EXECUTIVE SUMMARY



Executive Summary

This Coral Reef Ecosystem Monitoring Report for American Samoa: 2002–2006 provides 

the most comprehensive integrated ecosystem assessment of the coral reefs of American 

Samoa performed to date. This benchmark report is the culmination of interdisciplinary 

surveys accomplished during three American Samoa Reef Assessment and Monitoring 

Program (ASRAMP) research cruises completed in 2002, 2004, and 2006. These ASRAMP 

cruises were part of the National Oceanic and Atmospheric Administration (NOAA) Coral 

Reef Conservation Program’s broad-scale Pacific RAMP, which conducts extensive benthic 

habitat mapping, ecological and environmental assessment and monitoring, and applied 

management-relevant research to support improved ecosystem-based management and 

conservation of the United States (U.S.)-affiliated Pacific Islands. Each of the Pacific RAMP 

research cruises, including ASRAMP, are led by the Coral Reef Ecosystem Division (CRED) 

of the Pacific Islands Fisheries Science Center, in close collaboration with key partners from 

other NOAA offices, federal, state, and territorial agencies, academia, and nongovernmental 

organizations. In particular, late Governor Sunia and Governor Tulafono, and the many 

individuals of the American Samoa Coral Reef Advisory Group agencies played pivotal roles 

in planning and implementing all three ASRAMP surveys discussed in this report. 

The vast quantity of ecosystem information gathered during the three ASRAMP surveys 

has been thoroughly processed and analyzed for user-friendly graphical presentation and 

discussion in this report, thus allowing complex ecosystem observations and concepts to be 

more easily interpreted by resource managers, policymakers, and key stakeholders. Since 

these integrated ecosystem observations are consistent with and comparable to other Pacific 

RAMP observations in the Hawaiian Archipelago, the Territory of Guam, the Commonwealth 

of the Northern Mariana Islands, and the Pacific Remote Island Areas, they provide an 

unprecedented opportunity to better understand the condition and health of the coral reefs of 

American Samoa relative to other reefs across the Pacific. 

The first chapter of the Coral Reef Ecosystem Monitoring Report for American Samoa: 2002– 

2006 presents the background, goals, objectives, operational and research scope, and inherent 

limitations of Pacific RAMP. The second chapter describes the methodologies used to collect, 

process, and analyze field observations and discipline-specific datasets. Chapters three through 

seven provide detailed spatial and temporal analyses for each of the five island/atoll groups 

within American Samoa (Tutuila and Aunu`u Islands, Ofu and Olosega Islands, Ta`u Island, 

Swains Island, and Rose Atoll). Each of these island/atoll chapters includes presentations 

of data and discussions on each of the following topic areas: geopolitical context, survey 

effort, benthic habitat mapping and characterization, oceanography and water quality, coral 

and coral disease, algae, benthic macroinvertebrates, reef fish, and an island summary and 

integration that discusses relationships among these different ecosystem components. The 

final chapter examines similarities and differences in each of these ecosystem components 

between the different islands across American Samoa. 

The benthic habitat mapping and characterization sections present comprehensive results 

based on extensive multibeam bathymetry, backscatter, and photographic data collected 

during the three ASRAMP surveys. These data revealed a number of previously unknown, 

unrecognized, or poorly understood submarine features. 
EXECUTIVE SUMMARY

A large and complex relict barrier reef and several submerged bank structures were 

comprehensively mapped around most of Tutuila, northwest of Ofu, and southeast 

of Olosega. These relict reefs and submerged banks include some areas with high (> 

50%) live coral cover in waters deeper than 20 m.

Towed-diver habitat surveys completed during ASRAMP 2002 discovered two areas 

with massive (5-6 m × ~ 14 m) and ancient Porites coral colonies (estimated to be 

between 500 and 1000 years old) off the east and southwest coasts of Ta`u. The areas 

around the largest coral colonies are currently under consideration for designation as 

possible marine protected areas by the American Samoa Government. 

Multibeam bathymetric surveys in 2004 and 2006 revealed a series of small seamounts 

between Ta`u and Olosega. Underwater video cameras showed the discovery of a 

luxuriant coral reef in water depths of 38 m and deeper. 

