Feeding Selectivity Of Dominant Copepods And The Influence Of Key Red Tide Algae On Their Feeding Behavior

Copepods occupy a large proportion of Marine zooplankton,which is an important component of Marine ecosystem and plays a key role in the Marine food web.Copepods feed on phytoplankton to control algae outbreaks and provide suitable bait for larva of large economic fish.The research on copepods has always been a hot spot in the field of Marine plankton ecology.It is generally believed that copepods have feeding selectivity.However,due to the characteristics of copepods,such as large species,small individuals,fast feeding speed,smaller food size and various species,the research on its feeding selectivity has been slow.The frequent occurrence of dinoflagellate red tide has become the focus of Marine ecological environment research in the world,but the research on the control of dinoflagellate red tide and its ecological effect by mesozooplankton copepods is relatively weak.Whether copepods have feeding selectivity to dinoflagellates of different red tide and whether dinoflagellate concentrations have feeding effects on copepods are the directions that need further studyIn this study,we studied the feeding selectivity of copepods by using microhigh-speed photography,and selected Paracalanus parvus,the dominant species of Paracalanus parvus in Chinese waters,to photograph its feeding on bait of different particle sizes in natural water bodies.By analyzing the feeding behavior characteristics of Paracalanus parvus,we explained the feeding mechanism of Paracalanus parvus on bait of different particle sizes.Based on the results of the study on the feeding selectivity of Paracalanus parvus to different size classes of natural food,we further studied its feeding on the key red tide algae.According to the frequency and harm degree of dinoflagellates red tide in our country,we selected Prorocentrum minimum containing diarrheal shellfish toxins(DSTs)and Alexandrium minutum containing paralytic shellfish toxins(PSTs),which were compared with the non-toxic Thalassiosira.weissflogii.At the same time,based on the ecological characteristics of dinoflagellates red tide outbreak,We studied the feeding behavior characteristics of Paracalanus parvus on dinoflagellates of different concentrations.By analyzing the feeding behavior parameters of Paracalanus parvus on the key red tide dinoflagellates,such as the frequency of appendage beating,beating time,rejection,etc.,to prove whether copepods have feeding selection behavior,and to conclude the feeding selection mechanism(physical and chemical).In order to identify the key factors influencing dinoflagellate ingestion by copepods,and to further evaluate its influence on dinoflagellate ingestion.Intuitively analyzing the characteristics of copepods feeding behavior can provide more data support for the existing research results of copepods feeding ecology,and provide theoretical basis and methodological guidance for further research on the feeding relationships among other plankton.The main research results of this paper are as follows:1.In the study of the feeding selectivity of Paracalanus parvus on natural water food with different particle sizes(0.7-10 μm、10-20 μm、20-50 μm、50-100 μm、100-250 μm、>250 μm),indicate that Paracalanus parvus has a feeding range of 0.7-250 μm.As a small copepod(body length<1 mm),Paracalanus parvus has a feeding range of 0.7-250 μm.Compared with the results of feeding selectivity of large and medium-sized copepods(Calanus sinicus and Centropages dorsispinatus),there were both obvious niche boundaries and partial overlap.At the same time,it was found that Paracalanus parvus has an obvious tendency to avoid food in the size range of 20-50 μm.Combined with the analysis of the composition of food in the size range of 20-50 μm,it was found that dinospira(Ceratium furca、Ceratium fusus、Neoceratium horridum and others)was the dominant species in the composition of food in the size range of 20-50 μm.Therefore,we speculated that Paracalanus parvus obviously avoided food in the size range of 20-50 μm.However,they tended to feed on the bait of the two adjacent sizes.It was not the size class that caused them to avoid feeding,but the dinoflagellates in the size range that influenced the feeding selection of Paracalanus parvus.2.Based on the possibility of feeding selectivity of Paracalanus parvus on dinoflagellates,we further studied the feeding selectivity of Paracalanus parvus on dinoflagellates and diatoms through a controlled experiment.The results showed that:Compared with the non-toxic diatoms in the control group,the frequency and time of the appendage beating were significantly decreased when Paracalanus parvus was feeding on the toxic dinoflagellates.At the same time,the feeding rejection rate(7.95%for Prorocentrum minimum and 8.15%for Alexandrium minutum)was 1.65～1.69 times higher than that of the control group(4.83%for Thalassiosira.weissflogii).Based on this,we demonstrated the influence of toxic dinoflagellates on the feeding selectivity of copepods.Copepods avoided the toxic effects by actively reducing the frequency and time of appendage beating of toxic algae.At the same time,copepods would actively reject the toxic dinoflagellates when the feeding appendages came into contact with them.3.Combined with the ecological characteristics of dinoflagellate outbreaks,we further analyzed the feeding selectivity of Paracalanus parvus to dinoflagellate at different concentrations.The results showed that the high concentration of protodinoflagellates had an effect on the feeding behavior of Paracalanus parvus.As the concentration of food increased,the frequency of appendage beating decreased and reached the lowest value at the concentration of 1000 cells/ml,indicating the influence of Alexandrium minutum on the feeding behavior of Paracalanus parvus.However,there was no significant difference in the frequency of appendage beating between different concentration groups(except for 250 cells/ml),indicating that the non-toxic Thalassiosira.weissflogii had no above toxic effect on Paracalanus parvus.4.Based on the micro-high speed imaging technology,we identified the feeding mode(feed-current type)of Paracalanus parvus.By comprehensive analysis of feeding selectivity parameters of Paracalanus parvus a on natural food and toxic dinoflagellates,we showed that the filter feeding copepods can sense and capture the food particle size.And the different concentrations of non-toxic diatoms had the change of feeding behavior.When the diatom reached the concentration of red tide,its feeding behavior did not change.The toxic dinoflagellates show different feeding selectivity depending on their concentration and toxicity.In the Prorocentrum minimum environment,the feeding tendency of Paracalanus parvus decreased significantly when the concentration was>100 cells/ml.However,in the Alexandrium minutum environment,the feeding tendency of Paracalanus parvus decreased when the concentration was 1000 cells/ml.And the detection method may be different at different concentrations,but can be converted.In other words,copepods detect and capture prey in the high-concentration food environment by using the near-harvesteld mechanoreception method,and switch to the remote detection method when feeding the low-concentration food.