Study On The Thermal Tolerance Of The Common Nektons In Shidao Bay,the Yellow Sea

There are plenty of large scale coal-fired power plants and nuclear power plants in the coastal region of China,which discharge a large amount of waste heat emissions into the ocean generally in the direct-current cooling way.The large amount of thermal discharge leads to the high temperature zone in the coastal local waters.It not only changes the physicochemical properties of the receiving waters,but also affects the reproduction,ontogeny and growth of all marine organisms,which results in serious impacts on the marine ecological environment.Temperature is an important environmental factor which influenced the growth and metabolism of aquatic organisms.The thermal tolerance experimental research of marine organisms helps us understand the thermal physiology of the species and the effects of thermal pollution on marine organisms.Shidao Bay is an important habitat for fishery species in the northern Yellow Sea,China.The operation of the under-construction nuclear power plant in this area will discharge a large amount of waste heat emissions to the receiving waters near the Shidao Bay,which could generate thermal effects on the marine organisms of this region.Determining the thermal tolerance of aquatic organisms at natural temperatures and different temperature-rise rates provides scientific information for better understanding the thermal effects of thermal discharge on marine ecosystem,assessing impacts on the biological resources of Shidao Bay caused by the thermal discharge from nuclear power plants and improving the temperature control standards of thermal discharge.This study uses dynamic method and static method to quantify the critical thermal maximum?CTM?at different acclimatization temperatures?5.0?,9.0?,11.0?,13.0?,17.0? and 26.0??and temperature-rise rates?0.5?/h,1.0?/h,2.0?/h,3.0?/h,4.0?/h,6.0?/h,9.0?/h,12.0?/h and 15.0?/h?and 24-h upper incipient lethal temperature(24-h UILT₅₀)at different acclimatization temperatures?5.0?,11.0?,13.0?,17.0? and 26.0??of the eight species?Sebastes schlegeli,Hexagrammos otakii,Chaeturichthys stigmatias,Platichthys bicoloratus,Sebastiscus marmoratus,Oratosquilla oratoria,Charybdis japonica,Hemigrapsus penicillatus?.The main results are as follows:?1?Acclimatization temperature and temperature-rise rate significantly affect the CTM of the eight species.The CTM of each species is positively related to the acclimatization temperature.The thermal tolerance of each species increases significantly with the acclimatization temperature.For example,at the acclimatization temperature of 5.0?,the CTM of Hexagrammos otakii at each temperature-rise rate is 25.1?-29.1?;at 26.0?,the CTM ranges from 30.5? to 32.9 ?.The CTM of Chaeturichthys stigmatias at each temperature-rise rate increases significantly from 29.7 ?-34.2 ? at 5.0 ? to 35.7 ?-38.1 ? at the acclimatization temperature of 26.0?,respectively.The effect of temperature-rise rate on CTM varies among species and acclimatization temperatures.At the acclimatization temperature of 26.0?,the CTM of each species increases with temperature-rise rate.However,at 5.0?,9.0?,11.0?,13.0?and 17.0?,the CTM of each species at different temperature-rise rates varies with different species,depending on acclimatization temperatures.?2?The 24-h UILT₅₀ of each species is positively related to the acclimatization temperature,which increases significantly with the acclimatization temperature.The 24-h UILT₅₀ differed significantly among species.With the increasing of acclimatization temperature from 5.0? to 26.0?,the 24-h UILT₅₀ of Sebastes schlegeli,Hexagrammos otakii,Chaeturichthys stigmatias,Platichthys bicoloratus,Sebastiscus marmoratus,Oratosquilla oratoria increases from 25.1?,22.7 ?,28.6?,25.7?,24.3?,27.1? to 29.8?,29.1?,35.2?,30.0?,29.6?,31.9?,respectively.For Charybdis japonica,the 24-h UILT₅₀ increases from 30.7? at 11.0? acclimatization temperature to 36.4? at 26.0?.The 24-h UILT₅₀ of Hemigrapsus penicillatus increases from 31.2? at the acclimatization temperature of 11.0? to 36.1? at 17.0?.According to the 24-h UILT₅₀ of each species,the thermal tolerance of the eight species follows a ranking order of Hemigrapsus penicillatus > Charybdis japonica > Chaeturichthys stigmatias > Oratosquilla oratoria > Platichthys bicoloratus > Sebastes schlegeli > Sebastiscus marmoratus > Hexagrammos otakii.In conclusion,CTM and 24-h UILT₅₀ are two of the most important parameters in thermal tolerance experimental studies,both of which generally increase with the rise of acclimatization temperature.However,at the same acclimatization temperature,the CTM of each species is commonly higher than the 24-h UILT₅₀.Acclimatization temperature and temperature-rise rate are important factors which affect the thermal tolerance of nektons.The thermal tolerance significantly varies among species.The thermal tolerance of crustacean such as crab is generally higher than other experimental species.