Hat Tip: Auckland Blog – Cr Aaron Bhatnagar
Hauraki Gulf Marine Toxin Response
A selection of frequently asked questions – FAQ’s
1. What organisms are affected
Our testing confirms a toxin present in vomit of one of the dogs from Narrowneck Beach, North Shore Auckland, and from a single grey side-gilled sea slug (Pleurobranchaea maculata).
2. What are these sea slugs, are the native and where are they found.
Adult grey side-gilled sea slugs reach up to 100 mm in length. They are a soft sea slug with no shell. The body is smooth to touch but covered with minute puckers and folds. Colour is pale grey, densely patterned with short, brownish-black lines. The feathery gill is partly hidden under the right side and extends further when the animal gets stressed. The slug is not usually common in the Auckland region but its population can very widely depending on favourable breeding conditions and diet. They live in all habitats from inter-tidally in harbours and to depths of 250 m off open rocky coasts. They are fast, active hunters eating sea anemones, marine worms and molluscs.
3. What else has been tested for toxins
Cawthron has analysed organic and inorganic samples collected from North Shore and Eastern Suburb Beaches. These include jelly fish, seaweed, pilchards, algal mats, mussels, seawater, sediment/sand, sponges, limpets, and other sea slugs. All were negative for known toxins.
3. What has affected the sea slugs?
Cawthron Institute has identified a high concentration of tetrodotoxin (TTX) in the sea slug and lesser amounts in the dog vomit. This is an unusual finding as it has not been previously described in New Zealand.
4. Are other toxins involved?
Not conclusive but analysis by Cawthron has eliminated the usual suspects normally associated with shellfish poisoning and blue-green algal blooms.
5. Does the presence of TTX explain the clinical symptoms displayed by the sick dogs
Partly, TTX poisoning could explain the symptoms exhibited by the dogs affected at Narrowneck beach; they died rapidly typically within an hour without evidence of central nervous system agitation or seizures, but symptoms observed in other dogs affected beyond Narrowneck suggest another, as yet, identified cause. Further review is underway by the National Poisons Centre.
6. Is the sea slug naturally toxic
No, such a situation has not been previously described in this species although these types of organisms can have chemical defences to protect themselves from predators but not in a known association with TTX.
7. Can we say conclusively how the sea slug got TTX in such a concentration and potency
No. Multiple pathways are possible. TTX is most likely to have been inadvertently ingested by the sea slug. There is no evidence of host-specificity between TTX and the sea-slug, i.e. we do not consider this to be a symbiotic/parasitic relationship due to the mortality of juvenile sea slugs observed at Narrowneck beach
8. Were sea slugs found beyond Narrowneck?
The survey of Auckland North Shore and Eastern beaches located about 120-150 individuals at Narrowneck Beach and a single specimen at Cheltenham Beach. No sea slugs beyond these two areas. The bulk of the sea slugs present along the length of Narrowneck Beach were collected at the time. The animals were all found in the area of Narrowneck beach between mid and low tide amongst clumps of seaweed that were washed up on the shore The bulk of the animals were found dead, with only 4 larger individuals found alive. The animals ranged in size from about 30mm to 80mm with the bulk in the 30-50mm range.
9. Do sea slugs wash up normally?
Yes, it is quite common to see dead individuals washed up on the beach. This in itself is not unusual and not normally a cause for concern. The sea slug is an annual species and adults die after reproduction. It is less common to see dead juveniles on the beach. The cause of their death is not known, TTX could be a factor but multiple other causes are also possible.
10. Are the dead sea slugs hazardous?
It is best to be cautious and avoid contact with them. We currently know that one individual from Narrowneck beach tested positive for TTX and that this has been found in the vomit of one dog. Results from further tests of sea slugs found beyond Narrowneck pending.
11. How long are the sea slugs hazardous?
Assuming that the toxin is present in more than the one individual, it is really difficult to know how long the toxicity will persist. If the ingestion of TTX was from a single discrete source then the hazard should abate but if ingestion was from multiple continuous sources then the hazard could remain. It is best to remain cautious until the source has been identified or future samples are clear of the TTX. Most factors point to a natural, albeit very rare event perhaps associated with climatic patterns.
12. Where does TTX come from?
It can be found in common, naturally occurring marine bacteria. The association between these bacterium and TTX is known from tropical regions, sometimes found in a symbiotic or parasitic relationship with higher order animals. Symbiosis is not considered likely in the sea slug and other mechanisms including absorption or ingestion through inadvertently consuming an infected prey item is suspected. The relationship of TTX with a NZ marine bacteria has not been previously described and further investigations are required. We do not believe this is indicative of any immediate change in the health of the Hauraki Gulf rather this is the first time that a link has been found between the death of a dog, a sea slug and the presence of a common toxin. Most factors point to a natural, albeit very rare event perhaps associated with climatic patterns.
13. What about the penguins and pilchards? Are they related?
Ecologists do not believe this to be the case. Isolated incidences of pilchard and penguins deaths at this time of the year are not ordinarily unusual and natural causes of death are considered a likely scenario. Many of the penguins examined were in poor condition and showed signs of starvation; a not uncommon situation for this time of the year. The cause of the pilchard mortality is still being investigated but is not believed to be related to the dog deaths.
14. What does this say about the health of the Hauraki Gulf
We do not believe this is indicative of any immediate change in the health of the Hauraki Gulf rather there has been a series of isolated, localised, probably natural events. It is the first time that a link has been found between the death of a dog, a sea slug and the presence of this toxin. The toxin has only been identified at a single, specific location. There is no evidence to indicate that it is more widespread than this. At this stage, the deaths of other marine organisms have not been linked in any way to this toxin.