Ok, just wanting to clear this up..
WHAT CAUSED THE DEATHS OF DOGS ALONG THE HAURAKI GULF RECENTLY?
There has been a huge amount of misreporting of the cause of dog deaths and deaths of other marine life around the Hauraki Gulf a month or two ago.
What is known it that it was poisoning by 'tetrodotoxin'.
According to many tabloids however (the latest being in Thames this week), "toxic sea slugs" are to blame for the tetrodotoxin causing deaths.
THIS IS NOT TRUE.
Some sea slugs do indeed have toxins in their bodies - they use it as a chemical defense mechanism. Indeed the slugs found at the scene of the event were identified by scientists at the Cawthron Institute as conatining the toxin tetrodotoxin.
HOWEVER,...
The circumstances of the deaths actually all point to a toxic algal bloom. (As does the fact that most of the media images purportedly showing the slugs that have washed ashore in the Gulf were clearly of dead specimens.)
The logical pathway for tetrodotoxin poisoning such as the recent spate in the Gulf to occur is via fish and invertebrates grazing on the toxic algae. In the case of benthic invertebrates such as the slugs this usually occurs when the bloom begins to collapse and the cells settle on to the bottom. It was exactly this pathway that caused a spate of human paralytic shellfish poisonings in Hawke’s Bay in the mid 1990’s. The shellfish involved then were paua and catseye (bubu).
It has been known that dinoflagellates, specifically Alexandrium species, have been producing tetrodotoxin since at least 1996. Simply type Alexandrium into google and read yourself from the many scientific publications and reports.
Alexandrium blooms have occurred close to the Gulf in the past. A report to the ARC by AquaBio Consultants Ltd in 2003 states:
“Exposure may vary with geographical location. For example, Alexandrium species produce resting cysts that may lie dormant in the sediment for years until the right conditions for germination occur. There is thus a greater risk of an Alexandrium species bloom in areas where blooms have previously occurred."
And...
"This species bloomed extensively over many months on the western coast of the North Island in 2000. There is a potential risk of introducing this species into the Hauraki Gulf Marine Park through the transfer of cysts in bilge water, ballast water, dredged sediment etc.”
The Cawthron Institute has also isolated Alexandrium tamarense from Marsden Point in the past.
It is therefore possible that the poisonings that have occurred around Auckland are the result of blooms originating from an introduction of this species occurring in the Port of Auckland. In which case, we can expect to see instances of tetrodotoxin poisoning occurring further and further away from Auckland as this organism spreads.
And in case those of you who know me are wondering if I'm saying this just because I'm a sea slug geek - I'm NOT.
By pointing the finger at toxic seaslugs and ignoring the most probable cause there is a risk of humans being poisoned through ignorance.
It's important we are all aware of the facts and take appropriate action.
Cheers
K