High levels of toxic algae has seen a shellfish poisoning warning issued for the Bay of Plenty and Thames/Coromandel coastline. But what does that mean?

Toxin levels in shellfish are more than 20 times the level at which warnings are issued, and may still be rising, says MPI Principal Adviser Animal Products, Jim Sim.

This video has been produced to highlight ocean acidification as a potential issue affecting the NZ shellfish aquaculture industry. Video courtesy of NIWA.

The area covered by the toxic shellfish warning has been extended to include the entire coastline from Whakatane Heads in the Eastern Bay of Plenty, all the way along the coast to Waihi Beach, and up the eastern side of the Coromandel Peninsula to Opito Bay.

All harbours, estuaries and islands along this coastline are included in the warning.

'The toxic algae species making shellfish poisonous is Alexandrium minutum, which produces the most toxic compounds of the various toxic algal species in New Zealand waters,” explains Jim.

While it's not known what causes a toxic algal to bloom, Alexandrium minutum has a resting cysts stage which remain in an area after a bloom and, when conditions are right it, reappears.

NIWA, the National Institute of Water and Atmospheric Research, has produced a video to highlight ocean acidification as a potential issue affecting the New Zealand aquaculture industry.

The video is a direct result of the collaborative New Zealand-United States workshop 'Future proofing New Zealand's shellfish aquaculture: monitoring and adaptation to ocean acidification', organised by NIWA, MPI, the Cawthron Institute and US colleagues in December 2013.

Featured in the video are scientists and US and NZ industry representatives, as well as officials from the funding agencies MPI, MBIE and the US Embassy.

While ocean acidification is not directly affecting New Zealand shellfish, experts are warning that now is not the time to be complacent. Watch the video above to find out why.