Invasive alga reaches California

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The alga has been identified that threatens to smother Californian coastal ecosystems.


The recent discovery of the marine green alga Caulerpa taxifolia on the Californian coast1,2 has raised public concern about the potential danger of a new invasion similar to the one endured by the Mediterranean Sea over the past decade. A small colony of C. taxifolia introduced into the Mediterranean in 19843,4 from a public aquarium5 has spread to more than 6,000 hectares today, outcompeting native species and seriously reducing diversity in areas of the northwestern Mediterranean6. This invasive strain of C. taxifolia differs from tropical populations in that it is much larger, grows more vigorously, does not rely on sexual reproduction, and is resistant to low temperatures4,6,7. Here we evaluate the risk of invasion by Californian C. taxifolia by comparing it genetically with the Mediterranean and aquarium strain, as well as with native tropical populations. Our results show that the Californian alga is the same as the invasive Mediterranean strain, calling for its rapid eradication to prevent a new invasion.

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Figure 1: Phylogenetic tree of C. taxifolia inferred from 160 complete ITS (internal transcribed spacer) ribosomal DNA sequences by using the neighbour-joining method applied to pairwise sequence distances calculated by the Kimura two-parameter method.


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Correspondence to O. Jousson.

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