| A dispersal filter is generally used to explain the attenuation of mangrove richness from 35 species in the Indo-West Pacific to 3 species in Samoa. Bruguiera gymnorrhiza and Xylocarpus moluccensis are widespread Old World mangroves that have easternmost distributions in American Samoa. Rhizophora mangle is a New World mangrove with outlier populations in Samoa, Tonga, Fiji and New Caledonia. It has been assumed that the Pacific Ocean creates too great a barrier for propagules of R. mangle to naturally become established in the SW Pacific and some researchers believe this species was introduced by early Polynesians. To explain the distribution of 3 Samoan species and why five other western Pacific species are not found in Samoa, propagules of 8 mangrove species found in Tonga and Fiji were floated for up to 8 months in seawater tanks. Viability was determined by out-planting sub-samples in a greenhouse at monthly intervals. Concomitantly, residents near mangrove areas in Samoa, Tonga and Fiji were interviewed to compare the importance of relevant species. Results indicate that propagules of R. mangle and X. moluccensis were viable after 8 months of floatation. This is 8 times longer than those of B. gymnorrhiza and more than 2.5 times longer than the western species Rhizophora stylosa. Based on household interviews in Tonga and Fiji, there was no preference for R. mangle over R. stylosa. B. gymnorrhiza was preferred over both species of Rhizophora in Tonga for tapa dye and reported as a food source in Fiji. Molecular analysis of B. gymnorrhiza from Fiji, Tonga and Samoa revealed that there was no genetic variation among populations, which suggests that this species may have been intentionally introduced by early Polynesians. Comparison of RAPD markers among populations of R. mangle in Fiji, Tonga, Samoa and Ecuador demonstrates that there is much less genetic variation in the Southwest Pacific, suggesting these populations were originally colonized from South America. However, 23% of the variable loci from all populations were unique to the Southwest Pacific, which supports the conclusion that this species was established in the SW Pacific before Polynesians were voyaging in the Eastern Pacific. |
