Red seaweed infested waves at Waipu Cove has turned the water off the popular swimming beach to a thick soup.
Photo / Michael Cunningham
Red seaweed infested waves at Waipu Cove has turned the water off the popular swimming beach to a thick soup.
Photo / Michael Cunningham
Northland could experience a marine heatwave this summer, prompting a warning from a marine biologist that it has the potential to affect food supply for both sea organisms and humans in the long term.
The Tasman Sea and New Zealand coastal water temperatures warmed considerably during October, particularly near the North Island, driven by warmer than average air temperatures, plenty of sunshine, and lighter winds.
According to Niwa's season climate outlook for November to January, marine heatwave conditions may develop between now and January that will see sea temperatures in the low to mid-20s degC.
Rainfall is likely to be near normal, soil moisture and river flows below average, and temperature above average in Northland for the next three months.
Niwa's Southwest Pacific Tropical Cyclone Outlook indicates the risk of an ex-tropical cyclone passing near New Zealand between November and April as sea and air temperatures heat up.
Marine biologist Clinton Duffy said there was already an influx of tropical fish and other marine invertebrates in Northland waters while some migratory species like marlin and tuna were not spending much time in the upper North Island.
A La Nina cycle, he said, also has an impact on oceanic biological production along the north-east coast where it shut down the upwelling — a process in which deep, cold water rises towards the surface — of nutrients from the bottom of the water.
"The northerly offshore winds blow water offshore along the east coast and that creates a conveyor belt and that draws down the nutrients which lots of small animals feed off.
"It encourages the settlement of tropical and subtropical species along the coast. That happens fairly regularly but if it increases in frequency with global climate change, we'll see a shift towards a more tropical marine environment.
"That will see two common species, the tropical urchins and crustaceans, becoming more prevalent and seaweed which is a habitat for juvenile reef fish dwindling."
Duffy said birds that relied on small fish along the coast could also struggle to find food.
He said Kiwis could also find poisonous fish species in New Zealand waters as a result of warmer than usual sea temperatures.
Apart from marine life, Duffy said warmer waters could also bring red algae the likes of which rolled out at the southern end of Waipū Cove five years ago.
A marine heat wave from rising sea temperatures in Northland could bring flooding as a result of an ex-tropical cyclone this summer.
Photo / Peter de Graaf
Niwa principal scientist in marine biology Dr Wendy Nelson said seaweeds were really important for a lot of sea species that have different sea temperature tolerance levels.
She is New Zealand's leading authority on seaweeds and there are more than 350 different species of seaweeds in Northland.
"Seaweeds are important for habitat, food, nutrient uptake, stabilisation of reefs, and carbon culture. It's not just the temperatures but how long heatwaves last for that will have an impact on marine biology," Nelson said.
"There's also the beauty of diving through seaweeds and seeing all these rich communities and the variety of life they support, so there's going to be multiple impacts – likely to be different for different species - but we are not sure at this stage how serious it will be."
Niwa meteorologist Ben Noll said New Zealand started experiencing marine heatwaves towards the end of 2017, beginning of 2018 when sea temperatures in parts of the country reached the mid 20s degC.
"People like surfers head to the beach and experience warmer than normal seas. It makes going to the sea without having to wear a wetsuit a bit more enjoyable.
"On the flip side, there's the impact on marine life and can lead to a shift in the distribution of marine organisms.
"This spring has so far been quite dry and farmers and growers are concerned they may have to go through another drought but the chances of that are low with rainfall likely to be near normal."
The discovery of sea creatures like this bluebottle jellyfish found on Matauri Bay this year is attributed to warmer sea temperatures.
Photo / Francesca Jago
Noll said La Nina would bring moisture and warm seas that could also fuel ex-tropical cyclones.
He said the warmth, along with humidity, could prove difficult for some people with certain underlying medical conditions.
A recent Atmosphere and Climate Report by the Ministry of Environment said the impacts of rising temperatures would be more prevalent in areas that were already drier, including eastern parts of Northland and places in the Far North district that struggled with water supplies this year.
The frequency of droughts and wildfires are likely to increase in the next four to five decades, the report says. Northland has had six droughts in the past 10 years.
Those conditions present Northland with a golden opportunity to venture into growing more tropical fruits like bananas and pineapples.
