Question

Changing pH can disrupt biological systems. Which of the following would do you feel would be most affected by a change in the ocean pH: the cellulose in kelp algae, or the digestive enzymes in jellyfish? Explain your answer with logical chemistry-based concepts to support your answer.

Answer 1

When carbon dioxide (CO2) is absorbed by seawater, chemical reactions occur that reduce seawater pH, carbonate ion concentration and saturation states of biologically important calcium carbonate minerals. Calcium carbonate minerals are the building blocks for the skeletons and shells of many marine organisms. Ocean acidification is expected to impact ocean species to varying degrees.Photosynthetic algae and seagrasses may benefit from higher CO2 conditions in the ocean, as they require CO2 to live just like plants on land. On the other hand, lower environmental calcium carbonate saturation states can have a dramatic effect on some calcifying species, including oysters, clams, sea urchins, shallow water corals, deep sea corals and calcareous plankton.

At lower pH levels, these organisms have to spend more energy to build their structures, which can even suffer dissolution. A lot of effort has been invested in investigating the effects of climate change and ocean acidification on marine environments.

Seaweeds are key ecosystem builders in shallow water areas. In these environments, they uptake inorganic carbon from the carbonate system pool when performing photosynthesis(raising pH) and release CO2 with respiration(lowering pH) so seawater pH is also regulated by biological activity.

The rise in temperature in the oceans affects marine life and ecosystems, but it is accompanied by another problem caused by an increase of CO2. Atmospheric CO2 dissolves and reacts with seawater, forming the chemical compounds that we call the carbonate system. Essentially, CO2 and water react to form carbonic acid which quickly dissociate into bicarbonate, releasing a proton. This bicarbonate ion can dissociate in to a carbonate ion with the release of another proton.These reactions are reversible and in equilibrium, being the main source of the capability of seawater to keep its pH stable.

The most noticeable of these changes is a decrease in seawater pH: mean pH used to be about 8.2, but this value now is below 8.1. Also, the relative concentrations of the different compounds forming the carbonate system change with pH with an overall reduction of carbonate ions and an increase of bicarbonate ions and CO2.

Ocean acidification potentially affects all marine life, from phytoplankton to fish, but especially calcifying species (corals, echinoderms, mollusks, calcareous algae).