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Chapter 7 Swains Island

7.1 Geopolitical Context

Swains Island is the northernmost island in the Territory of American Samoa, situated 1228 

km south of the equator and approximately 350 km north of Tutuila Island. Geologically, it 

is not a part of the Samoan hot-spot track, but part of the Tokelau volcanic chain. Swains is 

approximately 2.4 km in diameter, containing a 2.6-km

2

 ring of highly vegetated sand and 

coral rising no more than 6 m above sea level, with a rain-fed lagoon of brackish water that 

is cut off from the ocean. 

The island retains a relatively small population, with as many as 164 full-time residents on 

the island in the 1950s. Swains had seen a steady decline since then, with only 16 people 

reported in 1990. The island is currently inhabited by 30 people or less at any particular time, 

primarily in the northwest village of Taulaga, to retain private ownership by the Jennings 

family and as part of the Territory of American Samoa. An additional village in the southeast 

(Etaena) remains largely abandoned. It remains covered by a circle of coconut trees; however, 

it is not run as an active plantation. The population on Swains survives primarily by farming, 

specifically bananas, taro, breadfruit and papaya, and subsistence fishing. 

7.2 Survey Effort

Physical and biological data have been collected around Swains since 2002 as part of the 

Pacific Islands Fisheries Science Center (PIFSC) Coral Reef Ecosystem Division’s (CRED’s) 

American Samoa Reef Assessment and Monitoring Program (ASRAMP). The extent and 

timeframe of these survey efforts are discussed below. To aid in the discussion of spatial 

patterns of ecological and oceanographic observations around the island throughout this 

chapter, four geographic regions are delineated in Figure 7.2a.

Benthic habitat mapping data were collected around Swains using acoustic multibeam 

survey methods, which completed mapping a total survey area of 256 km

2

 during ASRAMP 

2006. These data are further examined in Section 7.3: Benthic Habitat Mapping and 

Characterization.

Table 7.2a. Numbers, areas, and depths of REA and towed-diver surveys around Swains during ASRAMP 

2002, 2004, and 2006.

Year REA Surveys Towed-diver Surveys

Number of 

Surveys

Mean Depth 

(m) 

Number of 

Surveys

Survey Area 

(ha)

Mean Depth 

(m)

2002 10* 15.5 (SD 2.9)

9 23.1 10.3 (SD 4.9)

2004 8* 18.1 (SD 1.9) 14 26.5 12.5 (SD 6.9)

2006

8 14.5 (SD 0.6)9 18.6 14.9 (SD 3.0)

* No coral disease surveys were conducted in 2002 and 2004.
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Figure 7.2a shows the locations of Rapid Ecological Assessment (REA) and towed-diver 

survey efforts during ASRAMP 2002, 2004 and 2006. The number, mean depth, and area of 

these survey efforts are presented by year in Table 7.2a. 

Depth ranges from towed-diver surveys are presented for each year in Figures 7.5.1b (2002), 

7.5.1e (2004), and 7.5.1m (2006). Although the towed-diver survey methodology is aimed at 

following specific isobaths, the actual depths surveyed are often quite variable. These figures 

illustrate the depth variability observed during towed-diver surveys and should be referenced 

when further exploring the towed-diver datasets. 

Spatial and temporal observations of key oceanographic and water quality parameters 

influencing reef conditions around Swains were collected using a diverse suite of long-term 

moored instrumentation packages and closely spaced conductivity, temperature, and depth 

(CTD) surveys of the vertical structure of the water column during ASRAMP 2002, 2004, and 

2006 (see methods Chapter 2, Section 2.3: Oceanography and Water Quality). A summary 

of deployed instruments and collection activities is provided in Table 7.2b and are examined 

further in Section 7.4: Oceanography and Water Quality.

Figure 7.2a. Locations of REA and towed-diver surveys around Swains during ASRAMP 2002, 2004, and 

2006. Four arbitrary geographic regions have been delineated to aid in discussion of spatial patterns. 
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Table 7.2b. Numbers of oceanographic instrument deployments and shallow- and deep-water CTD casts 

around Swains during ASRAMP 2002, 2004, and 2006. Instrument types include ocean data platform (ODP) 

and subsurface temperature recorder (STR). Shallow-water CTD casts were conducted from the surface to a 

30-m depth. Deep-water CTD casts were conducted from the surface to a 500-m depth. Deep-water CTD cast 

information is presented in Chapter 8: Archipelagic Comparisons.

Observation Type 2002 2004 2006

ODP100

STR013

Shallow-water CTD casts 19 29 27

Deep-water CTD casts 1089
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7.3 Benthic Habitat Mapping and Characterization

Benthic habitat mapping and characterization around Swains were conducted using acoustic 

multibeam sonar in depths between ~ 10 and ~ 3000 m. The shipboard Towed Optical 

Assessment Device (TOAD) could not be safely deployed around Swains because of the 

steep terrain and associated navigational concerns. Nearshore habitat mapping was conducted 

during towed-diver benthic surveys in depths between ~ 10 and 30 m.

7.3.1 Acoustic Mapping

Multibeam mapping was conducted around Swains in early 2006 (Fig. 7.3.1a). Continuous 

coverage was achieved in depths between ~ 10 and 3000 m. An additional noncontiguous 

swath was surveyed during deep-water acoustic Doppler current profiler transects that 

extended the bathymetric mapping to depths greater than 4000 m. TOAD optical surveys 

were not conducted around Swains because of the difficulty of maneuvering vessels close 

to this extremely steep seamount and limited areas within the depth range limitations of the 

TOAD optical equipment. 

Multibeam mapping surveys show Swains to be a steep, conical emergent seamount/atoll with 

Figure 7.3.1a. Multibeam bathymetry acquisition around Swains was conducted between ~ 10 and 

~ 4000 m in March 2006 from the National Oceanic and Atmospheric Administration (NOAA) Ship Hi`ialakai 

and the R/V Acoustic Habitat Investigator (AHI). The island drops steeply on all sides to form an intact, conical 

volcanic pedestal.
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rift zones that extend from each corner of the reef down to at least 3000 m. The bathymetry 

immediately adjacent to the exposed reef is very steep and shows no evidence of significant 

spur-and-groove structures. However spur-and-groove features are evident at some locations 

on the reef crest and shallow forereef. The sides of the seamount are relatively smooth and 

exhibit no signs of mass wasting. Based on the bathymetric data collected, it is apparent 

that reef communities around the island do not benefit from the protections provided by the 

insular shelves found at other islands in American Samoa.

Backscatter acquisition results from around Swains (Fig. 7.3.1b) showed a high-magnitude 

return surrounding the entire island. This result suggests that the seafloor surrounding Swains 

is composed of hard substrate. Towed-diver imagery and diver observations confirm that 

much of the benthos within the top 30 m of the water column is colonized by coral dominated 

communities.

Figure 7.3.1b. Backscatter imagery was acquired in March 2006 during multibeam surveys around Swains 

from the NOAA Ship Hi`ialakai and the R/V AHI. Lighter shades represent low-intensity backscatter and 

likely indicate substrates that are acoustically absorbent and typically indicate unconsolidated sediment. Darker 

shades represent high-intensity backscatter and likely indicate consolidated hard-bottom and coral substrates.
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7.3.2 Habitat Characterization

Towed-diver benthic survey observations around Swains from ASRAMP 2002, 2004, and 

2006 were concatenated into mean spatial distributions (see Chapter 2, Section 2.2.3: Optical 

Validation Surveys) of the following benthic components: habitat complexity (Fig. 7.3.2a), 

percent cover of sand (Fig. 7.3.2b), hard substrate/pavement (Fig. 7.3.2c), rubble (Fig. 7.3.2d), 

and live coral (Fig. 7.3.2e). Since these habitat characterization maps represent different and 

complementary components of the same habitats, it is useful to analyze them in relation to 

one another as well as to the local watersheds and exposure to prevailing oceanographic 

conditions. 

Habitat complexity was elevated on all coasts of the island, but appeared highest along 

the west region, specifically along the southwestern-facing shore of the atoll (Fig. 7.3.2a). 

Complexity was also elevated in the northeast along the dividing line between the north and 

east regions. 

Figure 7.3.2a. Mean benthic habitat complexity concatenated from towed-diver survey observations around 

Swains during ASRAMP 2002, 2004, and 2006. Habitat complexity was subjectively rated by divers over 5-min 

ensembles (~ 200 m × 10 m) over a 6-point scale representing low (1), medium-low (2), medium (3), mediumhigh (4), high (5), and very high (6) topographic complexity. Yellow colors indicate low habitat complexity, and 

dark green colors indicate high habitat complexity.
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True to Swains’ nature as a steep, conical seamount, towed-diver observations indicated low 

levels of sand, except for small scattered deposits located around the northeast corner of the 

island (Fig. 7.3.2b), indicative of steep spur-and-groove features along the forereef crest 

when coupled with moderate-to-high habitat complexity in the same region.

Figure 7.3.2b. Mean percent cover of sand concatenated from towed-diver habitat survey observations around 

Swains during ASRAMP 2002, 2004, and 2006. Sand composition was subjectively rated by divers over 5-min 

ensembles (~ 200 m × 10 m) over a 1–100% scale. Light shades indicate high percent cover of sand, and dark 

shades indicate low percent cover of sand.
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Hard substrate/pavement composition appeared relatively uniform around the island, with 

slightly elevated cover along the windward east-facing coastline (Fig. 7.3.2c). 

Figure 7.3.2c. Mean percent cover of hard substrate/pavement, concatenated from towed-diver survey 

observations around Swains during ASRAMP 2002 and 2004. Hard substrate/pavement composition was 

subjectively rated by divers over 5-min ensembles (~ 200 m × 10 m) on a 1–100% scale. Dark shades indicate 

high percent cover of hard substrate, and light shades indicate low percent cover of hard substrate.
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Mean percent cover of coral rubble appeared highest around the northwest corner of the 

west region (Fig. 7.3.2d), which may have been biased higher than normal by inclusion 

of extensive coral fracturing and breakage observed during ASRAMP 2004 following the 

passage of Hurricane Heta. Additional patches of elevated coral rubble were recorded along 

the east corner and in the southeast region; these areas were widely scattered and localized 

(Fig. 7.3.2d). 

