Effects Of Ocean Acidification Driven By Rising CO₂ On Several Economic Marine Mollusks

Ocean acidification(OA)can cause the decrease of seawater pH and calcium carbonate saturation state,which may adversely affect survival of calcareous organisms including mollusks.In the present research,OA effects on larvae and adults of 5 economic mollusks(Haliotis diversicolor,Haliotis discus,Crassostrea angulata,Babyloniaareolata and Mytilopsis saller)were studied.In order to make sure the accuracy of the experiments,two instruments which simulate future atmospheric CO2 concentration were designed to examine the effects of OA on molluscan larvae and adults.4 OA levels(800,1500,2000 and 3000 ? atm)were set in larval experiments while 2 OA levels(800 and 1500 ? atm)in adult experiments.The study was divided in 3 parts:(1)Effects of OA on larvae of 5 mollusks;(2)Combined effects of OA and other environmental factors on larvae of C.angulata and H.discus hannai;(3)Long term effects of OA on adults of H.diversicolor and H.discus hannai.Tolerance to OA of the 5 molluscan larvae in the order from weak to strong is H.diversicolor,H.discus,C.angulata,B.areolata and M.salleirespectively.Abalones are subtidal species which habitat is stable in physiochemical properties and therefore are susceptible to pH change.H.discus hannai originates from temperate region where pH is lower than tropic region,thus its tolerance to OA is better than subtropical species H.diversicolor.C.angluata as an intertidal species lives in environment with frequent pH change and may adapt to low pH.Tolerance of B.areolata to OA may be related to its contact to low pH environment during feeding and low calcification rate during larval development.M.sallei is an euryhaline species with a strong ion-regulation capacity which could effectively expel excess proton out of its body,therefore exhibits a very strong tolerance to OA.OA can affect thermo tolerance of C.angulata larvae,especially weakening its tolerance to low temperature,and consequently narrow its thermo window.OA can alleviate the inhibition effect of Cu2+ and Zn2+ on fertilization of C.angulata and also alleviate the inhibition effect of Zn2+ on fertilization of H.discus hannai.However,OA enhances the inhibition effect of Cu2+ on fertilization of H.discus hannai and this may be due to the dissolution of gel around the abalone eggs by Cu2+ which changed the egg structure.OA can enhance the toxic effect of Cu2+ on larval normality of C.angulata and so does for Cu2+ and Zn2+on larval normality of H.discus hannai.OA can also enhance the inhibition effect of Cu2+ and Zn2+on larval calcification of H.discus hannai.However,no synergic effect was found in combined treatment of OA and the two metals on calcification of C.angulata larvae.Generally speaking,OA could decrease the tolerance of molluscan larvae to suboptimal environmental conditions,but inter-specific variance exists in this phenomenon.Two abalone adults(H.diversicolor and H.discus hannai)were cultured in 2 OA conditions(800 and 1500?atm)for 1 year.Mortality of H.diversicolor significantly increased in 800?atm while in 1500?atm for H.discus hannai.Metabolism rate and ammonia excretion significantly decreased and O:N increased in OA condition for H.diversicolor.Reduced metabolism rate is a sign of energy saving mechanism,which may indicate adaptation to long term OA exposure.No significant change was detected for H.discus hannai regarding the physiological indices above.Feeding rate has an insignificant increasing trend with rising pCO2 for both abalones.The results of hematology indicate that:haemolymphe pH significantly reduced with rising pCO2 for both abalones.THC,ALB,ALT,AST,ACP,SOD,CAT,GSH,Glu and Ca2+ in serum were unchanged in different pCO2 condition.GLB significantly increased with rising pCO2 for H.discus hannai indicating that OA may enhance the immune level of H.discus hannai.ALP significantly decreased with rising pCO2 for H.diversicolor which may be attributed to pH decrease in haemolymph.GLB in H.diversicolor and ALP in H.discus hannai were unaffected by increasing pCO2.For H.diversicolor,egg diameter and egg diameter/egg yolk diameter were significantly higher in 800 ? atm than the other two pCO2 levels and egg yolk diameter did not change by OA,while for H.discus hannai egg diameter,egg yolk diameter and egg diameter/egg yolk diameter were all unaffected by OA.Sperm velocity and motility were all unaffected by pCO2 for both the abalones.Offspring from adults H.diversicolor cultivated in pCO2=800?atm condition and offspring from adults H.discus hannai cultivated in pCO2=800 and 1500?atm condition exhibited stronger tolerance and calcification ability compared with offspring from adults cultivated in normal pCO2 condition.Therefore transgenerational responses were observed in the above condition.However,offspring from adult H.diversicolor cultivated in pCO2=1500?atm condition is weaker in OA tolerance and calcification compared with offspring from adults cultivated in normal pCO2 condition.Transgenerational responses of H.diversicolor in pCO2=800?atm condition may be related to maternal provision,leading to larger eggs."Bleaching" effects of periostracum layer were observed for both abalones and stripping of periostracum layer was observed in 1500?atm treatment which is more evident for H.diversicolor.Number of spirobid on abalone shell was significantly reduced in high pCO2 condition and no fouling organisms were found in 1500patm.Shell length increment for H.diversicolor and shell weight/length for H.discus hannai were all significantly reduced in high pCO2 condition.Mg/Ca and Sr/Ca in shell both significantly increased in high pCO2 condition for both the abalones.These signs all suggested inhibition on calcification by OA.Ratio of nacre layer and prismatic layer thickness significantly increased and amount of nano-asperities of nacre layer platelet significantly reduced in shell formed in high pCO2 condition for H.diversicolor not for H.discus hannai.Vickers-hardness of prismatic layer and nacre layer significantly reduced with rising pCO2 for H.diversicolor.For H.discus hannai no hardness decrease was observed in high pCO2 and nacre hardness significantly increased in 800?atm.Changes in shell ultra-structure in H.diversicolor may lead to reduced crushing force in OA condition.Although H.discus hannai was less affected in shell ultrastructure,diminishing calcification in OA condition may also reduce its crushing force.Comparing the 2 abalone adults,H.diversicolor is more sensitive to OA than H.discus hannai.