New Year’s Day, 1967. North of Auckland, marine biologist Bill Ballantine decides he’ll kick off the year by taking the temperature of the sea. This is how one of the longest ocean-temperature records in the Southern Hemisphere begins. In 2022, the record chalks up its hottest year: the Hauraki Gulf is in heatwave mode 86 per cent of the time.
It’s the same story for the rest of the country. The oceans surrounding New Zealand reached their highest-recorded temperatures either in 2022 or 2023, according to data released last month by Stats NZ. Our coastal waters warmed between 0.74 and 1.35°C in the past four decades.
What does this mean for sea life? Fifty million Fiordland sponges were wiped out by an intense heatwave in 2022, New Zealand scientists report in Global Change Biology—the largest such dieoff ever recorded worldwide. Now, Stats NZ is keeping an eye on phytoplankton, the invisible plants which sustain marine food chains. Their numbers have been decreasing in New Zealand waters since 2019.