Figure 7.3.2d. Mean percent cover of coral rubble, concatenated from towed-diver survey observations around 

Swains during ASRAMP 2002 and 2004. Rubble composition was subjectively rated by divers over 5-min 

ensembles (~ 200 m × 10 m) on a 1–100% scale. Light shades indicate low percent cover of coral rubble, and 

dark shades indicate high percent cover of coral rubble.
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Mean percent cover of live scleractinian (stony) coral was exceptionally and consistently 

high around Swains compared with the other islands in American Samoa (Fig. 7.3.2e). Coral 

cover values were highest in the windward east region, with values ranging from 50% to 

100%. Coral cover values were likewise high in the north and southeast regions, with values 

ranging from ~ 40% to ~ 75%. Though some high coral cover values were recorded in the 

west region, this side and the southwest corner had much more variable coral cover with 

values ranging from ~ 5% to ~ 75%. This formed an apparent gradient with the highest cover 

on the northeast, ranging down to the lowest cover on the southwest. Still, less cover was 

found on the corners of the island bracketing the southwestern side (Fig. 7.3.2e). 

Figure 7.3.2e. Mean percent cover of live scleractinian (stony) coral, concatenated from towed-diver survey 

observations around Swains during ASRAMP 2002, 2004, and 2006. Live coral cover composition was 

subjectively rated by divers over 5-min ensembles (~ 200 m × 10 m) on a 1–100% scale. Blue colors indicate 

low percent cover of coral, and reddish colors indicate high percent cover of coral.
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7.4 Oceanography and Water Quality

Oceanographic and water quality observations were collected in the waters surrounding 

Swains between 2002 and 2006. Instrumentation and equipment descriptions and locations, 

and a subset of results are discussed below. Specific details of deployments and additional 

data are presented in Appendix II, Table II. ii.

7.4.1 Hydrographic Data

2002 Spatial Surveys

During ASRAMP 2002, 19 shallow-water CTD casts were conducted between February 9

and 10 in nearshore waters around Swains and within the lagoon (Fig. 7.4.1a). 

Data from these vertical profiles around the outside of the island show little variability in 

temperature, salinity, or density (Fig. 7.4.1b). The north side of the island in the north and 

east regions (A–C), and the eastern portion of the southeast region were marginally cooler 

(29.46°–29.52°C) than the southern side of the island (29.54°–29.56°C). However, salinity 

and density showed little vertical structure (well-mixed) or horizontal variability, with the 

exception of a single CTD at the northwest point where a low salinity tongue was observed 

throughout the water column. The reason for the lower salinity water is not clear, but the 

weak gradient of lowest salinity water near the bottom suggests the possibility of a subsurface 

Figure 7.4.1a. Shallow-water CTD cast locations, shown as blue dots, expressed sequentially in a clockwise 

direction around Swains (A–E) during ASRAMP 2002, February 19–20.
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Figure 7.4.1b. Shallow-water CTD cast profiles to a 30-m depth around Swains during ASRAMP 2002, 

February 19–20, including temperature (°C), salinity (psu), and density (kg m-3). Profiles are shown sequentially 

in a clockwise direction around the island (A–E), as shown in Figure 7.4.1a.
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freshwater spring at the northwest corner. 

Analysis of the following physical water properties at a 20-m depth during this survey period 

(Fig. 7.4.1c) shows relatively little spatial variance or range in measured values: temperature 

(29.49°–29.56°C), salinity (34.82–34.84 psu), and density (21.75–21.78 kg m-3). Though 

gradients were small, general weak patterns were apparent. Waters at 20-m depths were 

warmer in the west and south regions and cooler in the north and northeast, where one CTD 

cast at the northeast corner recorded noticeably cooler temperature. The salinity minimum 

described at the northwest corner is strikingly apparent at the 20-m depth. The area to the 

northeast corner with cool water was also observed to have high salinity, resulting in a 

localized area of high density. 

Figure 7.4.1c. Interpolated water temperature (top left), salinity (top right), and density (bottom right) at a 20-

m depth derived from shallow-water CTD casts around Swains during ASRAMP 2002, February 19–20. Beam 

transmission data were not collected (botom left).
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2004 Spatial Surveys

During ASRAMP 2004, 29 equally spaced shallow-water CTD casts were conducted in 

nearshore waters around Swains between February 15 and 18 (Fig. 7.4.1d). Data from these 

vertical profiles around the outside of the atoll showed limited variability in temperature, 

salinity, and density (Fig. 7.4.1e). Surface waters (0–5 m) in the north and east regions (A–C) 

and the eastern portion of the southeast region of the atoll were warmer by 0.2°–0.3°C than 

those on the south and west coast (C–E). The most significant feature observed was a lower 

temperature (29.7°C), higher salinity (34.8 psu), and higher density (21.55 kg m-3) body of 

bottom water (> 20 m) around the east side of the island (B–C). The west side of the island 

had a region of low salinity (34.6 psu) and transmittance (93.5%), with some evidence of 

stratification toward the south and west sides (D–E). Beam transmission levels were only 

slightly variable with the highest along the southeast shore (> 94%) and lowest along the 

west shore (~ 93%).

Figure 7.4.1d. Shallow-water CTD cast locations, shown as blue dots, expressed sequentially in a clockwise 

direction around Swains (A–E) during ASRAMP 2004, February 15–18. Notice 10 additional CTD locations 

within the brackish lake of the island. 
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Figure 7.4.1e. Shallow-water CTD cast profiles to a 30-m depth around Swains during ASRAMP 2004, February 

15–18, including temperature (°C), salinity (psu), density (kg m-3), and beam transmission (%). Profiles are 

shown sequentially in a clockwise direction around the island (A–E), as shown in Figure 7.4.1d.
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Spatial patterns of physical water properties at 20-m depths around Swains during ASRAMP 

2004 were observed, though differences were typically small (Fig. 7.4.1f). Ranges of key 

properties varied as follows: temperature (29.73°–29.84°C), salinity (34.60–34.72 psu), 

beam transmission (93.30–94.97%), and computed density (21.51–21.61 kg m-3). Alternating 

from relatively warm to cool to warm, the small temperature differences did not reveal any 

specific spatial pattern. For salinity, the most striking feature was an area of low salinity 

(34.6 psu) around the south point between the west and southeast regions. This area was 

also characterized by low beam transmission (high turbidity), which suggests possible weak 

seepage of lagoon waters into the nearshore environment. 

Figure 7.4.1f. Interpolated water temperature (top left), salinity (top right), beam transmission (bottom left) and 

density (bottom right) at a 20-m depth derived from shallow-water CTD casts around Swains during ASRAMP 

2004, February 15–18. 
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2006 Spatial Surveys

During ASRAMP 2006, 27 CTD casts were conducted in nearshore waters around Swains 

between February 12 and 13 (Fig. 7.4.1g). Water samples were collected for nutrient analysis 

at 1-, 10-, 20-, and 30-m depths, where possible, at 11 of these shallow CTD sites. Dissolved 

inorganic carbon (DIC) samples were also collected at these locations. 

Shallow-water CTD profiles from ASRAMP 2006 showed primarily well-mixed waters 

with little spatial variability in temperature, salinity or density around Swains (Fig. 7.4.1h). 

Temperatures on the east and southeast (B–D) regions were marginally higher than the 

north (A–B) and west (D–A) sides and were uniform with depth. Salinity, density and beam 

transmittance showed very little spatial or vertical variability around the island. The lagoon 

at Swains appeared to have little effect on the physical properties of the ocean outside the 

perimeter in 2006. This is caused by the lack of outflow from the inner lagoon to the ocean 

and to the low-lying geography, little vegetation, and no anthropogenic sources to affect 

rainfall runoff.

Figure 7.4.1g. Shallow-water CTD cast, nutrient and DIC water sample locations around Swains (A–E) during 

ASRAMP 2006, February 12–13.
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Figure 7.4.1h. Shallow-water CTD cast profiles to a 30-m depth around Swains during ASRAMP 2006, February 

12–13, including temperature (°C), salinity (psu), density (kg m-3), and beam transmission (%). Profiles are 

shown sequentially in a clockwise direction around the island (A–E), as shown in Figure 7.4.1g.
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Physical water properties at a 20-m depth around Swains showed limited, but noticeable, less 

discernable spatial patterns in the vertical sections (Fig. 7.4.1i). The actual spatial differences 

and ranges of the following properties around the island were small: temperature (28.97°–

29.03°C), salinity (34.86–34.88 psu), beam transmission (94.75–95.61%), and density 

(21.95–21.98 kg m-3). The northwest corner of the island was observed to have a weak signal 

of increased temperature, salinity and density, and decreased beam transmission, possibly 

related to water discharge through the reef channel from the shallow reef flat surrounding the 

island.

Several spatial patterns of observed water quality properties at 20-m depths existed around 

Swains during ASRAMP 2006. Water quality analyses of the in situ samples collected at 20 

m display the following ranges (Fig. 7.4.1j): chlorophyll-a, only 1 sample at 0.36 μg L-1; 

phosphate (PO

4

), 0.14–0.16 μM; silicate (SiO

2

), 0.95–1.24 μM; and total nitrogen (Ntot = NO

3

+ NO2-), 0.07–0.19 μM. Although the actual ranges in values were small, Swains exhibited 

higher PO

4

 concentrations than the other islands in the archipelago, with the highest values 

falling on the east and west sides of the island. The measured nitrogen components also 

showed the greatest values from the sites sampled on the east and west sides of the island. 

Silicate, conversely, showed the greatest concentration on the south side of the island.

Figure 7.4.1i. Interpolated water temperature (top left), salinity (top right), beam transmission (bottom left), and 

density (bottom right) at a 20-m depth derived from shallow-water CTD casts around Swains during ASRAMP 

2006, February 12–13. 
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7.4.2 Temporal Comparison—Hydrographic Data

In each of the hydrographic survey periods of Swains, water properties and nutrient concentrations 

exhibited little spatial variability around the island. This is not a surprising result given the 

small size of the island; most small-scale processes, and certainly all large-scale oceanographic 

processes, would influence waters on all sides of the island. These results will act as a baseline 

from which to compare future oceanographic and water quality datasets.

