinophysis spp.,and Protoperidinium spp.were easily enriched in the stomach of bivalves;(3)bivalves in different habitats preferentially ingested different algae species,this difference may be related to the physiological characteristics and nutritional requirements of shellfish and the composition of phytoplankton community in the water;(4)the main pigments accumulated in the stomach of five bivalves were Fuco and Peri,the concentrations of Pras in the stomach sampleswas very low,indicating that diatom and dinoflagellate were the main food for bivalves,while prasinophytes could be less retained by bivalves. |
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