Geology Reports⌕ Search

Geology topics

Research about American Samoa

Source-linked reports with geographic coverage including American Samoa.

At least 19 recordsLinked to original sources
USGS2024

Reproductive ecology and egg parasitism of the Samoan swallowtail butterfly

We investigated the reproductive ecology and effects of egg parasitism on the Samoan swallowtail butterfly ( Papilio godeffroyi ), which survives only on Tutuila Island, American Samoa, after having disappeared from the much larger islands of Upolu and Savai‘i in independent Samoa. During monthly surveys of its only known host plant, Micromelum minutum , across eight sites in 2013 and 2014, we collected eggs, eggshells, larvae, pupae, and pupal exuviae. Live specimens were reared under laboratory conditions to determine reproductive outcomes, developmental rates, and sex ratios, as well as parasitoid attack frequencies, brood sizes, and sex ratios. Sixty-six of 448 (14.7%) eggs produced larvae, 47 of which became adults. The sex ratio was approximately even overall and within each developmental stage. Eggs were slightly larger on individual host trees and in host tree stands that yielded more eggs per unit of foliage, indicating that ovipositing females responded to some features of host trees and stands. Eggs hatching female or male larvae were similar in size, and the sexes developed at similar rates. A newly described species of parasitoid wasp, Ooencyrtus pitosina (Encyrtidae), emerged from 73.6% of 382 butterfly eggs that failed to hatch in the laboratory (62.7% of 448 eggs overall). Forty-one other eggs contained dead parasitoid larvae. An additional, unidentified Ooencyrtus wasp species emerged from a single P. godeffroyi egg. No parasitoids were reared from P. godeffroyi larvae or pupae. Of 656 P. godeffroyi eggshells collected in the field and examined in the laboratory, 62.2% showed signs of having been parasitized by O. pitosina. There was no evidence that parasitism rates were density-dependent. O. pitosina brood sizes ranged from 1 to 5, with the sex ratio skewed toward females (2.40 F:1.00 M). Larger parasitoid broods were associated with slightly larger host eggs, indicating that female wasps may adjust brood size according to host egg size or that fewer wasp larvae are able to complete development in smaller eggs. Techniques used to rear both P. godeffroyi and O. pitosina in the laboratory could be applied to a captive-rear, wild-release program, which may facilitate reestablishment of the species in Samoa.

Tutuila Island↗
USGS2024

Volcanoes of American Samoa

Upu Amata (Introduction) O le Atu-Samoa o le tasi lenei o faʻasologa motu mauga mu i le Vasa Pasefika i Saute. O motu e pito i sasaʻe o nei faʻasologa mauga mu o le Atu-Samoa, o motu ia o Amerika Samoa. E tofu lava mauga mu taʻitasi o Amerika Samoa ma ona talaaga aemaise tulaga e tutupu e ono pa ai i le lumanai. O loʻo galulue faʻatasi le Ofisa o le U.S. Geological Survey (USGS) ma le National Oceanic and Atmospheric Administration Ofisa Vaʻai Tau i Pago Pago e faailoa i tagatanuʻu ma tagata asiasi o tulaga lamatia e ono tutupu. O loʻo faʻapupula atili atu iʻi auala na gaosia ai motu nei faʻapea auala o loʻo fesoasoani ai le vaega e mataʻituina mauga mū e puipui tagata ma mea-totino mai tulaga lamatia o mauga mū. American Samoa comprises the easternmost islands of a volcanic island chain in the South Pacific Ocean. Each island of American Samoa has a unique eruptive history and a possibility for future eruptions. The U.S. Geological Survey (USGS) collaborates with the Pago Pago office of the National Oceanic and Atmospheric Administration National Weather Service to inform residents and travelers of potential hazards. Insights are provided herein on how the islands formed and how volcano monitoring helps protect people and property from volcanic hazards.

Fact Sheet↗
USGS2023

Ooencyrtus pitosina (Hymenoptera: Encyrtidae)–A natural enemy of Samoan swallowtail butterfly Papilio godeffroyi (Lepidoptera: Papilionidae)

A new species of encyrtid wasp, Ooencyrtus pitosina Polaszek, Noyes & Fusu sp. n., (Hymenoptera: Encyrtidae: Encyrtinae) is described as a gregarious parasitoid in the eggs of the endemic Samoan swallowtail butterfly Papilio godeffroyi (Lepidoptera: Papilionidae) in the Samoan archipelago. It is described here because it is an important natural enemy of this butterfly, and to facilitate identification for future work with this parasitoid and its host.

