Rose Atoll Research Articles

Abundance, production, and migrations of nesting green turtles at Rose Atoll, American Samoa, a regionally important rookery in the Central South Pacific Ocean

Sea turtles are a taxon of conservation concern and are highly migratory, exposing them to a variety of threats (e.g., fisheries bycatch, direct harvest) across their lifetime. Understanding the abundance of nesting females, hatchling production, and migratory movements - three of the most basic biological data needs for this species group - is imperative for population assessment. This study summarizes novel data most relevant to population assessments of the endangered central south Pacific (CSP) green turtle (Chelonia mydas) population, determined from annual rapid assessment surveys (mean survey duration=7.6 days year-1, n=61 survey days over 8 nesting seasons) and satellite telemetry at Rose Atoll, American Samoa, from 2012 to 2019. A minimum of 138 unique females nested in the Rose Atoll National Wildlife Refuge (RANWR) over the study period with 218 total females observed. Satellite tracks of post-nesting females suggest Fiji (n=33/48, 70.2%) is the primary foraging ground for turtles nesting at RANWR, though other areas throughout the south Pacific Ocean are also important. Limited data suggest hatchling production was high (average hatching success=92.3%) and nest temperature data collected from 2017-2019 suggest primary sex ratios were likely balanced during this time. These are positive signs for the resilience of this nesting population, but climate change poses threats to RANWR and other low-lying tropical islands throughout the central south Pacific, as nesting areas are potentially exposed to beach erosion, tidal inundations, and increasing temperatures leading to sex bias and embryonic death.

Distribution and structure of deep-sea demersal fish assemblages across the central and western Pacific Ocean using data from undersea imagery

Demersal deep-sea fish assemblages from islands and seamounts are poorly described, even in the Hawaiian archipelago. Knowledge across all depths, in similar settings, is even sparser for other archipelagos in the central and western Pacific. However, recent remotely operated vehicle (ROV) explorations and archived video from human-occupied submersible dives conducted by the Hawai`i Undersea Research Laboratory (HURL) provide an opportunity to explore the structure of these assemblages. Here we describe demersal fish assemblages across the central and western Pacific, including in four Marine National Monuments, and examine the relationship of the assemblages to depth and environmental conditions. We used data collected from 227 underwater vehicle dives resulting in the identification of 24,837 individuals belonging to 89 families and 175 genera. The most frequently occurring genera at depths of 250-500 m were Epigonus, Setarches, Polymixia, and Antigonia, between 500-1000 m were Chlorophthalmus, Aldrovandia, and Neocyttus, and between 1000-3000 m were Synaphobranchus, Kumba, Halosaurus, Ilyophis, and Ipnops. There are strong changes in the fish assemblages with depth and region, and assemblages become more similar between regions with greater depth. Depth and region explained the most variance in assemblage structure followed by seafloor particulate organic carbon flux (a food supply proxy), concentrations of dissolved oxygen, and salinity. The Line Islands and Tokelau Ridge had the highest values of seafloor particulate organic carbon flux for all depth zones investigated (250-3000 m) and the highest abundance of fishes at 250-500 m and 500-1000 m, respectively. Taxon accumulation curves indicated that diversity at the genus level within all regions and depth bins (except 1000-2000 m and 2000-3000 m) had not been reached with the existing sampling effort. However, when combining samples from all regions, diversity generally appeared to decrease with depth. Overall, this study demonstrates that there are significant regional differences in the composition of the deep-sea fish fauna as well as differences across depth. Such distribution patterns suggest that the four Marine National Monuments (Papahānaumokuākea, Marianas Trench, Pacific Remote Islands, and Rose Atoll Marine National Monuments, encompassing an area of 3,063,223 km2) are not replicates of diversity, but complementary components of the regional fauna.

Diversity, habitat associations and stock structure of odontocete cetaceans in the waters of American Samoa, 2003-06

