The flora of the Pitcairn Islands: a review

vascular plant flora of the Pitcairn Islands, south-central Pacific Ocean, is described based on extensive new collections made in 1991 and previously published records. Two vascular plants occur on Ducie Atoll; one (Pemphis acidula) is a new record. Sixty-three native vascular plants occur on Henderson, of which nine are endemic; Canavalia rosea, Operculina lurpethum, Psilotum nudum and Solanum americanum are new records for the island. Oeno Atoll has 16 native vascular plants; the single endemic (Bidens hendersonensis var. oenoensis) was not found in 1991 despite careful searches. Triumfetta procumbens was new for Oeno. Sixty-six native vascular plants have now been recorded from Pitcairn Island, there are two endemic ferns and seven endemic angiosperms in this number. A number of non-native taxa were new to Pitcairn. Some of the previously described taxa could not be found on Pitcairn, probably because they are very rare and only a small amount of time was spent collecting on Pitcairn. Many of the Pitcairn taxa are threatened by the spread of introduced species, especially Syzygium jambos.     

Initial checklist of fishes from Henderson Island, Pitcairn Group

Notes are given on the presence and distribution of reef fishes at Henderson Island (24^o21'S, 128^o19'W) from two separate visits in 1971 and 1991. Limited collections were made in 1971, whilst 1991 records are based on confirmed sightings and in situ photographs. 183 species from 49 families are listed, with museum numbers and lengths being given for collected specimens. This is thought to represent 80–90% of species present. The family with the greatest representation is the Labridae with 21 species. Only 31% of species appear to be shared with neighbouring Ducie Atoll, 390 km to the east, from where 138 species have been recorded, though this low percentage may simply reflect the greater recording effort undertaken at Henderson. Levels of endemism in the Pitcairn Group as a whole appear low (<2%).     

The Foraminifera of the Pitcairn Islands

Foraminifera were recovered from 18 samples collected in the Pitcairn Islands, 12 from Henderson Island (including the best and most comprehensive collections) and three each from Oeno Atoll and Pitcairn Island itself. Although both algae and sediment samples were collected, the living Foraminifera came, almost exclusively, from phytal (attached or clinging) habitats. Foraminifera in the sediment samples are mainly thanatocoenoses. The fauna is an exclusively calcareous, relatively low diversity assemblage, dominated by large soritids [Marginopora, Amphisorus, Sorites) and Amphistegina , all of which are ubiquitous throughout the tropical Pacific. These larger Foraminifera are usually accompanied by small miliolids in particular, as well as by small attached Foraminifera (discorbids and the like). Typical reefal Foraminifera are generally under-represented. So far, no endemic species have been found. Of more significance, perhaps, is the apparent absence of Calcarina , small rotaliids, elphidiids and agglutinating species, so common in the western Pacific islands. One sample of fossil Foraminifera was analysed, from a shelly sand (c. 30 m above present sea-level) on Henderson Island. Though, for the most part, like the Recent assemblages, this was characterized by Archaias , a soritid which was not found in any of the modern collections made by the 1991– 92 Expedition. This could either be a sampling artifact or refer to a real environmental change since the Pleistocene.     

Lessons from the Tōhoku tsunami: A model for island avifauna conservation prioritization

Earthquake‐generated tsunamis threaten coastal areas and low‐lying islands with sudden flooding. Although human hazards and infrastructure damage have been well documented for tsunamis in recent decades, the effects on wildlife communities rarely have been quantified. We describe a tsunami that hit the world's largest remaining tropical seabird rookery and estimate the effects of sudden flooding on 23 bird species nesting on Pacific islands more than 3,800 km from the epicenter. We used global positioning systems, tide gauge data, and satellite imagery to quantify characteristics of the Tōhoku earthquake‐generated tsunami (11 March 2011) and its inundation extent across four Hawaiian Islands. We estimated short‐term effects of sudden flooding to bird communities using spatially explicit data from Midway Atoll and Laysan Island, Hawai'i. We describe variation in species vulnerability based on breeding phenology, nesting habitat, and life history traits. The tsunami inundated 21%–100% of each island's area at Midway Atoll and Laysan Island. Procellariformes (albatrosses and petrels) chick and egg losses exceeded 258,500 at Midway Atoll while albatross chick losses at Laysan Island exceeded 21,400. The tsunami struck at night and during the peak of nesting for 14 colonial seabird species. Strongly philopatric Procellariformes were vulnerable to the tsunami. Nonmigratory, endemic, endangered Laysan Teal (Anas laysanensis) were sensitive to ecosystem effects such as habitat changes and carcass‐initiated epizootics of avian botulism, and its populations declined approximately 40% on both atolls post‐tsunami. Catastrophic flooding of Pacific islands occurs periodically not only from tsunamis, but also from storm surge and rainfall; with sea‐level rise, the frequency of sudden flooding events will likely increase. As invasive predators occupy habitat on higher elevation Hawaiian Islands and globally important avian populations are concentrated on low‐lying islands, additional conservation strategies may be warranted to increase resilience of island biodiversity encountering tsunamis and rising sea levels.     

