Beaches turning to seafood chowder under chronic summer heat
Tuesday, 30 January 2018
Welcome to the summer of 2018, where it's so hot that shellfish are cooking in the sand.
Experts say extended hot spells across the country could be 'stressing out' pipi, cockles and juvenile tuatua, potentially causing mass deaths such as those seen on the Kāpiti Coast, north of Wellington, this week.
Meanwhile, swimmers around Wellington are finding themselves floating a gelatinous 'soup' of jellyfish lookalikes called salp, which are appearing in huge numbers as the weather gets unusually warm.
Residents in Peka Peka, on the Kāpiti Coast – where temperatures have exceeded 30 degrees Celsius over the past week – have reported finding dead shellfish, and a bad smell wafting from the beach.
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Fishery scientist James Williams, from the National Institute of Water and Atmospheric Research (Niwa), said it was possible the extreme heat caused the mass die-off.
Bivalves such as pipi, cockles and young tuatua lived between high and low tides on beaches, and could be dying from heat stress.
'Bivalves are influenced by the temperature around them, so they can't control their own internal body temperature … as the water warms up, their rate of breathing and feeding increase to a point when they can't take it any more, and they get stressed out.'
They would be particularly affected when there was a low tide in the middle of the afternoon, exposing them to increased heat. 'If we get chronic heat conditions day after day, they might get stressed out.'
Other shellfish that lived in deeper water would be less affected.
In Wellington, many beaches have turned into a 'soup' of gelatinous creatures called salps, which are often mistaken for jellyfish.
Tom Stacey, from Thorndon, a regular at Oriental Beach, said he and many others had noticed thousands of salps at the beach this week.
Salps are jellyfish-like creatures that can be found in Wellington's waters most summers, but have appeared in huge numbers this year.
The almost translucent creatures can be seen in a chain resembling a living diamond necklace. When they are broken up, they appear as tiny water droplets.
'It's an unusual effect when you are swimming to have sort of this jelly-like stuff, sort of buffeting you,' Stacey said.
'Normally when you brush against something in the water, you've got some solid sort of substance that you can see … but in this instance they're not, they're just clear, they're transparent.'
Dennis Gordon, emeritus researcher for Niwa, said salps did not sting and ranged in size from a fingertip to the size of a hand.
'There's lots of those, and it's a bit like swimming in soup, and that's throughout Wellington Harbour.'
There were also some jellyfish making their way into the harbour, mostly the lion's mane, a true, stinging jellyfish.
'There numbers are not unusual, they're quite moderate for this time of year … but we have been getting on south coast beaches another kind of jellyfish called a crystal jelly.
'You only get crystal jellies … when there's warm water incursions.'
He said there was a strong likelihood the plankton on which salps feed had grown faster in the hotter temperatures, increasing numbers of salps up the food chain.
The random combination of winds, tides and currents also affected numbers.