Terry M. Bella
An oyster, clam, snail, mussel, urchin, sea star, crab, or lobster is a more likely familiar sea creature to our students than coral or phytoplankton. They have likely seen a lobster and held seashells. They may not be aware of the internal shell forming of the urchin or sea star, but acquiring the dried versions for you classroom is relatively easy. Many of these organisms, especially the bivalves and mollusks will struggle as sea water becomes more acidic as they will expend more energy to generate shell material as they compete with the increased rate at which it is dissolving. Oyster larvae are particularly susceptible as they need to generate their shells shortly after hatching, if they are not able to make and maintain a shell they perish. The acidic water is dissolving the shell faster than they can produce it. It is not only the shells that are in peril, the attachment fibers, byssal threads, that a mussel utilizes have a more difficult time adhering to surfaces in waters with a decreased pH (11).
The echinoderms, although likely stressed by the reduction of carbonate ions, are faring well. The shell of an urchin is covered in organic layer that which helps to shelter it from the surrounding water wherein it will more readily, than in the recent past, dissolve. The organic covering allows for the maintenance of a microenvironment more suitable for the production and maintenance of the shell. This is likely the case for other echinoderms (12). Although that may be promising more recent studies, focusing on juvenile sea urchins, find that ocean acidification has deleterious effects on the growth of these organisms. In the juvenile stage sea urchins more rapidly mineralize their skeletons and spines, the acidic conditions of the ocean are working against this chemical process (13).
Interestingly, crustaceans that which also use an organic layer over their carapace, called an epicuticle, show increased ability to form shells in a more acidic than normal environment (13). Lobsters, shrimp, and crabs are being found to produce stronger shells as the pH drops within the projected IPCC range (12).
Near the bottom of the oceanic food chain we find the zooplankton. The shell formers fall under two major categories, pteropods and foraminifera. Their aragonite shells are dissolving more easily as pH decreases and their need to adapt is more pressing (12). The high reproductive rates of these miniature creatures bolster their potential to evolve fast enough in response to the anthropogenic changes the ocean is experiencing. Quite simply, the more offspring, whether it be do to rate or yield, the more likely advantageous mutations will arise. The current selective pressures on these organisms include increasing ocean temperatures and decreasing carbonate availability, both due to anthropogenic atmospheric carbon.