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Chapter 5 Ta`u Island

TA`U ISLAND

5.1 Geopolitical Context

Ta`u Island is the easternmost member of the Manu`a Island group, located ~ 150 km 

northeast of Tutuila Island and ~ 20 km east of Olosega Island. Ta`u, with a land area of 44 

km2, is an extremely steep volcanic island ringed by sea cliffs, some nearly 600 m high, with 

limited low altitude, level land areas. The seafloor surrounding Ta`u drops steeply, sometimes 

almost vertically, to abyssal. Collapse and landslides off the remnants of the southern caldera 

resulted in a south-facing embayment with a steep headwall that overlooks several flat 

benches, with the most prominent being the Liu Bench overlooking Papaloaloa Point (Fig. 

5.1a). Between Olosega and Ta`u lies an unnamed submerged volcanic ridge and cone that 

was previously active in 1866 (Craig, 2002), and more recently mapped between 2004 and 

2006. The broader area is still considered to be geologically active since the submerged 

volcanic cone of Vailulu`u Seamount is rapidly (in a geologic sense) forming approximately 

50 km east of Ta`u. 

Ta`u is divided into three counties: Faleasao County, Fiti`uta County, and Ta`u County. The 

population of Ta`u has mirrored similar trends reported at Ofu and Olosega Islands, with 

larger populations recorded in the mid-20th century that have seen a steady decline over the 

course of the last 60 years. Cyclones Tusi (1987), Ofa (1990), and Val (1991) resulted in 

Figure 5.1a. Watershed boundaries, streams, landmarks and villages for Ta`u. Also shown is the boundary for 

the National Park of American Samoa (NPAS).
TA`U ISLAND

224

approximately one-third of the population moving to Tutuila (Meehl, 1996). The current 

population of Ta`u was recently estimated at a total of 873 people (U.S. Census Bureau, 

2000), with 135 people in Faleāsao County, 380 in Ta`u County, and 358 in Fiti`uta County. 

The residents of Ta`u rely primarily on subsistence farming, agroforestry, and fishing. There 

is a relatively low level of tourism to the island. The majority of the residential, agricultural, 

and commercial land remains in the north and west sides of the island, while the southern and 

eastern portions remain mostly under the jurisdiction of the NPAS.

Several particular areas and landmarks of Ta`u are notable. A boat harbor is located in the 

northwestern corner of the island between Utumanu`a Point and Si`ulagi Point near the 

village of Faleāsao (Fig. 5.1a). The village of Ta`u is located to the south of Faleāsao, along a 

road that ends halfway down the western coastline. From Ta`u, the same road continues east 

of Faleāsao passing the airport runway, located near Fiti`uta Point and the village of Fiti`uta, 

and continues along the eastern coastline before ending near Tufu Point in the southeast. 

Finally, the NPAS begins halfway between Fiti`uta Point and Tufu Point, and continues along 

the southern coastline, ending near Si`ufa`alele Point in the southwest. 

5.2 Survey Effort

A large amount of physical and biological data have been collected around Ta`u since 2002 as 

Figure 5.2a. Locations of (Rapid Ecological Assessment [REA] and towed-diver surveys around Ta`u during 

ASRAMP 2002, 2004, and 2006. Four arbitrary geographic regions have been delineated to aid in discussion 

of spatial patterns.
225

part of the Pacific Islands Fisheries Science Center (PIFSC) Coral Reef Ecosystem Division’s 

TA`U ISLAND

(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 Ta`u throughout this 

chapter, four geographic regions were delineated based on cardinal directions (Fig. 5.2a). 

Benthic habitat mapping data were collected around Ta`u using a combination of acoustic 

and optical survey methods, the extent of which is summarized in Table 5.2a. These are 

further examined in Section 5.3: Benthic Habitat Mapping and Characterization.

The locations of REA and towed-diver survey efforts during ASRAMP cruises in 2002, 2004, 

and 2006 are shown in Figure 5.2a. The number, mean depth, and area of these surveys are 

presented by year in Table 5.2b. 

Table 5.2a. Total area of benthic habitat surveyed from acoustic multibeam sonar and Towed Optical Assessment 

Device (TOAD) surveys around Ta`u during ASRAMP efforts between 2002 and 2006.

Survey Type 2002 2004 2006

Acoustic Multibeam Sonar 0 82.3 km2* gap filling only

TOAD 0 tows 11 tows 5 tows

* Total multibeam surveying conducted across the Manu`a Islands.

Table 5.2b. Numbers, areas, and mean depths of REA and towed-diver surveys around Ta`u 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 5* 13.7 (SD 0.0) 10 28.3 8.8 (SD 2.7)

2004 9* 15.2 (SD 0.7) 18 36.9 11.3 (SD 4.7)

2006 9 14.3 (SD 0.6) 15 35.8 14.9 (SD 2.6)

* No coral disease surveys were conducted in 2002 and 2004.
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226

Depth ranges from towed-diver surveys are presented for each year in Figures 5.5.1a (2002), 

5.5.1d (2004), and 5.5.1j (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 variability of depths observed during towed-diver surveys and can be 

referenced when further exploring the towed-diver datasets.

Spatial and temporal observations of key oceanographic and water quality parameters 

influencing reef conditions around Ta`u 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 water properties during ASRAMP 2002, 2004, and 

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

instruments/collection activities is provided in Table 5.2c, and are further examined in Section 

5.4: Oceanography and Water Quality.

Table 5.2c. Numbers of oceanographic instrument deployments and shallow- and deep-water CTD casts around 

Ta`u during ASRAMP 2002, 2004, and 2006. Instrument types include sea surface temperature (SST) buoys, 

and subsurface temperature recorders (STRs). 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

SST 2 1 2

STR 0 2 1

Shallow-water CTD casts 30 37 35

Deep-water CTD casts 15* 7* 17*

* Total deep-water CTD casts conducted across the Manu`a Islands. 
227

5.3 Benthic Habitat Mapping and Characterization

TA`U ISLAND

Benthic habitat mapping and characterization of the nearshore waters around Ta`u were 

conducted using acoustic multibeam sonar, underwater video and still imagery, and toweddiver survey observations between ~ 1 and ~ 250 m (and deeper). Acoustic multibeam sonar 

mapping provided bathymetric and backscatter data products for depths between ~ 20 and 

~ 250 m. Optical validation and benthic characterization via underwater video, still imagery, 

and diver observations were performed using both shipboard towed cameras (i.e., TOAD) in 

depths between ~ 20 and ~ 80 m and towed-diver surveys in depths between ~ 1 and 30 m. 

5.3.1 Acoustic Mapping and Optical Validation

Because Ta`u is a steep volcanic island with almost no offshore bank areas, depths of 350 

m and greater were found less than 1 km offshore (Fig. 5.3.1a). A series of small, relatively 

shallow, seamount features were discovered ~ 2 km to the northwest of Utumanu`a Point on 

the northwestern corner of Ta`u. Some of these seamount summits are as shallow as 38 m. 

The backscatter imagery acquired during the ASRAMP 2004 surveys was successfully used 

as a predictive guide for determining sites for the optical surveys conducted during ASRAMP 

Figure 5.3.1a. Multibeam bathymetry acquisition around Ta`u in depths between ~ 10 and ~ 350 m was 

completed in March 2004, from the R/V Acoustic Habitat Investigator (AHI). The island drops steeply from 

all sides and is connected to Olosega via a series of small seamounts along a submerged ridge tending toward 

the northwest.
TA`U ISLAND

228

2006 (Fig. 5.3.1b). For example, observations of high backscatter intensity on the seamounts 

to the northwest of Ta`u suggested they were likely composed of hard-bottom habitat, possibly 

including some live coral. During TOAD camera surveys of these seamounts during ASRAMP 

2006, video observations confirmed the presence of living corals. Similarly, the southwest 

point of Ta`u was ground-truthed as hard-bottom habitat and areas in the west region with 

lower backscatter intensity were determined to include more sedimentary habitats. 

