珊瑚生态系统coralreefecosystem

1、THE EFFECT OF OCEAN ACIDIFICATION ON CORAL REEF ECOSYSTEM The Effect of Ocean Acidification on Coral Reef Ecosystem yapu wang999619961Ecosystem and Environment Change November 26, 2014AbstractOcean acidification has become the most serious environmental issue, which is mainly caused by increasing CO

2、2. The health of the worlds coral reef ecosystem has been in jeopardy since industry revolution, as the seawater PH levels have been destroyed and the carbonate equilibrium has changed. The Intergovernmental Panel on Climate on Climate Change (IPCC) outlined that CO2 levels in the atmospheric should

3、 keep at around 800L/ L, a safe level that could ensure the health of coral reef ecosystems. However, scientists predict that not only may corals be more prone to bleaching from ocean acidification in the future, but this also could influence the lives of coral reef ecosystem. Scientific evidence in

4、dicates that the root cause of ocean acidification is increasing pressure from global warming and human activities; other factors are emerging, such as sedimentation and eutrophication. In order to reduce the degree to which ocean acidification influences sea ecosystems, a long-term and systematic m

5、onitoring system, including laboratory testing and sea experiments, should be established. At the same time, using physiology and molecular biology techniques, combined with ecology research tools to study coral reef ecosystems on an individual, community, or even a whole ecosystem level, could be u

6、sed. In addition, improving the adaptive capability of marine organisms is also important in order to be prepared to address the ocean acidification situation in the future.Key words: CO2, global warming, ocean acidification, coral reef ecosystem, calcification rates, coral bleaching. 1. Introductio

7、n CO2 concentration in the atmosphere plays a key role on regulating the global climate system and its various ecosystems (Crowley and Berner, 2001). National Oceanic and Atmospheric Administration (NOAA) indicated that the figures (As table 1 shows) at Mauna Loa Observation (2011): before the indus

8、trial revolution, the CO2 concentration in the atmosphere was around 180-300L / L. Since the industrial revolution, it has increased to 40%, a result of climate change, global warming and ocean acidification, which have occurred mostly in recent decades. CO2 in the atmosphere dissolved in the ocean

9、by air and water being exchanged in order to achieve a balance, however, increasing CO2 concentration levels in the atmosphere have changed the oceans chemistry. This has impacted the ocean by breaking the original carbonate equilibrium system, reducing the PH levels of seawater, carbonate ion conce

10、ntration, and calcium carbonate saturation level, resulting in ocean acidification. (Kleypas, Feely & Fabry, 2005). Since the 1950s, increasing CO2 concentrations in the atmosphere and ocean acidification has caused a global concern. Joint Global Ocean Flux Study (2001) demonstrated the occurren

11、ce of CO2 in the atmosphere diffusion to ocean and ocean acidification diffusion phenomenon. Ocean acidification directly affects the structure and health of marine ecosystems. For coral reefs, ocean acidification has become a key factor, which determines the likelihood of a coral reefs survival, bu

12、t moreover, continued acidification may trigger the sixth mass extinction (Invers et al., 2002; Goriran et al., 1996). Impact on coral reef ecosystems caused by rising CO2 concentrations in the atmosphere is multifaceted. This paper analyzes the current studies of effect of ocean acidification on co

13、ral reef ecosystem and summarizes them in order to provide a reference for future research and study.2. Effects of Ocean Acidification on Coral Reef Ecosystems2.1 Impact on Scleractinian CoralsOn the one hand, scleractinian corals are main builders of coral reefs; on the other hand, it is a typical

14、representative of the marine calcifying organisms. Current research on the effects of the ocean acidification on scleractinian coral have mostly concentrated in the area of calcification, rather than about other physiological processes of scleractinian coral and the impacts they have on other biomes

15、 in coral reefs, which are poorly understood. Research shows that when the CO2 concentration in atmosphere is double (560L / L ), the PH level of the seawater, it will be 0.14 lower than it is now; calcification rate of Acropora palmate, Porites coral reef, and other types of scleractinian coral wil

16、l decline by 3% to 60%, and coral reef photosynthesis efficiency are unlikely to change significantly (Leclercq, Gattuso, Jaubert, 2002). 2.1.1 The Decrease in The Calcification Rate of Scleractinian Coral There was a simulation experiment showed that, compared with the glacial period, the calcifica

17、tion rate of scleractinian coral will drop 30% in 2100; when compared with the current situation, the calcification rate of scleractinian coral will fall by 11% (Marubini et al., 2003). In short, research and experiments indicate that when ocean acidification intensifies, the calcification rate of c

18、oral reefs will decrease. Table 2 shows that the variation of calcification in Porites corals over time. Calcification was regarded as a combination of extension (centimeters per year) and density (grams per cubic centimeter). These data are based on 19002005 data for all colonies. (modified from De

19、ath et al, Science, 2008). 2.1.2 The Symbiosis of Coral and The Destruction of Zooxanthellae In order to provide more than 95% nutrients and energy for coral metabolism, symbiotic algae absorb light energy and nutrients to carry out photosynthesis (Muscatine, 1990). Anthony (2009) said: “because of

