Ocean Acidification

Copyright: © Graham Edgar

A global citizen science project has handed scientists fresh insights into how climate change might affect ocean species and their ecosystems.

A new study, involving New Zealand co-authors and divers, suggested warming oceans could push fish species away from the equator, while driving a decline in the diversity of invertebrates like crabs, lobsters, sea urchins and octopus.

Just published in the journal Science Advances, the research offered the first evidence of how ecological interactions affect marine species’ abundance at global scales.

It was built off data collated by the Reef Life Survey (RLS), a citizen science project involving hundreds of scuba divers around the world, including staff and students from the University of Auckland’s Leigh Marine Laboratory.

It now included information on 4000 species in 50 countries, allowing a better understanding of how and why species are distributed, while also providing an early-warning mechanism for climate-driven changes.

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The new study followed a 10-year science stocktake by Niwa which suggested climate change was slowly shifting the chemistry of New Zealand’s oceans.

Between 1909 and 2009, New Zealand’s sea-surface temperatures had warmed by a statistically significant 0.71C, while pH levels of subantarctic waters had dropped by 0.0015 units per year since 1998.

Globally, the oceans’ average pH is currently 8.1, which is 0.1 lower than it was 250 years ago – a decrease of just one pH unit represented a 10-fold increase in the acidity.

The decline in pH was projected to continue in line with the increase in atmospheric CO2, leading to the most rapid decrease in ocean pH in the past 50 million years.

The effect was associated with decreases in nutrients such as nitrate and phosphate in the surface ocean, where most marine organisms live.

Even small shifts had big consequences: mussels and paua might struggle to build their carbonate shells, while some fish species could experience changes in behaviour, physiology and even habitat distribution.

Niwa scientists estimated that perhaps 25 per cent or less of the existing cold water coral locations around New Zealand will be able to sustain their growth by 2100 due to ocean acidification.

Another five-year, $800,000 study has also just been launched to investigate why some New Zealand species may be able to cope more easily with ocean acidification.

Because of their highly soluble calcium carbonate skeletons, reef-building algae were widely considered to be among the species most at risk.

But marine botanist Dr Christopher Cornwall has challenged this idea, suggesting certain species of calcifying algae might pack the physiological machinery needed to tolerate change.

He aimed to find out whether the resilience seen in some populations of local coralline algae was due to them having evolved in more variable pH environments.

Jamie Morton, The New Zealand Herald, 22 October 2017. Article.