INVASIVE MARINE SPECIES STUDIES

Molecular tools for invasive species in Hawai‘i

Rob J. Toonen, Greg Concepcion, Sam Kahng, and Marc Crepeau

Together with funding from Hawai‘i Sea Grant, Hawai‘i Coral Reef Initiative and the Hawai‘i Invasive Species Council, we have recently developed novel molecular tools that provide the greatest phylogenetic resolution of any genetic markers developed to date. We hope that these markers will be able to identify the source of invasive species introductions into the Hawaiian Archipelago. Evaluating the relative risk of introductions requires detailed surveys of the presence and abundance of invasive species on ships hulls, ballast water, and derelict fishing gear (see report by Jokiel et al.). Although the presence or absence of fouling on any individual ship hull or competent larvae in ballast water tells us that such transport is possible, those data do not provide us with the actual source of any introduction, and in some cases even the species identity of such propagules is controversial. Molecular data can provide us with a tool by which to examine the history of species movement, and we are currently developing the tools to go beyond what might have happened to what most likely happened.

We focused on the invasive octocoral, Carijoa riseii, in Hawai‘i, and used this funding to leverage additional support with which to develop the necessary tools to examine other species throughout the Hawaiian Archipelago. As the appropriate tools become available, future efforts will expand to include other invasive species. To date, our accomplishments include:

Figure 1. Global sampling of Carijoa. To date, 320 samples are included from throughout the Atlantic, Caribbean, Indo-Pacific, and Western Pacific. Samples from throughout the Atlantic and Caribbean show little genetic variation, and none of those genetic variants are found among samples from throughout Hawai‘i. In contrast to previously published reports, Carijoa in Hawai‘i are not from the Caribbean, and instead appear to be derived from multiple Pacific sources. (Click on the image to open a larger version.)

Figure 2. Phylogenetic tree of Carijoa samples. Some individuals (D) identified by taxonomic experts as Carijoa are more closely-related to our outgroup, Tubipora musica (C), than they are to the other samples of Carijoa (B) or to various representative species from other octocoral families (A). (Click on the image to open a larger version.)

Developing and testing a nuclear (nDNA) intron and two new mitochondrial DNA (mtDNA) markers which can provide reliable sequencing results to support our phylogeographic analysis (Concepcion et al., 2006); this is a significant achievement because mtDNA markers commonly used in other organisms have repeatedly proven useless in understanding patterns of colonization by corals (reviewed by Shearer et al. 2002).
Securing Carijoa samples from over 20 locations in the Pacific and Atlantic (see Figure 1) in collaboration with the Bishop Museum; Museum and Art Gallery of the Northern Territory, Australia; Florida Museum of Natural History; Coral Reef Research Foundation, Palau; University of the Virgin Islands, US Geological Survey, University of Puerto Rico; Universidade de Madeira; and Tel Aviv University. We have also sampled Carijoa from each of the Main Hawaiian Islands where it occurs. We have sequenced over 250 individuals for our mtDNA markers, and are currently working to complete sequencing of the nDNA markers as well. Our data thus far clearly indicates a need to revisit the taxonomy of Carijoa world-wide, because some samples sent to us and identified by taxonomic experts as Carijoa riseii are clearly not the same species: they are more closely related to corals in a completely different family of octocorals than they are to other species of Carijoa (see Figure 2).
Developing a novel nuclear DNA (nDNA) marker: Signal Recognition Protein 54 intron (Concepcion et al. in prep). Despite considerable effort, no lab in the world has successfully isolated nuclear intron markers for phylogenetic studies in corals, and this is the first such marker to be used in a coral study. Among Carijoa samples sequenced to date, these genetic markers are roughly ten times more variable than previously available markers, have the potential to discriminate species identity, and will hopefully serve to identify the source from which Carijoa first colonized Hawai‘i. Our success thus far has led to interest in collaboration from members of the Cnidarian Tree of Life consortium, and a collaborative proposal with Yehuda Benayahu (Tel Aviv University) and Cathy McFadden (Harvey Mudd) that was recently submitted to the U.S.-Israeli Binational Science Foundation.

Our study has already uncovered some very surprising results with regard to the dispersal history and biogeography of Carijoa in Hawai‘i:

Carijoa appears to be native to both the Atlantic and the Western Pacific with high and unique genetic diversity in each (i.e., the Indo-Pacific population of Carijoa is not a modern introduction from the Caribbean or Atlantic, and vice-versa).
The coral identified as Carijoa riisei in Hawai‘i does not appear to be all the same species. Preliminary data suggests that there are multiple species of Carijoa in Hawai‘i which are currently unidentified because of poor taxonomic resolution in the group worldwide. We are beginning to sequence our novel nDNA markers from all samples to resolve the taxonomic status of the group.
Several specimens identified as Carijoa riisei by taxonomic experts are not closely related to any other Carijoa samples in our database. The taxonomy of Carijoa clearly requires a major revision based on our research findings.
In contrast to published reports, Carijoa in Hawai‘i almost certainly originated from a Pacific source, not the Caribbean or Atlantic as previously reported.
There appear to be multiple introductions of Carijoa into Hawai‘i; sources of these introductions were likely locations throughout the Indo-Pacific, although based on the current molecular data we cannot date the invasion of the Hawaiian Archipelago by Carijoa.

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