Only a limited amount of optical data were collected around Ta`u (Fig. 5.3.1c) because of the 

difficulties and inherent hazards of maneuvering large vessels close to the island, along with 

the inherent depth limits imposed on TOAD optical equipment (~ 80 m). Eleven optical data 

videos were collected from the National Oceanic and Atmospheric Administration (NOAA) 

Ship Oscar Elton Sette in 2004 (examples seen in Fig. 5.3.1d), and an additional five tows 

were conducted aboard the R/V AHI in 2006. Optical data collected during the 2006 TOAD 

surveys are still being processed and are not included in these results. However, surveys 

from both 2004 and 2006 indicate the presence of significant coral communities, both off the 

southeastern corner of the island and the seamount 2 km northwest of Utumanu`a Point.

Figure 5.3.1b. Backscatter imagery was acquired in March 2004 during multibeam surveys around Ta`u 

from 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.
229 TA`U ISLAND

Figure 5.3.1c. TOAD tracks around Ta`u during ASRAMP surveys in 2002 and 2004. The video imagery are 

post processed to identify substrate type (e.g., sand, rock), living cover (e.g., coral, macroalgae), and other 

characteristics. The TOAD survey tracks display percentage of live scleractinian coral classified using a point 

count method with a mean spacing of 20 m along each track. Yellow indicates 0% coral cover, orange colors 

indicate 0–20% coral cover, and red colors indicate 20–50% and 50–100% coral cover. 

Figure 5.3.1d. Optical validation images acquired during TOAD surveys over the small seamount northwest 

of Ta`u, showing an abundance of live scleractinian corals at depths of ~ 40–45 m. (Photographs provided by 

NOAA PIFSC CRED)
TA`U ISLAND

230

5.3.2 Habitat Characterization

Towed-diver benthic survey observations around Ta`u from ASRAMP 2002, 2004, and 2006 

were concatenated into mean spatial distributions of benthic composition (see Chapter 2, 

Section 2.2.3: Optical Validation Surveys). These analyses for Ta`u are presented as mean 

distributions of habitat complexity (Fig. 5.3.2a) and percent cover of sand (Fig. 5.3.2b), 

hard substrate/pavement (Fig. 5.3.2c), rubble (Fig. 5.3.2d), and live coral (Fig. 5.3.2e). Since 

these habitat characterization maps represent different complementary components of the 

same habitat, it is useful to analyze them in relation to each other, the local watersheds, and 

exposure to prevailing oceanographic conditions. 

Habitat complexity was observed to vary significantly around Ta`u, with observations ranging 

from low to very high (Fig. 5.3.2a). Habitat complexity appeared high to very high in portions 

of the east, south, and north regions. High to very high habitat complexity was observed 

along an ~ 1 km stretch of the forereef slope in the east region, specifically the area near the 

midpoint between Tiafou Point at the northeast corner and Tufu Point at the southeast corner. 

In this particular area, towed divers have recorded observations of extremely large massive 

Porites coral heads, some exceeding 5-6 m in height and 14 m in diameter (Figs. 5.3.2f and 

Figure 5.3.2a. Mean benthic habitat complexity concatenated from towed-diver survey observations around 

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

ensembles (~ 200 m × 10 m) on 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.
231 TA`U ISLAND

5.3.2g). An additional area of high complexity was noted along the south coast, specifically 

under the Liu Bench embayment and underneath the headwall surrounding Papaloaloa Point. 

In this area, divers observed a dramatic vertical rock wall descending as far as visibility 

allowed (~ 40 m). Few areas of high habitat complexity were also observed widely scattered 

in the north region. Areas of lower habitat complexity were recorded in a number of regions, 

specifically near Si`ufa`alele Point along the southwest corner of the island, in the vicinity 

of the village of Ta`u in the west region and in isolated, clearly defined areas in the north 

region. 

Towed-diver observations concur with backscatter imagery and towed-diver benthic 

complexity data on the location of several prominent sand channels scattered in the north 

region, and with the presence of accumulations of sand at the base of the forereef slope in the 

west region (Fig. 5.3.2b). Both sources suggest that the sand deposits are patchier and less 

substantial than similar deposits on the islands with more pronounced insular shelves (i.e., 

Tutuila, Ofu, and Olosega).

Figure 5.3.2b. Mean percent cover of sand concatenated from towed-diver benthic survey observations around 

Ta`u during ASRAMP 2002, 2004, and 2006. Major streams (blue lines) overlay the topographic map of the 

islands, indicating the location of inputs of freshwater runoff into the marine ecosystem. 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.
TA`U ISLAND

232

The mean percent cover of hard substrate/pavement around Ta`u was generally evenly 

distributed, with several localized increases (Fig. 5.3.2c) near the base of the Liu Bench and 

Papaloaloa Point in the south region, around Si`ufa`alele Point at the southwest corner of the 

island, and in the north in a region directly adjacent to one of the sand channels previously 

identified with backscatter, complexity, and percent sand cover. 

Figure 5.3.2c. Mean percent cover of hard substrate/pavement concatenated from towed-diver benthic 

survey observations around Ta`u during ASRAMP 2002 and 2004. Hard substrate/pavement composition was 

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

high percent cover of hard substrate, and light shades indicate low percent cover of hard substrate. 
233 TA`U ISLAND

Generally, the mean percent cover of coral rubble around Ta`u from towed-diver survey 

observations was consistently low, with typical values less than 5% (Fig. 5.3.2d). In a few 

areas, particularly along the forereef slope in the west region, there were stretches where 

observed values were closer to 25%. There appeared to be a slight correlation between the 

increases of sand and rubble in the west region, suggesting the area may be subjected to 

increased runoff, weathering, bioerosion or combination of these and/or other unknown 

causes.

The highest observed mean percent covers of live scleractinian coral were recorded in the 

east region between Tiafou Point and Tufu Point, with values ranging from 30% to 75%, and 

in the eastern portion of the south region near Ulufala Point, with similar high values (Fig. 

5.3.2e). The high coral cover area in the central portion of the east region coincides with 

observed high levels of habitat complexity and observations of extremely large colonies of 

massive Porites sp. discussed previously in this section. These massive colonies are thought 

to be among the oldest known living coral colonies in the world. A similar community of 

ancient massive Porites sp. colonies was also discovered on the opposite side of the island 

in the southern portion of the west region (Figs. 5.3.2f and 5.3.2g). Several colonies were 

huge and were estimated to be between 500 and 1000 years old. Unfortunately, many of these 

massive corals in this region had also suffered mortality or near-mortality events. It is not 

Figure 5.3.2d. Mean percent cover of rubble concatenated from towed-diver survey observations around Ta`u 

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

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

indicate high percent cover of coral rubble.
TA`U ISLAND

234

known when or why these massive colonies died off. 

In the south region, and to a lesser extent, percent cover of live coral was moderately high 

(20–50%) in the area east of Papaloaloa Point. Interestingly, the area in between the two 

high coral cover areas in the south region was highly complex, but generally contained 

much lower coral cover (0–20%). This may be a result of freshwater inputs running off the 

southern-facing, stair-step caldera complex off of the Liu Bench, geologic activity (e.g., 

rockslides) or a combination of these and/or other environmental factors. Additional areas of 

high coral cover included several areas in the north region between REA sites TAU-10 and 

TAU-04 and two sites in the west region, north of Si`ufa`alele Point near REA sites TAU-09 

and TAU-12 (Figs. 5.2a and 5.3.2e). 

Figure 5.3.2e. Mean percent cover of live scleractinian (stony) coral concatenated from towed-diver survey 

observations around Ta`u 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.
235 TA`U ISLAND

Figure 5.3.2f. Massive Porites sp. coral heads first discovered by the CRED towed-diver observers on the 

southwest side of Ta`u during ASRAMP 2002. (Photograph provided by NPAS)

Figure 5.3.2g. Massive Porites sp. coral heads thought to be roughly 500–1000 years old, possibly among 

the oldest known coral colonies in the world, and are one of the most unique findings by CRED scientists in 

American Samoa. (Photograph provided by NPAS)
TA`U ISLAND

236

5.4 Oceanography and Water Quality

Oceanographic and water quality data have been collected in the waters surrounding Ta`u 

over the period between 2002 and 2006. Instrumentation and equipment descriptions, 

deployment dates and locations, and a subset of the results are discussed below. Specific 

details of deployments and additional data are presented in Appendix II, Figure II. iii.

