| Ocean acidification refers to the phenomenon that the seawater pH decreases over the years and mainly results from the increase of CO2 emissions due to human activity.It is a well-known global issue.The studies of the influence of ocean acidification on marine organisms and ecosystem still occupies the mainstream research direction.Ocean acidification is closely related to fishery resources dynamics.The influence of ocean acidification on the marine species is abundant.In addition,marine species exist complex response to ocean acidification.At the fisheries ecology perspective,ocean acidification might cause fisheries stock collapse,change the community and ecosystem structure,and damage the fisheries economies.Therefore,this study starts from the macro perspective to assess the potential risks of fishing industry in the exclusive economic zone of all countries in the world under the condition of ocean acidification.Then the species in East Bering Sea continetial shelf water was selected as the research object.Firstly,combining with the observation data,the temporal and spatial trends of ocean acidification in recent years were described.Secondly,spatial and thermal variations of fisheries species abundance and distribution under ocean acidification were analyzed.Finally,based on the ecosystem model,this study combined the effects of ocean acidification and fishing to explore their impacts to fishey species and marine ecosystem.The coping strategies were alsao analyzed.The research could provide a logical and theoretical framework for fisheries science and management to study the impact of ocean acidification and climate change on fisheries and the corresponding response strategies.The followings are the main conclusions for this study:(1)Risk assessment of marine fishing industry in exclusive economic zones under ocean acidification.Based on the surface pH data in 2050-2054 predicted by two scenarios in the climate model(ssp1-2.6 and ssp5-8.5,respectively,representing the most moderate and severe case of ocean acidification in the future),nowadays pH data(2010-2014),and the indicators related to global coastal catch production and social economic fators related to fishing industry,the potential risk of marine fishing industry in exclusive economic zones of all countries under ocean acidification were constructed.The risk assessment model was used to assess the potential risks to the marine fishing industry in the exclusive economic zone of the world in the middle of the 21 st century(2050-2054).This model includes the hazard degree related to ocean acidification,the exposure degree related to fishing yield and fishing structure,and the vulnerability degree related to social,economic and fishery industry adaptability.The results showed that under the future variations of ocean acidification,countries with high development level and low vulnerability might be subject to extremely low to medium risks.Countries and regions with low development level and high vulnerability might be subject to medium to high risks;countries and regions with large fishing production or high-level production of mollusks and crustaceans would be subject to extremely low to medium risks medium to high risk.Different countries should make their own response strategies according to their different fishery characteristics.Our results showed that the potential risks of fishing industry under ocean acidification mainly come from fishing structure,economic factors and the adaptability of fishing industry to the changes of industrial structure and production capacity.(2)Temporal and spatial variations of ocean acidification and it's effect factors in Ease Bering Sea continental shelf water.This study described the temporal and spatial variations of the surface water acidification in the continental shelf and its impart factors.The aragonite saturation(?ar)was used as the index of acidification calculated from the fugacity of carbon dioxide(f CO2),temperature and salinity.A ?ar simulated model was established to analyses the affecting factors based on the year,month,latitude,longitude,sea surface temperature(SST),sea surface salinity(SSS)and chlorophyll-a(chl-a).The results showed the spatial and temporal variations of ocean acidification in this area.Annual decline rate of ?ar was 0.0037 units,and there were fluctuations in its decline.?ar increased during Match to May and then decreased from June to October.March to April and October was easy to occur acidification.Spatially,the degree of ocean acidification decreased from nearshore waters to the open waters.Nearshore area was easy to occur ocean acidification.The studies indicated that the seasonal variation(the influence of month)of ?ar isgreater than that of year.The other factors affecting ocean acidification in this area might include freshwaterrunoff,temperature and biological factors.Conclusion of this study will be helpful to the study of the impact of ocean acidification on fishery resources and marine ecosystem and its mechanism.(3)Effects of pH variation on the fishery resource habitat in the East Bering Sea continental shelf water.Based on the data of bottom trawl in the East Bering Sea continental shelf from 1982 to 2014 and the data of seawater pH,the spatial distribution of 147 species(fish,crustaceans and molluscs species)and the habitat changes(distribution center and habitat area)under the current ocean acidification were analyzed by using correlation analysis and suitability index model.Results showed that the spatial distribution of the bottom pH in the continental shelf of the East Bering Sea is gradually decreasing from the near shore to the open ocean.Compared with 1982-1991,the bottom pH area decreased by 0-0.07 units in 2005-2014,among which the internal water area decreased by a large margin,while the pH in the open ocean and the northern area decreased by a small margin.The habitat pH of fish,crustaceans and molluscs also decreased year by year.It was found that 27.78% of fish species,37.93% of crustaceans species and 15.38% of molluscs species in this study changed their distribution centers due to pH decrease.Most species shifted to the open ocean and the north areawhere the pH decreased to a low degree.At the same time,current pH decline in the bottom water would also affect the habitat area changes of 19.70% of fish species,27.58% of crustaceans species and 32.69% of molluscs species.By analyzing the form of suitability index curve,four forms were found:(a)a certain range of suitability index(SI),with the decrease of pH,the suitability index might be(b)increased,(c)decreased or(d)stady firstly and then decreased rapidly.The results indicated that,to analyze the habitat change of fishery resources under pH fluctuation,we should pay special attention to the pH suitable range of species.