GLOBAL WARMING In a recent paper published in the New Zealand Journal of Marine and Freshwater Research, scientists have used two Earth System Models and four climate change scenarios to project how New Zealand waters will be affected by 2100. The bestcase scenario involves a cessation in the production of carbon dioxide in the next few years, with the worst-case being business as usual in which carbon dioxide levels keep rising. The average warming around New Zealand is 2.5°C by the end of this century, which will affect how the ocean mixes and the nutrients available for plankton growth, with knock-on effects on the foodweb and fisheries. The surface ocean has a ‘density step’ between the surface water and the lower, deeper water where the nutrients come from, which acts like a physical barrier to nutrient movement between the layers. With further warming, there’s a stronger density step and less nutrient supply for the surface waters so phytoplankton doesn’t grow so well and productivity drops down. This has already happened in the water just off Tasmania and the south-east corner of Australia, which is warming rapidly as the East Australian current pushes warmer water further south, causing huge changes to the ecosystem. There, coastal ecosystems are changing with an increase in subtropical species, which can impact the economy. We are predicted to get an equivalent amount of warming by the end of the century, so what’s happening to the ecosystem off Tasmania might be a good proxy for what we’re going to see in New Zealand waters. The paper reports that one of the most affected areas for nutrient decline will be the Chatham Rise to the east of New Zealand, which currently provides about 60% of the country’s 128 ANNUAL DIRECTORY 2018 commercial fish catch. Another vulnerable area is the sub Antarctic waters to the south of New Zealand which also home to some commercial fisheries. All regions will see a reduction in food supply, because of a decrease in particulate material sinking from the surface – and that is what links climate change to our fisheries. The fishing industry may need to think about being more agile in terms of the species it catches and where it catches them. For example, if fish go deeper to maintain their temperature, they will have to adjust their practices to account for that. Acidity in the ocean will increase by 130% by the end of the century which will cause changes to shellfish. For example, we can speculate that shells of paua and mussels may be affected – it doesn’t mean that we lose them from our ecosystems, just that they might become smaller in response to their diversion of energy to maintain their shells. Changes WARMING OCEAN WILL AFFECT KIWI FISHERIES BY 2100 Rapid warming of the ocean near Tasmania may provide a good indication of how the water around New Zealand will change as the planet warms, NIWA marine biogeochemist Professor Cliff Law says.
FT-Annual Directory 2018-eMag
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