Tahiti's native flora endangered by the invasion of Miconia calvescens DC. (Melastomataceae)

Abstract. The native flora of tropical oceanic islands is known to be particularly susceptible both to displacement and extinction, following the invasion of alien organisms. Miconia calvescens DC. (Melastomataceae), first introduced to Tahiti (French Polynesia, South Pacific Ocean) in 1937 as an ornamental plant, now covers over two-thirds of the Island. As it forms dense monotypic stands which have progressively overwhelmed the native forests, this plant pest is a direct threat to the rich Tahitian indigenous flora. Between 40 and 50 species of the 107 species endemic to Tahiti are thought to be on the verge of extinction. M. calvescens was finally declared a'noxious species in French Polynesia'in 1990. Without efficient control efforts and effective endangered plant conservation and protection legislation, M. calvescens could cause Tahiti and all the high islands of French Polynesia to become ecological deserts.     

Engineering Enemy-free Space: An Invasive Pest that Kills its Predators

The biological invasion of the glassy-winged sharpshooter, Homalodisca coagulata, into French Polynesia presents a novel threat to Pacific Island ecosystems. Widely known as an agricultural pest because of its role as a vector of numerous lethal plant diseases, H. coagulata may pose a substantial and immediate risk to arthropod predators on invaded islands in French Polynesia. Controlled feeding experiments revealed that island spiders can be killed following predation on H. coagulata. Spider mortality appeared to result from lethal intoxication, although no form of chemical defense has been reported in H. coagulata. In the two spider species tested, approximately half of all individuals that attacked H. coagulata nymphs or adults died. As populations of this insect increase in size and range on invaded islands in French Polynesia, H. coagulata will increasingly encounter these and other arthropod predators, raising the possibility of population-level impacts on susceptible predator species. Field surveys of island spiders across nine sites on H. coagulata-invaded and H. coagulata-uninvaded islands suggest that this insect may already have adversely impacted an endemic spider on at least one island. Work is needed to identify the nature of the lethal agent harbored within H. coagulata and the taxonomic and geographic breadth of predators vulnerable to it. The generality of H. coagulata-lethality and the capacity of afflicted predator species for population-level adaptation or learned avoidance in response to this spreading pest will determine the magnitude of the threat H. coagulata poses in the South Pacific.     

Ambient temperature effects on the extrinsic incubation period of Wuchereria bancrofti in Aedes polynesiensis: implications for filariasis transmission dynamics and distribution in French Polynesia.

Temperature effects on development of the human filarial parasite Wuchereria bancrofti (Cobbold) (Filaridea: Onchocercidae) in the main Pacific vector Aedes polynesiensis Marks (Diptera: Culicidae) are analysed in relation to ambient climatic conditions. A statistical model of the extrinsic cycle duration as a function of temperature is described and used to distinguish three patterns of W. bancrofti transmission dynamics: continuous, fluctuating and discontinuous, occurring from north to south geographically among French Polynesian archipelagos. In the northerly Marquesas Islands (8-11 degrees S) filariasis transmission is continuous and very active, facilitated by perennially high temperatures combined with constantly high rates of man-vector contact. In the southerly Australes Islands (21-28 degrees S) filariasis transmission is seasonally discontinuous and, during the cooler months (May-September), the model predicts virtually no transmission because the cycle duration exceeds the life expectancy of the vector. In the Society Islands (16-18 degrees S), between the Marquesas and Australes, transmission is predicted to be intermediate as expected from their latitude, with seasonally fluctuating transmission potential. In the Tuamotu Islands (also geographically intermediate: 14-23 degrees S), with theoretically perennial transmission potential, transmission occurs only intermittently, being limited by other human and environmental factors whereby man-vector contact is confined to seasonal agricultural situations. Generally, among French Polynesian archipelagos where Aedes polynesiensis is the vector, the transmission potential for W. bancrofti and resulting disease manifestations of lymphatic filariasis in humans are correlated with ambient temperature due to the degree of southern latitude.     

Microbioerosion in Tahitian reefs: a record of environmental change during the last deglacial sea-level rise (IODP 310)

The main motivation for Integrated Ocean Drilling Program Expedition 310 to the Tahitian Archipelago was the assumption that the last deglacial sea‐level rise is precisely recorded in the coral reefs of this far‐field site. The Tahitian deglacial succession typically consists of coral framework subsequently encrusted by coralline algae and microbialites. The high abundance of microbialites is uncommon for shallow‐water coral reefs, and the environmental conditions favouring their development are still poorly understood. Microbioerosion patterns in the three principal framework components (corals, coralline algae, microbialites) are studied with respect to relative light availability during coral growth and subsequent encrustation, in order to constrain the palaeobathymetry and the relative timing of the encrustation. Unexpectedly for a tropical, light‐flooded setting, ichnotaxa typical for the deep‐euphotic to dysphotic zone dominate. The key ichnotaxa for the shallow euphotic zone are scarce in the analysed sample set, and are restricted to the base of the deglacial succession, thus reflecting the deglacial sea‐level rise. At the base of the deglacial reef succession, the ichnocoenoses present in the corals indicate shallower bathymetries than those in the encrusting microbialites. This is in agreement with radiocarbon data that indicate a time gap of more than 600 years between coral death and microbialite formation. At the top of the deglacial reef succession, in contrast, the microbioerosion patterns in the three framework components indicate a uniform palaeobathymetry, and radiocarbon ages imply that encrustation took place shortly after coral demise. An enigma arises from the fact that the ichnocoenoses imply photic conditions that appear very deep for zooxanthellate coral growth. During the deglacial sea‐level rise increased nutrients and fluvial influx may have led to (seasonal?) eutrophication, condensing the photic zonation. This would have exerted stress on the coral ecosystem and played a significant role in initiating microbialite development.     