5.4.1 Hydrographic Data

2002 Spatial Surveys

During ASRAMP 2002, 30 shallow-water CTD casts were conducted in nearshore waters 

around Ta`u between February 11 and 13 (Figs. 5.4.1a and 5.4.1b). Data from these profiles 

show evidence of vertical stratification of the water column around all sides of the island 

surveyed (A–J; Fig. 5.3.1b), although this stratification was weaker around the southwest 

sector of the island (G–J) in the south and west regions. The mid-depth (~ 10–30 m) portion 

of the water column in the north region (A–D) was generally cooler, more saline (> 35.5 psu) 

and more dense (> 22.4 kg m-3) than in the south and west regions (E–J). The western portion 

of this north region (A–B) had particularly strong stratification with warmer surface waters 

(~ 30°C) and relatively cool bottom water (~ 28.5°C). Though temperature was stratified in 

Figure 5.4.1a. Shallow-water CTD cast locations, shown as blue dots, expressed sequentially in a clockwise 

direction around Ta`u (A–J) during ASRAMP 2002, February 11–13.
237 TA`U ISLAND

the southwest sector (G–J), with warm surface water (< 5 m) and cool bottom water (> 20 m), 

salinity (~ 35.2 psu) and density (~ 22 kg m-3) were relatively well-mixed in the mid-depth 

portion of the water column. These observations suggest surface heating with limited vertical 

Figure 5.4.1b. Shallow-water CTD cast profiles to a 30-m depth around Ta`u during ASRAMP 2002, February 

11–13, including temperature (°C), salinity (psu), and density (kg m-3). Profiles are shown sequentially in a 

clockwise direction around the island (A–J), as shown in Figure 5.3.1a.
TA`U ISLAND

238

mixing because of this sector’s location in the lee of the island. 

Spatial analyses of these physical water properties at a 20-m depth from the ASRAMP 2002 

surveys shows moderate ranges in temperature (29.09°–29.83°C), salinity (35.13–35.33 

psu), and computed density values (21.99–22.53 kg m-3; Fig. 5.4.1c). In general, waters in 

the south and west regions of Ta`u were warmer, less saline, and less dense than observations 

in the north region of Ta`u where the waters were notably cooler and more saline, particularly 

the western portion (A–B) of the north region.

2004 Spatial Surveys

During ASRAMP 2004, 37 evenly spaced shallow-water CTD casts were conducted in the 

nearshore waters around Ta`u between February 4 and 5 (Fig. 5.4.1d). Data from these CTD 

profiles show a relatively well-mixed water column along the north coast (A–C) from just 

north of Utumanu`a Point on the northwest corner to Tiafou Point on the northeast corner, 

with increased stratification in the waters below ~ 25 m, where waters were noticeably cooler 

and more saline than the waters above (Fig. 5.4.1e). Around the southeast point of Ta`u 

(D–E), a pronounced increase in temperature from ~ 29.45° to ~ 29.7°C throughout the upper 

~ 25 m was not obviously correlated with significant changes in salinity or density. There was 

an observed increase in beam transmission in this warm water tongue. Along the entire south 

Figure 5.4.1c. Interpolated water temperature (top left), salinity (top right), and density (bottom right) at a 20-

m depth derived from shallow-water CTD casts around Ta`u during ASRAMP 2002, February 11–13. Beam 

transmission data (bottom left) were not collected.
239 TA`U ISLAND

coast from Tufu Point to just past Si`ufa`alele Point (E–G), the most striking feature was the 

presence of relatively cold (29.2°C), saline (35.4 psu) bottom water (~ 30–35 m depths), and 

moderate vertical stratification through the water column. The stratification of the water off 

the southern shores was likely because of the calmer waters within the embayment allowing 

surface heating and limited mixing from wind and wave forcing.

The patterns of observed physical water properties at a 20-m depth around Ta`u during 

ASRAMP 2004 showed clear spatial structure with small to moderate ranges in temperature 

(29.35°–29.69°C), salinity (34.78–35.09 psu), computed density (21.87–22.26 kg m-3), and 

beam transmission (92.27–93.94%; Fig. 5.4.1f). For temperature, warmest waters were 

observed along most of the coast in the east region, in the same area with the highest observed 

coral cover, high habitat complexity, and large Porites coral heads. Coolest waters at a 20-m 

depth were observed along most of the south shore region, including Si`ufa`alele Point at the 

southwest corner of the island. For salinity, the entire north region had relatively low salinity 

water compared to the more saline south region. These combined temperature and salinity 

patterns at the 20-m depth resulted in low-density waters along the north coast and highdensity waters along the south region. For beam transmission, the patterns appeared more 

variable with highest values (low turbidity) and lowest values scattered at three separated 

areas along the north region of the island. 

Figure 5.4.1d. Shallow-water CTD cast locations, shown as blue dots, expressed sequentially in a clockwise 

direction around Ta`u (A–H) during ASRAMP 2004, February 4–5.
TA`U ISLAND

240

Figure 5.4.1e. Shallow-water CTD cast profiles to a 30-m depth around Ta`u during ASRAMP 2004, February 

4–5, including temperature (°C), salinity (psu), density (kg m-3), and beam transmission (%). Profiles are shown 

sequentially in a clockwise direction around the island (A–L), as shown in Figure 5.3.1d.
241 TA`U ISLAND

2006 Spatial Surveys

During ASRAMP 2006, 35 CTD casts were conducted in nearshore waters surrounding Ta`u 

between March 2 and 4 (Fig. 5.4.1g). In addition, water samples for nutrient and chlorophyll 

analysis were collected at 1-, 10-, 20-, and 30-m depths, where possible, at seven of these 

shallow-water CTD sites. Dissolved inorganic carbon (DIC) samples were collected at each 

of these seven sites (Fig. 5.4.1j).

Vertical profiles of water properties from shallow-water CTD surveys around Ta`u during 

ASRAMP 2006 indicate three main features (Fig. 5.4.1h). The first feature was an alternating 

pattern of well-mixed regions of the water column along the north and east coasts of the island 

(B–E) with different characteristics. Most of this stretch was characterized by relatively cool 

(29°C) water with moderate salinity values. At the northeast corner near Cape Papatele, a 

well-mixed warm (29.3°C) tongue was observed from the surface to the bottom. Although 

salinity was not different in this area, the warm temperature resulted in a corresponding 

tongue of low density water. The second feature was a region of warm (> 29.5°C), low salinity 

(< 34.5 psu) surface water and a moderately well-mixed subsurface water column along the 

south coast (E–F). The third feature was a stratified, relatively cool (< 28.75°C), dense (> 

Figure 5.4.1f. 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 Ta`u during ASRAMP 

2004, February 4–5.
TA`U ISLAND

242

22.2 kg m-3), saline (> 35 psu) mass of bottom water in the leeward west region of the island 

(G–A). These bottom temperatures were strikingly lower than any others observed around 

the island. Because of a faulty sensor, beam transmission data collected during ASRAMP 

2006 were insufficient to develop any conclusions.

The moderately well-mixed waters of the north and east regions (B–E) of Ta`u were exposed 

to wave and wind action during the observation period, causing mechanical mixing of warm 

surface water with cooler bottom waters. Relatively protected waters in the embayment 

on the south side of Ta`u (E–F) may have been subjected to surface heating and limited, 

wave-induced mixing in the upper water column. Additionally, river and land runoff, and 

possibly subsurface springs, are likely to be prevalent within this embayment. Runoff may 

be indicated by the low salinity (34.4 psu) and density (21.5 kg m-3) values observed in the 

upper water column (E–F).

Physical water properties at a 20-m depth during the 3-day survey around Ta`u in 2006 showed 

a moderate range in temperature (28.64°–29.23°C), with cooler waters observed to the west 

and warmest waters observed around Cape Papatele at the northeast corner of the island 

(Fig. 5.4.1j). As with temperature, observed salinity showed moderate variability (34.78–

35.09 psu) around the island. The spatial pattern in salinity was marked by low salinities on 

the west half of the island and moderate salinities on the eastern half. The lowest salinities 

are observed at Utumanu`a Point in the northwest and Si`ufa`alele Point at the southwest 

Figure 5.4.1g. Shallow-water CTD cast and nutrient and DIC water sample locations around Ta`u (A–H) 

during ASRAMP 2006, March 2–4.
243 TA`U ISLAND

Figure 5.4.1h. Shallow-water CTD cast profiles to a 30-m depth around Ta`u during ASRAMP 2006, March 

2–4, including temperature (°C), salinity (psu), density (kg m-3), and beam transmission (%). Profiles are shown 

sequentially in a clockwise direction around the island (A–J), as shown in Figure 5.4.1g.
TA`U ISLAND

244

corner. Beam transmission observations were limited because of instrument problems but 

varied between 96.35% and 99.36%, with highest values (lowest turbidity) observed in the 

northeast corner and lowest values observed in the east and west regions (near Si`ufa`alele 

Point). A point source of terrigenous input, or land-based sediment, was potentially the cause 

of the notable increases in turbidity, particularly since Si`ufa`alele Point also had low salinity. 

