One of the main issues with ocean acidification is the impact that it will have on marine organisms over the coming years, and whether or not they are able to adapt to the more acidic waters?
The impact upon some marine species may become more of a problem if they play an important role in the food chain, and therefore may eventually affect humans as fish are the main food source for some communities around the world.
Research into ocean acidification has found that certain organisms experience reduced calcification or enhanced dissolution when they are exposed to elevated CO2. Many organisms rely on the ocean’s current pH in order to survive. The major benthic calcifying organisms on coral reefs are the corals, calcifying macroalgae, benthic foraminifera, molluscs, and echinoderms. Corals typically live in compact colonies of many identical individual “polyps.” Part of this group includes the reef builders, these are important because as the name suggests, they build the reefs. They secrete calcium carbonate to form a hard skeleton and these skeletons can be used as bio-implants for human surgery.
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A coral reef is a community of many species, such as the corals, plants, invertebrates, fishes, and some other vertebrate animals, such as turtles. The lowering of the oceans pH reduces the ability of coral to produce calcium carbonate and with the conditions expected ocean acidification will compromise carbonate accretion. (Website, 2009) This causes corals to become increasingly rare on reef systems.
A large number of species make up tropical coral reefs; however coral communities in cold waters are only made up of one or two species yet provide shelter for many other marine species. (Website, 2009) With ocean acidification reducing the number of coral and as many marine species use the coral as their home and for shelter, the coral reef communities would also be affected and become less diverse and carbonate reef structures will fail to be maintained. (Hoegh-Guldberg, O. et al, 2007)
Coccolithophores are single-celled algae, protists and phytoplankton and are found in large numbers throughout the surface euphotic zone of the ocean and ocean acidification seems to have the opposite effect on them compared with other calcifying organsims. (Website, 2010) Coccolithophores are major calcium carbonate (CaCOâ‚ƒ) producers in the world’s oceans today accounting for about a third of the total marine CaCO3 production. Whereas ocean acidification reduces the calcium carbonate production in many organisms, studies have shown that it actually causes coccolithophores to increase their CaCO3 production. (website, 2005) Coccolithophores are distinguished by calcium carbonate plates which have an uncertain function and are called coccoliths calcareous nanoplankton, and these are important microfossils. (website, 2011) When coccolithophores make these plates they release carbon dioxide. Whereas some believe that because of this coccolithophores will actually contribute to the rise in COâ‚‚, it is actually unclear of what affect the increase in CaCO3 production will have. This is because these organisms use CO2 during photosynthesis. It is the balance between calcification – which produces carbon dioxide – and the consumption of CO2 by photosynthesis that will determine whether coccolithophores act as a “sink” (absorbing CO2) or as a source of CO2 to the atmosphere. So the extra CO2 produced may simply be counteracted by the extra photosynthesis. (Website, 2008)
An example of how ocean acidification affects certain marine species is the pteropod Limacina helicina. Their shell is made of calcium carbonate; however studies have shown that the shell is developing at a slower rate due to the lowering of pH. It is anticipated that by 2100 the increase of ocean acidification will slow the development of the shell by 30%. (Website, 2009)
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Aside from calcification, other organisms may suffer from other adverse effects. Such as physiological or reproductive effects or they may be affected by the negative impacts on food resources. An example of a species that is directly affected by ocean acidification on the lugworm Arenicola marina. There is a simple experiment that can be carried out to show how pH affects the lugworm reproduction simply by keeping the lugworms in seawater of different pH’s; some at the current seawater pH, 8.2, some at a pH of 7.8 and some at 6.5. The results show (fig. 1) that as the pH lowers the reproduction of the lugworm is affected. The lower the pH gets the less successful fertilization is. If as predicted by 2100 and the pH of the seawater has lowered to 7.8 then the lugworms may struggle to adapt and therefore may decline in number.
Brittle stars (Ophiothrix fragilis) may also see a change in their reproduction as they produce fewer larvae, because they are using more energy maintaining their skeletons in more acidic seas. This has a knock on affect as the brittle star larvae are a key food source for herring. It is clear that ocean acidification in time will have an impact on food chains causing problems for many other organisms that are not at first affected by ocean acidification. It is also possible that tiny algae such as Calcidiscus leptoporus will be unable to survive. These very important algae have been declining by 1% each year; some believe ocean acidification could be the cause as the acidity may make certain nutrients that the algae need less available or that it might even promote the growth of bacteria which damages the natural plankton growth cycle. Ocean acidification also affects the navigation and communication of whales and dolphins. This is because the seas are becoming ”noisier”. As the acidity increases, sound travels further. Navigation is important to whales and dolphins as they use it for migration, which is important as they migrate to colder waters to feed and to warmer waters to give birth.
It is not just the organisms that live in the oceans that are being affected. Marine mammals such as; polar bears, sea lions, seals, and walruses and also seabirds would see a knock on affect due to ocean acidification and the other impacts of climate change. The main issue is the effect ocean acidification has on the food chain because if one organism that is a main part of the food chain declines then the problem continues up the food chain. So if numbers of fish decline from a lack of food, then the birds that feed on the fish could also decline. However unlike many organisms affected by climate change, it has been discovered that seabirds can actually adapt to the changing environments. So the lower availability of their preferred prey may not be a problem as the birds seem capable of modifying their diets. (Grémillet, D. 2009)
Ocean acidification will have a definite impact on marine life, as many organisms will be affected. The main issue that can be seen is the impact ocean acidification will have on the food chain, as primary producers may decline then so will the organisms that prey on them and so on as the trend continues up the food chain until it reaches the consumer. If ocean acidification continues at its current rate, by 2100 we could see a vast different in ocean ecosystems. Many species may decline as a direct result of ocean acidification, such as the coral reefs due to reduced calcification. The coral reefs form some of the most diverse ecosystems on earth; therefore many other organisms would be indirectly affected by ocean acidification with the decline of corals. The coral reefs also play an important role for fisheries and fishing communities in poorer countries, a decline of the coral reefs would see a decline in a much needed food source for many humans.
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