With respect to the inherent geographic, geologic, and geopolitical factors, analyses of the 

extensive biological, benthic habitat, and oceanographic observations reveal both direct and 

inverse relationships with parameters such as island area and topography, location, population, 

and/or temporal events (e.g., hurricanes). In some instances, it was relatively straightforward 

to ascertain relationships among certain ecosystem parameters. However, because many of 

the geographic, geologic, and geopolitical parameters are themselves interrelated, many of 

the ecosystem relationships are complex and difficult to interpret. For example, the largest 

islands generally have the highest human population densities (coupled with the associated 

anthropogenic impacts), as well as the more extensive surrounding bank habitat areas. Some 

of these complex relationships may eventually be better understood as additional comparative 

analyses are completed using the broader basin-wide surveys of Pacific RAMP. 

Some of the more consistent and straightforward observed correlations may be explained by 

the theory of island biogeography, which states that larger islands support greater biodiversity 

as a result of an increased number of habitat types. Tutuila, which has both the largest land 

area and bank area (almost 10 times larger than any other island) in American Samoa, was 

observed to have greater diversity of corals, algae, and noncoral invertebrates than the smaller 

islands, although fish diversity was not.

Island-wide, the number of coral genera was greatest around Tutuila (~ 35 genera) 

and least around Swains (~ 14 genera). More genera were observed around each of 

the larger high Manu`a Islands (Ofu, Olosega, and Ta`u) than the smaller low islands/

atolls (Swains and Rose). 

Mean coral generic richness was highest around the larger high islands (e.g., ~ 22 

genera per site around Ofu and Olosega) and lowest around the smaller low islands 

(e.g., ~ 7 genera per site around Swains).

Significantly more algal genera and functional groups were found around Tutuila 

than the other smaller islands. The three geographically close, high volcanic Manu`a 

Islands exhibited the second highest number of recorded algal genera and Rose and 

Swains the lowest.

Although the numbers of both coral and algal genera exhibited positive correlations with 

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EXECUTIVE SUMMARY

island size, both habitat complexity and live coral cover were negatively correlated with 

island size. Island-wide mean habitat complexity was estimated to be very high around both 

Swains and Rose, but only high to medium-high around the larger high islands. Mean live 

coral cover was highest around Swains with a value of ~ 45% and consistently lower around 

the other islands with values between 20% and 30%. 

Sea urchins and sea cucumbers were relatively more abundant around the larger, high islands 

and uncommon around Rose and Swains. Although the mean density of giant clams was 

highest around Ta`u, the largest localized concentration was found at Rose.

Rose and Swains are both small, low islands with no substantive terrigenous inputs to the 

nearshore water and no surrounding bank or shelve habitats, with slopes plunging steeply 

to abyssal depths. In contrast, the larger high islands (Tutuila, Ofu, Olosega, and Ta`u) have 

surrounding banks where sand can accumulate. Towed-diver surveys observed that mean 

sand covers around Rose and Swains were less than 5%, while it was 9–15% around the larger 

islands. Sand habitats generally had low topographic complexity and coral cover. Since both 

Rose and Swains have no or very low human populations, higher habitat complexities than 

the larger islands, and fewer low complexity/low coral cover sand flats, it is hypothesized 

that the steepness of the forereef slopes, island area, and/or the low human populations could 

be causative factors for the higher coral or crustose coralline algae cover around Swains and 

Rose, respectively. 

Swains, which had substantially higher mean live coral cover than any other island in 

American Samoa, lies 350 km north of the other islands and experiences notably different 

oceanographic conditions. The waters around Swains were generally warmer, less saline, 

more productive (higher chlorophyll-a), and less windy than the waters around the other 

islands. The relatively high coral cover around Swains, which ranged from 20% to 75%, 

can most likely be explained by its geographic location and more favorable oceanographic 

conditions.