Tutuila Island↗
USGS2023

Reproductive response of the Samoan swallowtail butterfly to variability in host plant and habitat characteristics

The Samoan swallowtail butterfly ( Papilio godeffroyi ) has become restricted to Tutuila Island, American Samoa. Factors driving its extirpation on other islands may be partly due to the availability and suitability of habitat, given the singular association we observed of P. godeffroyi with its host plant, Micromelum minutum. We expected that as a host plant specialist, P. godeffroyi might respond to variation in the physical traits and habitat context of M. minutum , which could help identify conservation opportunities throughout its present and former range. Because the ecology of P. godeffroyi is largely unknown, we conducted systematic surveys during 15 months in 2013 and 2014 on Tutuila to investigate its reproductive response to the physical and phenological variability of individual host trees and to the structural and geographical variability of the stands in which they occurred. We searched foliage for eggs, larvae, and pupae and monitored seasonal trends in herbivory and production of leaves, flowers, and fruits on 117 host trees in 8 rainforest stands, mostly within the National Park of American Samoa (NPSA), starting in March 2013 and ending in August 2014. We observed high variability in butterfly reproductive output between individual trees and stands, due largely to a strong negative relationship between leaf biomass (at both tree and stand levels) and oviposition density (number of eggs per foliar biomass) and frequency (number of eggs per survey). Distribution patterns of larvae and pupae were less distinct but generally followed trends in oviposition. Our findings indicate that the butterfly is reproducing widely across Tutuila and is likely to respond positively to management to increase the availability of small host trees in low-density stands. Thus, the species is a good candidate for conservation management focusing on habitat.

Tutuila Island↗
USGS2022

High-resolution observations of submarine groundwater discharge reveal the fine spatial and temporal scales of nutrient exposure on a coral reef: Faga'alu, AS

Submarine groundwater discharge (SGD) can deliver substantial nutrient and contaminant loads to nearshore coral reefs. Correctly scaling SGD rates from a point source to a reef is generally a linear process involving simplified assumptions on the hydrogeology, bathymetry, and nearshore hydrodynamics that are essential to properly assess SGD scale and impact to individual coral heads. Here, we apply high-resolution SGD techniques to provide information at the scale of individual coral heads in Faga’alu Bay, American Samoa, where focused SGD delivers a plume of freshened and nutrient-rich water directly to the adjacent coral reef. Unoccupied Aerial System-based measurements were used to acquire remotely sensed, calibrated, high-resolution thermal infrared imagery that were coupled with traditional in-situ SGD observations. This approach permits a detailed assessment of SGD and associated nutrient loadings to individual coral heads as a function of time and enables a more realistic method to quantify SGD impact.

Faga’alu Bay↗
USGS2022

Status of landbirds in the National Park of American Samoa

The National Park of American Samoa (NPSA) was surveyed in 2011 and 2018 using point-transect distance sampling to estimate trends in landbird distribution, composition, population density, and abundance. Surveys were conducted within the Ta‘ū Unit and Tutuila Unit, each on separate islands of American Samoa. We detected a total of 14 species during surveys and there were sufficient detections of seven species to allow for density estimation and abundance within each unit. We assessed differences in density between surveys with a two-sample z -test and found significant declines of Blue-crowned Lorikeets ( Vini australis ) in the Ta‘ū Unit, and of Samoan Starlings ( Aplonis atrifusca ) in the Tutuila Unit. Density estimates of the Crimson-crowned Fruit Dove ( Ptilinopus porphyraceus ), Pacific Kingfisher ( Todiramphus sacer ), Polynesian Wattled Honeyeater ( Foulehaio carunculatus ), and Samoan Starling (in the Ta‘ū Unit) were also lower in 2018 than 2011, but differences were inconclusive because of relatively large variance estimates. Densities of the Polynesian Starling ( Aplonis tabuensis ) and Pacific Imperial Pigeon ( Ducula pacifica ) in the Ta‘ū Unit were higher in 2018 than 2011, but differences were similarly inconclusive. Lower 2018 densities could be due to Tropical Cyclone Gita that struck the islands just four months before the surveys. We provide indices of relative occurrence and abundance for the remaining seven species detected, which include the Many-colored Fruit Dove ( Ptilinopus perousii ) and the rarely detected Spotless Crake ( Zapornia tabuensis )—both of which are species of concern in American Samoa.

