Using gigartinine to track the distribution of an alien species of <Emphasis Type="Italic">Gracilaria</Emphasis> in New Zealand

The presence of gigartinine has been used previously as a taxonomic marker for the positive identification in Manukau Harbour (west coast, Auckland) of Gracilaria sp., which has apparently been introduced to New Zealand waters and is easily confused morphologically with the native species, G. chilensis. Thirty two estuarine/harbour populations of Gracilaria in New Zealand were screened for the presence of gigartinine to further test the utility of gigartinine as a reliable species marker. DNA fingerprinting was used to confirm the identity of a subset of the specimens surveyed. Using genetic rather than chemical characterisation, it was discovered that Gracilaria sp. is also present in Orakei Basin (east coast, Auckland). Although a sample from the wild did not have the anticipated gigartinine content, tank cultivation of thalli from this population in an artificially elevated nitrogen environment allowed the plant to accumulate nitrogen as gigartinine. This confirmed the unusual ability of this species of Gracilaria to store nitrogen in this form, unlike the widespread, morphologically similar, G. chilensis.