May 2015 was yet another record-breaking month. Average atmospheric carbon dioxide levels reached 403.70 part per million (ppm), some 53.70 ppm above what is considered to be the upper safety limit.  Our warming planet, the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report Synthesis Report released in November 2014 say with 95% certainty, is primarily down to humans, and mainly from our greenhouse gas emissions.

With greenhouse gas emissions also altering the carbonate chemistry of the ocean, climate change’s “evil twin” ocean acidification is also a growing cause for concern.  Climate change also impacts the ocean, and these changes will in turn impact a variety of marine life, including those caught for mariculture feed - and mariculture species themselves...

Ocean warming is a particular issue for mariculture species because they are poikilothermic – their internal body temperature varies with the environment.  As such, mariculture species have upper and lower thermal tolerances, and optimal temperature ranges in which metabolic functions and related activities, such as reproductive potential, growth, and disease resistance are at their most efficient.  For farms located in areas where their cultured species are at the upper end of their thermal tolerance limits, increased temperatures pose a significant threat to the future of the farm. 

Work lead by Joao Ferreira (Institute of Marine Research, Portugal) suggests that shellfish fisheries based in Northern Ireland’s Strangford Lough would see declines in mean weight and length, and overall productivity with predicted water temperature.  However assuming thermal tolerances thresholds are not crossed, increased winter temperatures may extend the growing season in some species.  This is assuming that the cultured animals are able to cope with another impact of warmer waters – decreased oxygen levels.  Warming temperatures may render many current mariculture sites unsuitable, but may also open up new opportunities elsewhere, as can sea level rise.

Temperature changes can impact more than the animals being farmed themselves.  Research by Audun Stien (University of Tromsø) and Mark Costello (University of Auckland) suggests that warmer waters, particularly during winter months, can reduce sea lice life-cycles, potentially increasing infestations in farmed (and wild) fish.   Disease may also become more prevalent – not just because increasing water temperature can place metabolic stress on the infected individual itself, but by creating conditions more that increase the spread of the pathogens themselves. 

A study published in 1998 by Rutgers University demonstrated how the parasite responsible for Dermo disease in the American oyster expanded its range, resulting in epizootic outbreaks of Dermo in north-eastern America.  The primary cause of this expansion, the researchers concluded, was increasing winter water temperatures. 

Whilst harmful algal blooms (HABs) are a natural phenomenon, they are on the rise because of human activity.  Nitrification of coastal waters from agricultural and urban runoff into the sea plays a big role in HAB formation, but a number of studies has suggested warming surface waters exacerbate the situation.  HABs can have a detrimental impact on industry.  The first salmon farm in New Zealand’s Stewart Island failed when an algal bloom hit the farm.  It took just 18 hours for the venture to incur losses of N$1 million.  This year in Ireland, some 10,000 tonnes of mussels were lost due to an algal bloom that closed farms in west Cork and Kerry for over 5 months. 

Predicted changes to climatic patterns also pose potential problem for mariculture, particularly those located in tropical and subtropical regions.  Increases the frequency and magnitude of storm events brings with it increased risks of mariculture infrastructure becoming damaged.  Nets may be torn, mussel ropes ripped from their moorings. 

The economic costs of storm damage isn’t just limited to repairing or replacing damaged equipment, but loss of the cultured population itself.  During the 1994-1995 El Nino, fish mariculturalists in southern Chile were faced with losses of several million fish from damaged sea cages.  For those farms placed in bay that remain sheltered from storms, runoff from the land may increase with increasing precipitation.  As well as increasing nutrient loads in some coastal areas, runoff can bring with it a range of pollutants from agriculture, industrial, and urban environments, as well as heavy metals naturally found in soil. 

Changing climatic patterns may in some circumstances also alter salinity levels enough to cause stress on the animals being farmed, with risk of mortality.  Increases in warm air temperature can increase evaporation which increases salinity whereas increased freshwater input can decrease salinity. In parts of Florida, such conditions are experienced by hard clam mariculturalists.

With mariculture species varying considerably in tolerance limits and optimal ranges, differing mariculture systems, and the impacts of climate change being highly variable across the globe, it is impossible to say exactly how individual mariculture farms will be impacted – for better or for worse.  What is perhaps more clear is that mariculture, like fisheries, will need to adapt to our changing world.

This story appeared at The Fish Site.