Global warming has the potential to have major impacts on aquaculture. Over the past century, global warming (both human-caused and deriving from natural cycles) has increased the average global air temperature by around 1 degree Fahrenheit, 0.6 degrees Celsius. The world’s oceans, which have a vastly greater thermal mass than the atmosphere, have changed by only 0.18 degrees Fahrenheit (0.1 degree Celsius), with nearly all of that warming occurring in the surface layers. Even this relatively small change is enough to have major impacts on human food production in the ocean.
One significant impact from global warming is likely to be the reduction in the growth rate of krill. Krill are a family of tiny crustacean species that live in all of the world’s oceans and are the foundation of the aquatic food chain. Krill feed on phytoplankton and zooplankton, and are in turn consumed by fish and other aquatic animals in enormous quantities. Krill are fished commercially and used as a feedstock for aquaculture operations. As ocean temperatures rise, the reproductive rate of krill has been shown to decline significantly. This will make food stocks for aquaculture more expensive.
A major fraction of aquaculture is conducted in areas immediately offshore and in riparian (river) environments. Rising ocean temperatures may disrupt these operations by altering the sea level, changing coastlines and impacting river systems. Rising ocean temperatures alter the sea level in two ways – first, by causing increased melt rates at the polar ice caps, and also because of the fact that warmer water expands and takes up a larger volume. Even very small increases in temperature can have measurable impact on sea level. In riparian aquaculture, increased incursions of salt water can reduce yield or make operations untenable. Changes in water salinity also has enormous impacts on the presence and prevalence of species, which can throw aquaculture operations into chaos.
Further offshore, higher ocean temperatures are likely to cause stronger and more frequent storms. This is problematic for deep-water aquaculture operations, requiring a more robust infrastructure and increasing costs from storm damage. Warmer temperatures can also cause instability in marine ecosystems, as invasive species enter areas that were formerly too cold for them. This can cause issues for aquaculture operations that were predicated on a particular local ecosystem. Inshore operations are not immune to this change; many aquaculture operations rely on the monsoon season and it is expected that changing water temperatures will tend to disrupt this major weather pattern.
A significant portion of global aquaculture comes from the cultivation of mollusks. Mollusks as a group tend to be very temperature sensitive, and as waters warm, mollusk-growing operations will need to move to colder waters in order to maintain yield. When that is not possible, that portion of the aquaculture system could cease to function.
One major, albeit indirect, disruption could come from changing availability of freshwater inshore. Ecologists anticipate that global warming will cause reductions in the availability of freshwater, particularly in Africa and Asia, and as a result of this water stress, water for aquaculture development may simply not be available.
Unfortunately, it seems likely that future water temperature increases will have an increasing impact on the development of new aquaculture projects. Currently, the majority of world aquaculture is in the tropics, and although those areas are still growing strongly, new development is likely to center around the temperate zones of our planet. Increases in ocean temperature is expected to be significantly higher in the colder northern and southern waters than in the equatorial zone. That means that new aquaculture projects, for example off the eastern seaboard of the United States, are likely to be severely impacted by water temperature changes.