The journal article was written to provide an overview of physical and chemical processes affecting changes in coral reef ecosystem. These changes are influenced by anthropogenic greenhouse gas emission (Hoegh-Guldberg, Mumby and Hooten 1737) that triggers physical processes involving laws of thermodynamics. The journal article also shows how the basic principle and theory of thermodynamics occur at global scale over a long period of time. Consequently, the physical processes influence the chemical processes that eventually lead to further changes in ocean ecosystem.
The article introduces reader to the existing phenomena of warming and acidifying of the seas (Hoegh-Guldberg, Mumby and Hooten 1737) that represent physical and chemical processes respectively. The article refers to global carbon dioxide concentration in earth’s atmosphere and temperature data from Vostok ice core study as the basis of the analyses. These Vostok ice core datasets show oscillation of temperatures and carbonate ion concentration in seawater during the past 420,000 years (Hoegh-Guldberg, Mumby and Hooten 1737). Historical data show trend of correlation between atmospheric carbon dioxide concentration and the global temperature (Hoegh-Guldberg, Mumby and Hooten 1738). This trend suggests a role of carbondioxide in influencing the atmospheric temperature, and subsequently the seawater temperature.
The article also explains the chemical process involving absorption of atmospheric carbon dioxide by seawater that creates carbonic acid. The carbonic acid lowers the seawater pH and creates acidic seawater environment (Hoegh-Guldberg, Mumby and Hooten 1738). From ecological perspective, the seawater temperature and pH (acidity) are highly relevant with the resilience of coral and other marine organisms. There are temperature and pH thresholds that would allow corals to adapt, the combination of both thresholds it is known as resilience tipping point (Hoegh-Guldberg, Mumby and Hooten 1739), and the conditions below this resilience point are considered as equilibrium.
Increase in seawater temperature beyond the resilience point creates a thermal stress marked with disassociation of corals and their endosymbiotic dinoflagellates Symbiodinium spp (Hoegh-Guldberg, Mumby and Hooten 1739). These dinoflagellates coexist with the corals, help the corals’ metabolism and ensure calcification of the corals. Coral calcification is an indication of how the dinoflagellates trap and convert the energy for metabolism. Additionally, the paper also describes how increase of seawater temperature and acidification affects a network of organisms in a coral reef ecosystem (Hoegh-Guldberg, Mumby and Hooten 1740).
Study of climate change also involves the development of trajectories to predict the global temperature based on historical and current data. Global temperatures are projected to increase rapidly above 1.8o C above today’s average (Hoegh-Guldberg, Mumby and Hooten 1740). This increase is predicted to impact seawater temperature, acidification and the subsequent changes in the coral reef ecosystem. Despite the predicted increase of seawater temperatures, there are several coral species that are more thermally tolerant. This tolerance is due to the strong association between the coral and the dinoflagellates. Additionally, there are also coralline species that are metabolically “costly”, as they require more energy compared to the other coral species. Coralline species is the key pioneer species in coral recruitment process.
Recruitment process is crucial in coral reef recovery, as it defines the pace of coral re-colonization and growth. Coral re-colonization and growth will depend on coral-dinoflagellate symbiosis and will require energy intake to allow optimal metabolism. Changes in seawater temperature may reduce the coral reef growth, as fewer coralline species will be likely to survive (Hoegh-Guldberg, Mumby and Hooten 1741). This decline in coral growth will influence coral-associated fauna such as grazing fish, and eventually coral users (including human). The reef rugosity is an important element that drives reef productivity, and reduced reef productivity will occur once the rugosity is compromised.
It is estimated that 156,000 km2 of reef is needed to support anticipated population growth in 2050 (Hoegh-Guldberg, Mumby and Hooten 1750). This fact shows that the dependency of human population on reef ecosystem will remain high, and the reef productivity has a strong link with socio-economic aspects. Under the Intergovernmental Panel for Climate Change (IPCC) scenario described in the paper, the impact of increasing seawater temperature will be devastating, so effective plan for management intervention is required to avoid the negative impacts of climate change and ocean acidification.
The analysis greenhouse gas and climate change outlined in this article is highly relevant with the first law of thermodynamics where energy cannot be created or destoyed. The climate change analysis shows a transfer of radiation energy from the sun into heat due to the presence of greenhouse gas (carbon dioxide) in the atmosphere. The presence of carbon dioxide serves as an insulation that traps the sun’s energy and retains it within the earth’s atmosphere as an energy balance. Furthermore, the law of thermodynamics states that the energy balance (equilibrium) is facilitated through transformation from the heat load to the increase of atmospheric temperature. The climate change phenomenon shows that the heat load transfer also occurs from atmosphere (air) to the seawater causing the increase in seawater temperature. Historical records from Vostok ice core study indicates that the climate change created changes in global temperature over a long period of time. This is consistent with the first law of thermodynamics where energy from the sun is conserved and is transformed into heat. The Vostok ice core data shows that the heat load transfer occurs continuously.
The article also presents examples of interface between physical and chemical processes through energy transformation from sun’s energy into useable energy for metabolism. The microorganisms known as dinoflagellates live in symbiosis with the corals and have the ability to trap useable energy from the sun into energy for metabolism. This is an example of how physical properties from the environment come in contact with chemical properties of living organisms. The increase of seawater temperature (as a result of increase in atmospheric temperature) can be seen as a mechanism to reach equilibrium. However, in the case of climate change the equilibrium is never reached and the entropy constantly increases (second law of thermodynamic). The increase of entropy can be associated with the increase of seawater temperature that causes negative effects on reef organism as the resilience point or thermal stress is surpassed. Once the thermal stress is surpassed, the equilibrium of reef organisms is violated resulting in the demise of these organisms.
Coral reef Reef can serve as an energy container for sustaining the global population. Energy from the sun is transferred to corals and coral grazers that eventually constitute an overall reef productivity. This is an example of the first law of thermodynamics where the energy is conservered and is transformed into useable energy to support the reef ecosystem and also a global population. Massive energy is needed to initate a reef colony (known as coral recruitment), where coral species with calcification ability will be the pioneer. Under this condiction, the energy balance will be able to sustain metabolic needs of corals and other reef organisms. Energy balance also occurs when more energy is available to support the growth or the expansion of the coral reef. Energy exchange and transfers continue to take place among reef organisms through intricate food chains and food web interactions. Eventually, the reef productivity is associated with fishery productivity. The energy balance from the reef enters the context of human population from fishery aspects.
Under the normal circumstances, energy balance in the sea ecosystem (derived from sun’s energy) can be passed on to living organism starting from microorganisms such as dinoflagellates, coral, coral grazers, fish and humans. This is a clear example of the conservation of energy (the first law of thermodynamics). Furthermore, the first and the second laws of thermodynamics allow prediction of the trends of global temperatures based on historical and current data sets.This is shown as the development of trajectories in response to climate change. Consequently, the laws of thermodynamics can be applied to develop strategies for mitigating the negative effect of climate change.
Works Cited
Hoegh-Guldberg, O, et al. "Coral Reefs Under Rapid Climate Change and Ocean Acidification." Science 318 (2007): 1737-1742. Print.