More data are needed to properly assess the nature of the signal. Computed density values 

(21.87–22.26 kg m-3) show similar distributions as salinity; the lowest and highest density 

values occurred on the northwest, west, and southwest portions of the island.

The in situ nutrient data collected at Ta`u displayed the following ranges: chlorophyll-a 

(Chl-a), 0.26–0.69 μg L-1; phosphate (PO4), 0.04–0.15 μM; silicate (SiO2), 0.6–1.21 μM; 

and total nitrogen (Ntot = NO3 + NO2-), 0.23–0.64 μM. Water samples showed an increase in 

Chl-a concentrations near the harbor area, while most other nutrient concentrations showed 

increased values along the south shore of Ta`u (Fig. 5.4.1j). The south shore of Ta`u has the 

highest SiO2 values in the American Samoa Archipelago. The south shore also exhibited a 

spike in PO4 and NO2- values. The vast majority of the population resides on the west coast, 

where nitrogen levels appeared elevated. There is also a small airport on the northeast corner 

of the island, although no increase in nutrients was observed in that area. 

Figure 5.4.1i. 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 Ta`u during ASRAMP 2006, March 2–4.
245 TA`U ISLAND

5.4.2 Temporal Comparison—Hydrographic Data

During each of the ASRAMP survey periods in 2002, 2004, and 2006, the nearshore 

shallow-water CTD and water quality observations showed noteworthy spatial structure. 

Temperature, salinity, and density values each varied spatially during each survey periods, 

although observed patterns were not consistent between survey periods. Ta`u was similar 

to Ofu and Olosega in terms of nutrient results. Site-to-site variability within nutrient value 

results was slightly less than the variability seen around Tutuila. These results are a baseline 

for comparison with future nutrient datasets. It is important to note that substantial rainfall 

Figure 5.4.1j. Interpolated Chl-a (top left), 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 Ta`u during ASRAMP 2006, March 2–4.
TA`U ISLAND

246

occurred during the survey period and that resulting terrestrial runoff affected results of the 

nutrient sampling.

5.4.3 Time Series Observations

A suite of moored instruments were deployed around Ta`u over the period between 2002 

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

reef conditions (Fig. 5.4.3a). Deployment and retrieval dates of each instrument are detailed 

in Appendix II, Table II.iii. Figure 5.4.3b shows a time series of in situ and remotely sensed 

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

Pathfinder SST data from Ta`u showed predominantly seasonal variability with warmest 

temperatures (~ 30.0°C) observed during January–March and coolest temperatures 

(~ 27.5°C) in June–August (Fig. 5.3.2b, top panel). A particularly cool episode, with 

temperatures reaching nearly 1.5°C below SST climatology, was observed in austral winter 

2002 before temperatures rose sharply to climatologically normal values in late 2002. In situ 

SST data were observed to be cooler and more variable when compared to Pathfinder SST 

temperature. Throughout most of the in situ record (July 2002–2004), moored SST values 

were observed to be 0°–3.5°C cooler than that observed via satellite and, for the most part, 

cooler when compared to the SST climatology. Telemetered in situ SST data from March 

2004 to February 2005 correlated well with both Pathfinder SST and climatology. 

Figure 5.4.3a. Locations and types of oceanographic instrument moorings deployed around Ta`u between 2002 

and 2006. Moored instrument types include STR and SST.
247 TA`U ISLAND

Temperature time series from three STRs during the 2004 to 2006 time period show 2°–3°C 

temperature fluctuations because of seasonal variability (Fig. 5.4.3c). In each of the time 

series, minimal (< 1°C) diurnal temperature fluctuations were observed.

Modeled significant wave height data for Ta`u showed weak seasonal variation 

superposed 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) during the summer months. Two extremely large swell events were observed in the 

time series: one in January 2004 produced by Cyclone Heta and the other in February 2005 

produced by Cyclones Olaf and Percy (Fig. 5.3.2b, bottom panel).

24

26

28

30

32

Water Temperatures and Wave Height Tau, AMSM: Jan2002 − Apr2006

bleaching threshold

C( er tu ar ep meT o

)

03−Jul−2002 19−Jan−2003 07−Aug−2003 23−Feb−2004 10−Sep−2004 29−Mar−2005 15−Oct−2005

0

2

4

6

8

10

kTC0201 kOES0402 kHI602

Hs ) m(

SST Climatology Pathfinder SST in−situ SST Modelled Hsig

Figure 5.4.3b. SST and wave height time series around Ta`u between January 2002 and April 2006. Remotely 

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

from Wave Watch III are overlaid with CRED in situ temperature observations. The horizontal red and vertical 

orange bars represent the bleaching threshold and the ASRAMP research cruise dates, respectively. In situ (15-

min sampling frequency) and telemetered data (4-hour mean) were used to produce the Ta`u time series record 

shown.

Figure 5.4.3c. Time series observations of temperature between March 2004 and February 2006 from three 

STRs deployed at different locations and depths around Ta`u, American Samoa (see Figure 5.3.2a for mooring 

locations). 
TA`U ISLAND

248

5.5 Coral and Coral Disease

5.5.1 Coral Surveys

2002 Spatial Surveys

Ten towed-diver surveys along the forereef slopes of Ta`u were conducted in 2002, with a 

mean depth of 8.9 m (Fig. 5.5.1a). Individual towed-diver survey depths varied from 7 m (SD 

1) to 10 m (SD 3). Estimates of live coral percent cover were 30.8% (SE 2.7; Fig. 5.5.1b), and 

estimates of recently dead coral cover were 2.4% (SE 0.6; Fig. 5.5.1c).

The highest live coral cover was observed during two towed-diver segments within the 

north region of Ta`u (mean: 62.5%). Other areas of high coral cover included the northeast 

windward coastline, beginning at Fiti`uta Point and heading south past Tiafou Point (6 tow 

segments, mean: 51.7%) and two tow segments along the west region of Ta`u (mean: 52.5%). 

Estimates of dead coral were low and variable around most of Ta`u, with the highest dead 

coral (up to 10%) observed on the northwest corner, from Cape Papatele south past Tiafou 

Point, as well in the south region, from Ulufala Point west to Papaloaloa Point. 

Figure 5.5.1a. Towed-diver survey tracks around Ta`u during 2002 ASRAMP. 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.
249 TA`U ISLAND

During ASRAMP 2002, towed-diver observers first discovered unique massive Porites sp. 

communities in the east and west regions of Ta`u, as first mentioned in Section 5.3.2: Habitat 

Characterization. In the west region, these massive coral colonies were estimated to be 5-6 m 

in height and 14 m in diameter (Figs. 5.3.2f and 5.3.2g). Through simple comparisons with 

known coral cores, these massive coral heads within this unique and isolated community are 

estimated to be between 500 and 1000 years old and are among the oldest known living coral 

colonies in the world. The finding of this massive and ancient community in 2002 is one of 

the most unique and exciting discoveries by CRED scientists in all of American Samoa. 

Figure 5.5.1b. Percent live scleractinian (stony) coral cover around Ta`u from towed-diver benthic survey 

observations 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 m2). The ramped color scheme 

expresses the range of percent live coral cover on the benthic habitat. Note that coral cover was measured as a 

direct percentage of overall benthic cover in 2002. 
TA`U ISLAND

250

REA coral surveys during ASRAMP 2002 were the first surveys conducted in American 

Samoa by CRED. Although six sites were surveyed around Ta`u by a CRED coral biologist, 

the main focus of those surveys was to explore different coral monitoring methodologies. 

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

more quantitative report. 