Feral cats (Felis catus) as predators of hatchling green turtles (Chelonia mydas)

In many parts of the world feral animals have been reported to have severe effects on marine turtle hatchling production. In this study, green turtle ( Chelonia mydas ) hatchlings were shown to be an important component of the diet of the feral cat ( Felis catus ) on Aldabra Atoll, Seychelles, and feral cat activity in the coastal areas was found to be concentrated on the beaches used most intensively by turtles for nesting. The impact of the feral cat's predation on green turtle recruitment could not be determined. However, despite cat predation, the size of the Aldabran green turtle nesting population has increased considerably since human exploitation ceased.     

The breeding biology of the gadfly petrels Pterodroma spp. of the Pitcairn Islands: characteristics, population sizes and controls

This paper reports the breeding biology and nesting seasons of the gadfly petrels which nest on the four islands of the Pitcairn group, Pitcairn, Henderson, Oeno and Ducie. The species currently breeding are Murphy's petrel Pterodroma ultima , Kermadec petrel P. neglecta , Herald petrel P. heraldica and Henderson petrel P. atrata. Of these, Murphy's petrel is the most numerous; an estimated 250000 pairs bred on Ducie, which is probably the major breeding station of the species. Novel basic breeding data for Murphy's petrel are presented. Incubation spells, averaging 19.3 days, are exceptionally long for a petrel. Phoenix petrel P. alba appears to have ceased to breed on the Pitcairn Islands since the 1922 surveys of the Whitney Expedition. Nesting success was low on Henderson Island during the study. For all four breeding species, less than 20% of eggs laid yielded fledglings. Failure occurred at the early chick stage and observations indicated that it was due to predation by Pacific rats Rattus exulans. Although rats are present on Ducie, predation was apparently less severe there. The situation on Oeno may be intermediate. I consider how the populations of Henderson are maintained in the face of this intense predation. The Murphy's petrel population may be sustained by immigration from Ducie while the Herald and Henderson petrel populations could be undergoing a long-term decline on Henderson. It is not clear how the Kermadec petrel population is maintained. The conservation implications of these findings are discussed.     

The Pitcairn Islands, South Pacific Ocean: plate tectonic and climatic contexts

The remote Pitcairn Group in the South Pacific Ocean comprises a volcanic island (Pitcairn Island), two low coral atolls (Oeno, Ducie) and a raised coralline island (Henderson Island). The geological history of these islands, on anomalously thin oceanic lithosphere, is related to the development of two subparallel island chains (Oeno-Henderson-Ducie; Pitcairn) associated with intra-Pacific plate 'hotspot' activity; the surface manifestation of this activity has been partly determined by structural lineations in the plate inherited from past plate history. The climate of the Pitcairn Islands is determined by the position of the subtropical high pressure system and the South Pacific Convergence Zone. Variations in the strength of this atmospheric circulation system, measured by changes in the Southern Oscillation index of pressure difference, provide a partial explanation of the long-term variability of mean annual rainfall at Pitcairn Island. Knowledge of past climates in the Pitcairn Group remains speculative. Maps of the Pitcairn Islands and a report of climate at Henderson Island (2/91-1/92) are included in the paper.     

The phytogeographical affinities of the Pitcairn Islands – a model for south‐eastern Polynesia?

