Anthropogenic climate change has been hypothesized for centuries (discussed in Le Treut 2007) before the careful measurements of scientists in the mid-20th century. From 1833 to 1997, Stanhill (2001) calculated that the climate change science doubled every 11 years. The impact of carbon dioxide concentrations in the ocean was recognized early on with measurements and analyses taken by Revelle and Suess (1957). While research on ocean acidification has made great strides in the last two decades (reviewed in Doney et al. 2009), the surface has barely been scratched with understanding how lower pH affects the already downtrodden commercial fisheries that serve as the foundation of many livelihoods and economies.
Commercial fisheries have worn the brunt of excess and experiments in regulations for several decades. Many fishing quotas are set using recent historical catch data and based on a maximum sustainable yield. The commercial fishing industry has much to be concerned about. Reduced yields will devastate livelihoods and jobs in areas where fishing is the only, or by far the largest, industry. Subsidence fishing, typical in impoverished areas, will be threatened and inhabitants will need to procure new sources of protein.
Much of the current research has focused on animals with carbonate skeletons. Acidic oceans will degrade molluscan shells, making them particularly susceptible as larvae and as adults to mortality. Corals provide habitat for many commercial stocks of finfish, with nearly 10% of worldwide landings coming from reefs (Carpenter et al. 2008). Deep-sea coral reefs in cold, dark waters support juvenile commercial finfish stocks, such as roughy and codling (Hall-Spencer et al. 2002, Rogers 1999). Furthermore, larval and adult fish and marine mammals who rely on planktonic food sources will be nutrient limited if their prey have difficulty adapting to changing pH.
One area that will need particular attention is the physiological effects on already overfished commercial stocks. Preliminary experiments in cod suggest they are able to adjust enzyme levels, with motor control unaffected, to cope with the 2000 ppm levels of carbon dioxide projected not too far into the future (Meizner et al. 2008). Larval fish are likely to be more susceptible to changes in pH as they are less protected from changes in the environment, expend lots of energy for physiological processes, and experience high natural mortality. Lower ocean pH makes acid-base regulation more difficult since diffusion plays a stronger role than in adults where active ion-transport accounts for the majority of physiology.
Much research is needed, particularly with larval fish and invertebrates, to understand what lower pH means to their physiology, growth and survival. Commercial fisheries and consumers will need to adjust their seafood-consumption lifestyles to accommodate lower sustainable yields. The socioeconomics of reduced fishing capacity needs to be addressed at a global scale. I fear that fisheries will be attacked synergistically by all these forces – climate and fishing pressure – and hope people smarter than I can come up with tenable solutions.
It is likely not all doom and gloom. We humans have a remarkable ability to adapt when the will is strong. The sooner we address the changes that need to take place, the better off the ecology of the oceans are, the better off fishermen and their livelihoods and culture are, and the better off seafood consumers are. My plea is not merely for more research in ocean acidification and its effects on fisheries, but an integrative approach that accounts for our consumptive lifestyle.
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