Figure 5.5.1c. Towed-diver benthic survey observations of dead coral cover around Ta`u 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 m2). Symbol size represents the percent dead coral cover on the benthic 

habitat.
251

2004 Spatial Surveys

TA`U ISLAND

Eighteen towed-diver benthic surveys along the forereef slopes of Ta`u were conducted 

during ASRAMP 2004, with a mean depth of 11.4 m (Fig. 5.5.1d). Individual towed-diver 

survey depths varied from 6 m (SD 3) to 17 m (SD 5). Island-wide live coral percent cover 

was 22.7% (SE 2.9; Fig. 5.5.1e), with an estimate of 5.8% (SE 1.2) of the live coral appearing 

stressed (pale or white; Fig. 5.5.1f). 

Figure 5.5.1d. Towed-diver survey tracks around Ta`u 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 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.
TA`U ISLAND

252

Estimates of live scleractinian (stony) coral cover were variable, with generally higher coral 

cover observed within the east and south regions. The highest live stony coral cover was 

recorded during nine towed-diver segments along the south region forereef, close to Ulufala 

Point (mean: 60.4%). Other areas of higher coral cover included the area surveyed along the 

east region, south of Tiafou Point (5 tow segments, mean: 59.0%).

Figure 5.5.1e. Towed-diver benthic survey observations of live scleractinian (stony) coral cover around Ta`u 

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 m2). Symbol size represents the percent live coral cover 

on the benthic habitat.
253 TA`U ISLAND

Estimates of stressed corals (pale and white) were variable with relatively high percentages 

of stressed coral recorded in a number of areas. Continuous areas of high coral stress were 

observed on the southwestern point, from Papaotoma Point west to Si`ufa`alele Point (15 tow 

segments, mean: 16.5%), along the west region south of Utumanu`a Point (9 tow segments, 

mean: 12.7%), and along two stretches off the north region, from Siulagi Point east to Loto 

Point (10 tow segments, mean: 16.6%) and west of Fitu`ata Point (10 tow segments, mean: 

14.7%). 

It is important to note that most areas exhibiting high percentages of stressed coral had 

relatively low percent live coral cover. In 2004, the towed-diver methodology reported an 

estimate for percent live coral cover and stressed (pale/white) coral cover separately for each 

5-min observation segment. To standardize the presentation of towed-diver benthic cover 

data between 2002 and 2004, live coral and stressed coral values from 2004 were summed to 

produce the total live coral category and then stressed coral was calculated as the percentage 

of live coral that was estimated as stressed. This may partially explain the high coral stress 

values reported for most areas where low coral cover was reported.

Figure 5.5.1f. Towed-diver benthic survey observations of stressed coral cover around Ta`u 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 m2). 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.
TA`U ISLAND

254

Nine coral REA surveys were conducted around Ta`u during ASRAMP 2004. At least 

32 anthozoan/hydrozoan genera were observed around Ta`u with members of the genera 

Montipora, Astreopora, Favia, and Porites each contributing more than 10% of the total 

number of colonies recorded around the island (Fig. 5.5.1g). Montipora was the most common 

coral genus at most sites, making up on average 21% of each site’s coral community. Corals 

of the genus Favia were generally more common at sites TAU-04, TAU-05, and TAU-10 in 

the north region, especially at site TAU-10 where Favia was the dominant coral genus (64% 

of coral colonies). Porites was generally more common at sites TAU-05, TAU-10, and TAU11 in the north region and at site TAU-09 in the west region, accounting for an average of 

15.6% of the coral community compared to only 4.8% of the coral community at the other 

sites around the island. 

Generic richness was variable with a mean of 18.2 (SE 2.1) coral genera recorded per site. 

Patterns of generic richness were similar to those for percent coral cover and coral density, 

with the lowest generic diversity (5 coral genera) recorded at site TAU-10 in the north region 

and the highest generic diversity (25 coral genera) recorded at site TAU-02 in the south 

Figure 5.5.1g. Relative abundance of coral genera and generic richness from REA surveys around Ta`u 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.
255 TA`U ISLAND

region (Fig. 5.4g). Site-specific data regarding the relative abundance of coral genera, by 

colony counts within belt transects, are available in Appendix III, Table III. v.

The mean percent live scleractinian coral cover around Ta`u was 24.3% (SE 5.2; Fig. 5.5.1h). 

Visual estimates of coral cover were relatively low at REA sites TAU-04, TAU-05, and 

TAU-10 in the north region of Ta`u, ranging between 1% and 10%. Percent coral cover was 

relatively higher at sites TAU-07 in the east region and sites TAU-02 and TAU-08 in the 

south region of Ta`u, with the highest live coral cover being recorded at site TAU-02, near 

the Lafuti stream outfall on the south shore.

During ASRAMP 2004 surveys around Ta`u, a total of 2887 coral colonies were counted 

within a total survey area of 610 m2. Mean coral densities per site at Ta`u were 5.5 colonies 

m-2 (SE 1.1; Fig. 5.5.1h). Coral density was fairly consistent at sites throughout the island, 

except for site TAU-10 in the north region (0.6 colonies m-2) and site TAU-02 in the south 

region (11.2 colonies m-2), where the lowest and highest coral densities were recorded, 

respectively.

Figure 5.5.1h. Live scleractinian (stony) coral cover and coral colony density from REA surveys around Ta`u 

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.
TA`U ISLAND

256

Size-class distribution of scleractinian corals shows the majority of corals (63.9%) had 

diameters less than 20 cm (Fig. 5.5.1i). High abundance of small corals (diameters less than 

5 cm) was generally observed at sites TAU-05 and TAU-10 in the north region and at sites 

TAU-09 and TAU-12 in the west region of Ta`u. Abundant large corals were only observed 

at TAU-11, off the northwest tip of Ta`u, with corals greater than 80 cm accounting for 14% 

of all colonies recorded. Interestingly, sites TAU-07, TAU-02, and TAU-08, which contained 

the highest proportions of the larger coral size classes, also had some of the highest coral 

cover seen around Ta`u. Coral size-class information is not recorded during towed-diver 

benthic survey observations; however, the divers noted many large Porites coral heads in the 

area south of REA site TAU-07 and in the area near TAU-12.

Figure 5.5.1i. Scleractinian coral size-class distribution around Ta`u 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. 
257

2006 Spatial Surveys

TA`U ISLAND

Fifteen towed-diver benthic surveys were conducted along the forereef slopes of Ta`u during 

ASRAMP 2006, with a mean depth of 14.9 m (Fig. 5.5.1j). Individual towed-diver survey 

depths varied from 14 m (SD 3) to 17 m (SD 3). Island-wide estimates of live coral percent 

cover were 19.3% (SE 2.0; Fig. 5.5.1k), and estimates of stressed (pale and white) coral were 

2.0% (SE 0.3; Fig. 5.5.1l).

The highest live scleractinian stony coral cover was observed during a towed-diver survey 

along the south region forereef, close to Ulufala Point (3 tow segments, mean: 45%) and 

east of Papaotoma Point (7 tow segments, mean: 26.4%). Other areas of higher coral cover 

included the area surveyed along the east region coast (16 tow segments, mean: 30%) and 

along the east side of the north region (7 tow segments, mean: 25%). 

Figure 5.5.1j. Towed-diver survey tracks around Ta`u 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.
TA`U ISLAND

258

Estimates of stressed coral were low for most of the forereef around Ta`u. Areas of elevated 

coral stress were noted along the north region shoreline from Siulagi Point to Loto Point (8 

tow segments, mean: 7.5%) and past Loto Point heading east (3 tow segments, mean: 7.5%), 

as well as along the east region shoreline near Tiafou Point (2 tow segments, mean: 7.5%).

Figure 5.5.1k. Towed-diver benthic survey observations of live scleractinian (stony) coral cover around Ta`u 

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 m2). 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.
259 TA`U ISLAND

Figure 5.5.1l. Towed-diver benthic survey observations of stressed coral cover around Ta`u 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 m2). 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.
TA`U ISLAND

260

A total of nine coral REA surveys were conducted around Ta`u during ASRAMP 2006. 

Colonies belonging to at least 29 anthozoan/hydrozoan genera were reported around Ta`u. 

Members of the genera Montipora and Astreopora were the most common corals found, 

composing a mean of 16% and 15% of the coral community at each site, respectively (Fig. 