20、the supply that come from symbiotic algae, coral calcification rate can maintain at a high rate.” Anthonys research documented that ocean acidification could lead to the bleaching of coral reefs and the destruction of the symbiosis of coral and zooxanthellae. However, the current situation of ocean

21、acidification, is complicated due to the relationship between coral reef calcification and photosynthesis activity still being quite complicated, thus, science requires more time to study the impact on symbiosis between coral and zooxanthellae.2.1.3 Larvae Supplement and Community Recovery Will Be M

22、ore Difficult Coralline algae play an important role for attachment of larvae to the scleratinia coral. However, it is quite sensitive to ocean acidification, and researchers predict that most of coralline algae will disappear in the next two or three decades (Heyward, Negri, 1999). Therefore, ocean

23、 acidification will significantly impact the coral sexual reproduction process. In addition, under the influence of global climate change and human activities, a large number of coral reefs have died which have left a large space for the invasion algae. Large algae constrain coral reproduction and g

24、rowth, since algae compete with corals for light and living space.2.2 Ocean Acidification Promotes The Dissolution Phenomenon of The Coral Reef System Ocean acidification can not only lead to a lower calcification rate of coral reef systems, but also promote the dissolution phenomenon of coral reef

25、systems. Some researches show that even in healthy coral reef areas, dissolution continues to occur simultaneously with calcification. With the increasing of ocean acidification, the dissolution rate of coral reef has risen rapidly, so when the dissolution rate reaches or exceeds its calcification r

26、ate, some coral reef may experience negative growth. Such a phenomenon has been found in some degraded marginal coral reef areas. For example, Gattuso (1997) found that the Moorea coral reef has changed to Algae-dominated reefs, due to global climate change (global warming) and human activities (oil

27、 spill, overfertilization and so on). Meanwhile, he pointed out that the entire coral reef is dissolving at a rate of 0.8 mmol m-2 d-1. At the same time, Walter and Burton (1990) performed similar experiments at a coral intertidal zone and they found that this coral reef is dissolving at a rate of 1

28、3.7 mmol m-2 d-1. Dissolution of coral reefs is generally weak, however, near coastal zone, dissolution is more severe (Kleypas, Langdon, 2000). Therefore, some unhealthy coral reefs will dissolve first when ocean acidification becomes more intense. On the other hand, some healthy reefs can offset t

29、he dissolved quantity to some extent and postpone the arrival time of the net dissolved state. But there are a large number of the simulation experiments results which show that when the CO2 concentration in atmosphere reaches 560L / L, the seawater aragonite saturation in the majority of the worlds

30、 coral reef area will drop to 3.0arg or less. By this time, even healthy coral reefs would have a dissolution rate and calcification rate roughly equal. Thus, most of the worlds coral reef will face a transition from a net increase rate to a net loss rate (Silverman et al., 2009).2.3 Impact on The O

31、ther Key Features of Biology in Coral Reef Areas In recent years, as research continues, there are some reports on the impact of ocean acidification on other biological populations in the areas of coral reefs, as the table 3 indicates that the major biological populations included: coralline algae,

32、benthic communities, and fish.Coralline algae is one of the most important members of coral reef system, it acts as “glue”, which helps a coral reef maintain its stability and it is the most important food resource for sea urchins, parrotfish and some mollusks (Crowley, Berner, 2001). Meanwhile, enc

33、rusting coralline algae also provide an important rigid attachment to the bottom of coral larvae (Crowley, Berner, 2001). However, resent studies show that ocean acidification will lead to a significant reduction of the calcification of coralline algae and may cause fatal consequences for coralline

34、algae. Benthic mollusks, bryozoans and echinoderms in a coral reef area are crucially important for maintaining the three-dimensional structure of a coral reef. Studies show that calcification rates of bivalves can be affected by ocean acidification. In addition, due to organisms in the early stages

35、 of life being more sensitive to the environment than the mature ones, ocean acidification can influence younger ones easily (Gazeau et al., 2007). In short, ocean acidification is likely to affect their early growth and life history for the majority marine organisms, which will have a serious impac

36、t on marine ecosystems.Coral reef fish are the foremost part of a coral reefs ecosystem and play an important role in the material cycle of a coral reefs ecosystem, so maintaining a healthy coral ecosystem is important. Increasing of CO2 in seawater can cause acidosis for marine organisms, including

37、 fish, thus, it could affect the physiological behavior of animals (Gazeau et al., 2007). Acid-base status of fish, their respiration, blood circulation, and nervous system function can be affected by a high rate of CO2 in the short term, while growth and reproduction rates can be influenced in long

38、 term (Ishimatsu, Kita, 1991).3. Synergistic Effects of Ocean Acidification With Other Key Factors on Coral Reef Ecosystems With ocean acidification, sea warming, rising sea levels, nutrient enrichment, and source input, which are caused by global change and human activities, which can impact a cora