Quantitative observations of coral and crustose coralline algal disease were initiated 

during ASRAMP 2006. The mean overall prevalence of coral diseases and afflictions (e.g., 

predation lesions) around American Samoa was relatively low with a recorded value of 

0.34%. In contrast, observations from both the Caribbean and the Great Barrier Reef have 

reported prevalence values an order of magnitude higher. Coral disease prevalence values 

around American Samoa were comparable to values reported at other remote Pacific Island 

locations. While the highest mean coral disease prevalence values were observed around 

Rose (~ 0.96%), most of these afflictions were caused by predation. The next highest disease 

prevalence values were recorded around Tutuila (~ 0.15%), the largest and most populated 

island. Interestingly, the disease prevalence was higher on the less populated north side of 

the island than on the more populated south side of the island. The lowest mean coral disease 

prevalence values were found around Ofu and Olosega (0.05%) and the remote Swains 

(0.04%). Swains had the most evidence of predation lesions of any of the islands caused by 

an ongoing crown-of-thorns seastar (COTS) infestation.

The mean prevalence of crustose coralline algal disease was about 45% higher than that 

observed for coral diseases across the archipelago. Nearly 94% of these cases occurred 
EXECUTIVE SUMMARYaround Tutuila and Ofu and Olosega, 6% around Ta`u and Rose, and none around Swains. 

Intriguingly, Ofu and Olosega exhibited the highest relative abundance of coralline algal 

disease (higher than Tutuila), but the second lowest prevalence of coral disease. The most 

abundant type of coralline algal disease (92%) was the coralline lethal orange disease, which 

was distributed in an aggregated pattern, suggesting that this disease pathogen may be readily 

transmitted by grazing organisms. In contrast to coral diseases, coralline algal diseases were 

more prevalent on the south coast of Tutuila than the north coast, particularly in the region 

adjacent to Pago Pago Harbor watersheds. Distribution and abundance of disease, together 

with other coral reef ecosystem metrics, can provide proxies to ecosystem integrity and 

health. 

While the impact of human activity on several parameters (e.g., percentage of live coral 

cover, habitat complexity, and disease) can sometimes be difficult to interpret, a number of 

ecosystem observations reported here appear to be related to human activities: 

Total reef fish (all sizes) and large fish (> 50 cm) biomass were comparatively depleted 

around the populated islands of Tutuila and the Manu`a Islands (similar values for 

Tutuila and Manu`a Islands). This difference follows patterns throughout the U.S.-

affiliated Pacific Islands, where populated islands have depleted reef fish biomass and 

uninhabited areas have greater reef fish biomass (Schroeder et al., in press).

Total reef fish (all sizes) and large fish (> 50 cm) biomass were highest around the 

unpopulated islands. Total mean biomass around Rose (2.1 tons ha-1) and Swains (1.4 

tons ha-1) greatly exceeded the mean for the high islands (0.8 tons ha-1). Although 

higher than the populated islands, Rose had significantly lower biomass values than 

other uninhabited National Wildlife Refuge islands in the more remote parts of the 

Pacific (Schroeder et al., in press). 

Total reef fish (all sizes) and large fish (> 50 cm) biomass appeared to decline from a 

mean of ~ 1.0 tons ha-1 in 2002 and 2004 to a mean of ~ 0.5 tons ha-1 in 2006. 

Nutrient levels were generally highest and most variable around Tutuila, most likely 

caused by highly varying watersheds and population distributions.

Over a 7–week period in 2006, 23 of 34 vessels (67%) detected by an Ecological 

Acoustic Recorder in the National Park of American Samoa were detected during 

nighttime hours, providing resource managers a new awareness of local threats from 

human activity. 

Biological data collected around Rose have further elucidated the long-term impacts 

of shipwrecks on nearby coral reef ecosystems. In October 1993, a ship grounded on 

the reef at Rose and caused a fuel spill that killed corals and coralline algae over a 

broad reach of the southwest reef crest and upper reef margins. Later, dissolved iron 

from the wreckage stimulated growth of invasive cyanobacteria that still carpets much 

of the southwest reef crest and slopes. Although the U.S. Fish & Wildlife Service 

has removed much of the wreckage debris, the cyanobacteria mats have apparently 

slowed the recovery of coralline algae and corals, both of which show low diversity 

and low richness in the area of the grounding. In addition, the numbers and biomass 

of pooled herbivorous fish (surgeonfishes, parrotfishes, and angelfishes) were greater 

at the wreck site than at neighboring control sites. 

