Kina, sea cucumbers and some crayfish were spotted among the dead sea life washed up at Ahuriri on Thursday. Photo / Warren Buckland
Kina, sea cucumbers and some crayfish were spotted among the dead sea life washed up at Ahuriri on Thursday. Photo / Warren Buckland
Low dissolved oxygen levels from an algal bloom may have caused the mass deaths of sea life that washed ashore in Napier this week, according to Hawke’s Bay Regional Council scientists.
Thousands of creatures, mainly kina but also including crayfish, starfish and sea cucumbers coated the beach off Hardinge Rd, Ahuriri on Thursday, sparking warnings against taking or consuming the species pending an investigation that continued during the weekend.
Similar wash has since been reported on the Haumoana-Te Awanga coast, and the council has reiterated a warning that the sea life should not be touched or consumed, particularly while the causes remain uncertain.
Council science manager Anna Madarasz-Smith said the possibility of low dissolved oxygen from algal bloom, which has been present on the Napier coast since at least as long ago as mid-December, is the “current strongest working theory”.
But the council is “taking a wide line of inquiry to ensure no other potential causes are missed,” Madarasz-Smith said in a statement on Sunday.
“As the community has observed, there has been a persistent algal bloom around Napier for the last two months.
“Blooms are made up of millions of tiny, microscopic algae, and if these persist, or when they start to die off, they can use up a lot of the dissolved oxygen in the water, causing very low dissolved oxygen levels.”
Freshwater ecologist Dan Fake takes water samples at sea off Hardinge Rd, Ahuriri, and the Port of Napier. Photo / HBRC
“We have measured dissolved oxygen saturation levels in the bottom waters of the area as low as 34 per cent, when normal levels are between 90 and 110 per cent.
“The animals washing up live on the bottom of the seafloor, so are vulnerable.”
The regional council is looking at a number of theories to ensure no other potential causes are missed, and other theories the council is investigating include freshwater drowning, sediment smothering or a toxic spill.
“We aren’t convinced that freshwater drowning is the cause because results of our testing show that the bottom waters are still relatively saline,” Madarasz-Smith said.
A red algal bloom has been a near-constant feature of Hawke Bay this summer. Photo / Paul Taylor
“While sediment smothering of these animals is plausible, the river discharges have been high in sediment for many months and it would be unusual for this to cause a sudden, acute and localised issue.”
Madarasz-Smith said spills can also cause low dissolved oxygen levels in water, but compliance staff had been investigating the local area with “nothing unusual” found.
“With more animals washing up around Haumoana, then again a localised spill does not seem as likely,” she said.
The regional council has observed dead marine animals on Hardinge Road beach, Westshore beach and on late Friday was informed that they were on Te Awanga and Haumoana beaches. Testing is being undertaken in all those areas.
“We strongly urge people to not gather or consume any dead sea life washed up on the beaches,” she said.
Recent storms have also resulted in huge amounts of debris flowing into the ocean and being washed back ashore, including dead and decaying farm animals. An apparent pig carcass was a source of interest to the public near Westshore on Saturday.
