MANGROVES AS ALIEN SPECIES - THE CASE OF HAWAII

Prior to the early 1900s, there were no mangroves in the Hawaiian Arch ipelago. In 1902, Rhizophora mangle was introduced on the island of Mo lokai, primarily for the purpose of stabilizing coastal mud flats. Thi s species is now well established in Hawaii. and is found on nearly al l of the major islands. At least five other species of mangroves or as sociated species were introduced to Hawaii in the early 1900s and whil e none has thrived to the degree of R. mangle, at least two have estab lished self-maintaining populations (Bruguiera gymnorrhiza and Conocar pus erectus). Mangroves are highly regarded in most parts of the tropi cs for the ecosystem services they provide, but in Hawaii they also ha ve important negative ecological and economic impacts. Known negative impacts include reduction in habitat quality for endangered waterbirds such as the Hawaiian stilt (Himantopus mexicanus knudseni), colonizat ion of habitats to the detriment of native species (e.g. in anchialine pools), overgrowing native Hawaiian archaeological sites, and causing drainage and aesthetic problems. Positive impacts appear to be fewer, but include uses of local importance, such as harvesting B. gymnorrhi za flowers for lei-making, as well as some ecological services attribu ted to mangroves elsewhere, such as sediment retention and organic mat ter export. From a research perspective. possible benefits of the pres ence of mangroves in Hawaii include an unusual opportunity to evaluate their functional role in coastal ecosystems and the chance to examine unique or rare species interactions.