5.5.1m). Porites was common at REA sites TAU-04, TAU-05, and TAU-10 in the north 

region of Ta`u, with a mean of 14% of the total coral community, in comparison to only 5% 

of the total coral community at all other sites off Ta`u. Other coral genera that were locally 

abundant include octocorals at site TAU-02 in the south region, Pocillopora at site TAU-08 

in the south region, and Goniastrea at several sites.

Generic richness of corals was relatively high with 19.7 (SE 0.1) coral genera recorded per 

site (Fig. 5.5.1m). Coral richness was relatively similar at most sites around Ta`u, ranging 

from 17 to 23 coral genera per site. Interestingly, site TAU-11 in the northwest corner had 

both the lowest generic diversity (17 genera) and the highest percent coral cover (54%). Sitespecific data regarding the relative abundance of coral genera, by colony counts within belt 

transects, are available in Appendix III, Table III. vi.

TAU-09

TAU-08

TAU-07

TAU-05

TAU-04

TAU-02

TAU-12

TAU-11

TAU-10

19

22

18

18

20

22

23

17

18

0 2 4 Km

Porites Other

Octocoral

Pavona

Pocillopora

Acropora

Astreopora

Favia

Goniastrea

Coral Genera

Montastrea

Montipora

Ta'u Island, American Samoa

Rapid Ecological Assessment, 2006

Coral Generic Richness and Relative Abundance

*Genric Richness

Number of genera recorded at each site. Pie chart size is proportional to richness value.

14*

Figure 5.5.1m. Relative abundance of coral genera and generic richness from REA surveys around Ta`u 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.
261 TA`U ISLAND

Percent live scleractinian coral cover around Ta`u, derived from the line point intercept 

method, was 29.7% (SE 4.3; Fig. 5.5.1n). Live coral cover was highest (54%) at site TAU-11 

off the northwest point of the island. Relatively high coral cover (38–45%) was also observed 

at sites TAU-02 and TAU-08 in the south region of Ta`u. Coral cover was similar at the 

remaining six sites (19–25%).

During ASRAMP 2006 surveys around Ta`u, a total of 3436 of coral colonies were counted 

within a total survey area of 400 m2. Coral density per site was variable, with a mean of 9.0 

colonies m-2 (SE 1.1; Fig. 5.5.1n). High coral densities were generally observed off the west 

and south coasts, with most sites having densities greater than 10 colonies m-2. The lowest 

coral density (3.5 colonies m-2) was observed at site TAU-10 in the north region. 

Figure 5.5.1n. Live scleractinian (stony) coral cover and coral colony density from REA surveys around Ta`u 

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

262

Size-class distribution of scleractinian corals indicated the majority of corals (78.8%) had 

maximum diameters less than 20 cm, with the greatest number of colonies occurring in the 

10–20 cm size class (Fig. 5.5.1o). Corals less than 5 cm in diameter were common, with six 

out of nine sites around Ta`u having more than 10% of their coral colonies within this size 

class. Larger corals were common at only two sites, TAU-05 and TAU-10, both off the north 

coast. At both sites, more than 10% of coral colonies had maximum diameters greater than 

40 cm.

Figure 5.5.1o. Scleractinian coral size-class distribution around Ta`u 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. 
263

5.5.2 Coral Disease Surveys

TA`U ISLAND

2006 Spatial Surveys

Coral health and disease REA surveys were conducted at nine sites around Ta`u during 

ASRAMP 2006 and covered a total survey area of 3850 m2. Within this area, a total of 

56 cases of coral disease, predation, and other types of lesions were enumerated. Of the 

nine sites surveyed, eight (89%) contained disease (Fig. 5.5.2a). Figure 5.5.2b illustrates the 

variation in prevalence of disease and predation among sites. Overall mean prevalence was 

0.10% (SE 0.03). REA sites TAU-11 in the northwest corner and TAU-07 in the east region 

exhibited the greatest prevalence (0.27% and 0.29%, respectively; Fig. 5.5.2b).

Skeletal growth anomaly was the most prevalent coral disease; 22 cases were detected, and 

within this disease category the scleractinian genera Astreopora and Montipora exhibited 50% 

of the documented cases. At site TAU-11, on the northwest corner, 50% of island-wide cases 

were detected. Bleaching was also detected at Ta`u, although with low prevalence (0.03%). 

Similarly to the other islands in the archipelago, bleaching was mild and focal. Scleractinian 

genera exhibiting bleaching included: Montipora, Porites, Pocillopora, and Montastrea. 

Other coral diseases observed at the survey sites included four cases of hyperpigmentation 

(dark spots) on Astreopora, Pavona varians, Montipora, and Coscinaraea (Fig. 5.5.2b).

Figure 5.5.2a. Prevalence of predation, bleaching, growth anomalies, tissue loss, black band disease, and 

other lesions at Ta`u during ASRAMP 2006. Prevalence was calculated relative to the average colony density 

estimates and is indicated by the size of the respective symbols. 
TA`U ISLAND

264

5.5.3 Temporal Comparison—Coral and Coral Disease

High live scleractinian coral cover was consistently reported by towed-diver observers for 

surveys completed in 2002, 2004, and 2006 (Fig. 5.5.3a), specifically along the east region 

windward coastline, beginning at Tiafou Point and heading south (42%, 38%, and 33%). 

Area surveyed along the south shore also recorded high coral cover in 2004 and 2006. 

Variations between years may be because of natural variation, changes in data collection 

protocol, trackline spacing (i.e., variation between towed-diver survey tracks between years), 

and observer variability resulting from changes in scientific personnel.

Average percent live coral cover from 2004 REA surveys (24.3%, all nine sites) compared 

favorably with 2006 REA surveys (29.4%, same nine sites; Fig. 5.5.3a). When site TAU-10 is 

removed from the analysis (as transect lines were laid over substantially different substrate in 

each year), the cover estimates for both years become even more congruent (27.3% in 2004 

vs. 30.5% in 2006). When comparing the estimates between years from site TAU-11, there are 

substantial differences (25% in 2004 vs. 54% in 2006). Visual estimates were used in 2004 

to report coral cover whereas the line point intercept technique was used in 2006, and visual 

Figure 5.5.2b. Prevalence of predation, bleaching, growth anomalies, tissue loss, black band disease, and other 

lesions at Ta`u 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. 
265

estimates can vary from those derived from the line point intercept technique even when 

TA`U ISLAND

made concurrently. CRED’s coral survey methods have evolved over time; ideally, there 

should be two observers conducting coral surveys and the surveys should include quantitative 

population parameters and coral disease observations. This will allow for improved sitespecific comparisons to be made to surveys conducted in the future.

Overall, mean generic richness did not vary substantially between 2004 and 2006 (Fig. 

5.5.3b). Mean colony densities increased from 5.5 colonies m-2 (SE 1.1) in 2004 to 9.0 

colonies m-2 (SE 1.1) in 2006 (Fig. 5.5.3c). Even when site TAU-10 is removed from the 

analysis, there is a substantial difference in mean coral density around Ta`u between 2004 

and 2006 (6.1 colonies m-2 [SE 0.9] vs. 9.7 colonies m-2 [SE 1.0], respectively). As with 

the apparent increase in coral density at Ofu and Olosega from 2004 to 2006, it is difficult 

to know if this apparent change, which could result from new recruits to the population or 

fragmentation/fissioning of existing colonies, is real or is an artifact of survey area. That is, 

610 m2 of benthic substrate were surveyed in 2004 (by two biologists), but only two-thirds 

of that area (400 m2) could be examined by the single biologist allocated to coral population 

parameters in 2006. Again, it is hoped that personnel allocations and survey protocols will be 

the same in future years so that improved comparisons can be made.

0

5

10

15

20

25

30

35

40

2002 2004 2006

% Coral Cover (± SE)

TDS

REA (VE)

REA (LPI)

Figure 5.5.3a. Temporal comparison of mean percent live coral cover from REA surveys and towed-diver 

surveys around Ta`u during ASRAMP 2002, 2004, and 2006. 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.
TA`U ISLAND

266

Figure 5.5.3c. Temporal comparison of mean coral colony density from around Ta`u during ASRAMP 2004 

and 2006 REA surveys.

Figure 5.5.3d. Coral colony size-class mean density around Ta`u for ASRAMP 2004 and 2006 REA surveys.

