“Implications of Ocean Acidification on Coral Reef Systems”
Summary
“Ocean acidification due to increased atmospheric carbon dioxide,” a report compiled by a team of European researchers and published by The Royal Society of London, illustrates the causes as well as the implications of increasing atmospheric carbon dioxide levels upon oceanic ecosystems. In summary, it discusses the sources of worldwide spikes in CO2 levels, sheds light on the effects of rapid pH changes upon fragile coral reef systems, provides calculations on the state of the oceans in our near future, and offers recommendations for this foreboding epidemic.
Corals
A diverse number of biological organisms on Earth produce shells, plates, and skeletons composed of the mineral calcium carbonate (CaCO3). These “calcareous” organisms rely on calcification to precipitate shells from aqueous carbonate ions (CO32-) and calcium ions (Ca2+) present in the water column. The products of this synthesis are the naturally-occurring CaCO3 minerals calcite or aragonite.
Modern corals, called scleractinids, are both solitary and reef-building animals which build skeletons composed of aragonite (Levin 344). While aragonite is chemically identical to calcite, it is a more soluble and less stable carbonate mineral. Coral reef systems are unique biological organisms, acting as vital anchors to their ecosystems. Typically occurring in well-lit, warm shallow waters, normally high calcification rates in these environments allow corals to develop scaffolding and frameworks which provide shelter and food to a host of marine organisms such as fish, bivalves, sponges, and algae (Levin 417; Royal Society).
Corals require water saturated in carbonate (CO32-) and calcium (Ca2+) ions in order to begin the calcification process. However, a deficiency in aqueous CO32- ions in the world’s seawater is increasingly becoming observed as a result of ocean acidification. The calcium carbonate which forms the skeletons of corals is also one of the geologic minerals most susceptible to chemical weathering, namely from exposure to acids. It is for these reasons that coral reefs constitute one of the most sensitive and fragile ecosystems in the world.
Acidification
The combustion of fossil fuels by electric plants, factories, industrial complexes, and automobiles produces enormous amounts of gaseous CO2, sulfur and nitrous oxides, and other pollution; other contributors to CO2 emissions stem from deforestation, agriculture, and cement production (Campbell 55; Royal Society). Coal-burning electric power plants produce more of these oxides than any other single source (Campbell 55). These pollutants are carried away by winds and precipitated as acidic rainfall or are absorbed from the atmosphere by the world’s largest bodies of water, the oceans.
Surface waters of the world’s oceans are naturally slightly alkaline, with an average pH of about 8.2 (Royal Society). But the pH of the oceans is predictably becoming more acidic. Carbon dioxide, when dissolved in water, forms weak carbonic acid (H2CO3). Increasing levels of atmospheric CO2 result in higher amounts of H2CO3 forming in seawater, which, as explained later, lowers the pH of the water. Products involved with the dissociation of H2CO3 and increased oceanic acidity pose an extremely uncertain situation for the survival of carbonate-depending organisms.
Implications
Over the past 200 years, the world’s oceans have absorbed approximately half of the CO2 produced by industrial processes (Royal Society). Calculations comparing pre-industrial pH levels to those seen today indicate that the saturation of CO2 in oceans has led to a drop in the pH of surface seawater by 0.1 units (Royal Society). This is by no means any small number— such a decrease in pH is equivalent to a 30% increase in the concentration of hydrogen ions, a main indicator of acidity.
The implications of a more acidic ocean are far-reaching and worldwide.