Figure 7.4.1j. Interpolated total nitrogen (top right), nitrate (middle left), nitrite (middle right), phosphate 

(bottom left) and silicate (bottom right) concentrations, at a 20-m depth derived from water samples collected in 

concert with shallow-water CTD casts around Swains during ASRAMP 2006, February 12–13. Chlorophyll-a 

interpolation is not included in this figure because there was only one data point for this parameter.
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7.4.3 Time Series Observations

A limited suite of moored instruments were deployed around Swains over the period between 

2002 and 2006 to collect time series observations of key oceanographic properties influencing 

reef conditions (Fig. 7.4.3a). Deployment and retrieval dates are detailed in Appendix II, Table 

II. iv. Figure 7.4.3b shows a time series of in situ and remotely sensed sea surface temperature 

(SST) and modeled wave properties from January 2002 to April 2006.

Pathfinder SST and in situ temperature observations around Swains show strong seasonal 

variation with warmest temperatures (~ 30.5°C) observed during January–March and coolest 

temperatures (~ 28.5°C) in June–August (Fig. 7.4.3b, top panel). Pathfinder-derived SST and 

in situ temperature data showed similar variability; however, in situ observations were warmer 

(0°–2.0°C) than those measured via satellite, particularly during austral winters. This trend is 

also consistent when comparing Pathfinder climatology with in situ observations.

One STR was deployed at Swains from 2004 to 2006 (Fig. 7.4.3a). The STR sensor showed 

2°–3°C temperature fluctuations caused by seasonal variability in addition to minimal (< 1°C) 

diurnal temperature fluctuations during this time (Fig. 7.4.3c). 

Modeled significant wave-height data for Swains revealed weak seasonal variability 

superimposed with episodic, cyclone-derived extreme wave events. Larger wave heights 

(~ 3–4 m) typically occurred during winter months compared to smaller wave heights (~ 2 m) 

Figure 7.4.3a. Locations and types of oceanographic instrument moorings deployed around Swains between 

2002 and 2006. Moored instrument types include ODP and STR.
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during the summer months. Two extreme swell events were observed during the time series 

record. The first, in January 2004, was produced by Cyclone Heta and the second in February 

2005 was produced by Cyclones Olaf and Percy (Fig. 7.4.3b, bottom panel). 

Figure 7.4.3b. SST and wave height time series around Swains between January 2002 and April 2006. Remotely 

sensed data (SST climatology and weekly Pathfinder-derived SST) and modeled significant wave-height data 

derived from Wave Watch III are overlaid with CRED in situ temperature observations from an ODP deployed 

at a 15-m depth at site SWA001, and an STR deployed at a 14-m depth at site SWA002 (locations shown in 

Fig. 7.4.3a). The horizontal red and vertical orange bars represent the bleaching threshold and the ASRAMP 

research cruise dates, respectively.

Figure 7.4.3c. Time series observations of temperature from March 2004 to February 2006 collected from an 

STR deployed at SWA002 at a 14-m depth at Swains. See Figure 7.4.3a for mooring locations.
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7.5 Coral and Coral Disease

7.5.1 Coral Surveys

2002 Spatial Surveys

Nine towed-diver benthic surveys, with a mean depth of 10.3 m, were conducted around Swains 

during ASRAMP 2002. Individual towed-diver survey track depths ranged from 6 m (SD 2) to 

23 m (SD 2; Fig. 7.5.1a). High live scleractinian (stony) coral cover characterized the benthic 

community surrounding Swains, with an island-wide mean of 60.0% (SE 4.6) live scleractinian 

(stony) coral cover (Fig. 7.5.1b). Dead coral percent cover observations were recorded as an 

independent component of the benthic community, with an island-wide mean of 4.0% (SE 0.8; 

Fig. 7.5.1c). 

Figure 7.5.1a. Towed-diver survey tracks around Swains during ASRAMP 2002. Towed-diver survey tracks 

are color coded with mean depths for each 5-min segment. Mean depths and standard deviations for each 

towed-diver survey are shown in black text. Depth histogram and statistics (counts, minimum depth, maximum 

depth, mean, and standard deviation) from 30-sec depth recordings during towed-diver surveys are included.
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High live coral cover typified the benthic community around Swains (Fig. 7.5.1b). However, 

specific hotspots of elevated live coral cover were observed during the 2002 towed-diver surveys. 

The northwest corner of the island, intersecting both the north and the west regions, was observed 

to have exceptionally high live coral cover (4 tow segments, mean: 73.8%). Other high coral 

cover areas included the east region (10 tow segments, mean: 71.8%) and the west region (6 

tow segments, mean: 65.8%). Dead coral cover (Fig. 7.5.1c) was sporadically distributed around 

Swains, with increased levels observed in the west region (northwest corner of the island, 8 tow 

segments, mean: 8.9%) and in the north region (5 tow segments, mean: 6.6%).

Figure 7.5.1b. Towed-diver benthic survey observations of live scleractinian (stony) coral cover around Swains 

during ASRAMP 2002. Each colored point represents an integrated estimate over a 5-min observation segment 

covering a survey swath of ~ 200 m × 10 m (~ 2000 m

2

). Symbol size represents the percent live coral cover on 

the benthic habitat. Note that coral cover was measured as a direct percentage of overall benthic cover in 2002. 

For more information, see Chapter 2, Section 2.4.2: Towed-diver Surveys.
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REA coral surveys during ASRAMP 2002 were the first surveys conducted in American Samoa 

by CRED. Although 15 sites were surveyed around Swains by a coral biologist, much of the 

focus of those surveys was to compile species inventories and explore different coral monitoring 

methodologies. Since the surveys were exploratory and qualitative in nature, no data are presented 

in this more quantitative report. 

Figure 7.5.1c. Towed-diver benthic survey observations of dead coral cover around Swains during ASRAMP 

2002. Each colored point represents an integrated estimate over a 5-min observation segment covering a survey 

swath of ~ 200 m × 10 m (~ 2000 m

2

). Symbol size represents the percent of dead coral cover on the benthic 

habitat. 
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2004 Spatial Surveys

A total of 14 towed-diver benthic surveys were conducted around Swains during ASRAMP 

2004. The mean towed-diver survey depth was 12.5 m, with individual towed-diver survey 

depths ranging from 5 m (SD 2) to 16 m (SD 8; Fig. 7.5.1d). 

As a result of the numerous towed-diver survey tracks in 2004 and the shift to using dive 

computers instead of decompression tables, towed-diver surveys were intentionally conducted 

in three depth ranges (as reflected in the depth histogram in Fig. 7.5.1d): shallow (~ 5 m), 

mid-depths (~ 10–15 m), and deep (20–25 m). 

Figure 7.5.1d. Towed-diver survey tracks around Swains during ASRAMP 2004. Towed-diver survey tracks 

are color coded with mean depths for each 5-min segment. Mean depths and standard deviations for each 

towed-diver survey are shown in black text. Depth histogram and statistics (counts, minimum depth, maximum 

depth, mean, and standard deviation) from 30-sec depth recordings during towed-diver surveys are included.
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An island-wide mean percent cover of live scleractinian coral was 30.5% (SE 2.7; Fig. 7.5.1e). 

Coral cover was much more spatially variable during the 2004 surveys than observed during 

2002. Areas of high coral cover were observed in the east region (16 tow segments, mean: 46.0%) 

and in the west region (5 tow segments, mean: 46.2%). Interestingly, the northwest corner, which 

had exceptionally high coral cover during 2002, and the southwest corner of Swains had the 

lowest observed live coral cover values during ASRAMP 2004, with values ranging from 1–5% 

to 20–30%.

Figure 7.5.1e. Towed-diver benthic survey observations of live scleractinian (stony) coral cover around Swains 

during ASRAMP 2004. Each colored point represents an integrated estimate over a 5-min observation segment 

covering a survey swath of ~ 200 m × 10 m (~ 2000 m

2

). Symbol size represents the percent live coral cover on 

the benthic habitat. For more information, see Chapter 2, Section 2.4.2: Towed-diver Surveys.
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The island-wide mean of stressed coral, which was recorded as a subset value of percent live coral 

cover, was particularly high during ASRAMP 2004 (7.8% [SE 2.0]; Fig. 7.5.1f). High levels of 

stressed coral cover were observed in the west and north regions (most northwestern corner, 15 

tow segments, mean: 30%). This clump of elevated coral stress was not associated with an area of 

high live coral cover in 2004, though this area had high observed coral cover during 2002 surveys. 

High coral stress was observed in the west and southeast regions, particularly the southern corner 

(13 tow segments, mean: 16.8%). Coral stress in this region was seen in the deeper tow segments, 

and similarly to the west/north region; these deeper sites with elevated coral stress had lower 

live coral percent cover. Results from 2004 indicated that coral stress on Swains was relatively 

independent of live coral percent cover and may be more directly associated with deeper coral 

communities. More importantly, the high levels of coral stress observed around Swains during 

2004 most likely reflect significant coral breakage caused by Hurricane Heta 1 month prior to the 

Figure 7.5.1f. Towed-diver benthic survey observations of stressed coral cover around Swains during ASRAMP 

2004. Each colored point represents an integrated estimate over a 5-min observation segment covering a survey 

swath of ~ 200 m × 10 m (~ 2000 m

2

). Symbol size represents the percent of stressed coral cover of the total 

coral benthic coverage. Note that stressed coral cover was measured as a percentage of overall coral cover in 

2004. 
SWAINS ISLAND

395

surveys and a significant crown-of-thorns seastar (COTS) infestation that was observed at the 

time of these surveys, as described in Section 7.7.1: Benthic Macroinvertebrate Surveys.

