Studies have revealed that the uptake of anthropogenic CO2 by the ocean, and the resulting changes in the chemistry of seawater have adverse effects on many calcifying marine organisms (think anything with a shell). This is because elevated concentration of CO2 in seawater reduces calcium carbonate saturation (the stuff shells are made from), resulting in low calcification rates (i.e. accumulation of calcium salt in body tissues). Studies have shown that many marine invertebrate species such as corals and clams are threatened by ocean acidification, hindering their shell and exoskeleton formation ability and therefore would require a higher energy budget for calcification. Some species such as blue crabs, lobsters and shrimps were found by Justin Ries, a marine scientist at the University of North Carolina, to have grown thicker shells with increasing acidity which could make them more resistant to predators, but this is probably costing them in terms of energy for reproduction and growth. Therefore, the responses to ocean acidification by marine species could either be favourable or unfavourable depending on the physiology and adaptive mechanisms of species.
Closer to home researchers at the MACE Lab at UKZN were comparing photographs of abalone from farms 17 years ago and those taken last year. What they noticed was startling: abalone grown on South African farms 17 years ago had much higher numbers of Spirorbid worms (a genus of very small (2 – 5 mm) polychaete worms, usually with a white coiled shell) on their shells.