0.0

5.0

10.0

15.0

20.0

25.0

2004 2006

Coral Genera per site

(± SE)

Figure 5.5.3b. Temporal comparison of mean coral genera per site from around Ta`u during ASRAMP 2004 

and 2006 REA surveys. 
267 TA`U ISLAND

In total, three fewer genera were reported from Ta`u in 2006 than in 2004 (29 vs. 32, 

respectively). Those genera that were only reported in a single year, however, were rare 

(Diploastrea, Echinophyllia, Goniopora/Alveopora, Heliopora, and Merulina; 1–5 colonies). 

In both years, Montipora, Astreopora, and Porites were among the four most abundant 

genera. In 2004, Favia was the third most abundant genus (11.9% of colonies) while in 2006 

Goniastrea was the third most abundant genus (9.3% of colonies). This apparent difference 

in generic dominance could easily result from the difference in survey area, as discussed in 

the preceding paragraph. In both 2004 and 2006, site TAU-02 on the south region was the 

site with the greatest generic diversity. It is interesting to note that biodiversity was highest 

along the south region of both Ofu/Olosega and Tutuila. TAU-10, despite placing the transect 

lines to include more hard-bottom substrate in 2006, displayed the lowest coral diversity in 

both years. Overall coral colony size-class distributions computed from 2004 and 2006 REA 

surveys are highly similar (Fig. 5.5.3d).

5.6 Algae

5.6.1 Algal Surveys

2002 Spatial Surveys

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 cm2 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. 

Figure 5.6.1a. Percent cover of fleshy macroalgae (including turf algae) and crustose coralline algae from 

towed-diver benthic surveys around Ta`u 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 m2). 
TA`U ISLAND

268

Ten towed-diver surveys around Ta`u during ASRAMP 2002 found that combined fleshy 

macroalgal and crustose coralline red algal cover was 49.8%. The percent cover of crustose 

coralline red algae was relatively higher than fleshy macroalgae around Ta`u, with each 

functional group covering 34.9% (SE 1.3) and 14.9% (SE 1.2) of the benthic substrate, 

respectively (Fig. 5.6.1a). Crustose coralline red algal cover abundance was lowest along the 

northwestern corner of the island, while fleshy macroalgal cover abundance was among the 

highest.

Qualitative REA algal surveys were conducted in 2002 around Ta`u, and six 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

Eighteen towed-diver surveys were conducted around Ta`u during ASRAMP 2004 and 

revealed that 54% of the benthic substrate was covered with fleshy macroalgae and crustose 

coralline red algae. Fleshy macroalgae were slightly more common than crustose coralline 

red algae, with each category averaging 31.7% (SE 1.1) and 22.3% (SE 1.0), respectively 

(Fig. 5.6.1b). Fleshy macroalgae were relatively uniform along the forereefs of Ta`u except 

for one towed-diver benthic survey near Siulagi Point in the north region, where percent 

cover averaged 58%. 

Algal surveys were conducted at nine sites around Ta`u during ASRAMP 2004 (Fig. 

5.6.1c). A total of 14 macroalgal genera (7 green, 6 red, and 1 brown) and 3 additional algal 

functional groups (turf algae, crustose coralline red algae, and cyanophytes) were observed 

in the field. Diversity of large, easily observed macroalgal genera (some of which contain 

multiple species) at each site ranged from 0 to 8. However, once laboratory-based taxonomic 

Figure 5.6.1b. Percent cover of fleshy macroalgae (including turf algae) and crustose coralline algae from 

towed-diver benthic surveys around Ta`u 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 m2). 
269 TA`U ISLAND

identification of all algal species (including 

turf algae, epiphytes, and crustose coralline 

red algae) from each site is completed, algal 

diversity for each site will be much higher. Site 

TAU-12 in the west region had more than twice 

the recorded macroalgal generic diversity as 

observed at most other sites with eight genera 

recorded. Five genera were recorded at site 

TAU-05 in the north region; all other sites 

contained four or fewer macroalgal genera. 

No macroalgae were found at site TAU-10, 

located on the north central side of the island.

Around Ta`u, turf algae were the dominant 

marine flora found, being observed in more 

than 75% of sampled quadrats in all locations 

except site TAU-10 in the north region (Fig. 

5.6.1c). Similarly, crustose coralline red algae 

were dominant at most sites around the island 

(50–100% of sampled photoquadrats per site), 

Figure 5.6.1c. Percent occurrence of select macroalgal genera and algal functional groups from REA algal 

surveys around Ta`u 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. 

Figure 5.6.1d. A species of the calcified, sandproducing alga, Halimeda, from Ta`u. This alga 

can often form extensive draperies or mats over 

the benthic substrate. (Photograph provided by 

NOAA PIFSC CRED; P. Vroom, JIMAR)
TA`U ISLAND

270

but as with turf algae, were completely lacking at site TAU-10. Cyanophytes were lacking 

from photoquadrats at all three northern stations but were found in relatively low abundance 

at western, eastern, and southern sites with the highest abundance in the southwest corner. 

Macroalgae were not abundant around Ta`u, with the calcified sand producing green alga 

Halimeda (Fig. 5.6.1d), being the most abundant by occurring in 42% of photoquadrats at 

site TAU-02. The green alga Dictyosphaeria, the brown alga Lobophora, and the red alga 

Peyssonnelia were found in 25% of photoquadrats at only one site each: TAU-09, TAU-05, 

TAU-08, and TAU-12, respectively. Macroalgae were extremely scarce at all other locales. 

The northern shores were essentially depauperate of macroalgal genera, with only turf algae 

being recorded in select photoquadrats at site TAU-10. 

2006 Spatial Surveys

Fifteen towed-diver surveys around Ta`u during ASRAMP 2006 reported an average algal 

substrate cover of 37%. The percent cover of crustose coralline red algae was relatively 

higher than fleshy macroalgae around Ta`u, with each functional group covering 27.8% (SE 

1.3) and 9.1% (SE 0.5) of the benthic substrate, respectively (Fig. 5.6.1e). Crustose coralline 

red algae were most abundant during tows along the east coast of the island, from Tiafou 

Point to Tufu Point, covering up to 50% of the benthic habitat.

Quantitative algal surveys were conducted at eight of the same nine sites around Ta`u as were 

monitored in 2004 (site TAU-08 was not resurveyed; Fig. 5.6.1f). A total of 24 macroalgal 

genera (9 green, 13 red, and 2 brown) and 3 additional algal functional groups (turf algae, 

crustose coralline red algae, and cyanophytes) were observed in the field. Diversity of large, 

easily observed macroalgal genera (some of which contain multiple species) at each site 

ranged from 8 to 18, although once laboratory-based taxonomic identification of all algal 

species (including turf algae, epiphytes, and crustose coralline red algae) from each site is 

completed, algal diversity for each site will be much higher. Sites TAU-05 and TAU-09 in the 

north and west regions, respectively, exhibited the highest macroalgal generic diversity with 

18 and 15 genera recorded, respectively. Divers recorded 8–9 genera at most other sites.

Figure 5.6.1e. Percent cover of fleshy macroalgae (excluding turf algae) and crustose coralline algae from 

towed-diver benthic surveys around Ta`u 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 m2). 
271 TA`U ISLAND

Around Ta`u, turf algae were the dominant marine flora found, being observed in more than 

75% of sampled quadrats in all locations (Fig. 5.6.1f). Similarly, crustose coralline red algae 

were dominant at most sites around the island (50–100% of sampled photoquadrats per 

site). Cyanophytes were surprisingly high in abundance, being found in more than 50% of 

photoquadrats at eastern, western, and southern sites. They were of lowest abundance on the 

north shore, being completely lacking at site TAU-05.

Macroalgae were extremely abundant around Ta`u during ASRAMP 2006 with several genera 

occurring in more than 75% of sampled photoquadrats at multiple sites. Site TAU-04, on the 

northeast corner of the island, had among the highest abundances of several taxa with the red 

algal genera Peyssonnelia and Jania, and the green algal genus Dictyosphaeria occurring in 

more than 75% of sampled photoquadrats (Fig. 5.6.1f). Additionally, an unidentified genus 

in the red algal order Gelidiales occurred in more than 80% of photoquadrats sampled at the 

site. In addition to their high abundance at TAU-04, Peyssonnelia, the unidentified member of 

the Gelidiales, and Jania were among the most common macroalgae found around the island, 

occurring at every site sampled. The brown alga, Dictyota, and the green alga, Dictyosphaeria, 

occurred at all sites except TAU-11 and TAU-10 in the north region, respectively.