Eight REA coral surveys were conducted around Swains during ASRAMP 2004. Coral 

communities at Swains were very similar across sites (Fig. 7.5.1g). Fifteen anthozoan and 

hydrozoan genera were observed, with members of the genera Montipora and Pocillopora 

dominating the coral fauna. Each genus contributed an island-wide mean of 31% (Montipora) 

and 51% (Pocillopora) to the total number of coral colonies recorded (Fig. 7.5.1g). Porites was 

more common at sites SWA-03, -05, -06, and -08 in the west and north regions (10% mean of 

the coral community), compared to less than 1% of the coral communities at the remaining sites 

around Swains. Generic richness of corals at Swains was relatively low (8.9 coral genera per 

site [SE 0.8]), ranging from 6 to 12 coral genera observed at each site (Fig. 7.5.1g). Site-specific 

data regarding the relative abundance of coral genera, by colony counts within belt transects, are 

available in Appendix III, Table III. vii.

Figure 7.5.1g. Relative abundance of coral genera and generic richness from REA surveys around Swains 

during ASRAMP 2004. Percent relative abundance of key coral genera are indicated by color-coded portions 

of the pie charts. Size of the pie charts and black numbers in the center of the pie charts indicate the number of 

coral genera observed at each REA site. 
SWAINS ISLAND

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Figure 7.5.1h. Coral communities at Swains are typified by shelving colonies of Montipora. (Photograph 

provided by NOAA PIFSC CRED; J. Kenyon, JIMAR)

Figure 7.5.1i. Older dead portions of the Pocillopora colony are covered with coralline algae, but new damage 

in the form of storm-induced coral breakage was observed as well. (Photograph provided by NOAA PIFSC 

CRED; J. Kenyon, JIMAR)
SWAINS ISLAND

397

Figures 7.5.1h and 7.5.1i illustrate common Montipora and Pocillopora morphologies that typify 

the coral communities around Swains.

The mean percent live scleractinian (stony) coral cover (derived through visual estimates) 

observed during REA surveys at Swains was high, with an overall mean of 46.5% (SE 5.9; 

Fig. 7.5.1j). Coral cover was highest at sites SWA-06, -07, and -08 on the north and east region 

forereefs, ranging from 55% to 70%. 

During ASRAMP 2004, a total of 3073 coral colonies were counted within a survey area of 642 m2

. Coral densities around Swains were variable (5.6 colonies m-2 [SE 1.2]) with the highest coral 

densities observed at north region sites (Fig. 7.5.1j). High coral densities were observed at sites 

SWA-06 and -08, both off the north coast of Swains, with 7.7 colonies m-2 and 13.3 colonies 

m-2, respectively. The lowest coral density (2.1 colonies m-2) was recorded at SWA-10 in the 

southeast region. 

Figure 7.5.1j. Live scleractinian (stony) coral cover and coral colony density from REA surveys around Swains 

during ASRAMP 2004. The size of the symbol is proportional to the value of each parameter. It is important to 

note that coral percent cover was determined by qualitative visual estimates.
SWAINS ISLAND

398

Size-class distribution shows that 41.9% of coral colonies had maximum diameters between 20 

and 40 cm (Fig. 7.5.1k) during ASRAMP 2004 surveys. Spatial patterns in coral size distributions 

were not apparent. Five of eight sites surveyed at Swains had more than 25% of corals with 

diameters larger than 40 cm (SWA-01, -03, -06, -07, -14). Corals with diameters less than 5 cm 

were uncommon at all sites around Swains.

Figure 7.5.1k. Scleractinian coral size-class distribution around Swains from REA surveys during ASRAMP 

2004. The height of the y-axis in each size-class chart represents 100%. The seven observed size classes (0–5, 

6–10, 11–20, 21–40, 41–80, 81–160, and > 160 cm) are color coded in size frequency diagrams at each REA 

site. 
SWAINS ISLAND

399

2006 Spatial Surveys

Nine towed-diver benthic surveys were conducted around Swains during ASRAMP 2006, with 

a mean towed-diver survey depth of 12.7 m. Individual survey depths ranged from 10 m (SD 3) 

to 16 m (SD 3), and were fairly uniform around the island (Fig. 7.5.1l). The island-wide mean of 

live scleractinian (stony) coral cover was 43.9% (SE 4.4; Fig. 7.5.1m). Stressed coral was also 

characterized during these surveys and was gathered as a subset percentage of live coral percent 

cover. The island-wide mean stressed coral cover was 1.9% (SE 0.4; Fig. 7.5.1n), substantially 

lower than observed during 2004.

Figure 7.5.1l. Towed-diver survey tracks around Swains during ASRAMP 2006. Towed-diver survey tracks are 

color coded with mean depths for each 5-min segment. Mean depths and standard deviations for each toweddiver survey are shown in black text. Depth histogram and statistics (counts, minimum depth, maximum depth, 

mean, and standard deviation) from 30-sec depth recordings during towed-diver surveys are included.
SWAINS ISLAND

400

Exceptionally high live coral cover was observed in the east (northeastern corner) region of 

Swains (6 tow segments, mean: 79.5%). The tow segments were also some of the shallowest 

sites surveyed around Swains in 2006, suggesting that coral communities were stratified by depth 

around the island. Coral cover was moderately high (30–50%) around most of the remainder of 

the island. Stressed corals were low in abundance around Swains in 2006, with only one hotspot 

of stress observed in the west region (southernmost corner of the region, 5 tow segments, mean: 

7%).

Figure 7.5.1m. Towed-diver benthic survey observations of live scleractinian (stony) coral cover around 

Swains during ASRAMP 2006. Each colored point represents an integrated estimate over a 5-min observation 

segment covering a survey swath of ~ 200 m × 10 m (~ 2000 m

2

). Symbol size represents the percent live coral 

cover on the benthic habitat. See Chapter 2, Table 2.4.2b for more information on benthic towed-diver binning 

categories during ASRAMP 2006.
SWAINS ISLAND

401

Figure 7.5.1n. Towed-diver benthic survey observations of stressed coral cover around Swains during ASRAMP 

2006. Each colored point represents an integrated estimate over a 5-min observation segment covering a survey 

swath of ~ 200 m × 10 m (~ 2000 m

2

). Symbol size represents the percent of stressed coral cover of the total 

coral benthic coverage. See Chapter 2, Table 2.4.2b for more information on benthic towed-diver binning 

categories during ASRAMP 2006.
SWAINS ISLAND

402

Eight REA coral surveys were conducted around Swains during ASRAMP 2006. At least 12 genera 

of anthozoan and hydrozoan corals were reported around Swains (Fig. 7.5.1o). Members of the 

genera Montipora and Pocillopora dominated the coral fauna, and the community composition 

was quite different between northern and southern sites. Montipora dominated sites with southern 

exposures (SWA-01, -04, -07, -10, -14, mean: 83% of the coral community), while Pocillopora 

was common at northern sites (SWA-05, -06, -08, mean: 58% of the coral community). Generic 

richness of corals at Swains was relatively low at 6.0 coral genera per site (SE 0.6), with between 

3 and 8 coral genera observed at each site. Site-specific data regarding the relative abundance 

of coral genera, by colony counts within belt transects, are available in Appendix III, Table III. 

viii. 

Figure 7.5.1o. Relative abundance of coral genera and generic richness from REA surveys around Swains 

during ASRAMP 2006. Percent relative abundance of key coral genera are indicated by color-coded portions of 

the pie charts. Size of pie charts and black numbers in the center of the pie charts indicate the number of coral 

genera observed at each REA site. Note that SWA-03 (surveyed in 2004) was not resurveyed but substituted 

with SWA-04 in 2006 to improve spatial coverage of survey sites.
SWAINS ISLAND

403

Island-wide mean percent scleractinian (stony) coral cover around Swains was relatively high, 

with an island-wide mean of 42.8% (SE 5.2). Coral cover was greatest at sites SWA-06, -07, and 

-08 on the north and east region forereefs and ranged from 54% to 65% (Fig. 7.5.1p). Relatively 

lower coral cover was reported at sites SWA-04 and -01 (22% and 28%, respectively) in the west 

region and south corner.

During ASRAMP 2006 surveys around Swains a total of 2739 coral colonies were counted 

within a total survey area of 400 m

2

. Mean coral density between REA sites was variable with 

6.9 colonies m-2 (SE 0.6) reported. Relatively higher coral densities were recorded at sites in the 

north region, with 8.2 colonies m-2 and 10.4 colonies m-2 recorded at SWA-06 and -08, respectively 

(Fig. 7.5.1p).

Figure 7.5.1p. Live scleractinian (stony) coral cover and coral colony density from REA surveys around Swains 

during ASRAMP 2006. The size of the symbol is proportional to the value of each parameter. 
SWAINS ISLAND

404

During ASRAMP 2006, coral size-class distributions showed that 40.6% of coral colonies had 

maximum diameters between 10 and 20 cm (Fig. 7.5.1q). Small corals were common at Swains, 

with six out of eight sites having more than 10% of corals with diameters less than 5 cm. The 

only two sites that did not have abundant small corals were located off the north shore sites SWA06 and -08. Corals larger than 40 cm were not common at any sites.

Figure 7.5.1q. Scleractinian coral size-class distribution around Swains from REA surveys during ASRAMP 

2006. The height of the y-axis in each size-class chart represents 100%. The seven observed size classes (0–5, 

6–10, 11–20, 21–40, 41–80, 81–160, and > 160 cm) are color coded in size frequency diagrams at each REA 

site.
SWAINS ISLAND

405

7.5.2 Coral Disease Surveys

2006 Spatial Surveys

Coral health and disease surveys covered a total survey area of 3200 m

2 around Swains during 

ASRAMP 2006, with 80 cases of coral disease, predation, and other lesions observed. Figure 

7.5.2a illustrates the variability in prevalence of the different health states among sites. Coral 

diseases around Swains were uncommon, with only two of the eight sites surveyed containing 

disease. The estimated mean overall prevalence was 0.04% (SE 0.03; Fig. 7.5.2a), and all cases 

occurred at sites SWA-04 and -05, on the west region of the island. Growth anomalies totaled 

three cases, all on Porites spp. and in deeper water (16–18 m). In addition, lesions involving 

hyperpigmented irritations were also noted around Swains (two on Porites cf. rus and P. cf. 

monticulosa, and the other one on Pocillopora eydouxi). One case of mild bleaching was also 

observed at SWA-06. 

