The Characteristics Of Behavioral Response Of Perinereis Aibuhitensis To The Tidal Cycle

Infauna,as one of typical intertidal organisms,are interactive with the intertidal environment.Tidal fluctuations are reflected by the physiological and behavioral rhythmicity of infauna.The abrupt change in temperature,salt,dissolved oxygen,and water exchange at the intertidal zone have important consequences for the physiology and behavior of infauna when tidal changes occur.Infauna carry a strong adaptive capacity to the intertidal zone.On the one hand,infauna show extreme environmental tolerance,i.e.,physiological adaptation strategies.On the other hand,infauna are able to adapt to environmental changes in the intertidal zone through bioturbation,i.e.,behavioral adaptation strategies.At present,there have been many reports on the physiological adaptation strategies of infauna,but lacking studies on their behavioral adaptation strategies.Revealing behavioral adaptation strategies of infauna are important for understanding the reciprocal relationship between infauna and the intertidal environment.In this study,Perinereis aibuhitensis,a common large benthic polychaete in the intertidal zone,is used to quantitatively reveal the burrow structural characteristics and its behavioural response to tides from field investigations and indoor modelling studies.The main research content is as follows:1.Annual variation of burrow architecture characteristics of Perinereis aibuhitensisBioturbation of infauna plays an important role in the biogeochemical processing of sediments.Infaunal animals build burrows and enlarge the sediment-water interface by their activities and so bioturbation is closely related with burrow structure and animal behavior in the sediment.The purpose of this study is to explore the characteristics of P.aibuhitensis burrow structures with the factors of time of the year and animal size,which would also provide useful knowledge for improving polychaete aquaculture technology.The dimension and complexity of the burrows of P.aibuhitensis were measured by dissecting sediments.The results showed that there were three burrow shapes of P.aibuhitensis,i.e.,I,Y and U shapes.Overall,the order of abundance of each of the three burrow shapes were I > Y > U.Larger P.aibuhitensis are inclined to build Y-and Ushaped burrows in summer.The tunnel diameter,burrow depth and burrow length increased significantly with the increase of polychaete size(P < 0.05).In February and August,the burrow depths and burrow lengths of P.aibuhitensis individuals with body weights of 1-2 g and 2-3 g were significantly greater than in other months(P < 0.05).P.aibuhitensis individuals of 1-2 g and 3-4 g body weight had significantly more burrow openings and branches in August than in February(P<0.05).Within the same month,the burrow HEindex increased with increasing polychaete size,and when the sizes were 1-2g,2-3 g and 3-4 g,the complexity in August was higher than that in other months.This study suggests that I-shaped burrow dominants the burrow architecture of P.aibuhitensis.The polychaete with large size has a higher HEindex(burrow complexity)indicating a strong bioturbation ability.Y-shaped burrows are more conducive to the survival of P.aibuhitensis in hot weather.In order to adapt to outside environmental stresses,P.aibuhitensis usually builds deeper burrows.The large tunnel diameters and curling behavior observed in winter suggest that P.aibuhitensis possibly has a hibernation habit,which needs further research to identify.2.Variation of burrow microenvironment of Perinereis aibuhitensis during low tideThe life activities of aquatic animals are closely related to the habitat.Tidal changes have a great impact on the habitat environment of aquatic animals,and aquatic animals will have different behavior performance in this process.The purpose of this study is to explore the changes of water quality in P.aibuhitensis burrow microenvironment during tide.The variation of water quality indexes in P.aibuhitensis burrow microenvironment before ebb tide,10 minutes after ebb tide and 3 hours after ebb tide were investigated.The results show that the overlying water environment of P.aibuhitensis burrow microenvironment changes with the year,in which the temperature difference between February and August is the largest,and the difference between dissolved oxygen and ammonia nitrogen is the largest.Under the condition of high temperature,the temperature of sediment decreases with the increase of depth,and under the condition of low temperature,the temperature of sediment decreases with the increase of depth.The dissolved oxygen concentration of burrow water is the highest in February and the lowest in August.With the increase of P.aibuhitensis size,the dissolved oxygen concentration of burrow water decreased.After the ebb tide,the dissolved oxygen concentration in the large-scale P.aibuhitensis burrow will fluctuate up and down in the decline procedure,but it will eventually decline and stabilize to a lower dissolved oxygen concentration range.After ebb tide,the p H of burrow water gradually decreases,but it is still slightly alkaline.With the increase of P.aibuhitensis specification,the p H of burrow water increased slightly.The nutrient content of burrow water increased gradually after ebb tide,and the ammonia nitrogen content in June and August increased significantly after ebb tide(P < 0.05).During the whole ebb tide process,there was no dead individual of the P.aibuhitensis.The results show that sediment temperature may affect the habitat depth of P.aibuhitensis.After ebb tide,P.aibuhitensis will actively pump water to resist the decrease of dissolved oxygen in burrow water after ebb tide.After ebb tide,although the P.aibuhitensis burrow microenvironment will deteriorate and the nutrient content will increase,the nutrient content is in a safe concentration range for P.aibuhitensis.3.Behavioral response to the tidal cycle of Perinereis aibuhitensisTidal replacement has a significant impact on the physiology and behavior of intertidal organisms.Infauna can establish a suitable microenvironment to adapt to intertidal environment through the behavioral process.In this experiment,the behavioral response of Perinereis aibuhitensis to tidal alternation were studied by behavioral observation device.Three temperature grades(15 ℃,20 ℃ and 25 ℃)and four time periods(T1: before ebb tide,T2: low tide,T3: within 30 minutes after rising tide and T4:30 minutes after rising tide)were set up for the experiment,with six replications for each experimental group.The results showed that at the same time period,the radial undulation frequency,radial undulation pumping rate,axial crawling velocity and the frequency of head-tail exchange of P.aibuhitensis tended to increase with the increase of temperature(15,20 and 25 ℃),while the time of head-tail exchange tended to decrease.At the same temperature,the radial undulation frequency,axial crawling velocity,radial undulation pumping rate,radial undulation pumping efficiency,axial crawling time and the frequency of head-tail exchange of P.aibuhitensis in T3 were higher than those of other time periods,while the time of one head-tail exchange was lower.There was no significant difference in all behavioral indexes between T1 and T4(P > 0.05).At 20 ℃,the radial undulation frequency and pumping rate of P.aibuhitensis in T3 were higher than T1.At the same time period,the radial undulation time and axial crawling time of P.aibuhitensis were at the maximum and minimum at 20 ℃,respectively.There was no significant difference in axial crawling velocity of P.aibuhitensis at 15 ℃ and 20 ℃ in T1 and T3.However,at 25 ℃,the axial crawling velocity in T3 was significantly higher than T1(P < 0.05).The results indicate that the motion intensity of P.aibuhitensis increased with the increase of temperature.The motion state of P.aibuhitensis was better at 20 ℃.After ebb tide,it is an important time for P.aibuhitensis to forage for sediment,and its axial crawling motion is relatively slow.At the beginning of the rising tide,the motion intensity of P.aibuhitensis increased significantly.30 minutes after the rising tide,the motion of P.aibuhitensis gradually returns to a state similar to that before the ebb tide.P.aibuhitensis can deal with the adverse effects of tidal replacement through a series of behaviors.