(4)Effects of pH variation on the abundance of fishery resources in the East Bering continental shelf water.Based on the data of bottom trawl in the East Bering Sea continental shelf from 1982 to 2014 and the data of seawater pH,the dynamic regression model was used to study the resource variation of fishes,crustaceans and mollusca.Based on the model analysis,it is found that 40.63%,36.8% and 33.33% of the species richness of fish,mollusca and crustaceans are affected by the change of pH respectively,the effect of pH variation on species richness is species-specific,especially having negative effect on mollusca(excluding cephalopods)and crustaceans.The responses of species richness to pH decreasing were different(including up,down and up first and then down).The variation of pH can affect the abundance of fishery resources by directly increasing or decreasing and changing the suitable habitat range of species.It was found that it is not enough to analyze the effect of pH on species,and the food web and life history should be analyzed.The study shows that ocean acidification will have an impact on the abundance of different fishery resources,which can provide a reference for the sustainable development and utilization of resources.5)The ecosystem model simulation for the East Bering Sea shelf water fishery ecosystem under ocean acidification.The Ecopath model was used to construct the corresponding fishery ecosystem in the East Bering Sea from 2005 to 2014.Then the Ecosim model was based to simulate the change of fisheries biomass and their yield,ecosystem variations under the additional mortality from the crustaceans and mollusks species caused by ocean acidification From the perspective of the affected fishery resources,this study simulated how to adjust the fishing strategy(fishing mortality)to maintain the stability of fishery and ecosystem.Results showed that the total biomass and catches and each fishery species(expect for pelagic species)biomass and catches would have decreasing trends under future ocean acidification.The crab species might have most serve influence from ocean acidification.In 2100,compared with 2015,future ocean acidification might cause a decrease of 11.65%-26.80% in crab biomass and a decrease of 18.03%-39.43% in total catch.Ocean acidification might also lead to the decrease of marine biodiversity and the increase of the mean trophic level of catches.However,the overall ecosystem biomass would be shift to the low trophic level(the decrease of high trophic level biomass is more than the decrease of low trophic level biomass),indicating that the community structure of ecosystem is changing under ocean acidification.The effects of fishing and ocean acidification on marine species might be opposite or synergetic.In the synergetic results,due to the food web factors(predator-prey relationship),the combination of the effects of fishing and ocean acidification might intensify the negative effects to the biomass(such as Pacific cod and mollusk)or slow down these common negative effects(such as shrimp and crab).Coping strategy scenarios analysis showed that fisheries might cope with ocean acidification in some degree by adjusting the fishing mortality.This need fishery management to pay attention to the species directly affected by ocean acidification or indirectly affected from food web.Compensating the mortality brought by ocean acidification by reducing the fishing mortality could delay the effetcts of ocean acidification,marine organisms and ecosystem.(6)Main conclusions.The impact of ocean acidification to the costal fisheries varies with fishing structure,economic factors and the adaptability of fishery industry to the changes of industrial structure and production capacity.In the continental shelf waters of the East Bering Sea,ocean acidification had occurred in the recent 20 years.Based on the analysis of fishery resources in this area,it's found that the spatial distribution of species and the temporal change of resource abundance are affected by ocean acidification,which varied with species and the range of suitable pH.molluscs and crustaceans were most vulnerable to ocean acidification.Combined with ecosystem,ocean ac idification would affect other species through the food web.The common effects of fishing and ocean acidification would have opposite and synergetic effects on on species.In addition,ocean acidification might also cause the change of ecosystem community structure.The analysis showed that in response to ocean acidification,fishery industry should do the following aspects:(1)strengthen scientific research.Scientific research includes not only single species research,but also multi species at ecosystem level to understand which species are vulnerable to be affeced under ocean acidification.These studies provide knowledge that how to adjust fishing structure(such as fishing effort or fishing death coefficient)to reduce the exposure to ocean acidification at certain objectives.Specifically,coping with ocean acidification by fisheries needs to pay attention to the species directly affected by ocean acidification and those indirectly affected by food web.In practice,we need to reduce the fishing mortality specifically according to the response of different species.Although this would lead to the decrease of catch in the following years,the increase of species abundance could compensate this decrease due to the recovery ability of resources.And catch also could be recoverd.Through the conservation of ocean acidification related species in the ecosystem by reducing fishing mortality to compensate for the mortality caused by ocean acidification,the effects of ocean acidification on marine species and ecosystems could be delayed and the stability of marine ecosystems could be maintained;(2)on the economic level,we should reduce the fisheries dependence on crustacean and mollusc products and develop the corresponding aquaculture industry;(3)on the social level and adaptability,it's important to develop the overall economy of the country,strengthen education,and improve situation at the employment rate and the choice of employment;(4)monitor the dynamic state of ocean acidification continuously.This includes a focus on the change of ocean acidification parameters(such as pH)and the response of species.So the management could adjust the coping strategy in time. |
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