Lesions attributable to Acanthaster and Drupella predation were quite abundant and common 

(Figs. 7.5.2a, 7.5.2b, and 7.5.2c). The estimated mean overall prevalence of predation was 0.33% 

(SE 0.05). Predation scars were the most numerous at SWA-01, where coral cover values were 

among the lowest reported for the island. SWA-06 exhibited the second greatest number of scars 

per area surveyed and also exhibited the highest percent of live coral cover for the entire island. 

Even though montiporid corals composed more than 66% of live coral cover, predation scars 

were more abundantly observed on Pocillopora (42%). 

Figure 7.5.2a. Prevalence of predation, bleaching, growth anomalies, tissue loss, black band disease, and other 

lesions at Swains during ASRAMP 2006. Prevalence was calculated relative to the average colony density 

estimates and is indicated by the size of the respective symbols.
SWAINS ISLAND

406

Figure 7.5.2b. Prevalence of predation, bleaching, growth anomalies, tissue loss, black band disease, and other 

lesions at Swains during ASRAMP 2006. Prevalence was calculated relative to the average colony density 

estimates. PRE—Acanthaster and/or Drupella predation; OT—other lesions, including hyperpigmented 

irritations; BBD—black band disease; TL—tissue loss; GA—skeletal growth anomalies; and BL—bleaching.

Figure 7.5.2c. Corallivore Drupella gastropods feeding on platy Montipora (left panel), and COTS (Acanthaster

planci) feeding on Montipora sp. (right panel). (Photographs provided by NOAA PIFSC CRED; B. VargasAngel, JIMAR)
SWAINS ISLAND

407

7.5.3 Temporal Comparison—Coral and Coral Disease

Very high live scleractinian coral cover observed during the towed-diver benthic surveys 

around Swains during the three ASRAMP cruises typified the reef ecosystem. The overall 

towed-diver island-wide mean percent cover of live coral ranged from a high of 60.0% (SE 

4.6) in 2002 to a low of 30.5% (SE 2.7) in 2004, and then back up to 43.4% (SE 1.7) in 

2006 (Fig. 7.5.3a). Moreover, island-wide mean percent cover of stressed coral was 7.8% 

in 2004 and 1.9% in 2006. Combined, these island-wide means for live coral cover and 

percent stressed coral may reflect a progression from a relatively unperturbed ecosystem 

in 2002 to an ecosystem affected by both Hurricane Heta and a COTS infestation in 2004 

(see Section 7.7: Benthic Macroinvertebrates), followed by a partial recovery stage from the 

storm damage by Hurricane Heta, but continued perturbation by COTS in 2006. In either 

case, exceptionally high mean values of live coral cover have been consistently observed 

around Swains, particularly when compared with coral cover observations at most other sites 

surveyed around the United States-affiliated Pacific Islands as part of Pacific RAMP.

Island-wide live coral percent cover, as recorded by REA surveys, was very similar between 

2004 (46.5% [SE 5.9]) and 2006 (42.8% [SE 5.2]; Fig. 7.5.3a). Although these values are 

similar, it is important to note the methods to estimate coral percent cover were different in 

2004 (visual estimates) and 2006 (line point intercept technique). The highest REA coral 

cover values were observed in the north and east regions in both 2004 and 2006 (Figs. 7.5.1j 

and 7.5.1p). Sites SWA-06 and -08 on the north coast had very high live coral cover values in 

both 2004 (55% and 60%, respectively) and 2006 (65% and 56%, respectively). Site SWA07 in the east region also had very high live coral in both 2004 (70%) and 2006 (54%). High 

coral cover at SWA-07 from REA results corroborated results obtained from towed-diver 

surveys.

Low generic diversity was observed around Swains, with 15 genera identified island wide 

in 2004 and 12 genera identified island wide in 2006. Per-site diversity was also low with 

8.9 genera per site (SE 0.8) in 2004 and 6.0 genera per site (SE 0.6) in 2006 (Fig. 7.5.3b). 

Montipora and Pocillopora dominated the coral community in both 2004 and 2006. The 

data from 2006 shows a division within the distribution of coral genera, with the southeast, 

west, and east region sites dominated by Montipora (83% of the coral community) and north 

region sites (in addition to SWA-05 in the west region) dominated by Pocillopora (58% of 

the coral community; Fig. 7.5.1o).

Coral colony density increased slightly between 2004 (5.6 [SE 1.2]) and 2006 (6.9 [SE 0.6]; 

Fig. 7.5.3c). High colony density was directly associated with regions of high coral percent 

cover, as demonstrated by the north region sites SWA-06 and -08. Density at these two 

sites in 2004 was 7.7 colonies m-2 (SWA-06) and 14.4 colonies m-2 (SWA-08). In 2006, 

density at the same two sites was 8.2 colonies m-2 (SWA-06) and 10.4 colonies m-2 (SWA08), respectively.

The majority of corals in 2006 had diameters between 10 and 20 cm, in contrast to observations 

in 2004 where the majority of corals had diameters between 20 and 40 cm (Fig. 7.5.3d). The 

difference in size-class distributions between the years may reflect one or several factors, 

including breakage from hurricane or other storm activity and interobserver variability.
SWAINS ISLAND

408

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

2004 2006

Coral Colonies m-2

(± SE)

Figure 7.5.3c. Temporal comparison of mean coral colony density from REA surveys at sites around Swains 

during ASRAMP 2004 and 2006.

Figure 7.5.3a. Temporal comparison of mean percent live coral cover from REA surveys and towed-diver 

surveys around Swains during ASRAMP 2002, 2004, and 2006 surveys. The purple bars represent observations 

collected during towed-diver habitat surveys. The green bar represents REA data collected by visual estimates 

during REA surveys, and the blue bar represents data collected by the line point intercept technique during 

REA surveys. See Chapter 2, Section 2.4: Reef Benthic (Coral, Algae, Macroinvertebrate) and Fish Surveys for 

considerations when comparing the results of these methodologies.

0.0

2.0

4.0

6.0

8.0

10.0

12.0

2004 2006

Coral Genera per site

(± SE)

Figure 7.5.3b. Temporal comparison of mean values of coral genera per site around Swains during ASRAMP 
SWAINS ISLAND

409

High coral cover on towed-diver surveys was not spatially linked with areas of high coral stress 

or dead coral percent cover, which indicates that other factors may have been responsible for 

the distribution of stressed or dead coral. Across the years of towed-diver surveys, the east 

region and the most southern tip of the west/southeast regions had the highest cover of live 

coral.

7.6 Algae

It is important to note when considering these results that turf algae, crustose coralline red algae, 

branched non-geniculate coralline red algae, and cyanophytes (blue-green algae) all need to be 

analyzed microscopically for proper taxonomic identification and therefore must be lumped into 

functional group categories in the field. Of these functional groups, turf algae are the most diverse 

with the possibility of up to 100 species occurring in a 10 cm

2 area. As well, macroalgae are large, 

fleshy, sometimes calcified entities that may be identifiable to genus or species in the field, but 

often require microscopic analysis to confirm taxonomic identities.

7.6.1 Algal Surveys

2002 Spatial Surveys

Nine towed-diver surveys were conducted around Swains during ASRAMP 2002, with fleshy 

macroalgae and crustose coralline red algae covering, on average, 32.7% of the benthic substrate. 

Mean fleshy macroalgal cover was 16.2% (SE 1.3), and mean crustose coralline algal cover was 

16.5% (SE 0.7) of the benthic substrate (Fig. 7.6.1a). Highest percent cover of fleshy macroalgae 

was observed along the north and west shores of the island. Percent cover of crustose coralline 0

50

100

150

200

250

300

350

400

0-5 cm 6-10 cm 10-20 cm 20-40 cm 40-80 cm 80-160 cm >160 cm

Coral Colony Size Class

Density (coral colonies 100 m-2 ± SE)

2004

2006

Figure 7.5.3d. Coral colony size-class mean density from REA surveys at sites around Swains during ASRAMP 

2004 and 2006.
SWAINS ISLAND

410

algae was fairly uniform around the perimeter of the island.

Qualitative REA algal surveys were conducted around Swains during ASRAMP 2002, and nine 

bags of algal voucher specimens were collected. These surveys provided baseline data used to 

design and scale the future methodology of algal REA surveys.

2004 Spatial Surveys

A total of 14 towed-diver benthic surveys around Swains during ASRAMP 2004 recorded a 

mean combined algal cover (including fleshy macroalgal, turf, and crustose coralline red algae) 

of 60.8% (Fig. 7.6.1b). Mean fleshy macroalgal cover (including turf) was 28.6% (SE 1.4), and 

mean crustose coralline algal cover was 32.2% (SE 0.9; Fig. 7.6.1b). Generally, higher cover of 

macroalgae was observed along the south coast than compared to other areas. Percent cover of 

crustose coralline algae was fairly uniform around the perimeter of the island.

During ASRAMP 2004, quantitative algal surveys were conducted at nine sites around Swains 

(Fig. 7.6.1c). A total of 10 macroalgal genera (4 green, 4 red, and 2 brown) and 4 additional algal 

functional groups (turf algae, crustose coralline red algae, branched non-geniculate coralline red 

algae, and cyanophytes) were observed in the field. Once completed, laboratory-based taxonomic 

identification of all algal species (including turf algae, epiphytes, and crustose coralline red 

algae) will greatly increase the known algal diversity. Crustose coralline red algal and turf algal 

functional groups (each containing numerous species) were the dominant algae found around 

Swains and observed in over 50% of sampled quadrats at 100% of sites.

Around Swains, the green alga Rhipilia orientalis was one of the dominant algal species found in 

high abundance at all sites assessed (Fig. 7.6.1c). Microdictyon umbilicatum (Velley) Zanardini, 

a green algal species in the order Siphonocladales, was also in high abundance at most sites 

at Swains. Surprisingly, the calcified siphonous green algal genus, Halimeda, which is usually 

common in tropical marine environments, was relatively uncommon at most sites monitored 

around Swains, only being found in photoquadrats at one southern site (SWA-14). The green 

algal genus, Dictyosphaeria, was present in low abundance at most sites. Of interest, the green 

Figure 7.6.1a. Percent cover of fleshy macroalgae (including turf algae) and crustose coralline algae from 

towed-diver benthic surveys around Swains during ASRAMP 2002. Each colored point represents an integrated 

estimate over 5-min observation segments covering a survey swath of ~ 200 m × 10 m (~ 2000 m

2

). 
SWAINS ISLAND

411

Figure 7.6.1b. Percent cover of fleshy macroalgae (including turf algae) and crustose coralline algae from 

towed-diver benthic surveys around Swains during ASRAMP 2004. Each colored point represents an integrated 

estimate over 5-min observation segments covering a survey swath of ~ 200 m × 10 m (~ 2000 m

2

).