Little is known about the species composition, distribution, abundance or stock structure of odontocetes in the central and western tropical Pacific Ocean, including those inhabiting the US Exclusive Economic Zone (EEZ) waters of American Samoa. While some information on species presence in this region has been gleaned from anecdotal sightings and whaling and stranding records, odontocete diversity in the waters of American Samoa has never been formally investigated. This lack of information precludes efforts to determine the sustainability of cetacean populations within US EEZ waters. This paper reports on the first dedicated surveys to document the presence and distribution of odontocete cetaceans in the waters of American Samoa. A series of small-boat photo-identification and biopsy surveys for cetaceans were conducted in the nearshore waters of Tutuila during 2003-06. In addition, ship-based visual surveys were conducted in the waters surrounding the Manu‘a Islands, Rose Atoll and Swains Island in summer 2006. A total of 58 groups of odontocete cetaceans were encountered during both small-boat and ship-based surveys: spinner dolphins (Stenella longirostris, n=34), rough-toothed dolphins (Steno bredanensis, n=10), sperm whales (Physeter macrocephalus, n=3), false killer whales (Pseudorca crassidens, n=5), bottlenose dolphins (Tursiops truncatus., n=1), dwarf sperm whales (Kogia sima, n=1), short-finned pilot whales (Globicephala macrorhynchus, n=1), and three groups of unidentified odontocetes. Photographs were analysed for quality and individuals with distinctive markings were selected for entry into a photo-identification catalogue. The resultant catalogue included 46 spinner dolphins, 41 rough-toothed dolphins, 2 bottlenose dolphins, 5 false killer whales, 4 pilot whales, 1 dwarf sperm whale and 4 sperm whales. Thirteen spinner dolphins and 14 rough-toothed dolphins were sighted in multiple years. To investigate stock structure, spinner dolphin genetic data were used to compare mitochondrial control region genetic diversity and allele frequencies between American Samoa and the Hawaiian Islands. American Samoa had a higher genetic diversity, and populations at the two locations were genetically distinct (FST = 0.21). The high diversity at American Samoa indicates that spinner dolphins at this location are not reproductively isolated, but the data do not rule out the possibility that these dolphins may be demographically isolated on ecological timescales.

Marine Benthic Macroalgae Of A Small Uninhabited South Pacific Atoll (Rose Atoll, American Samoa)

Forty-five species of marine benthic macroalgae were identified from the coral reefs of Rose Atoll, American Samoa (Rose Atoll Marine National Monument). The algal collections were made during the February 2002, February 2004, March 2006, and March 2008 Pacific Reef Assessment and Monitoring Program (Pacific RAMP) under the auspices of the U.S. National Oceanic & Atmospheric Administration (NOAA), Pacific Islands Fisheries Science Center (PIFSC), Coral Reef Ecosystem Division (CRED). The collections included 6 species of Cyanobacteria, 14 species of red algae, 4 species of brown algae, and 21 species of green algae. Nine species represented new records for the Samoan Archipelago (American Samoa and Samoa). Based on their occurrences, eight species of green algae were considered most broadly distributed among the stations during all four expedition years. The top three broadly distributed species were Halimeda taenicola, Halimeda micronesica, and Caulerpa cupressoides.

Baseline Assessment of Net Calcium Carbonate Accretion Rates on U.S. Pacific Reefs.

This paper presents a comprehensive quantitative baseline assessment of in situ net calcium carbonate accretion rates (g CaCO3 cm-2 yr-1) of early successional recruitment communities on Calcification Accretion Unit (CAU) plates deployed on coral reefs at 78 discrete sites, across 11 islands in the central and south Pacific Oceans. Accretion rates varied substantially within and between islands, reef zones, levels of wave exposure, and island geomorphology. For forereef sites, mean accretion rates were the highest at Rose Atoll, Jarvis, and Swains Islands, and the lowest at Johnston Atoll and Tutuila. A comparison between reef zones showed higher accretion rates on forereefs compared to lagoon sites; mean accretion rates were also higher on windward than leeward sites but only for a subset of islands. High levels of spatial variability in net carbonate accretion rates reported herein draw attention to the heterogeneity of the community assemblages. Percent cover of key early successional taxa on CAU plates did not reflect that of the mature communities present on surrounding benthos, possibly due to the short deployment period (2 years) of the experimental units. Yet, net CaCO3 accretion rates were positively correlated with crustose coralline algae (CCA) percent cover on the surrounding benthos and on the CAU plates, which on average represented >70% of the accreted material. For foreeefs and lagoon sites combined CaCO3 accretion rates were statistically correlated with total alkalinity and Chlorophyll-a; a GAM analysis indicated that SiOH and Halimeda were the best predictor variables of accretion rates on lagoon sites, and total alkalinity and Chlorophyll-a for forereef sites, demonstrating the utility of CAUs as a tool to monitor changes in reef accretion rates as they relate to ocean acidification. This study underscores the pivotal role CCA play as a key benthic component and supporting actively calcifying reefs; high Mg-calcite exoskeletons makes CCA extremely susceptible changes in ocean water pH, emphasizing the far-reaching threat that ocean acidification poses to the ecological function and persistence of coral reefs worldwide.

