Impacted Species

The Impacts of Ocean Acidification 
Ocean acidification impacts many species in different ways, but the most impacted species are calcifying species. This includes oysters, clams, sea urchins and corals among others. These organisms build their shells out of calcium carbonate, which decreases in concentration as acidity increases because the protons bind to the carbonate and prevent it from binding with calcium. In addition, the saturation state of calcium carbonate decreases which can actually cause the shells to disintegrate away or not be able to form in the first place.⁶ Some initial studies have also shown changes in prey behavior, such as decreased escape reactions possibly caused by interference with neurotransmitters from more acidic water. ²

Pteropods

A healthy pteropod, also sometimes
called a  'wing foot' or 'sea butterfly'
http://www.noaanews.noaa.gov/stories2006/
images/pteropod-limacina-helicina.jpg

These small, pelagic gastropods have been some of the most recognized victims of ocean acidification. They appear to be very vulnerable to changes in pH and begin to lose their calcareous shell.
Many other species feed on pteropods including fish and seabirds. In the Pacific Northwest, they are an important source of food for pink salmon.
Under the IPCC's business as usual projection, they are expected to be regionally extinct by 2050. The saturation state of aragonite is projected to reach below 1 in this model and therefore actually begin to dissolve from the shells of the pteropods back into the water. Pteropods' full impact on their ecosystem is unknown, but in addition to their important place in the food web, it is believed that they are also important for geochemical cycling. ¹²

The impacts of the ocean pH projected for 2100 on the pteropod.
Its shell is almost completely gone after 45 days.
http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F

Mussels

http://depts.washington.edu/nucella/
mussel-byssal-threads/
Credit: Emily Carrington/University of Washington

Ocean acidification doesn't just impact molluscs by preventing formation of their shells, mussel byssel threads were weaker and less extensible. Byssal threads attach mussels to the substrate on which they live and keep them form being carried away by tides. In addition to added difficulty in forming their shells, these mussels might not be able to withstand even normal waves and currents.²⁰

Coccolithophores

The calcified coccolith (look like armoured plates) of the
coccolithophore protects it from predators and damage.
http://ichef.bbci.co.uk/naturelibrary/images/ic/credit/640x39

5/c/co/coccolithophore/coccolithophore_1.jpg

There have been mixed results about coccolithophores. Some experiments have shown an increase in the strength and size of the coccolith (outer shell) with malformation occurring only in the presence of increased ammonium.¹³

Other studies have shown detrimental impacts in more acidic waters.⁴ This is a great example of science actually confounding what is truly happening. When the science is moving this quickly and the climate is as well, it can be very difficult to determine how to manage an area or protect vulnerable species.

Coralline Algae
These algae are very sensitive to the acidification of the ocean. They are characterized by a hard thallus that is created by calcium carbonate contained in their cell walls. Coralline algae perform important ecological roles such as acting as framework organisms, providing chemical cues to encourage the settlement of reef building coral larvae, producing carbonate sediments, protecting juveniles of urchins, chitons and limpets among others from predation, and protecting and facilitating settlement larvae of other species. Ocean acidification appears to decrease the ability of coralline algae to recruit and claim space particularly when competing with non-calcifying algae, which may actually experience an increase in abundance as a result of increased CO₂ levels.¹⁵


Non-calcifying algae
These algae may show an increase in biomass in response to ocean acidification. One reason for a possible increase is a decrease in competition from coralline algae. Another reason that there may be a positive impact on noncalcifying algae is that some of their predators, such as sea urchin, are projected to have decreasing population sizes. This increase can be seen as a benefit because many human disturbances have been very destructive to these macroalgae assemblages. There has been a drastic decrease recently in these algae because their predators, in particular sea urchins, have often benefited from overfishing and have proliferated. Some of these predators are now being negatively impacted by ocean acidification. Although ocean acidification may improve conditions in part for the non-calcifying algae, the biodiversity will likely decrease because of the loss of coralline algae and its important promotion of succession particularly in disturbed coast lines.³