Figure 7.6.1c. Percent occurrence of select macroalgal genera and algal functional groups from REA surveys 

around Swains during ASRAMP 2004. Percent occurrence is equivalent to the percentage of photoquadrats in 

which an algal genus or functional group was observed. Length of x-axis denotes 100% occurrence.
SWAINS ISLAND

412

alga Caulerpa serrulata was found during random collections made outside of quantitative 

photoquadrats and is a new record for Swains.

During ASRAMP 2004, some distributional trends were observed among macroalgal populations 

around Swains. The red algal genus, Peyssonnelia, was most abundant in photoquadrats at 

sites on the northwest corner of the island and was only observed in low abundance elsewhere. 

Alternatively, non-geniculate branched red algae were lacking from photoquadrats at northwestern 

sites but were fairly common at all other sites around the island. Sites on the west side of the 

island contained slightly lower algal species diversity than other areas.

2006 Spatial Surveys

A total of nine towed-diver surveys were conducted around Swains during ASRAMP 2006. 

Together, the mean cover of fleshy macroalgae (excluding turf) and crustose coralline algae 

made up 55.5% of the benthic substrate. Mean fleshy macroalgal cover was 36.1% (SE 1.8), and 

mean crustose coralline algal cover was 19.4% (SE 1.2; Fig. 7.6.1d). Macroalgal populations 

were greatest in the north region and were also elevated along southern-facing reefs. Crustose 

coralline algae were also of greatest abundance along the southern-facing reefs of Swains.

During ASRAMP 2006, quantitative algal surveys were conducted at eight sites around Swains, 

including seven of the eight sites surveyed in 2004 (Fig. 7.6.1e). A total of 11 macroalgal genera (7 

green, 2 red, and 2 brown) and 3 additional algal functional groups (turf algae, crustose coralline 

red algae, and cyanophytes) were observed in the field. The diversity of crustose coralline red algal 

and turf algal functional groups (each of which contains numerous species) were the dominant 

algae found around Swains, being observed in over 50% of sampled quadrats at 71% and 57% 

of sites, respectively (Fig. 7.6.1e). The green algal genus Rhipilia was one of the dominant algal 

species found in high abundance at all sites. Surprisingly, the calcified siphonous green algal 

genus, Halimeda, which is usually common in tropical marine environments, was absent around 

Swains. Microdictyon umbilicatum, a green algal species in the order Siphonocladales, was 

common at northern, eastern, and southern sites around Swains. The northwestern side of the 

island exhibited the lowest algal diversity and abundance. 

Figure 7.6.1d. Percent cover of fleshy macroalgae (including turf algae) and crustose coralline algae from 

towed-diver benthic surveys around Swains during ASRAMP 2006. Each colored point represents an integrated 

estimate over 5-min observation segments covering a survey swath of ~ 200 m × 10 m (~ 2000 m

2

).
SWAINS ISLAND

413

7.6.2 Coralline Algal Disease Surveys

2006 Spatial Surveys

No coralline algal diseases or afflictions were observed at Swains in 2006.

7.6.3 Temporal Comparison—Algae

Temporal comparisons of both REA algal data and towed-diver benthic survey data are shown in 

Figures 7.6.3a and 7.6.3b, respectively. Algal populations around Swains were similar between 

ASRAMP 2004 and 2006. The number of macroalgal genera observed around Swains was similar 

for both years, with 10 and 11 genera recorded, respectively. The red calcified, geniculate genera 

Amphiroa/Jania were uncommon only occurring on the northwest corner of the atoll. The calcified 

green algal genus Halimeda was lacking from all photoquadrats sampled. No large cyanobacteria 

outbreaks or monotypic stands of invasive algae were discovered in 2004 or 2006.

Figure 7.6.1e. Percent occurrence of select macroalgal genera and algal functional groups from REA surveys 

around Swains during ASRAMP 2006. Percent occurrence is equivalent to the percentage of photoquadrats in 

which an algal genus or functional group was observed. Length of x-axis denotes 100% occurrence.
SWAINS ISLAND

414

0

10

20

30

40

50

60

70

80

90

100 Amphiroa/Jania

Crustose Coralline Red Algae Branched Coralline Red Algae Peyssonnelia Dictyosphaeria Halimeda Microdictyon

Rhipilia Cyanophyte Turf Algae

% Occurrence (± SE) 

2004

2006

Figure 7.6.3a. Temporal comparison of REA algal genera and functional group percent occurrence around Swains 

between ASRAMP 2004 and 2006. See Chapter 2, Section 2.4: Reef Benthic (Coral, Algae, Macroinvertebrate) 

and Fish Surveys for considerations when comparing the results of these methodologies between years. 05

10

15

20

25

30

35

40

2002 2004 2006

% Algal Cover (± SE)

Fleshy Algae

(Macroalgae and Turf

Algae)

Crustose Coralline Red

Algae

Macroalgae

Figure 7.6.3b. Temporal comparison of towed-diver benthic survey algal percent cover results for fleshy 

crustose coralline and macroalgae for 2002, 2004, and 2006 ASRAMP surveys around Swains.
SWAINS ISLAND

415

7.7 Benthic Macroinvertebrates

7.7.1 Benthic Macroinvertebrate Surveys

2002 Spatial Surveys

Towed-diver benthic macroinvertebrate surveys around Swains during ASRAMP 2002 found that 

COTS were commonly observed around the entire island with a mean density of 1.0 organisms 

ha-1), but especially in the west, southeast, and north regions. No sea urchins or sea cucumbers 

were reported (Fig. 7.7.1a). Giant clam mean density was 0.4 organisms ha-1, found along the 

north section of the island. As mentioned in the introduction (Chapter 1, Section 1.6: Limitations 

of Pacific RAMP), surveys in 2002 were limited by shipboard logistics and methods development 

that may have contributed to the paucity of macroinvertebrates observed in that year. 

A total of 10 qualitative REA invertebrate surveys, focusing on general macroinvertebrate 

biodiversity, were conducted around Swains during ASRAMP 2002. These surveys provided 

baseline data used to design and scale the future methodology of macroinvertebrate REA surveys. 

No data are presented.

Figure 7.7.1a. Distribution of estimated population densities of COTS, giant clams, sea cucumbers, and sea 

urchins at Swains from towed-diver benthic surveys during ASRAMP 2002. Circle locations represent an 

integrated estimate over 5-min observation segments covering a survey swath of ~ 200 m × 10 m (~ 2000 m

2

). 

The sizes of the circles indicate the number of organisms counted or estimated in each ~ 2000 m2 segment with 

one scale for COTS, giant clams, and sea cucumbers (1–10, 11–25, 26–50, and > 50) and another scale for sea 

urchins (1–50, 51–250, 251–500, and > 500).
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2004 Spatial Surveys

Towed-diver benthic macroinvertebrate surveys around Swains during ASRAMP 2004 found 

few macroinvertebrates around Swains, with the exception of COTS (Fig. 7.7.1b). Only one 

giant clam was encountered during towed-diver surveys. Sea urchins (mean: 13.7 organisms ha-1) 

and sea cucumbers (mean: 0.1 organisms ha-1) were seen in very low densities around the island. 

A total of 91 COTS were observed around Swains (mean: 3.3 organisms ha-1). The distribution 

of COTS was variable with a slightly higher concentration observed around the southern corner 

of the island.

Figure 7.7.1b. Distribution of estimated population densities of COTS, giant clams, sea cucumbers, and sea 

urchins at Swains from towed-diver benthic surveys during ASRAMP 2004. Circle locations represent an 

integrated estimate over 5-min observation segments covering a survey swath of ~ 200 m × 10 m (~ 2000 m

2

). 

The sizes of the circles indicate the number of organisms counted or estimated in each ~ 2000 m2 segment with 

one scale for COTS, giant clams, and sea cucumbers (1–10, 11–25, 26–50, and > 50) and another scale for sea 

urchins (1–50, 51–250, 251–500, and > 500).
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417

During ASRAMP 2004, invertebrate species richness was relatively low at all REA sites around 

Swains, ranging from 2 species observed at SWA-14 to 10 species observed at SWA-05 and -03 

(Fig. 7.7.1c). No giant clams or sea urchins were recorded, while only a single sea cucumber, 

Thelonota ananas, was observed (SWA-05). Unlike towed-diver surveys, no COTS were recorded 

at REA sites.

Figure 7.7.1c. Macroinvertebrate species richness, and target macroinvertebrate distribution at Swains from 

REA surveys during ASRAMP 2004. Size of light blue circles and values in circles indicate target species 

richness values for each REA site. Other symbols indicate the presence of specific target species.
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2006 Spatial Surveys

Towed-diver benthic macroinvertebrate surveys during ASRAMP 2006 found few 

macroinvertebrates around Swains, with the exception of COTS (Fig. 7.7.1d). Two sea cucumbers 

were observed within the west region of Swains, while no giant clams or sea urchins were 

encountered. A total of 88 COTS were observed around Swains in 2006 for a mean density of 4.9 

organisms ha-1. COTS were relatively common in the west and southeast coasts of Swains, but 

encounters were far less frequent during towed-diver surveys along the north and east regions.

During ASRAMP 2006, target invertebrates were almost completely absent from REA surveys 

around Swains (Fig. 7.7.1e). Two species of sea urchins, Echinostrephus aciculatus and 

Echinometra mathei, were present at one site each (SWA-05 and -14, respectively). COTS were 

observed at three sites, all along the west coast of Swains. 