Humpback whale (Megaptera novaeangliae) song occurrence at American Samoa in long-term passive acoustic recordings, 2008–2009

Humpback whales (Megaptera novaeangliae) wintering in American Samoan waters belong to the endangered Oceania subpopulation (IUCN Red List), but survey effort in this region has been relatively limited. Humpback whale seasonal occurrence was assessed using long-term passive acoustic recordings from March 2008 to July 2009 at Tutuila, the most populous island of American Samoa, and October 2008 to September 2009 at the remote Rose Atoll, 240 km to the east. Humpback whale song occurred from mid-July through November at both locations. For days with song, the mean number of recordings per day with song was significantly greater at Tutuila than at Rose Atoll. Song incidence at Rose Atoll peaked at 82% of recordings/day in late September 2008, and at Tutuila 70-100% of recordings contained song in late August through early September 2009, when recording ceased. Song incidence at Rose Atoll decreased at midday and increased at midnight, whereas there was no significant diurnal pattern at Tutuila. The lower overall incidence of song and its episodic nature at Rose Atoll suggest lower densities of whales traveling through the likely smaller detection area there, whereas greater song incidence and longer peak periods at Tutuila suggest greater whale densities and longer residence times.

Passive acoustic monitoring of vessel presence at Rose Atoll and the National Park of American Samoa

American Samoa is in the process of evaluating the development of a network of marine protected areas (MPAs) to preserve coral reef environments and to prevent the decline of fish populations. Two long-standing MPAs in American Samoa are Rose Atoll Marine National Monument (RAMNM) and coastal marine regions within the National Park of American Samoa (NPSA) system. NPSA includes areas on the populated island of Tutuila, while RAMNM is approximately 130 miles away from the nearest population. Both are protected marine reserves where commercial and public recreational fishing are restricted, although the size and remoteness of the locations create a challenging task for observation and enforcement. A growing management concern over the decline of large fishes and possible illegal fishing has prompted interest in vessel incidence within the two MPAs. We gathered evidence of vessel presence with the use of long-term, autonomous passive acoustic monitoring within the two MPAs. Here we present results of vessel detection within acoustic recordings collected 2009–2010 at RAMNM and 2006–2007 and 2008–2009 at the NPSA Tutuila location. Results from this study highlight the patterns and seasonality of vessel incidence and provide managers with information to assist enforcement.

Spatio-temporal variability in macroalgal assemblages of American Samoa

Tribollet A.D., Schils T. and Vroom P.S. 2010. Spatio-temporal variability in macroalgal assemblages of American Samoa. Phycologia 49: 574–591. DOI: 10.2216/09-63.1Spatial and temporal variability of relative abundance of macroalgae at the genus and functional group levels was examined at 14 m depth across the six islands of American Samoa between 2004 and 2006. Diversity of common macroalgae was high with 54 taxa (50 genera and four algal functional groups) identified from sampled quadrats. The highest taxon richness (33) was found at the largest island, Tutuila. Crustose coralline algae, mixed turf algal assemblages, and the chlorophyte Halimeda were ubiquitous across all islands. Other algal genera or functional groups were, however, representative of specific areas. For instance, the chlorophyte Microdictyon was only found at Rose Atoll and Swains Island (the only low open-ocean atoll systems examined). Similarly, the siphonous green alga Rhipilia only occurred at Swains Island, where it was very abundant. Multivariate analyses revealed that macroalgal assemblages differed significantly among sites around a single island and among islands. All islands were significantly different from each other with Swains Islands having the most important dissimilarity with other islands. We hypothesize that Swains Island differs from the other islands because of its geographic isolation. Statistical analyses also highlighted significant differences in the relative abundance of macroalgae between years. The interaction between spatial and temporal variability was also significant, indicating that temporal changes in algal assemblages are island dependant, and spatial differences among islands are a function of the year in which surveys were conducted. Changes in algal assemblages between the 2004 and 2006 surveys were apparent for all islands except Swains Island and Tutuila, probably because of intense cyclone activity in the region during 2005 (Cyclone Olaf). This study contributes to the overall understanding of coral reef diversity and function in American Samoa and forms a baseline for future algal monitoring surveys.

Characterization of Coral Communities at Rose Atoll, American Samoa

Atoll Research Bulletin, no. 586. Characterization of Coral Communities at Rose Atoll, American Samoa.