Aim To identify how the Pitcairn group relates biogeographically to the south‐eastern Polynesian region and if, as a subset of the regions flora, it can then be used as a model for biogeographical analyses. Location The Pitcairn group (25°4′ S, 130°06′ W) comprises four islands: Pitcairn, a relatively young, high volcanic Island; Henderson, an uplifted atoll, the uplift caused by the eruption of Pitcairn; and two atolls, Ducie and Oeno. The remote location, young age and range of island types found in the Pitcairn Island group makes the group ideal for the study of island biogeography and evolution. Methods A detailed literature survey was carried out and several data sets were compiled. Dispersal method, propagule number and range data were collected for each of the 114 species that occurs in the Pitcairn group, and environmental data was also gathered for islands in Polynesia. Analyses were carried out using non‐metric multidimensional scaling and clustering techniques. Results The flora of the Pitcairn Islands is derived from the flora of other island groups in the south‐eastern Polynesian region, notably those of the Austral, Society and Cook Islands. Species with a Pacific‐wide distribution dominate the overall Pitcairn group flora. However, each of the islands show different patterns; Pitcairn is dominated by species with Pacific, Polynesian and endemic distributions, with anemochory as the dominant dispersal method (39.5%); Henderson is also dominated by species with Pacific, Polynesian and endemic distributions, but zoochory is the dominant dispersal method (59.4); Oeno and Ducie are dominated by Pantropic species with hydrochory as the most common dispersal method (52.9% and 100%, respectively). Main conclusions ? Habitat availability is the most significant factor determining the composition and size of the flora. ? South‐east Polynesia is a valid biogeographical unit, and should include the Cook, Austral, Society, Marquesas, Gambier, Tuamotu and Pitcairn Islands with Rapa, but should exclude Easter Island, Tonga and Samoa. ? Regionalization schemes should take island type into consideration. ? The Pitcairn Island group can serve as a useful model for Pacific biogeographical analyses.     

Foraminifera in Samples Taken Mainly from Eniwetok Atoll in 1956*

SYNOPSIS. The foraminiferal distribution in samples from the Western Pacific collected in the summer of 1956 is presented, particularly those of the islets comprising Eniwetok Atoll. Some information is based upon samples taken shortly after atomic tests had been conducted. The distribution of foraminifera from northern islets where the tests were conducted is compared with that from the southern islets of Eniwetok Atoll. Collections from Eniwetok Atoll are compared with those made the same summer from other locations in the Southern and Western Pacific. A comparison is also made with the survey made by Cushman et al. of the Marshall Islands prior to bomb testing.     

The modern avifauna of the Pitcairn Islands

Excluding the gadfly petrels Pterodroma spp. and the resident landbirds, this paper details the present status of bird species seen during an expedition to the Pitcairn Islands (Ducie, Henderson, Oeno and Pitcairn) in 1991 and early 1992. Ten species were recorded in the Islands for the first time. Several Southern Ocean petrels were recorded, most in the midwinter period of June and July. The populations of Christmas Island shearwaters breeding on Oeno and Ducie laid in synchrony every 9–10 months. The species is one of few with such a sub-annual, synchronized regime. The majority of other seabirds had an annual breeding cycle, laying between May and October. Around one percent of the world population of the bristle-thighed curlew passes the non-breeding season in the Pitcairn Islands.     

Systematic review of the land snails of the Pitcairn Islands

The land snails (and semi-terrestrial molluscs) of the four islands that comprise the Pitcairn group are reviewed and the indigenous species illustrated. The strictly terrestrial molluscan faunas from the two atolls (Oeno and Ducie) are poor, like many other atolls in the Pacific. Each supports less than six species with wide geographical ranges. In contrast, the terrestrial molluscan fauna from Henderson Island, an uplifted atoll, is more diverse with at least 16 species belonging to seven families. Over half these taxa appear to be endemic, at least at the level of sub-species. Two species of semi-terrestrial molluscs have also been found on Henderson. Analyses of archaeological deposits in caves near the North Beach have revealed that at least a further six species of land snail formerly occurred on Henderson. The volcanic island of Pitcairn, the only island in the group still inhabited, supports the greatest number of terrestrial molluscs. Twenty-six species of land snail (and one semi-terrestrial pulmonate) were found living there during the recent expedition and a further three taxa were recognized amongst museum material. At least seven of these species are thought to be recent adventives and a further three are likely to have been prehistoric introductions. One Henderson (Georissa hendersoni) and three Pitcairn endemics (Pacificella filica, Sinployea pitcaimensis and Diastole tenuistriata) are formally described as new species. Some of the Pitcairn endemics occur in very restricted areas (less than a hectare) and it is important that measures should be taken to prevent the spread of invasive plants, such as rose-apple, that would threaten their survival.     

