A Study On The Population Dynamics Of Two Species Of Sea Rotifers By Food And Temperature

Brachionus plicatilis belongs to Rotifer,Monogononta,Brachionidae,and its life history has generational alternations.Rotifer is one of the important zooplankton groups in aquatic ecosystem,and it plays an important role in the structure and function of the ecosystem.Asexual reproduction is performed when the environmental conditions are good,and sexual reproduction is performed when the environment is harsh to produce dormant eggs to survive the unfavorable environment.In this study,Brachionius manjavacas?hereinafter referred to as BM?from USA and Brachionisus plicatilis?hereinafter referred to as BP?from China were the research objects.A comparative study of the population response characteristics of two sea rotifers at different temperatures and food concentrations.The aim is to screen out the strains of marine rotifers that have the advantages of stable growth?high yield,stable population,etc.?,and provide a theoretical basis for the production of aquatic seed open biological bait.The results are as follows:1.Effects of food concentrations on population dynamics of two species rotifers The changes in population growth and population number,pre-reproduction time,lifespan,and number of offsprings of the two species of rotifers at different food concentrations(0.25,0.5,1,2,4,and 8×10⁶ cells m L^-1)were discussed.The results showed that the population growth rate and population number of the two species of rotifers increased rapidly and then decreased slowly as time goes on,indicating that the population will collapse gradually.When the food concentration was lower than 4×10⁶cells m L^-1,the population of BM was significantly higher than that of BP?P<0.05?;otherwise,it was lower than that of BP.The pre-reproduction time of the BM showed a downward trend with increasing food concentration,and the pre-reproduction time of the BP showed a wavy change with increasing food concentration,The longest pre-reproduction time of BM is 58h at the food concentration gradient of 0.25×10⁶ cells m L^-1 while the shortest is 45.83h at the concentration of 8×10⁶ cells m L^-1,and the longest life span of BP is 55.3h at the concentration of 5.3×10⁶ cells m L^-1while the shortest is 50h at the concentration of 4×10⁶ cells m L^-1;The total number of offsprings of the BM showed an increasing trend with the increase in food concentration,and the total number of offsprings of the BP showed a trend of obvious decrease and then increase;The lifespan of two species of rotifers first increased and then decreased with the increasing of food concentration.The longest lifespan was 364h for the BM and388h for the BP at the concentration of 4×10⁶ cells m L^-1.The results showed that food concentration has an effect on Brachionus plicatilis.In the sanme way,the proper concentration of Chlorella can promote the reproduction of rotifers,and the concentration of food required by different species of Brachionus plicatilis is obviously different.This chapter concludes that the BM is suitable for large-scale cultivation at a concentration lower than 4×10⁶ cells m L^-1 while the BP is more suitable when the concentration is higher than 4×10⁶ cells m L^-1.2.Effects of temperatures on population dynamics of two species rotifersThe changes in population growth rate and population number,pre-reproduction time,lifespan,and the number of offsprings of two species of rotifers at different temperatures?15°C,20°C,and 25°C?were disscussed.The research showed that the population growth rate and population number of Brachionus plicatilis.In both species increased originally and then decreased with time at 20°C and 25°C,and maintained a slow growth trend at 15°C.The changes of the population at 20°C and 25°C was significantly higher than 15°C,which may due to the excessively low temperature inhibiting the growth of rotifers.In the early stage,the population number and population growth rate at 25°C were higher than 20°C while the population numbers and population growth rates of BM at 25°C and 20°C in the later period were similar,which may be due to the reason that the maximum population capacity of the experimental group has been reached.In the later period,the population number and population growth rate of the BP at 20°C exceeded 25°C,probably because the BP specie had better tolerance at 20°C than 25°C.In addition,different rotifer species also have appropriate survival temperatures.The pre-reproduction time of the two species of Brachionus plicatilis.decreased with increasing temperature,and there was no significant difference between the two species.The highest total number of offsprings of the BM specie was 18.17 at 20°C,and the highest total number of the offsprings of the BP specie was 19 at 25°C;the lifespan of the two species decreased with increasing temperature.The lifespan of the BM specie was higher than the BP specie at all three gradient temperatures.The lifespan of BM specie is 294h at 25°C.The lifespan at 20°C is 354h,which is significantly longer than that at 25°C?20.4%,P<0.05?.The lifespan at 15°C is 392h,which is significantly longer than that at 20°C?11.8%,P<0.05?.The lifespan of BP specie at 25°C is 278h.The lifespan at 20°C is 322h,which is significantly longer than that at 25°C?15.8%,P<0.05?.The lifespan at 15°C is 358h,which is significantly longer than that at 20°C?11.1%,P<0.05?.The life extension of the BM specie is more obvious than that of the BP specie.In summary,the temperature has a significant effect on brachial worms in seawater.The optimal growth temperature of the BM specie should be about 25°C,and the optimal growth temperature of the BP specie should be in the rage between 20°C and 25°C,which is more biased towards20°C.Low temperature can extend the life of rotifer.3.Interaction of temperature and food concentration on two species rotifersUnder the combined action of different food concentrations(0.25,0.5,1,2,4,and 8×10⁶cells m L^-1)and different temperatures?15°C,20°C,and 25°C?,the changes in population growth rate and population number,pre-reproduction time,lifespan,and number of offsprings of two species of rotifers were discussed.The experimental results were analyzed by two-factor analysis of changes,indicating that the interaction of food concentration and temperature which had significant effects on the reproduction time,lifespan,offsprings and population changes of the two species of rotifers.At the temperature of 15°C,the population growth rate and population change of the two species of rotifers increased with the increasing of food concentration,and the change was relatively slow.The low temperature significantly inhibited the growth of rotifers.At the temperature of 20°C and 25°C,the population growth rate and population number of each concentration were significantly higher than that of 15°C.At the temperature of 15°C,there is no significant difference in population changes between the two species.At the temperature of 20°C,the population growth rate and population number of BP species are lower than those of BM species at low concentrations.At food concentrations gradients,BP species are higher than BM species.At the temperature of 25°C,the population of the BP specie was significantly higher than that of the BM specie at low concentrations,while there was no significant difference between the two species at high concentrations.The population changes between 20°C and 25°C were significantly higher than 15°C.At low temperatures,the pre-reproduction time of the two species rotifers were the longest.At the temperature of15°C,the concentrations of each food had no significant effect on the pre-reproduction time of rotifers.The pre-reproduction time of BM was higher than that of BP;at the temperature of 20°C and 25°C,different food concentration gradients had an effect on the pre-reproduction time of rotifers,and there was no significant difference between the pre-reproduction time of BM and BP.The number of offsprings generally increased with the increase of food concentration and increased with the increasing of temperature.At the temperature of 15°C,there was no significant difference in the number of offsprings between the two species at different concentrations,and at 20°C and 25°C,there were some differences between the two lines.As the temperature rising,the lifespan is significantly extended.At three different temperatures,obviously at the gradient of a concentration of 4×10⁶ cells m L^-1,the higher the concentration,the longer the lifespan was.The lifespan at 4×10⁶ cells m L^-1 and 8×10⁶ cells m L^-1 did not change significantly.At high concentrations,the lifespan of the BP specie is higher than that of the BM specie.