Figure 7.7.1d. Distribution of estimated population densities of COTS, giant clams, sea cucumbers, and sea 

urchins at Swains from towed-diver benthic surveys during ASRAMP 2006. Circle locations represent an 

integrated estimate over 5-min observation segments covering a survey swath of ~ 200 m × 10 m (~ 2000 m

2

). 

The sizes of the circles indicate the number of organisms counted or estimated in each ~ 2000 m2 segment with 

one scale for COTS, giant clams, and sea cucumbers (1–10, 11–25, 26–50, and > 50) and another scale for sea 

urchins (1–50, 51–250, 251–500, and > 500).
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7.7.2 Temporal Comparison—Benthic Macroinvertebrates

Temporal patterns of island-wide mean benthic macroinvertebrate density (# organisms m-2) 

around Swains from towed-diver benthic surveys during ASRAMP 2002, 2004 and 2006 are 

shown in Figures 7.7.2a (COTS), 7.7.2b (giant clams), 7.7.2c (sea cucumbers), and 7.7.2d (sea 

urchins). Towed-diver survey results show trends in density within each surveyed organism and 

between each sampling year.

With the exception of the COTS, macroinvertebrates were extremely rare around Swains during 

both 2004 and 2006 surveys. The average COTS sighting per hectare increased almost fivefold 

between 2002 and 2006, from 1 COTS ha-1 in 2002 to 4.7 COTS ha-1 in 2006 (Fig. 7.7.2a). Giant 

clams (Tridacna sp.) declined between 2002 and 2006, with no giant clams observed in 2006; the 

reason for this decline is unknown (Fig. 7.7.2b). Sea cucumbers and sea urchins were not seen in 

high densities in any years (Figs. 7.7.2c and 7.7.2d).

Figure 7.7.1e. Target macroinvertebrate distribution at Swains from REA surveys conducted during ASRAMP 

2006. 
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420

0.00

0.05

0.10

0.15

0.20

0.25

2002 2004 2006

Mean Density 

(organisms ha-1 ±SE)

Figure 7.7.2c. Mean density of sea cucumber (holothuroids) at Swains from towed-diver surveys during 

ASRAMP 2002, 2004, and 2006. 01234567

2002 2004 2006

Mean Density 

(organisms ha-1 ±SE)

Figure 7.7.2a. Mean density of COTS at Swains from towed-diver surveys during ASRAMP 2002, 2004, and 

2006.

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

2002 2004 2006

Mean Density 

(organisms ha-1 ±SE)

Figure 7.7.2b. Mean density of giant clams at Swains from towed-diver surveys during ASRAMP 2002, 2004, 

and 2006.
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05

10

15

20

25

2002 2004 2006

Mean Density 

(organisms ha-1 ±SE)

Figure 7.7.2d. Mean density of sea urchins (echinoids) at Swains from towed-diver surveys during ASRAMP 

2002, 2004, and 2006.
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7.8. Reef Fish

7.8.1 Reef Fish Surveys

2002 Spatial Surveys

Large fish (> 50 cm) biomass was relatively elevated and evenly distributed around Swains 

during ASRAMP 2002 (0.256 tons ha-1 [SE 0.130]; Fig. 7.8.1a). Barracudas clearly dominated 

biomass, followed closely by lower biomass of jacks and snappers. 

Sharks were most frequently sighted in the east and southeast regions and were represented 

by the grey reef shark (Carcharhinus amblyrhynchos) and the reef whitetip shark (Triaenodon 

obesus; Fig. 7.8.1a). Humphead wrasses (Cheilinus undulatus) were observed less frequently 

at various locations around the island. In addition, several large (> 1.5 m total length) dogtooth 

Figure 7.8.1a. Large fish biomass, family composition, and individual shark sightings at Swains recorded 

during ASRAMP 2002 towed-diver surveys. Large fish (length > 50 cm) biomass on each individual toweddiver survey is represented by the color of the survey track. Composition by trophic group is indicated by the 

family colors (green—mostly herbivores; other colors—mostly predators or mixed). Individual shark sightings, 

observed inside or outside the survey area, are represented by blue triangles.
SWAINS ISLAND

423

tunas (Gymnosarda unicolor) and a school of approximately 100 blackfin barracudas (Sphyraena 

qenie) were sighted.

Total fish biomass was similar at most sites around Swains during 2002 surveys (6.3 kg 100 m-2

[SE 3.6]), except for site SWA-07 which had an elevated biomass related to a rare shark sighting 

on one transect (Fig. 7.8.1b). Predators, mainly snappers, groupers, and triggerfish, were the most 

abundant trophic group at all sites. The most common snapper and grouper were Lutjanus bohar 

and Cephalopholis argus, respectively. Herbivores were observed in relatively low abundance.

Species richness was approximately 30 fish species at each REA site and fairly consistent around 

the island (Fig. 7.8.1b).

Figure 7.8.1b. Total fish biomass, family composition, and species richness of fishes at Swains recorded during 

ASRAMP 2002 REA belt-transect surveys. Total fish biomass (all species and size classes) is represented at 

each site by the size of the pie chart with the actual biomass value in the center (kg 100 m-2). Composition by 

trophic group is indicated by the family colors (green—mostly herbivores; other colors—mostly predators or 

mixed). Species richness at each REA site is indicated by numbers and the size of the beige circles.
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2004 Spatial Surveys

Results from towed-diver surveys during ASRAMP 2004 showed that barracudas composed most 

of the large fish (> 50 cm total length) biomass around Swains, followed by snappers and jacks. 

The blacktongue unicornfish (Surgeonfish; Naso hexacanthus) was especially abundant. Distinct 

schools of more than 100 barracuda (Sphyraena qenie) and bigeye trevally (Caranx sexfasciatus) 

were again encountered. Overall, large fish biomass was very high around the island (0.164 tons 

ha-1 [SE 0.102]), particularly in the north region (Fig. 7.8.1c).

Humphead wrasses (Chelinus undulatus) were seen in loose aggregations of up to 10 individuals 

(50 to > 150 cm total length), mostly in the west and east regions of the island. Behavior and 

densities suggest that this may be a resident spawning aggregation. In contrast to the abundance 

of other large fish taxa, shark sightings were relatively scarce (Fig. 7.8.1c).

During ASRAMP 2004, the overall fish biomass around Swains was around 29.3 kg 100 m-2

Figure 7.8.1c. Large fish biomass, family composition, and individual shark sightings at Swains recorded 

during ASRAMP 2004 towed-diver surveys. Large fish (length > 50 cm) biomass on each individual toweddiver survey is represented by the color of the survey track. Composition by trophic group is indicated by the 

family colors (green—mostly herbivores; other colors—mostly predators or mixed). Individual shark sightings, 

observed inside or outside the survey area, are represented by blue triangles.
SWAINS ISLAND

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(SE 20.1); the greatest biomass was around the north region of the island (~ 86 kg 100 m-2; Fig. 

7.8.1d). This observation remained constant even when the singular occurrence of a massive 

school of barracudas (Sphyraena qenie) encountered at site SWA-06 was removed from the 

analysis (~ 22 kg 100 m-2). Predators remained the dominant trophic group around the island 

(e.g., triggerfish, snappers, and groupers). 

Medium-large fish (> 25 cm total length) biomass recorded during stationary point count surveys 

was dominated by snappers, followed by surgeonfish and groupers. Moderate levels were recorded 

for triggerfish, parrotfish, and jacks.

Species richness was slightly higher than in 2002 (~ 40 species 100 m-2) and was distributed 

evenly around Swains (Fig. 7.8.1d).

Figure 7.8.1d. Total fish biomass, family composition, and species richness of fishes around Swains recorded 

during ASRAMP 2004 REA belt-transect surveys. Total fish biomass (all species and size classes) is represented 

at each site by the size of the pie chart with the actual biomass value in the center. Composition by trophic group 

is indicated by the family colors (green—mostly herbivores; other colors—mostly predators or mixed). Species 

richness at each REA site is indicated by numbers and the size of the beige circles.
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426

2006 Spatial Surveys During ASRAMP 2006, the overall large fish (> 50 cm total length) biomass (all families pooled) 

was on average of 0.132 tons ha-1 (SE 0.085; Fig. 7.8.1e). Similar to 2004, large fish biomass was 

mainly composed of jacks, barracudas, and sharks and was concentrated in the north and, to a 

lesser extent, south regions of the island.

A relatively high number of humphead wrasses were observed in 2006. Sharks were generally 

encountered in the north and south sections of the island during towed-diver surveys (Fig. 

7.8.1e).

Similar to previous years, the total reef fish biomass during ASRAMP 2006 was highest in 

the north section of the island (~ 11 kg 100 m-2) caused by a large school of jacks (Caranx 

sexfasciatus; Fig. 7.8.1f). Overall total biomass was a relatively low 6.5 kg 100 m-2 (SE 2.9).

Figure 7.8.1e. Large fish biomass, family composition, and individual shark sightings around Swains recorded 

during ASRAMP 2006 towed-diver surveys. Large fish (length > 50 cm) biomass on each individual toweddiver survey is represented by the color of the survey track. Composition by trophic group is indicated by the 

family colors (green—mostly herbivores; other colors—mostly predators or mixed). Individual shark sightings, 

observed inside or outside the survey area, are represented by blue triangles.
SWAINS ISLAND

427

Snappers still represented the highest biomass of medium-large (> 25 cm total length) taxa 

around Swains, based on stationary point count surveys. Surgeonfish, wrasses (including several 

humpheads), grouper, and jacks (e.g., schools of rainbow runner, Elegatis bipinnulata) were also 

common. Parrotfish were rare around the island. 

Fish species richness was slightly higher on the western side of the island (~ 30 species 100 m-2) 

compared to the eastern side (~ 25 species 100 m-2). In general, species richness was similar to 

2002, which was lower than 2004 (Fig. 7.8.1f).

