Preliminary Study On Behavioral Ecology Of Horseshoe Crab

Horseshoe crab is regarded as an indicator species and sentinel species for monitoring the health status of coastal environment due to special habitat needs.However,in the past 30 years,human disturbance has caused a serious decline in horseshoe crab resources,and the protection of horseshoe crabs is imminent.Artificial breeding and stock enhancement are effective measures to restore the resources of horseshoe crabs.At present,both stock enhancement and artificial breeding are in the exploratory stage,and there is a lack of scientific stock enhancement regulation and mature artificial breeding system.In this study,the effects of external environmental changes such as different sediment ratios,water flow rates,baits,heavy metals,and wind directions on the behavioral ecology of horseshoe crabs were explored.The aim was to establish a scientific field release procedure and mature artificial breeding system to effectively restore horseshoe crab resources in China.The main results are as follows:（1）Adult T.tridentatus fed with oyster had higher weight gain rate,specific growth rate and spawning rate.Feeding oysters increased the intestinal biodiversity of T.tridentatus.Oysters are more suitable as bait for adult T.tridentatus than frozen fish,with taurine,high protein and high unsaturared fatty acids and other nutrients,which can improve the growth and reproductive performance of adult T.tridentatus.But a high-protein diet promotes animal growth and reproduction while also providing nutrients for pathogen breeding.Breeding water should be replaced frequently to remove residual bait and prevent pathogen breeding.（2）In the dawn,morning,noon,afternoon,and night five time periods,juvenile Tachypleus tridentatus perform more actively in the dawn and night.The juveniles spent more time hidden in the sediment and less time exposed to the surface of the sediment（such as crawling,swimming,etc）.They preferred to submerge in sediment types with more silt,and buried in mud and sediment types longer than in sandy types.When exposed to the sediment surface,juveniles preferred to inhabit the sandy type.At the same time,the proportion of juvenile horseshoe crabs inhabiting in sediment environment for swimming time is higher than that of gravel bottom.Therefore,the sediment type should be preferred as the habitat of juveniles in field release and artificial breeding.（3）The gill contraction frequency of 1^stinstar T.tridentatus increased with the rise of water flow velocity（y=2.02 x-0.23,R²=0.89,P<0.05）.The swimming duration of juvenile horseshoe crab increased at first and then decreased with increasing water flow velocity（y=10⁶x³-387726x²+36885x-1062.80,R²=0.85,P<0.05）.The single maximum swimming duration of juvenile T.tridentatus up to 70s at different water flow velocity.The mean burst swimming time of 1^stinstar horseshoe crab demonstrated a decreasing trend with increasing water flow velocity（y=-239.53x+32.19,R²=0.90,P<0.05）.The average burst swimming distance at first decreased with the increase of water flow velocity（0.06～0.07 cm/s）,and then increased with the increase of water flow velocity（0.07～0.08 cm/s）,and decreased with the increase of water flow velocity（0.08～0.12cm/s）finally（y=-185351x²+37240x-1540.10,R²=0.67,P<0.05）.The mean ground burst swimming speed of 1^stinstar T.tridentatus increased initially and decreased later as the water flow velocity increased（y=3×10⁶x³-868691x²+79752x-2285,R²=0.58,P<0.05）.The suitable survival velocity of 1^stinstar T.tridentatus is 0.06～0.08 cm/s.The swimming behavior strategies of juvenile T.tridentatus were different at different water flow velocity,and the bay with less wind and waves should be selected for field release.（4）From 2014 to 2020,a total of 990 Carcinoscorpius rotundicauda were observed in Guangxi Shankou Mangrove Reserve,and the population showed a downward trend.The number of C.rotundicauda in the sixth survey year reduced by 94.60%compared to the first survey year.The trend line equation is logy=-1.4288x+2.5944,where x is the nth survey year,and y is the number of C.rotundicauda found in the corresponding survey year.In addition,the population dynamics of C.rotundicauda showed significant seasonal regularity.The population size of C.rotundicauda was summer>spring>autumn>winter.The population size of C.rotundicauda was significantly positively correlated with temperature and north and south wind direction state values（0 and 4）at a temperature of 11～35°C.（5）High Cd²⁺concentration caused oxidative stress in juvenile T.tridentatus.The hazards increase with increasing Cd²⁺concentration in juvenile T.tridentatus.Cell membrane composition and permeability and lipid metabolism changed in T.tridentaus under 0.25 mg/L Cd Cl₂stress.Transcriptomics and metabolomics analyses concluded that high Cd²⁺concentration resulted in the imbalance of glycerophospholipid metabolism in juvenile T.tridentatus to detoxify Cd.To comfirm the reliability of the results,the suitable reference gene（ARP5）for juvenile T.tridentatus was screened.