Climate variability, biological control and an insect pest outbreak on Australia’s Coral Sea islets: lessons for invertebrate conservation

Distant tropical coral sand islets in the Coral Sea have remained isolated from major human interference since their relatively recent inception. As a result they have highly impoverished faunas and floras consisting only of species capable of long distance dispersal. Despite this bias, they have established some degree of stability or equilibrium. In the 1990s, it became apparent that a scale insect, Pulvinaria urbicola Cockerell and at least one species of attendant ant, Tetramorium bicarinatum (Nylander) were undergoing a population explosion on two of these islets causing damage to Pisonia grandis, a tree important as a nesting site for sea birds. The same phenomenon as in the Coral Sea, (Coringa Herald group), was recorded about the same time in the Capricorn group of islets (Great Barrier Reef), on Palmyra Atoll and Samoa in the Pacific and in the Seychelles (Indian Ocean). Control measures, the application of systemic insecticides, poisoning of attendant ants and introduction of biological control agents were applied to some islands. Pest numbers subsequently fell, often within months, even where no control measures were applied, suggesting that the population decline was a natural phenomenon on some sites and not the result of recent invasions. It is suggested that climate variability is likely to be a contributing factor. Rising sea surface temperatures that reduce prey available to sea birds so causing a lower nitrogen input to soils during nesting activities, together with drier conditions, are likely to have put Pisonia trees under stress. Stressed trees mobilise nutrients making them more vulnerable to attack by herbivores. If climate variability is an indirect cause of the pest outbreak, it is important to carefully assess the benefits and disadvantages, both environmentally and economically, of any control measures, especially when biological control agents are concerned, the effects of which are irreversible.     

Do female green turtles (Chelonia mydas) exhibit reproductive seasonality in a year-round nesting rookery?

In circumglobal populations of sea turtles, little nesting activity occurs during cold seasons when the sand temperature on a nesting beach is inappropriate for successful egg incubation. However, it is not known whether reproductive seasonality also occurs in year-round nesting rookeries where the sand temperature may be suitable throughout the year. Therefore, we examined the hypothesis that female turtles exhibit reproductive seasonality even in a year-round nesting population. To determine whether the time of nesting of individuals fluctuates between successive nesting seasons, a year-round nesting rookery of green turtles Chelonia mydas at Huyong Island, Thailand, was patrolled on foot every night for 3190 consecutive days, and nesting females were identified using microchips and metal tags. The date of first nesting within a season for an individual (nesting date) was considered the nesting season of each individual. We identified 94 females and 463 nests (including 47 unidentified nests) during the survey. Nesting dates were distributed throughout the year. Nineteen turtles remigrated to the nesting beach, and the nesting dates of the remigrated females occurred in the same seasons. This indicates that females have a fixed individual nesting season even in a year-round nesting rookery. The year-round nesting of green turtles may be attributed to a wide variation in the nesting seasons of individuals. Satellite tracking revealed that the mean travelling duration of post-nesting migrations in this population was 13.5±6.1 days. The proximity of locations for reproduction and feeding may also play an important role in sustaining year-round nesting in this population.     

The composition and relationships of the marine molluscan fauna of the Pitcairn Islands

The recent expedition has doubled the number of marine molluscs known from the Pitcairn Islands. Over 80 taxa are recorded from Ducie and Pitcairn (both still poorly known), 240 from Oeno and 320 from Henderson. A total exceeding 400 taxa is now known from the group as a whole. Most of this increase results from a vastly improved knowledge of the small taxa that had been neglected in earlier surveys. Important faunal differences exist between the four islands in the group which are related to the different character of each island. These totals still underestimate the true diversities, but they provide data that are comparable in quality to those from adjacent regions. In this context the molluscan fauna from the Pitcairn Islands is seen to be impoverished when compared to those from islands further west. Most of the fauna is composed of widespread Indo-West Pacific species, but there are several taxa that have more restricted ranges centred on S.E. Polynesia. A few, including some undescribed taxa discovered on the expedition, appear to be endemic. Significantly, many of these are characterized by non-planktotrophic larval development. Comparison of the modern fauna from Henderson with the fossil fauna from the Pleistocene reef on its plateau reveals important differences. About 25% of the fossil molluscs are currently unknown from the group and about 5% appear to be undescribed. These high rates of turnover demonstrate that the faunas are temporally unstable.     

