The presence of gigartinine in a New Zealand Gracilaria species

Gigartinine, 5-(3-amidinoureido)-2-aminovaleric acid, serves as a chemotaxonomic marker to distinguish two species of Gracilaria with very similar morphologies. Gigartinine was identified by super(13)C-NMR spectroscopy and amino acid analysis of a cold-water extract from Gracilaria sp. nov., collected from a sheltered harbour locality at Blockhouse Bay, Auckland, New Zealand. Levels of this amino acid, naturally ca. 5% by dry weight of seaweed, were able to be depleted and then restored during a nitrogen pulsing experiment. In contrast, native and pulsed samples of Gracilaria chilensis from Point Arthur, Wellington showed no extractable gigartinine. Although these two species are unable to be distinguished in the field by morphological characteristics, they can be separated by the presence or absence of gigartinine.