National Park of American Samoa, Ofu-Olosega, Ta'u↗
USGS2021

Population density, distribution, and trends of landbirds in the National Park of American Samoa, Ta‘ū and Tutuila Units (2011–2018)

The National Park of American Samoa (NPSA) was surveyed for landbirds from June through July, 2018. Surveys were conducted using point-transect distance sampling methods to estimate bird densities. This information provides the second datum in the time-series of landbird monitoring for long-term trends in landbird distribution, density, and abundance within NPSA. The Ta‘ū Unit and Tutuila Unit, each on separate islands, were first surveyed in 2011 and we tested for changes in densities between each survey year.

American Samoa↗
USGS2018

Population vulnerability to tsunami hazards informed by previous and projected disasters: A case study of American Samoa

Population vulnerability from tsunamis is a function of the number and location of individuals in hazard zones and their ability to reach safety before wave arrival. Previous tsunami disasters can provide insight on likely evacuation behavior, but post-disaster assessments have not been used extensively in evacuation modeling. We demonstrate the utility of post-disaster assessments in pedestrian evacuation modeling for tsunami hazards and use the US territory of American Samoa as our case study. We model pedestrian travel times out of tsunami inundation zones recreated for the 2009 M w 8.1 Samoa earthquake, as well as for a probable maximum tsunami zone for future threats. Modeling assumptions are guided by fatality trends and observations of 2009 evacuation behavior, including insights on departure delays, environmental cues, transportation mode, and demographic characteristics. Differences in actual fatalities from the 2009 disaster and modeled population vulnerability suggest that a single set of estimated travel times to safety does not fully characterize evacuation potential of a dispersed, at-risk population. Efforts to prepare coastal communities in American Samoa for future tsunamis may be challenging given substantial differences in wave characteristics and evacuation potential of the probable maximum hazard compared to the 2009 event.

American Samoa↗
USGS2016

Benthic habitat map of U.S. Coral Reef Task Force Faga‘alu Bay priority study area, Tutuila, American Samoa

The coral reef in Faga‘alu Bay, Tutuila, American Samoa, has suffered numerous natural and anthropogenic stresses. Areas once dominated by live coral are now mostly rubble surfaces covered with turf or macroalgae. In an effort to improve the health and resilience of the coral reef system, the U.S. Coral Reef Task Force selected Faga‘alu Bay as a priority study area. To support these efforts, the U.S. Geological Survey mapped nearly 1 km 2 of seafloor to depths of about 60 m. Unconsolidated sediment (predominantly sand) constitutes slightly greater than 50 percent of the seafloor in the mapped area; reef and other hardbottom potentially available for coral recruitment constitute nearly 50 percent of the mapped area. Of this potentially available hardbottom, only slightly greater than 37 percent is covered with at least 10 percent coral, which is fairly evenly distributed between the reef flat, fore reef, and offshore bank/shelf.

American Samoa↗
USGS2012

Seismic hazard of American Samoa and neighboring South Pacific Islands--methods, data, parameters, and results

American Samoa and the neighboring islands of the South Pacific lie near active tectonic-plate boundaries that host many large earthquakes which can result in strong earthquake shaking and tsunamis. To mitigate earthquake risks from future ground shaking, the Federal Emergency Management Agency requested that the U.S. Geological Survey prepare seismic hazard maps that can be applied in building-design criteria. This Open-File Report describes the data, methods, and parameters used to calculate the seismic shaking hazard as well as the output hazard maps, curves, and deaggregation (disaggregation) information needed for building design. Spectral acceleration hazard for 1 Hertz having a 2-percent probability of exceedance on a firm rock site condition (Vs30=760 meters per second) is 0.12 acceleration of gravity (1 second, 1 Hertz) and 0.32 acceleration of gravity (0.2 seconds, 5 Hertz) on American Samoa, 0.72 acceleration of gravity (1 Hertz) and 2.54 acceleration of gravity (5 Hertz) on Tonga, 0.15 acceleration of gravity (1 Hertz) and 0.55 acceleration of gravity (5 Hertz) on Fiji, and 0.89 acceleration of gravity (1 Hertz) and 2.77 acceleration of gravity (5 Hertz) on the Vanuatu Islands.

