Mystery Sea Squirt probably native to new zealand

29 January 2002

Mystery sea squirt probably native to New Zealand

The taxonomic authority for Indo-West Pacific ascidians has advised the Ministry of Fisheries (MFish) that the sea squirt recently found in Whangamata Harbour, while previously undescribed, is likely to be native to New Zealand.

In October 2001 the Whangamata Harbourmaster noticed a growth dominating wharf piles in Whangamata Harbour (on the Coromandel Peninsula). Environment Waikato commissioned a study to describe the distribution and pest potential of the organism.

The organism is an ascidian (a sea squirt) belonging to the genus Didemnum, one of a colonial, mat forming group that is commonly found as part of the marine fouling community throughout New Zealand. The species from Whangamata, which is as yet unnamed, is particularly suited for colonising vertical structures such as wharf piles. Recent surveys have recorded what appears to be the same species in Tauranga and Nelson; it is highly likely that it will be present in other places around the country.

The Chief Technical Officer for Marine Biosecurity, Dr Chris O'Brien, said that it was not surprising that there was considerable uncertainty about the identity of the didemnid from Whangamata Harbour because our knowledge of New Zealand ascidians is very poor. However, he said the Ministry of Fisheries is currently managing a three year survey programme of New Zealand's major ports that will greatly improve our understanding of the marine creatures that live in our coastal areas.

The event in Whangamata Harbour is most likely a natural occurrence in the same vein as the recent toxic algal blooms and the influx of man of war (blue bottles) along the west coast of the North Island, Chaetopterous worms in Northland scallop areas, and the bloom of Ciona (another species of sea squirt) in Marlborough Sounds in the late 1990's. These events are common in the marine environment and are usually assisted by environmental conditions that favour one particular species and allow it to dominate. Past blooms of related ascidians have been seasonal and short-lived.

The Ministry of Fisheries is working with Environment Waikato and Environment BOP to inform people about the event and distribute information to vessel owners on how to reduce the spread of marine pests in general.

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For further information please contact:

Communications Unit
Ministry of Fisheries
04 494 2369