Basalts from Rose Atoll, American Samoa

Three specimens of lava float collected in 1939 from Rose Atoll consist of three distinct basalt types: holocrystalline olivine tholeiite, coarse vesicular picrite basalt and olivine-poor transitional basalt; the tholeiite contains coarser, late-stage segregations with a glassy, silicic mesostasis. In mineralogy and chemistry these basalts most closely resemble Ta'u Group lavas of the neighbouring Manu'a Islands. Differences exist that do not suggest their transport to Rose Atoll, even though no in situ basalts are known there. Incompatible primitive mantle-normalized trace element plots show strong depletion in K and Sr and enrichment in U, Pb and La. In Ba/Nb versus La/Nb plots Rose basalts lie between normal mid-ocean ridge basalt (N-MORB) and low 87Sr/86Sr oceanic island basalt (OIB) fields. They lie outside many plume-related OIB fields, including plume-related Samoan basalts. Trace element ratios for the Rose samples show little correspondence with end member MORBs and OIBs. This, and temporal and geographic plume reconstructions, indicate that the Rose basalts are derived from melting of unusual or mixed lithospheric sources. They seem unrelated to the main phases of Samoan plume activity, now located at Vailulu'u Seamount.

Migrations of green turtles in the central South Pacific

Migrations of seven post-nesting green turtles at Rose Atoll (American Samoa) were tracked by satellite transmitters in 1993–1995. Most turtles migrated 1600 km to foraging areas in Fiji and occupied home ranges averaging 27 km 2. Additional tag recaptures from other studies indicate a common pattern of turtle movement in the central South Pacific region. In total, the 26 recaptures of primarily post-nesting turtles from French Polynesia, American Samoa, and Cook Islands showed a similar course of direction and destination: 96% migrated westward after nesting, with 58% going specifically to Fiji. We propose that this pattern reflects the lower availability of turtle food east of Fiji where most islands are small, steep and have limited areas suitable for seagrass or algal growth. In contrast, Fiji's extensive pastures of seagrass and algae appear to be a significant resource for many green turtles in the region. These turtles apparently spend most of their adult life in Fijian waters, taking only brief migrations to other islands to nest.

NEST-SITE CHARACTERISTICS OF RED-TAILED TROPICBIRDS ON ROSE ATOLL, AMERICAN SAMOA

We examined nest sites of Red-tailed Tropicbirds (Phaethon rubricauda) on Rose Island of the Rose Atoll National Wildlife Refuge, American Samoa, to determine habitat features important for nest-site selection of this species. We quantified habitat characteristics at 27 nest sites and at 27 random sites during September 1991. All nests were located under beach heliotrope (Messerschmidia argentea) shrubs or pisonia (Pisonia grandis) trees. Nest sites were placed farther under the nest shrub, had more stems in the nest space, and greater percent shade cover than random sites. Nest sites averaged 24.9 m from their nearest neighbor, ≥20 m greater than has been reported elsewhere for this colonial species. We suggest that an overpopulation of Polynesian rats (Rattus exelans) may have influenced nest-site selection by Red-tailed Tropicbirds on Rose Island.

Population size and structure of giant clams at Rose Atoll, an important refuge in the Samoan Archipelago

Rose Atoll is an important refuge for giant clams (Tridacna maxima) that have been heavily exploited elsewhere in Samoa. During an extensive survey of six islands in the archipelago (50.5 ha surveyed in 420 transects), 97% of a total of 2853 clams were recorded at the atoll (42% of area surveyed). Clam densities were highest in the atoll lagoon, especially around the bases of the pinnacles (mean density=8870 ha-1). Estimated population size for the small atoll (615 ha) was approximately 27800 clams. Twenty four percent of the population consisted of mature clams (?12 cm), 70% of which occupied the pinnacles and shallow lagoon habitat. Estimated mortality was low (Z=0.3) and primarily due to natural mortality (M=0.3). Maximum recorded size (L max ) and asymptotic mean size (L ∞) were 25.0 cm and 27.8 cm respectively.

JIN SHIANG FA CASE STUDY: WHAT COULD HAVE BEEN DONE?

ABSTRACT On October 14, 1993, the fishing vessel Jin Shiang Fa grounded at Rose Atoll with 100,000 gallons of fuel on board. Rose Atoll is one of the most pristine atolls in the world. Due to its extreme remoteness, responders had very limited options and were unable to recover any fuel. Six weeks after the grounding, a salvage vessel arrived on scene and found the Jin Shiang Fa completely destroyed by a storm, and a third of the reef dead. No response expense was spared. Yet no fuel was ever recovered. When traditional response methods are not feasible, alternative options should be considered.

