Consequences of Ocean Acidification for Marine Life

 

Ocean acidification has dramatic effects for marine life.

Seawater calcium carbonate minerals concentration is supersaturated in some areas. However ocean acidification is making oceans undersaturated with respect to these minerals. In turn, calcifying organisms will be unable to construct and maintain their shells since they are built out of calcium carbonate minerals. Many marine organisms are calcifying species, such as oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton (NOAA).

Field observations as well as laboratories experiments show that shell pteropods start to dissolve as soon as they go under aragonite saturation horizon.

Thus ocean acidification means calcifying organisms would be negatively impacted. Warm, subtropical waters would be aragonite undersaturated from 1 700 to 2 800 ppmv (parts per million by volume). However, high latitudes, cold waters, which are abundant in planktonic shelled pteropods, have a lower undersaturation horizon. It is argued that subpolar waters will be undersaturated with respect to aragonite at a future 1 200 level representing 4 times preindustrial CO2 levels (Feely et al. 2004).

But this is being reconsidered. Orr et al. argue that even at twice preindustrial CO2 levels, undersaturation will occur. This is likely to happen in the next 50 years (2005).

A pteropod was put in water with the pH of predicted results in 2100. Here is what was observed.

Figure 1 Gradual decomposition of pteropod shell in acidic water. Source: Liittschwager 2007

Coral reef will be degraded. Under today's carbon dioxyde concentration, 60% of coral reefs are surrounded by undersaturated with respect to aragonite water. If CO2 levels keep rising up to 450ppm (which could happen in the next 20 years), this will be the case for more than 90% of coral reefs. Aragonite undersaturated waters make coral species bleach. There is serious danger that they may not survive the century (Pandolfi et al. 2011, Oceana 2014).

Many oher species will be negatively impacted by ocean acidification indirectly. Shell and coral organisms loss will have dramatic effects on the food chain since much of marine biology depend on these species. Humans will also suffer from these changes from shellfisheries.

Ocean acidification has mixed consequences for marine biodiversity. Seagrass and photosynthetic algae may profit from the increased acidification (Beaumont and Garrard 2014).

Thus ocean acidification bears consequences that go beyond alkalinity changes. Although some scientists remind this change is beneficial for a few species, there is general agreement that ocean acidification is overall negatively impacting marine life.