Molecular revision of the 'core' Caulerpa in the Hawaiian archipelago

Abstract

The historical sequence of epithets and subspecific ranks used from early investigators (1880 to 1934, see above) to Eubank (1946), Hodgson et al. (2002) and finally Abbott and Huisman (2004) demonstrate the taxonomic upheaval surrounding Caulerpa species. To this day, the classification of Hawaiian Caulerpa has relied on morphology only and needs to be confirmed molecularly. Hodgson et al. (2002) recognized that taxonomic boundaries in this group remain poorly understood and that future studies utilizing genetic and/or culture experiments might clarify the situation. Similarly, Abbott and Huisman (2004) mentioned that genetic identity within Caulerpa in Hawaii remains to be characterized with molecular tools for confirmation, representing the "next level" of investigation for the genus. For instance, the treatment of C. racemosa complex and peltate specimens (e.g. C. racemosa var. peltata, C. racemosa...) greatly differs between the successive revisions (Table 1). Developing a stable classification of the genus Caulerpa in the archipelago is key to establishing a proactive baseline for early detection of alien taxa in the event of a future invasion. The seizure of Caulerpa prolifera in an aquarium store of the Big Island of Hawaiʻi is proof that alien taxa might reach the archipelago via the aquarium trade on a regular basis. Hence, the present thesis seeks in clarifying Caulerpa species diversity in the Hawaiian archipelago (NWHI and MHI). In Chapter 2, morphologies reported in the latest revision of the genus in Hawaii (Abbott and Huisman 2004) are tested in a molecular context using the species level marker tufA and placed within a larger phylogeographic framework using GenBank meta-data for this marker. Morphologically plastic taxa are further confirmed with the fast evolving nuclear marker ITS2. Molecular investigations are focused on the 'core' Caulerpa clade, which encompass most of the diversity in the archipelago. Molecular confirmation of remaining members, C. verticillata (basal), and C. lentillifera and C. microphysa (Pyrenoid clade) is not included.