Colonization of the Hawaiian Archipelago via Johnston Atoll: a characterization of oceanographic transport corridors for pelagic larvae using computer simulation

Larval transport between Johnston Atoll and the Hawaiian Archipelago was examined using computer simulation and high-resolution ocean current data. The effects of pelagic larval duration and spawning seasonality on long-distance transport and local retention were examined using a Lagrangian, individual-based approach. Retention around Johnston Atoll appeared to be low, and there appeared to be seasonal effects on both retention and dispersal. Potential larval transport corridors between Johnston Atoll and the Hawaiian Archipelago were charted. One corridor connects Johnston Atoll with the middle portion of the Hawaiian Archipelago in the vicinity of French Frigate Shoals. Another corridor connects Johnston Atoll with the lower inhabited islands in the vicinity of Kauai. Transport appears to be related to the subtropical countercurrent and the Hawaiian Lee countercurrent, both located to the west of the archipelago and flowing to the east. A new analytical tool, termed CONREC–IRC is presented for the quantification of spatial patterns.     

Inter-island movements and population differentiation in a pelagic seabird

We used mark-resight data and amplified fragment length polymorphism (AFLP) markers to assess movements and gene flow between Central Pacific breeding colonies of the great frigatebird, Fregata minor. Of 715 adult frigatebirds marked on Tern Island and Johnston Atoll, 21.3% were resighted at other frigatebird colonies at least 582 km away. Mark-resight data indicated regular movement of males and females between Tern Island and Johnston Atoll (873 km apart), and less frequent movements to other islands; no birds marked on Tern or Johnston were seen on Christmas Island, but one was seen in the Philippines, 7627 km from where it was marked. Despite the regular occurrence of interisland movements, Bayesian analyses of AFLP data showed significant genetic differentiation between Tern Island and Johnston Atoll, and more pronounced differentiation between these two islands and the more distant Christmas Island. The AFLP profiles of three birds breeding on Tern Island fell within the profile-cluster typical for Christmas Island birds, both in a nonmetric multidimensional scaling analysis and in a population assignment test, suggesting dispersal events from Christmas Island to Tern Island. Several factors could explain the persistence of genetic structure despite frequent movements between colonies: many movements occurred during the nonbreeding season, many breeding-season movements did not involve mate-acquisition behaviours and individuals that do disperse may be selected against, as suggested by morphometric differences between colonies. The persistence of genetic structure among breeding colonies despite significant interisland movements suggests limits to the effectiveness of migration as a homogenizing force in this broadly distributed, extremely mobile species.     

Relationship between tropical cyclones and the distribution of sea turtle nesting grounds

Aim This study examines the relationship between the distribution of existing sea turtle nesting sites and historical patterns of tropical cyclone events to investigate whether cyclones influence the current distribution of sea turtle nesting sites. The results, together with information on predicted cyclone activity and other key environmental variables, will help in the identification and prediction of future nesting sites for sea turtles as changes to the coastal environment continue. Location Queensland, Australia. Methods We used data on the nesting distribution of seven populations of four species of sea turtles [green (Chelonia mydas), flatback (Natator depressus), hawksbill (Eretmochelys imbricata) and loggerhead (Caretta caretta)] from the eastern Queensland coast, and tropical cyclone track data from 1969 to 2007 to explore the relationship between (1) sea turtle nesting phenology and cyclone season, and (2) sea turtle nesting sites and cyclone distribution. Furthermore, using two green turtle populations as a case study, we investigated the relationship between cyclone disturbance and sea turtle reproductive output, nesting site and season. Bootstrapping was used to explore if current sea turtle nesting sites are located in areas with lower or higher cyclone frequency than areas where turtles are currently not nesting. Results All populations of sea turtles studied here were disturbed by cyclone activity during the study period. The exposure (frequency) of tropical cyclones that crossed each nesting site varied greatly among and within the various sea turtle populations. This was mainly a result of the spatial distribution of each population’s nesting sites. Bootstrapping indicated that nesting sites generally have experienced lower cyclone activity than other areas that are available for nesting. Main conclusions Tropical cyclones might have been sufficiently detrimental to sea turtle hatching success on the eastern Queensland coast that through a natural selection process turtles in this region are now nesting in areas with lower cyclone activity. Therefore, it is important that future studies that predict climate or range shifts for sea turtle nesting distributions consider future cyclone activity as one of the variables in their model.