Locals and visitors may see slimy algae, usually black or dark green, in the sea and on beaches across Tāmaki Makaurau this summer.
This could be the cyanobacteria Okeania spp. that has occurred during the last three summers. Last summer large quantities of the algae washed up on-shore at Waiheke Island and Kawakawa Bay.
Blooms have appeared at Blackpool and Surfdale beaches on Waiheke for the last three summer seasons and were also seen at Algies Bay, the Beachlands to Kawakawa coastline and in parts of the Manukau Harbour last year. This summer, algae has already been seen again at Algies Bay and Blackpool.
The algae could also appear on other beaches around the region this summer.
Taryn Crewe, General Manager Parks and Community Facilities, reassures the public there is no need for concern about the algae, but advises people to avoid touching it.
“During summer, it is common to see all types of algal blooms occurring. We continue to monitor Okeania spp. and are ready to act if required.
“In the meantime, if you see this slimy algae around the region, please avoid contact with it as it could lead to skin, eye and respiratory irritations. Keep an eye on your dogs and ensure they also avoid the algae.”
About cyanobacteria Okeania spp.
Cyanobacteria (or blue-green algae) are naturally occurring microscopic organisms that live in a range of aquatic environments, from near-pristine to those more impacted by land use.
Cyanobacteria occurs naturally in New Zealand waters. Some cyanobacteria (including Okeania spp. ) are known to produce toxins – collectively referred to as lyngbyatoxins – which could lead to skin, eye and respiratory irritations.
While we don’t know what causes it to bloom in different locations from year to year, the warm sea temperatures are extending the spring–summer growing season, which likely contributes to recurring blooms.
Generally, the drivers of cyanobacterial blooms are complex, and it is difficult to predict or explain where they may occur, as well as their size and duration. This is because numerous environmental conditions need to be met to enable the rapid growth of the cyanobacteria – this includes calm weather conditions, plenty of light, warm seawater temperatures and sufficient nutrients to sustain their growth.
It forms large mats that raft together and wash up on beaches, which do not naturally dislodge once onshore and can harden in place.
There is still much to find out about the ecology and toxicology of Okeania spp. However, we do know from previous observations that it grows in shallow seabed areas.
Because it is naturally widely distributed and grows below the tide line, it is impossible to remove it completely from the marine environment.
Where and when algae tends to appear
As well as Waiheke and Algies Bay, blooms have been reported in previous summers at Ōmana Beach, Musick Point, Eastern Beach, Howick, Kaitarakihi Bay, North Head and Beachlands.
January, February and March are the key months for nuisance algae in Tāmaki Makaurau.
Staying safe at affected beaches
- The beaches where this algae is present remain open to the public but Auckland Council advises the following:
- Avoid contact with the algae, including wading in affected areas, as it could lead to skin, eye and respiratory irritation
- If you feel unwell as a result of contact with the bloom, contact your doctor, or call Healthline on 0800 611 116
- Do not gather or take algae from the beach for things like using as compost on your garden – it is unsuitable
- Keep dogs away from the algae and any decomposing material which could cause a reaction
- Do not gather or consume shellfish from the affected beaches
- Members of the public can report significant accumulations by emailing healthenforcement@aucklandcouncil.govt.nz.
Are cyanobacteria common in New Zealand waters?
The cyanobacteria Okeania spp. occurs in low abundance throughout the Hauraki Gulf. Blooms of the filamentous cyanobacterium identified at the time as Lyngbya majuscula have been reported in various parts of the Hauraki Gulf particularly in the Ōmana Beach area.
Some of the earliest records of Lyngbya spp. go back to surveys in the 1950s and in the 1970s it was described as a seasonally dominant species on rock platforms around Motukaraka Island. Through the 2000s there were regular occurrences of blooms around the Beachlands and Ōmana areas.
Why is the cyanobacteria occurring now?
The drivers of cyanobacterial blooms are complex, and it is very difficult to predict or explain where they may occur, as well as their size and duration. This is because numerous environmental conditions need to be met to enable the rapid growth of the cyanobacteria.
Once dislodged, factors such as the tidal conditions and wind direction need to be understood to predict where blooms may eventually be deposited. These requirements mean blooms most commonly occur during spring and summer, and are a natural phenomenon in shallow, coasts. It is likely that a perfect combination of conditions in recent months has resulted in the current washed up bloom on Waiheke Island and Algies Bay.
What impact does cyanobacteria have on the environment?
Some cyanobacteria blooms can have serious impacts on aquatic ecosystems in general including potential toxic effects due to smothering and shading. However, there is a lack of research when it comes to the environmental impacts of Okeania spp.
What research is being carried out into the cyanobacteria?
Working closely with Auckland Council, Cawthron Institute has identified the dominant component of the cyanobacterial mats as Okeania. Dr Laura Biessy at Cawthron Institute has carried out some analysis to characterise the species responsible for these blooms on Waiheke Island and assess their toxicity. However, there is a lack of research surrounding the ecology, toxicity and impact on the environment of benthic cyanobacterial species such as Okeania.
Cawthron Institute recently published a study of shellfish collected from beaches on Waiheke Island that have been affected by Okeania blooms. They were tested for lyngbyatoxin-A (LTA) accumulation, and the results confirmed LTA had accumulated in marine snails, rock oysters and cockles collected near the algae mats. These results underline the need for further studies assessing the risks of human exposure to LTA through seafood consumption.
Dr Biessy is continuing work to isolate and culture this species to better understand its ecology, preferred conditions (temperature, salinity, nutrients, etc.) and habitat. These answers would allow us to predict when future blooms might occur and what could be done to mitigate these blooms.
