But the impact of the extreme ocean temperatures along the southern coast this summer could take much longer to fully understand.
There has been anecdotal evidence of subtropical fish species not ordinarily found in southern waters.
Southern rock lobsters have been described as weak, or lethargic, prompting concern in the $140 million-a-year industry.
And researchers have said they fear sea sponges in the hundreds of thousands might have disappeared along the Fiordland coast, which could have significant knock-on effects for the larger ecosystem.
Fiordland Marine Guardians chairwoman Rebecca McLeod said concerning accounts were coming in from around the country of widespread kelp die-offs, algae mats smothering reefs, sponges "melting" and signs of ill health in fish.
How marine life in coastal Fiordland would respond to repeated marine heatwaves was a worry, Dr McLeod said.
"The big unknown is how the marine life in coastal Fiordland will respond to these repeated heatwaves," she said.
"We worry about how Fiordland’s unique species will fare under these extreme conditions now, and in the future."
A few years ago no-one was talking about marine heatwaves - instead researchers were talking about the effects of climate change as possible sea-level rise and maybe ocean acidification, Dr McLeod said.
"I think people just assumed that warming waters would happen gradually and didn’t understand the concept of marine heatwaves."
The Moana Project website presently says sea surface temperatures around the country are forecast to drop by Thursday, but not before peaking with areas such as Otago and Stewart Island recording sea surface temperatures up to 4.5 degC above average.
"Strong" marine heatwaves were forecast for Wairarapa, Cook Strait, Banks Peninsula, Fiordland and the Chatham Islands with temperatures expected to be 2 degC to 3 degC above average.
MetService oceanographer and Moana Project scientist Joao de Souza said late last week temperatures forecast for marine heatwaves this year had gone beyond the threshold for "severe" marine heatwaves as "extreme" marine heatwaves around Stewart Island and Otago had been forecast for the second time this year.
The increases to sea surface temperatures went beyond the colour scale MetService first used to designate the warming as the temperatures had surpassed the scale.
University of Otago and Moana Project scientist Robert Smith said last month the extended southern marine heatwave this summer was not just an event taking place in the top metre of the ocean, but rather it extended to a "substantial depth".
"This is not something that is just going to be affecting organisms that live right near the sea surface," Dr Smith said.
"If you’re a crayfish in Fiordland at the moment it’s going to be hard for you to escape the heat.
"As our oceans warm long term as a consequence of anthropogenic climate change, that’s making it much easier for these local weather systems to come over and tip us into a marine heatwave state.