South Pacific Islands↗
USGS2010

Trip report: pilot study of factors linking watershed function and coastal ecosystem health in American Samoa

Coral reef resources in the territory of American Samoa face significant problems from overfishing, non-point source pollution, global warming, and continuing population growth and development. The islands are still relatively isolated relative to other parts of the Pacific and have managed to avoid some of the more devastating invasive species that have reached other archipelagoes. As a result, there are opportunities for collaborative and integrative research and monitoring programs to help restore and maintain biodiversity and functioning natural ecosystem in the archipelago. We found that the “Ridge to Reef” paradigm already exists in American Samoa, with a high degree of interagency cooperation and efficient use of limited resources already taking place in the Territory. USGS may be able to make contributions as a partner organization in the Coral Reef Advisory Group (CRAG) through deployment of sediment monitoring instrumentation to supplement stream monitoring by the American Samoa Environmental Protection Agency, by providing high resolution vegetation and land-use maps of main islands, by providing additional support to the American Samoa Department of Marine and Wildlife Resources and the National Park Service for monitoring of invasive species, by working with members of CRAG to initiate sediment transport studies on Samoan reefs, and by developing new projects on the effects of bacterial contamination and pollutants on coral reef physiology and demography.

Open-File Report↗
USGS2009

Porites randalli: A new coral species (Scleractinia, Poritidae) from American Samoa

A new species of scleractinian coral, Porites randalli spec. nov. (Scleractinia, Poritidae), previously known as Porites sp. 2, is described from American Samoa. P. randalli typically forms small pale green colonies that are usually Porites randalli spec. nov. is an example of cryptic diversity; it is a small coral that at first glance can be overlooked or mistaken for a young colony of other species.

American Samoa↗
USGS2009

Temporal variability in chlorophyll fluorescence of back-reef corals in Ofu, American Samoa

Change in the yield of chlorophyll a fluorescence is a common indicator of thermal stress in corals. The present study reports temporal variability in quantum yield measurements for 10 coral species in Ofu, American Samoa—a place known to experience elevated and variable seawater temperatures. In winter, the zooxanthellae generally had higher dark-adapted maximum quantum yield ( F v /F m ), higher light-adapted effective quantum yield (Δ F / F′ m ), and lower relative electron transport rates (rETR) than in the summer. Temporal changes appeared unrelated to the expected bleaching sensitivity of corals. All species surveyed, with the exception of Montipora grisea , demonstrated significant temporal changes in the three fluorescence parameters. Fluorescence responses were influenced by the microhabitat—temporal differences in fluorescence parameters were usually observed in the habitat with a more variable temperature regime (pool 300), while differences in F v /F m between species were observed only in the more environmentally stable habitat (pool 400). Such species-specific responses and microhabitat variability should be considered when attempting to determine whether observed i n situ changes are normal seasonal changes or early signs of bleaching.

American Samoa↗
USGS2008

Overgrowth of fungi (endolithic hypermycosis) associated with multifocal to diffuse distinct amorphous dark discoloration of corals in the Indo-Pacific

Coral disease surveys in American Samoa and Hawai‘i revealed colonies with a distinct dark discoloration affecting 20–60% of the colony surface (Fig. 1 a). In some cases, tissue loss with algal infiltration was present within discolored areas. On microscopy, these lesions had marked overgrowth of the coral skeleton and tissues with septate branching structures that stained positive with Grocott’s Methenamine Silver (fungal hyphae) accompanied by necrosis and fragmentation of coral tissues (Fig. 1 b). We have observed this condition grossly and microscopically in Pavona varians , Psammocora nierstraszi , and Montipora sp. in American Samoa and in Pavona maldivensis and P. varians in Hawai‘i. This condition resembles Dark Spots Disease from the Caribbean (Solano et al. 1993 ) that also shows endolithic hypermycosis (Galloway et al. 2007 ), suggesting that the association between dark discoloration of corals and overgrowth of endolithic fungi may be common (Western Atlantic, Indo-Pacific). Based on gross and microscopic morphology, tissue atrophy may precede overgrowth of endolithic fungi, but this awaits confirmation through systematic studies that monitor the development of lesions over time (pathogenesis). Using standardized terminology (Work and Aeby 2006 ) to describe lesions facilitates regional comparisons of coral disease.