Biogeography of the fauna of French Polynesia: diversification within and between a series of hot spot archipelagos

The islands of French Polynesia cover an area the size of Europe, though total land area is smaller than Rhode Island. Each hot spot archipelago (Societies, Marquesas, Australs) is chronologically arranged. With the advent of molecular techniques, relatively precise estimations of timing and source of colonization have become feasible. We compile data for the region, first examining colonization (some lineages dispersed from the west, others from the east). Within archipelagos, blackflies (Simulium) provide the best example of adaptive radiation in the Societies, though a similar radiation occurs in weevils (Rhyncogonus). Both lineages indicate that Tahiti hosts the highest diversity. The more remote Marquesas show clear examples of adaptive radiation in birds, arthropods and snails. The Austral Islands, though generally depauperate, host astonishing diversity on the single island of Rapa, while lineages on other islands are generally widespread but with large genetic distances between islands. More recent human colonization has changed the face of Polynesian biogeography. Molecular markers highlight the rapidity of Polynesian human (plus commensal) migrations and the importance of admixture from other populations during the period of prehistoric human voyages. However, recent increase in traffic has brought many new, invasive species to the region, with the future of the indigenous biota uncertain.     

A review of Polynesian Carposina Herrich‐Schäffer (Lepidoptera: Carposinidae), with descriptions of four new species

Hawaiian Carposina represent over 17% of the known world fauna of Carposinidae. In contrast, only two species are known for all of French Polynesia in the South Pacific. Here we describe four new species: two from the Hawaiian Islands, C arposina urbanae sp. nov. and C . gagneorum sp. nov. , and two from the Society Islands, C . longignathosa sp. nov. and C . brevinotata sp. nov. We further recognize another new Hawaiian species too worn to describe. Additionally, we present the first phylogeny for Polynesian Carposina, including 19 taxa, using one mitochondrial and two nuclear gene regions. The Hawaiian Carposina sampled thus far form a monophyletic clade. Lastly, we provide a framework to better understand the diversification and phylogeography of this group, and provide a summary of currently known host plant associations. Diversification appears to have resulted from interplay between host switching and geographic isolation across the Hawaiian Archipelago.     

The role of macroalgae in epiphytism of the toxic dinoflagellate Gambierdiscus toxicus (Dinophyceae)

Populations of the toxic, epiphytic dinoflagellate Gambierdiscus toxicus Adachi et Fukuyo are asSociated closely with Jania sp. on Hitiaa and Papara fringing reefs in Tahiti. Small populations were also observed to be asSociated with Amphiroa sp. and Halimeda opuntia (L.) Lamouroux. The cells attached themselves to the thallus by means of a short thread. When the thalli were irradiated, the cells began to detach from them and swim around the branches. The swimming cells stopped and attached to substrata when a disturbance occurred. The attached cells began to swim within a short time under light conditions when the thallus of Jania sp. were placed near the attached cells. Amphiroa sp. and H. opuntia also induced this re-commencement of swimming of the attached cells. These observations suggest that G. toxicus usually swims around macroalgal thalli on coral reefs. When sudden disturbance or strong water motion occurs, they attach to the surface of macroalgae and are not dispersed. Soon after water motion becomes slow, the cells begin to swim into the water around the thalli. The epiphytism of G. toxicus is different from epiphytic pennate diatoms, most of which adhere to the thallus all the time. The population of G. toxicus is maintained as an asSociation to a limited number of species of macroalgae which support the re-commencement of swimming after disturbance.     

Mapping and biomass estimation of the invasive brown algae<Emphasis Type="Italic"> Turbinaria ornata</Emphasis> (Turner) J. Agardh and<Emphasis Type="Italic"> Sargassum mangarevense</Emphasis> (Grunow) Setchell on heterogeneous Tahitian coral reefs using 4-meter resolution IKONOS satellite data

Turbinaria ornata and Sargassum mangarevense (Halophyte, Sargassaceae) are two Fucales that have strong biotechnological potential for the cosmetic industries. To plan for the harvesting of these two species on Tahiti (French Polynesia, South Pacific Ocean) reefs, their total biomass is estimated for three morphologically different reefs using a combination of field data and three 4-m resolution IKONOS satellite images. Fieldwork provided mean algal cover for each of the main habitats of the reefs and a ubiquitous relationship linking percent cover and biomass. Images were used to map the spatial extent of the habitats. Image classification resulted in an overall habitat map accuracy of 70%. For the three reefs, the total biomass was 153,565 ± 73,441, 561,718 ± 192,956, and 215,203 ± 75,012 tons of dry matter, which yielded a mean areal biomass of 0.173 ± 0.083 kg.m^–2, 0.133 ± 0.046 kg.m^–2, and 0.193 ± 0.067 kg.m^–2 (dry matter). The different total and areal biomass reflect different reef structures and the abundance of suitable substratum for algal settlement. Images reveal the spatial distribution of the algae, mostly located on the outer edges (crest and dense back-reef) of the reefs. Since percent cover data were collected during the cool season when algal densities are at their highest, the computed biomasses are maxima.