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Marine heatwave boiling our fish

Wairarapa’s waters were more than 1 degree Celsius warmer than usual last month, turning our normally cool seas into bathwater. 

National Institute for Water and Atmospheric Research [Niwa] said November’s sea surface temperatures were between 1.1 degrees Celsius to 1.8 degrees Celsius warmer than average, across New Zealand.

Although Wairarapa was on the lower end of the spectrum, it wasn’t exempt from a marine heating event scientists nicknamed “the blob”. 

An article published in the Proceedings of the National Academy of Sciences journal, The Drivers and the Implications of Marine Heatwaves, found that extreme marine heatwaves could have deadly impacts.

One of the largest recorded marine heatwaves was a goliath pool of warm water about 2.6  degrees Celsius above normal that appeared in the winter of 2013 in the Pacific Ocean. 

The article said tens of thousands of dead tuna crabs washed up on San Diego beaches, kelp forests vanished, and hundreds of thousands of seabirds died because of the blob.

The blob stuck around for about three years and caused the collapse of the cod fishing industry, worth $100 million per year.

Niwa meteorologist Ben Noll said Aotearoa had its own “blob” last summer in addition to one over 2017-2018.

“There were numerous impacts, direct and indirect – and I’m sure plenty that will be studied in the years to come.

“I’d say it’s only a matter of time before we get our next “blob”, whether it’s this summer or in a few years.”

Noll said that marine heatwave conditions could continue into the new year. 

“The years 2021 and 2017 saw two of New Zealand’s most significant marine heatwaves, and we’re tracking warmer than at the same point in those years.” 

He said although Niwa expected a cooler start to December, there was an indication that temperatures could become more unusually warm again during the second half of December into January.

Noll said marine heatwaves were classed as periods of unusually high sea surface temperatures, for more than five days.

Niwa principal scientist of marine ecology Dr Vonda Cummings said marine heatwaves could have concerning effects, with heat stress pushing marine organisms towards or beyond their thermal tolerance limits. 

“These events can upset the balance of marine food webs and disrupt ecosystems.”

She said increased stress on marine species could change their movements, with some species escaping to cooler waters that they had not resided in before. 

Cummings said our most vulnerable species would be those with limited temperature tolerances and those that were not very mobile and could not escape the heat.

Organisms that made rocky shores their home were some of the most at risk of decline because of marine heatwaves. 

Earlier this year, Niwa released research showing that marine heatwaves were set to get longer and hotter through the rest of the century.

It said it would be strongly influenced by human-made climate change, and drastically reducing emissions was one of the only ways to slow the rate of ocean warming.

Niwa said the ocean’s average temperature was now 1.5 degrees Celsius higher than it was 100 years ago, and in the past 30 years, the frequency of marine heatwave events had doubled.

If climate change was not mitigated, events like “the blob” would become more frequent across the ocean. 

Grace Prior
Grace Prior
Grace Prior is a senior reporter at the Wairarapa Times-Age with a keen interest in environmental issues. Grace is the paper’s health reporter and regularly covers the rural sector, weather, Greater Wellington Regional Council, and coastal stories.

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