Hawai'i↗
USGS2008

Distribution and morphology of growth anomalies in Acropora from the Indo-Pacific

We assessed the distribution and prevalence of growth anomalies (GAs) in Acropora from French Frigate Shoals (Hawaii, USA), Johnston Atoll and Tutuila (American Samoa), developed a nomenclature for gross morphology, characterized GAs at the cellular level and obtained preliminary indices of their spatial patterns and progression within coral colonies. Acropora GAs were found in all 3 regions, but the distribution, variety and prevalence of Acropora GAs was highest in American Samoa. GAs were grouped into 7 gross morphologies (exophytic, bosselated, crateriform, nodular, vermiform, fimbriate or annular). On histology, GAs consisted of hyperplastic basal body wall (calicodermis, mesoglea and gastrodermis apposed to skeleton) with 3 distinct patterns of necrosis. There was no evidence of anaplasia or mitotic figures (common but not necessarily required morphologic indicators of neoplasia). Compared to normal tissues, GAs had significantly fewer polyps, zooxanthellae within the gastrodermis of the coenenchyme, mesenterial filaments and gonads but significantly more necrosis. On 2 colonies with GAs monitored at 2 points over 11 mo, numbers of GAs per colony increased from 0.9 to 3 times the original number seen, and significant clustering of GAs occurred within colonies. The evidence of GAs being true neoplasias (tumors) is mixed, so a cautionary approach is urged in use of morphologic terminology.

Hawai'i↗
USGS2007

Identifying nutrient sources to three lagoons at Ofu and Olosega, American Samoa using δ15N of benthic macroalgae

Degradation of nearshore habitats is a serious problem in some areas of American Samoa, such as in Pago Pago Harbor on Tutuila Island, and is a smaller but chronic problem in other areas. Sedimentation, pollution, nutrient enrichment from surface runoff or groundwater, and trampling are the major factors causing the changes ( Peshut and Brooks, 2005 ). On the outer islands of Ofu and Olosega (Manu’a Islands; Fig. 1 ), there is an interesting contrast between relatively pristine lagoon habitats not far from comparatively degraded lagoon habitats. To’aga lagoon on the southeast side of Ofu Island ( Fig. 1 ) has clear waters, a high diversity of corals and fishes, no human habitations, and an undeveloped watershed with no streams. To’aga lagoon is within the boundaries of the National Park of American Samoa and is the site of long-term research on coral reef resilience and global climate change. Only 3 km to the east of To’aga is a degraded lagoon that fronts Olosega Village. The Olosega lagoon is similar in size but has significantly less live coral than To’aga, and blooms of filamentous algae have been reported to cover the Olosega lagoon/reef flat bottom (unpublished data, PC; Fig. 2 ). The islands are influenced by the same regional-scale and biogeochemical regimes, and both islands are remnants of a volcanic caldera ( Craig, 2005 ). Thus, local factors operating on the scale of a kilometer or less are thought to be driving the differences observed between lagoons. Land disturbance is limited to a road linking the villages, the clearing of vegetation for buildings, and two village dump sites located on the narrow strip of land between the steep slopes of the islands and the shoreline; there is no industry or associated pollution on either island. Cesspools are used for sewage disposal. Nutrient enrichment (from cesspools) of groundwater and the lagoon, as well as trampling during gleaning of reef organisms, are possible factors affecting the spatial relief and benthic composition of the lagoons. A pristine lagoon site (To’aga) and two that may be influenced by adjacent human populations (Ofu and Olosega Villages) were selected for study.

American Samoa↗
USGS2004

A new coccidian parasite, Isospora samoaensis , from the Wattled Honeyeater ( Foulehaio carunculata ) from American Samoa

A new species of Isospora is described from the feces of the wattled honeyeater, Foulehaio carunculata from American Samoa. Numerous oocysts of similar morphology were found in a single adult wattled honeyeater. Sporulated oocysts are ovoid, 28.9 × 26.1 (25-32 × 23-30) µm, with a smooth, colorless, bilayered wall; the inner wall is slightly thicker and darker than the outer wall. The average shape index is 1.1. No micropyle or oocyst residuum are present but the oocyst contains one or two ovoid polar granules. Sporocysts are ovoid, 17.1 × 10.9 (16-18 × 10-11) µm with a smooth single layered wall and an average shape index of 1.6. The Stieda body is broad, dome-like with a rather rectangular-shaped substieda body. Within the sporocyst is a large amorphous residuum composed of coarse granules and 4 randomly arranged, sausage-shaped sporozoites with a subspherical, posterior refractile body and a centrally located nucleus.

Acta Protozoologica↗