Terry M. Bella
The primary concern about ocean acidification is the disturbance to calcification activities. Countless organisms rely on calcium carbonate to build shells and skeletons, these organisms will be referred to as calcifying organisms. The calcium and carbonate ions had historically been readily available to organisms in the water column for them to assimilate into calcium carbonate structures. This had been the case as species evolved over the past several million years or longer. The current rapid change to the ocean’s chemistry is jeopardizing the supply of carbonate ions, thus jeopardizing calcifying organisms. The acidity of the water also dissolves the shells, thus energy must be invested by the organism to remake lost structures or worse yet, it impedes their ability to create the shell that they need for survival.
This disturbance to calcification processes threatens our coral reefs and the plankton that are the base of the oceanic food chain and significant source of atmospheric oxygen. The IPCC (Intergovernmental Panel on Climate Change) is predicting a pH of 7.8 by centuries end, this will reduce the concentration of carbonate by 50% (10).
Coral reefs are important for many reasons. They are the most diverse ecosystems in the ocean, also rivaling the tropical rainforests on land. This diversity not only provides fantastic economic value in scuba, fishing, and tourism but is essential to the health of the ocean. Diversity ensures the survival of some, following major environmental disturbances. The high number of occupied niches almost guarantees that there will be those that thrive following a catastrophic event. This is paramount to the long term recovery of the ocean but is unfortunate in the short term as the rate of acidification is so high that major diversity loss will be experienced. In fact, the growth rate of reefs will be on the decline in the foreseeable future as these organisms cope with the stress of changing pH. It helps to consider that organisms in the ocean have evolved in an environment that provided a constant pH for millennia, thus adaptability to fluctuations in pH was not a selective pressure. As it will be discussed later in this unit, some organisms adapt favorably, but the context of historical selective pressures is important to consider.
The coral reef landscape is changing for some reefs. Corals that are less branchy are faring better in this new more acidic environment. Considering two structures, one thin and branchy and the other thick and bulbous, and both being aragonite (calcium carbonate product), the thicker structure is favored as the aragonite is dissolved and weakened in the acidic ocean. Thus the dominant species on reefs is changing, consequently changing the landscape of the reef. Furthermore, some species of coral can utilize bicarbonate (HCO
3
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), an ion that is increasingly available in our new more acidic ocean waters. These organisms have a distinct advantage over corals that rely solely on carbonate ions.
Coral reefs provide opportunities for us to discover medicines to address human diseases. Drugs are developed from plants and animals of the reef. Through researching organisms scientists encounter new chemicals and observe biological solutions, to biological problems. The coral reefs potentially hold promise of remedies for cancers, immune system diseases, and antibiotics. The medical problems that humans face are not unique to humans and have often been overcome by another organism, but if we do not have the time to research natural solutions, they may forever be lost.
Coral reefs are nurseries for oceanic fish. Many fish spend their larval and even juvenile stages within coral reefs. The reefs offer food and shelter within their endless microhabitats. Some of the fish that rely on coral reefs as nurseries are the fish that humans rely on for commercial fishing. Humans cannot easily replicate what the reef naturally provides for these species. The reefs also directly supply food, many rely on fish and invertebrate reef inhabitants for sustenance.
Coral reefs also protect coastline from erosion, acting as wave breaks, lessening the severity of waves hitting the shore. As storm waves approach the coastline a coral reef can interrupt the wave, causing it to lose energy, decreasing the damage it may cause when it hits land. With ocean acidification not only is the ability of coral to secrete exoskeleton, which becomes the foundation of the reef, compromised, but the existing calcium carbonate structures are being dissolved. Both actions weaken the reef, increasing the likelihood that storm surge will cause more severe damage in the future as our reefs are less capable of absorbing the impacts.