Rose Atoll: an annotated bibliography

Rose Atoll: an annotated bibliography

Stable Isotope Profiles of Tridacna maxima as Environmental Indicators

To better understand the relationship between stable isotopic composition (13C/2C, 1801160) and symbiosis, ontogeny, and environment, detailed isotopic profiles were constructed for specimens of the giant clam Tridacna maxima and an encrusting bivalve (Chama cf savignyi) and coral (Montastrea spp.). Specimens were collected alive from depths of 1 m and 9 m within Rose Atoll (14?31' S, 168?1O' W) in the southwestPacific. Shells were sampled sequentially on the external shell layer along radial sections extending from the umbo to the outer shell margin, recording growth throughout the ontogeny of the organisms. Juvenile portions of the tridacnids accurately record seasonal water temperature fluctuations at the atoll. The amplitude of the 8QO profiles in tridacnids is greater in shallow specimens due to greater environmental variability. These shallower specimens have lower 8180 and 813C values compared to the deeper channel mouth specimen, probably because of higher temperatures and the greater influence of 13C-depleted carbon from oxidation of organic matter in sediments and from meteoric water. Ontogeny also influences the isotopic record of Tridacna. Once maturity is reached, growth is suppressed by high temperatures during summer. In addition, 813C values decline. Knowing the time of collection, we can correlate 8180 maxima and minima of different tridacnids, and of a tridacnid and its encrusting Chama. However, the shapes of the peaks often differ, suggesting that correlation of the 8180 profiles of fossil tridacnids would be difficult. No correlation is possible between the 813C records of live tridacnids. The similarity between the carbon isotopic composition of the symbiont-free bivalve Chama and the symbiont-bearing bivalve Tridacna it encrusts suggests that the presence of symbionts has no identifiable effect on the isotopic composition of Tridacna shells.

Stable isotopic investigation of physiological and environmental changes recorded in shell carbonate from the giant clam Tridacna maxima

The aragonitic shell of the photosymbiont-bearing bivalve Tridacna maxima contains a record of the physiological and environmental changes the organism has experienced during its lifetime. This record is preserved as chemical and microstructural variations throughout the shell. Stable isotopic analyses of oxygen (18O/16O) and carbon (13C/12C) in shell carbonate were combined with growth increment studies to interpret the shell record of specimens collected from the Rose Atoll (Lat. 14°31′S; Long. 168°10′W) in April 1982. The seasonal water temperature cycle is recorded in the oxygen isotopic signature of the clams, permitting the recognition of annual cycles in the δ18O profile. The total number of these cycles corresponds to the age of a specimen, while the cycle length is a measure of the yearly growth rate. Large-amplitude cycles, reflecting year-round calcification, characterize the early portion of the growth record. With the onset of sexual maturity and slower growth at an age of approximately ten years, the cycles decrease in amplitude and become more erratic. During this later growth phase calcification is limited to the cooler months of the year, perhaps in response to a re-ordering of energy priorities between growth and gametogenesis. A growth curve developed from the δ18O profile indicates rapid juvenile shell growth followed by slower growth thereafter producing a lifespan of several decades. Carbon isotopic analyses of T. maxima were compared to analyses of the symbiont-barren gastropod Terebra areolata collected from the same locality in April 1984. A 2‰ depletion in the δ13C composition of T. maxima shell carbonate is attributed to a symbiontenhanced metabolic rate and an increased flow of isotopically light, respired CO2 into the carbon pool used in calcification. Such a depletion may prove useful in identifying the presence of photosymbionts in extinct species of fossil mollusks.

A Summary of Information on Rose Atoll

A Summary of Information on Rose Atoll

Department of Marine Biology of the Carnegie Institution of Washington

THE Carnegie Institution has again materially added to our knowledge of the vegetation of the more outlying parts of the world by the publication of three treatises on American Samoa by Prof. W. A. Setchell. The first and third parts are devoted to the vegetation of two islands, Tutuila and Rose Atoll, and provide a comprehensive review of the nature and distribution of the flora and enumerations of the species recorded. In addition to his own work, the author has incorporated that of previous workers in this locality, and has received the assistance of specialists in the description of the general habitat factors and the enumeration of the species.