7.8.2 Temporal Comparison—Reef Fish

Total fish biomass distribution was variable among years, but this is mainly caused by the chance 

occurrence of very large schools at various sites (e.g., jacks, emperors, or barracudas). Swains was 

characterized by these large schools of predators and the general dominance of other predators 

Figure 7.8.1f. Total fish biomass, family composition, and species richness of fishes around Swains recorded 

during ASRAMP 2006 REA belt-transect surveys. Total fish biomass (all species and size classes) is represented 

at each site by the size of the pie chart with the actual biomass value in the center. Composition by trophic group 

is indicated by the family colors (green—mostly herbivores; other colors—mostly predators or mixed). Species 

richness at each REA site is indicated by numbers and the size of the beige circles.
SWAINS ISLAND

428

at practically all sites in all years surveyed. This also explains the high interyear variability in 

total fish biomass (Fig. 7.8.2a). Overall fish biomass for the island was around 1.84 tons ha-1 (SE 

0.86). 

Large fish biomass (> 50 cm total length) was high around the entire island but mainly concentrated 

in the northwest section. Large schools of barracudas and jacks were almost always encountered 

there. The bulk of the biomass was represented by barracudas, jacks, snappers, and sharks. 

Similar to Rose Atoll, large fish biomass around Swains appears to have decreased by half, from 

0.256 tons ha-1 in 2002 to 0.132 tons ha-1 in 2006 (Fig. 7.8.2b). Overall, large fish biomass around 

Swains is around 0.184 tons ha-1 (SE 0.105).

Sharks and humphead wrasses were frequently seen around the entire island. Shark species 

Figure 7.8.2a. Total fish biomass at Swains during ASRAMP 2002 (6 sites), 2004 (8 sites), and 2006 (8 sites) 

REA surveys.

Figure 7.8.2b. Large fish biomass at Swains during ASRAMP 2002 (9 surveys), 2004 (14 surveys), and 2006 

(9 surveys) towed-diver surveys.
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429

commonly sighted were grey and whitetip reef sharks. No evidence of bumphead parrotfish 

populations have been observed around the island. Dogtooth tuna (Gymnosarda unicolor) were 

more common here than at any other island in American Samoa.

Fish diversity, measured as species richness, was mostly homogeneous around Swains (~ 32 

species 100 m-2).

All the biomass per island means referenced in the above section can be found in Appendix IV, 

Table IV. i and Table IV. ii. Fish density per island means can also be found in Appendix IV, Table 

IV. iii and Table IV. iv.

7.9 Island Summary and Integration

Among the islands that make up American Samoa, Swains is the smallest in area (2.6 km

2

) and 

most distant in the archipelago, located about 350 km to the north of Tutuila. High-resolution 

bathymetry shows Swains as a steep, conical atoll with depths dropping off precipitously within 

close proximity to the island. Nearshore, the island is surrounded by a shallow (~ 1 m) reef flat 

from the shoreline to the reef crest, but lacks an insular shelf and is characterized by intermittent 

spur-and-groove features along the reef crest.

Habitat complexity was relatively high around all coasts of the island, but appeared highest along 

the west region, specifically along the southwestern-facing shore, and along the northeast side of 

the atoll near the dividing line between the north and east regions (Fig. 7.3.2a). Divers also noted 

small scattered deposits of sand in the northeast (Fig. 7.3.2b), which was indicative of spur-andgroove features along the forereef crest when coupled to habitat complexity observations (Fig. 

7.3.2a), bathymetry (Fig. 7.3.1a), and backscatter intensity (Fig. 7.3.1b) in the same area. 

Spatially, oceanographic conditions around Swains, because of its small size, geographic isolation, 

and lack of any prominent bathymetric features, were largely homogeneous at any given time as 

most small- and large-scale oceanographic processes influence waters on all sides of the island. 

Temporally, oceanographic conditions around Swains were principally dominated by seasonal 

variability with respect to temperature and wave heights (Figs. 7.4.1c, 7.4.1f, 7.4.1i, and 7.4.3b). 

The prevailing wave climate is shaped primarily by events originating from southeasterly 

directions. Episodic large swell (> 4 m) events derived from passing cyclones do occur, and in 

general, originate southeast of American Samoa and track northwest. As previously stated, the 

lagoon at Swains appeared to have little effect on the physical properties of the ocean outside 

the island perimeter. This is caused by the lack of outflow from the inner lagoon to the ocean 

and to the low-lying geography, limited vegetation, and lack of anthropogenic sources to affect 

nearshore nutrient loading during precipitation events.

Habitat complexity and the distribution and abundance of coral and invertebrate communities 

around Swains appear to be covariant. Habitat complexity, as observed by towed divers, was 

high along the north and west portions of the island, while the southeast side was characterized 

with low values (Fig. 7.3.2a). REA surveys recorded high values of mean coral cover and coral 

density also along the north and east (Figs. 7.5.1j and 7.5.1p, respectively), with the lowest 

values observed on the southeast side of the island. Towed-diver surveys also recorded high live 

coral cover (> 75%) on the east side of the island and the low cover (20–30%) at the southern and 

western points of the island (Fig. 7.3.2e). The high island-wide mean coral cover estimates from 

both REA and towed-diver surveys were somewhat exceptional when compared with most of 
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the other island and atolls surveyed as part of Pacific RAMP, suggesting that Swains is a unique 

ecosystem deserving thoughtful consideration for long-term management and conservation.

Coral size-class distribution at all REA sites was dominated by relatively small colonies; 

however, the 2006 surveys indicate a trend towards even smaller coral colonies on the southeast 

forereef (Figs. 7.5.1k and 7.5.1q). The relatively low habitat complexity and coral size and cover 

observed on the southeast side may be attributable in part to directional wave climatology of 

Swains, including the episodic large swell events that hit this region of the island.

Coral community composition in each of the survey years was principally composed of Monitpora 

and Pocillopora spp., although a shift in abundance by site and location was observed. During the 

2004 survey, Pocillopora was most common at all sites, while in 2006, Montipora was the most 

abundant at sites located on the southeast, east, and one site on the west side of Swains, while 

Pocillopora remained abundant to the north (Figs. 7.5.1g and 7.5.1o). Coral generic richness 

appeared more random in distribution, yet at all REA sites, richness decreased between the two 

survey periods. Coral diseases at Swains were uncommon, with diseases observed at only two of 

the eight sites surveyed (Fig. 7.5.2a).

Algal populations around Swains did not appear to be as covariant with habitat complexity, and 

they are slightly more evenly distributed relative to coral communities. In 2004, the green algal 

genera Rhipilia and Microdictyon were common at all sites around the island (Figs. 7.6.1c and 

7.6.3a). The geniculate (branching) red coralline alga Peyssonnelia, however, was only observed 

at sites located on the north and west where the non-geniculate corallines were concurrently 

lacking. Algal diversity was slightly higher on the eastern side of the island compared to the west 

(Figs. 7.6.1c, 7.6.1e, and 7.6.3a).

Invertebrate species richness at all REA sites was low around Swains (Figs. 7.7.1c and 7.7.1e); 

however, invertebrate distributions during the 2004 survey exhibited similar spatial patterns as 

those observed in live coral and habitat complexity. The greatest numbers of invertebrate species 

were recorded at sites SWA-05 and -03 in the west region, and the lowest numbers were observed 

at site SWA-14 on the southeast side (Fig. 7.7.1c). Target invertebrates were nearly absent from 

REA surveys around Swains during 2006 (Fig. 7.7.1e). Invertebrate data collected by towed 

divers found the distribution of COTS to vary between years; abundance was high along the 

southern tip of the island (Fig. 7.7.1b) in 2004, while in 2006, COTS were far less frequent in the 

north region compared to the southeast, west, and east regions (Fig. 7.7.1d). In addition, toweddiver surveys around Swains found high values of stressed coral (7.8%) in 2004 (Fig. 7.5.1f). 

This corresponded with both a threefold increase in COTS between 2002 and 2004 and the nearby 

passage of Hurricane Heta the month prior to the ASRAMP 2004 surveys. An additional category 

3 tropical cyclone (Percy), which produced 6-m wave heights, passed within close proximity 

(< 50 km) to Swains in 2005; however, significantly lower coral stress values were recorded in 

2006 (1.9%; Fig. 7.5.1n) in comparison with 2004. It is very likely that a combination of known 

and unknown oceanographic and biological interactions contributed to the COTS population 

increase, which will likely be further examined during future ASRAMP deployments.

Similar to algal populations, fish populations around Swains appeared more evenly distributed 

relative to coral and macroinvertebrate communities. Total fish biomass was high overall, but 

varied between years (e.g., chance encounters of jack, emperor or barracuda schools on quantitative 

surveys; Figs. 7.8.1b, 7.8.1d, 7.8.1f, and 7.8.2a). Large fish biomass was characterized primarily 

by schools of predators (including barracudas, jacks, snappers and sharks) that dominated at 
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431

most sites around Swains and were concentrated on the northwest corner (Figs. 7.8.1a, 7.8.1c, 

7.8.1e, and 7.8.2b). Species richness, a measure of diversity, was essentially uniform for fish 

populations around Swains.

Although it is difficult to adequately characterize the coral reef ecosystem of Swains with high 

spatial and temporal resolution from biennial surveys, the large amount of oceanographic, 

geological, and biological data collected during ASRAMP cruises since 2002 is sufficient to 

highlight many general ecosystem trends. Spatial patterns in habitat complexity and the distribution 

and abundance of corals and invertebrates appear well associated with the unidirectional nature 

of incoming wave energy. Consistent short period swell batters the southeastern shoreline of 

Swains, and although the specific nature of the physical-biological interactions requires further 

study, it appears the wave energy is reducing habitat complexity, reducing live coral growth, 

impinging upon coral densities and distribution, and affecting invertebrate distribution. Algae 

and fish distributions do not appear to have similar spatial variability or to be associated with the 

wave climatology data. Observed variability in the distribution and abundance of invertebrates, 

including COTS, and coral community composition and generic richness between ASRAMP 

cruises, was potentially caused by category 3 tropical Cyclone Percy that produced 6-m wave 

heights and passed within close proximity (< 50 km) to Swains in 2005. Integration of the 

ecosystem level components measured and observed around Swains between 2002 and 2006 

yields a picture of a small isolated island, with no notable human population, minor terrigenous 

input, and little bathymetric variability, and whose biological components are highly subject to the 

ambient physical oceanographic conditions including the seasonally variable wave climatology.
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