One of the key goals of the CRED integrated ecosystem observation and monitoring effort 

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is to effectively detect and differentiate spatial patterns and temporal changes in ecosystem 

health metrics to inform resource managers and improve decision making. Temporal events 

and trends include storms and their aftereffects, global warming, coral bleaching, ocean 

acidification, disease afflictions, and COTS infestations. Since the biennial ASRAMP surveys 

have been conducted only three times from 2002 to 2006, and some of the methodologies 

continued to evolve during that period, it is difficult to make statistically rigorous temporal 

comparisons over this short period. However, some notable spatial patterns and temporal 

effects and trends have been described. 

Since CRED initiated ecosystem monitoring around American Samoa, two major storms, 

Hurricane Heta (2004) and Hurricane Olaf (2005), have impacted the area. High levels of 

coral breakage and stress were observed at Swains one month after the passage of Hurricane 

Heta. The mean density of COTS was higher around Swains during the 2004 and 2006 

surveys than any of the other islands/atoll, where COTS were rarely observed. Whether COTS 

population levels increased at Swains as a result of the destructive activity of hurricanes 

on coral communities cannot be determined from the available data. In addition, low algal 

diversity and scoured benthic communities observed in the Manu`a Islands during ASRAMP 

2004 were hypothesized to be related to the passage of Hurricane Heta. By the time of 

the ASRAMP 2006 surveys algal diversity had apparently rebounded. No obvious direct 

ecosystem impacts were observed during the ASRAMP 2006 surveys despite the passage of 

Hurricane Olaf a year earlier. 

Although these initial time series observations do not cover a period sufficient for rigorous 

statistical analysis, long-term trends associated with climate change, such as ocean warming 

and acidification, sea-level rise, and changing storm tracks and intensities, are significant 

threats now facing coral reef ecosystems globally, including American Samoa. Known 

ecological impacts of these climate-change-induced threats include coral bleaching and 

disease, reduced calcification or even dissolution, decreased coral-growth rates, and localized 

destruction caused by storms. As noted previously, prevalence of coral disease was generally 

low throughout American Samoa. Some mild coral bleaching was observed around each 

of the islands of American Samoa in 2006. There was also an apparent overall net decline 

in coral cover between 2002 and 2006, but this observation might be the effect of different 

observers, survey locations, and/or methods rather than actual ecological changes and 

should be interpreted with caution. However, these initial integrated ecosystem observations 

around American Samoa and each of the other U.S.-affiliated Pacific Islands establishes an 

unprecedented baseline that can be used to measure future changes. 

Scientists are only beginning to understand the effects from global warming and ocean 

acidification on coral reef ecosystems, and the 5 years spanned thus far during ASRAMP 

surveys is much too short of a period in which to detect change in a statistically robust manner. 

However, this report provides an essential scientific foundation for informed decision making 

for the long-term conservation and management of the coral reef ecosystems of American 

Samoa. The spatial maps of all observed ecosystem components in this report allow managers 

the unique ability to evaluate spatial management options, such as determining the preferred 

locations of marine protected areas, based on multiple scientific criteria. The temporal 

comparisons and time series observations are useful in distinguishing between natural 

and anthropogenic ecosystem variability, which can be used to assist resource managers 
EXECUTIVE SUMMARYin evaluating the effectiveness of both existing and proposed management measures. In 

conclusion, the islands/atoll and archipelagic comparison chapters give resource managers 

and policymakers an unprecedented ability to examine the status and trends of each ecosystem 

around and among their respective islands, with the hope of protecting and conserving these 

unique resources for generations to come. 

References

Schroeder RE, Nadon M, Richards BL, Zgliczynski BJ, Sabater M (In press) Reef fish densities inversely follow human population levels across American Samoan Islands. In: 

Proceedings of the 11th International Coral Reef Symposium, Fort Lauderdale, FL, July 

7–11, 2008. Available from Pacific Islands Fisheries Science Center Coral Reef Ecosystem Division, 1125B Ala Moana Blvd., Honolulu, HI 96814.