Corrosion caused by CO2 saturated seawater can cause the extinction of coral reefs. Acid oceans threaten food webs and put sea life at risk.
Scientists report that a quarter of the carbon dioxide that humans generate is absorbed from the atmosphere by the oceans. Its dissolution produces carbonic acid and increases the acidification of seawater. It is a direct effect of human activity with consequences so severe that it can easily be considered a problem as serious as climate change. In fact, both problems have several things in common; for instance putting at risk species all over the planet.
The Ocean in a High CO2 World symposiums (ocean-acidification.net) have been held since 2004 every four years to consider the consequences on sea life and address its impact on humanity. The report “Ocean Acidification Summary for Policymakers 2009” published by the symposium organizers explains the situation. This article centres on the effects of ocean acidification on nature; the article “Ocean Acidification Risks Fisheries and Advances Climate Change” focuses on the effects on humanity.
Ocean Acidification and its Origin
The industrial revolution set a hallmark on history as it changed the world and the humans’ ecological footprint. The oceans changed as well: since then oceans’ acidity has risen by 30% and half of the increase happened in the last thirty years. To put it in perspective, this increase is one hundred times faster than any acidity change in the last twenty million years.
Marine organisms are used to adapting to changes in the environment but the speed of the increase is unusual in the planet’s history. Before the industrial revolution the average concentration of carbon dioxide was 280 ppm (parts per million), but now it is about 385 ppm; 38% more. In fact, current carbon dioxide emissions are higher than projected by the Intergovernmental Panel on Climate Change about a decade ago. Whether sea life can successfully adapt to this change is unknown.
Ecosystems’ Answers to Ocean Acidification
Shell and skeleton formations of marine organism show a decrease in calcification caused by acidification. Furthermore, early life stages of certain organisms are highly sensitive to acid. The morphology, metabolism and activities of organisms may be disrupted by high carbon dioxide accumulation in the body. Invertebrates and fish are not exempt: acidification affects sea life of all sizes from coccolithophores, a type of phytoplankton, to commercial fish species.
Elevated carbon dioxide levels aren’t always dangerous, nitrogen-fixing cyanobacteria might find it beneficial. Therefore some types of organism struggle while others thrive in this environment. As the bottom of the food web is altered organisms need to adapt. The consequences of these alterations to the food web have yet to be determined.
Coral reefs’ grow, allowing them to slowly expand but ocean acidification prevents calcification of deep-sea corals. By the middle of the century the erosion due to acid seawater will exceed the coral’s growth. In other words, many reefs will become unsustainable and disappear. By 2100, corrosive waters will have extended far beyond the poles with 70% of cold-water coral reefs exposed. The addition of coral bleaching due to higher water temperature severely risks coral reefs’ survival.
It is expected that organisms will adapt to seawater with high levels of carbon dioxide, selective breeding of a species of oyster show an increased resistance to acidification. However the ability of an organism to adapt to an environment with constantly increasing acidity is not known. When coupled with other environmental changes such as rising temperatures, over-fishing and pollution, the complexity of the situation multiplies.
Experiments in two species of crab show that acidification decreases resistance to temperature extremes. This restricts the species habitats and makes them more vulnerable to global warming. More information can be gathered from natural environments with high carbon dioxide concentration: areas receiving volcanic or hydrothermal carbon dioxide inputs, coastal zones under the influence of upwelling or river inputs. The high quantity of invasive species and low biodiversity observed in these zones give an idea of marine ecosystems’ futures.
Sea Life Can Become Extinct Because of Ocean Acidification
Ocean acidification is a problem constantly worsening. Atmospheric carbon dioxide concentrations rise and so does the concentration on the ocean. The ocean becomes more acid and less able to absorb carbon dioxide which increases the atmospheric concentration forcing more carbon dioxide on the ocean. This feedback is a clear example of how natural mechanisms interlink.
Constantly acidifying water presents a new environment that puts to the test species adaptability - extinction of several species is not beyond expectations. The collapse of sea life is not an isolated problem because all species are connected by the food web. The consequences of such a mass extinction won’t be minor and humans should remember that they are also part of the food web.