A number of adverse environmental impacts are projected to occur from global warming. Although several atmospherically located substances will drive temperature increases, significant levels of CO2 may acidify the oceans. Ocean acidification is the name given to the ongoing decrease in the pH (see Wikipedia on PH) of the Earth's oceans, which will be caused by the uptake of anthropogenic CO2 from the atmosphere. About a quarter of the carbon dioxide in the atmosphere goes into the oceans, where it forms carbonic acid, which will drive down pH levels. If global warming from CO2 proceeds apace, what will the impact be on marine ecosystems? Will acidification affect sea life? Some unique marine sites provide insight to what the future might look like.
Some unique marine sites provide a clue about what these effects may be. Researchers have been collecting data from marine sites off Italy, Baja California, and Papua New Guinea, where high concentrations of CO2 percolate out of the seabed from volcanic activity below. Directly above these CO2 seeps, pH plummets to at least 7.8, a value that is projected to occur widely by 2100 and that is substantially lower than the normal level for the area, 8.1. These sites may offer a preview of what may happen to seafloor ecosystems as CO2 levels continue to rise, causing ocean water pH to drop.
Compared with nearby "normal-pH" sites, species richness in low-pH zones was diminished by 30%. Coral and some algae, as well as sea urchins, were gone. Fish may be present, but unlike in areas with a normal pH, they did not deposit their eggs in the low pH areas. Although seagrasses appear to survive unaffected in the low-pH seawater, close inspection showed that fish had nibbled the fronds. One possible explanation for this behavior: At low pH, these grasses no longer produced the phenolic compounds (see Natural phenol) that deter grazing animals from eating the plants.
Researchers also transferred a host of healthy marine species to these areas to gauge the effect of these naturally acidic regions. Although many survived, once seasonal temperature increases occurred, many of the transplanted corals and mollusks died. Researchers concluded the impact of acidification plus temperature was a "double whammy." Laboratory experiments showed also that coral larvae exposed to low pH environments had their metabolism slow to 65% of normal; their ability to make energy from nutrients in the water also decreased. In essence, the coral larvae were slowly starving. Turf algae also had a decrease in the production of two key pigments that communicated to the larvae to settle on a particular spot; this impairment was confirmed in the natural sites.
Studies addressing these issues can be found at: http://phys.org/news/2012-02-british-scientist-aaas-threat-posed.html; http://www.ucar.edu/communications/Final_acidification.pdf; http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1533.html; & http://www.nature.com/nclimate/journal/v1/n3/full/nclimate1122.html.
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