39、l reefs ecosystem. As far as current research results go, the single effect and the combined effect could not be clearly distinguished and it is hard to separately quantify the ocean acidification on global coral reef degradation. Currently, scientists primarily focus on synergistic effects of ocean

40、 acidification by light, temperature, and nutrients.3.1 Synergistic Effects of Ocean Acidification with IlluminationLight is a necessary factor for maintaining and promoting the growth a coral reefs growth. Under appropriate lighting conditions, photosynthesis can be conducted by zooxanthellae, it c

41、ould provide an important energy source for a coral reef (Muscatine, 1990). Goiran (1996), whose experimental results show that in the absence of light conditions, it is easier for a coral reef to make net dissolve. Therefore, under the conditions of ocean acidification and light attenuation, a cora

42、l reef is more likely to experience negative growth.3.2 Synergistic Effects of Ocean Acidification and Temperature Global warming causes the temperature of the oceans surface water to increase. In some tropical and subtropical area, the ocean temperature has reached a point that is close to the cora

43、l reefs thermal limit. Increasing seawater temperature will have a significant impact on a coral reefs productivity, growth rate, calcification rate, and other aspects. Bleaching will occur when ocean acidification and high seawater temperature work together (Kleypas, Langdon, 2000). In the near fut

44、ure, with the increasing ocean acidification and seawater temperature, the global coral reef ecosystem will experience coral bleaching more frequently and severely, as well as experience disease, deaths and other benthod community function and biodiversity which will be severely affected (Anthony et

45、 al., 2009). 3.3 Synergistic Effects of Ocean Acidification and Eutrophication The experiments document that single nutrient enrichment and acidification cause coral reefs to growth inefficiently. If the response of a coral reef in its natural environment is consistent with the experiments results,

46、then the increasing of eutrophication and ocean acidification in coastal regions will have a negative impact on viability of coral reefs (Muscatine, 1990).4. Ocean acidification could lead to change and degradation of ecosystem population structure Because the impact of ocean acidification on coral

47、reefs has a larger species differences, along with the increasing ocean acidification, coral reefs population structure will undoubtedly experience change, specifically its structure is likely to move to a single specie, simple structure, and have a low production rate (Kleypas et al., 2000). Based

48、on previous observational studies and IPCC reports, coral reef ecosystems will face a serious threat in the future. In addition, only when the calcification rate is greater than the dissolution rate will the coral reef be able to grow normally, on the contrary, the coral reef will start dissolving.

49、At present, coral reefs around the world have suffered degradation, experienced a calcification capacity decrease, while an increase in the dissolution rate. With the growing ocean acidification, the dissolution of coral reefs will take just a matter of time. Thus, many serious consequences will occ

50、ur. First, the growth rate of coral cannot catch up with sea-level rise speed, resulting in coral reefs drowning. Second, some biological population will be lost, due to there not being a living space for other organisms (NOAA, 2011). Therefore, ocean acidification will exacerbate the degradation of

51、 coral reef ecosystems.Although most organisms in coral reefs have been through a few hundred million years of evolution, and have some ability to withstand environmental perturbation, in recent decades, worldwide rapid degradation and the death of coral reefs show that such degree of ocean acidific

52、ation in present times will be unable to be adapted by coral reef. With the intensification of ocean acidification, the health function of coral reef ecosystems will inevitably continue degrading. In summary, the combined effects of multiple factors make restoring coral reefs more difficult. If ther

53、e is not proper conservation, coral reef ecosystems will become fragmented and we will see their demise (Mumby et al., 2007).5. Future Research and StudyAt present, there is a lack of coral reef studies and evidence to support long-term biological experiments. Under the effect of ocean acidification

54、 and global change, the fate of coral reefs is not optimistic. There is a need to strengthen research and study the following aspects.5.1 Long-term Systematic Monitors on Seawater Carbonate System. Currently, there are only few sporadic observational studies about seawater carbonate systems in vario

55、us developing countries. It is not conducive for all countries to summarize the seawater carbonate system of coral reefs, influencing factors, and biological activities by ocean acidification, therefore, there is a need for an increase in time and space spent on its research. Seawater carbonate syst

56、em, which in coral reefs area (especially at coastal areas), is affected by many complex factors. Thus, when exploring characteristics and influencing factors, researchers need to combine: water quality, distribution of biological communities, water exchange capacity, water sources and other factors

57、 (Zhang, Chen, 2006). Therefore, completing such research requires a multidisciplinary approach. 5.2 Carry out laboratories and ocean acidification experiments International researches currently focus on the impact of ocean acidification on the calcification rate of coral reefs, while there is a lac

58、k of long-term experiments. It is necessary to carry out additional research or studies on the impact of ocean acidification on other organisms biological activities. At the same time, further experimental study could be through individual, community, and system level to explore different kinds of g

59、roup responses for ocean acidification. That can lead to a more comprehensive understanding of different responses of how a coral reef ecosystem works. In additional, due to the coral reef ecosystem being influenced by many complex factors, future research should incorporate other environmental factors and multi-factor experiments should be carried out when