Figure 5.6.1f. Percent occurrence of select macroalgal genera and algal functional groups from REA surveys 

around Ta`u during ASRAMP 2006. Percent occurrence is equivalent to the percentage of photoquadrats in 

which an algal genus or functional group was observed. 
TA`U ISLAND

272

5.6.2 Coralline Algal Disease Surveys

2006 Spatial Surveys

Afflictions to coralline algae were also observed at the study sites, but in low abundances 

(Fig. 5.6.2a). Figure 5.6.2b illustrates the variation in the relative abundance of coralline 

algal disease among sites. Around Ta`u, only 21 cases of coralline algal disease (CLOD and 

CFD) were detected, mainly concentrated at sites TAU-07 (52%) on the east-facing shore, 

and TAU-08 (43%) on the south shore. 

5.6.3 Temporal Comparison—Algae

A dramatic difference between the number of algal genera and their abundance was reported 

at Ta`u between the 2004 and 2006 sampling periods. In 2004, Ta`u exhibited the most 

meager algal community of all islands in American Samoa, but by 2006 it contained the 

most diverse and healthy algal community observed. Although Hurricane Heta did not pass 

over the Manu`a Island group, possibly severe wave energy generated from the storm in 

2004 scoured benthic communities around Ta`u shortly before 2004 surveys were conducted, 

shredding algal communities and making the island appear to have low algal diversity. By 

Figure 5.6.2a. Relative abundance of coralline algal diseases around Ta`u during ASRAMP 2006. Disease 

density is indicated by the size of the respective symbols. 
273 TA`U ISLAND

Figure 5.6.2b. Relative abundance of coralline algal disease around Ta`u during ASRAMP 2006. CLOD: coralline 

lethal orange disease; CFD: coralline fungal disease; and Other: undetermined coralline discolorations.

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 5.6.3a. Temporal comparison of REA algal genera and functional group percent occurrence around Ta`u 

between ASRAMP 2004 and 2006.
TA`U ISLAND

274

2006, the algal communities had fully recovered. Almost twice the number of genera was 

recorded in 2006 compared to 2004, and abundances of macroalgae in photoquadrats increased 

from < 25% to almost 100% at most sites (Fig. 5.6.3a). Macroalgal diversity, as determined 

through field observations of the relative abundance of macroalgae, was exceptionally higher 

along the northern shore of the island in 2006 as compared to 2004. As at Tutuila, a major 

difference between the 2004 and 2006 sampling periods was the presence of the red algal 

genera, Amphiroa/Jania, which were not recorded in 2004, but were extremely prevalent 

at almost every site in 2006. Populations of the green algae Halimeda and Dictyosphaeria

remained relatively constant in both years, although Dictyosphaeria was very abundant at 

TAU-04 in 2006, whereas it was completely lacking in 2004.

Figure 5.6.3b. Temporal comparison of towed-diver benthic survey algal percent cover results for fleshy, 

crustose coralline and macroalgae for ASRAMP 2002, 2004 and 2006 surveys around Ta`u.
275

5.7 Benthic Macroinvertebrates

TA`U ISLAND

5.7.1 Benthic Macroinvertebrate Surveys

2002 Spatial Surveys

Towed-diver benthic macroinvertebrate surveys around Ta`u during the 2002 ASRAMP 

cruise found no crown-of-thorns seastars (COTS) or sea cucumbers (Fig. 5.7.1a). Giant 

clams were found mostly along the north shore of the island (mean: 18.8 organisms ha-1). Sea 

urchin distribution was concentrated on the northwestern corner 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, which may have contributed 

to the low numbers of macroinvertebrates observed in 2002.

A total of six qualitative REA invertebrate surveys, focusing on general information about 

the macroinvertebrate communities, were conducted around Ta`u during ASRAMP 2002. 

These surveys provided baseline data used to design and scale the future methodology of 

REA surveys. No data are presented.

Figure 5.7.1a. Distribution of estimated population densities of COTS, giant clams, sea cucumbers, and sea 

urchins around Ta`u from towed-diver benthic surveys during ASRAMP 2002. Circle locations represent an 

integrated estimate over 5-min observation segments covering survey swaths of ~ 200 m × 10 m (~ 2000 m2). 

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). 
TA`U ISLAND

276

2004 Spatial Surveys

Towed-diver benthic macroinvertebrate surveys around Ta`u during ASRAMP 2004 found 

variable distributions of giant clams, sea cucumbers, and sea urchins (Fig. 5.7.1b). No COTS 

were observed. Giant clams were found predominantly in the north (mean: 36.7 organisms ha1

) and west regions (mean: 18.0 organisms ha-1). Sea urchins appeared at their highest numbers 

and densities on the northwestern and the southwestern corners (mean: 1620 organisms ha-1) 

of the island, while sea cucumbers remained rare and were found predominantly in the west 

region of the island (mean: 1.3 organisms ha-1). 

Invertebrate species richness at REA sites around Ta`u was variable, ranging from 9 to 27 

invertebrate species (Fig. 5.7.1c). High richness was observed at sites TAU-02 and TAU07 in the south and east regions. Sea urchins were present at five of seven REA sites, with 

Echinostrephus sp. being the most common urchin. Giant clams were present at all but one 

site, TAU-04 off the north coast of Ta`u. Three species of sea cucumbers were observed 

(Holothuria cinerascens, Bohadschia argus, and Holothuria whitmaei) around Ta`u at site 

TAU-11 in the northwest corner and site TAU-12 in the west region.

Figure 5.7.1b. Distribution of estimated population densities of COTS, giant clams, sea cucumbers, and sea 

urchins around Ta`u 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 m2). 

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, 250–500, and > 500).
277 TA`U ISLAND

Figure 5.7.1c. Macroinvertebrate species richness, and target macroinvertebrate distribution around Ta`u 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. 
TA`U ISLAND

278

2006 Spatial Surveys

Towed-diver benthic macroinvertebrate surveys around Ta`u during the 2006 ASRAMP 

cruise found varying distributions of giant clams, sea cucumbers, and sea urchins, and the 

absence of COTS (Fig. 5.7.1d). Giant clams were most common in the north region of Ta`u 

(mean: 14.6 organisms ha-1), but were also relatively common in the west region (mean: 

9.7 organisms ha-1) and east region (mean: 6.7 organisms ha-1). As in previous years, sea 

cucumbers remained uncommon, with the highest sea cucumber density found in the west 

region of the island (mean: 1.7 organisms ha-1). Similar to 2004, sea urchins were found 

in the highest densities on the northwestern, southwestern, and northeastern corners of the 

island.

Target macroinvertebrates were common around Ta`u during ASRAMP 2006, with sea urchins 

present at all nine REA sites (Fig. 5.7.1e). The boring urchin, Echinostrephus aciculatus, 

was the most common urchin species seen around Ta`u. Giant clams were present at eight 

of the nine REA sites. Sea cucumbers present at REA sites included Actinopyga mauritiana

and an unidentified holuthuroid seen at one site each. No COTS were observed during REA 

surveys.

Figure 5.7.1d. Distribution of estimated population densities of COTS, giant clams, sea cucumbers, and sea 

urchins around Ta`u 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 m2). 

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).
279 TA`U ISLAND

5.7.2 Temporal Comparison—Benthic Macroinvertebrates

Macroinvertebrate distributions were relatively similar along the forereefs of Ta`u, especially 

during 2004 and 2006 towed-diver surveys. However, results did show some temporal trends 

in organism densities. COTS were not present around Ta`u during any of the sampling years. 

Mean giant clams densities (Fig. 5.7.2a) were shown to fluctuate between sampling periods, 

which could be attributed to natural causes (e.g., population changes), changes in toweddiver survey depths and encounter rates, storm effects or through other (un)known causes. 

However, giant clams were common with slightly higher occurrences found off the north 

and west coasts of Ta`u in both 2004 and 2006. Sea cucumbers remained uncommon in both 

sampling years, with only small increases between years in the numbers encountered (Fig. 

5.7.2b). Most sea cucumbers were found in the west region of Ta`u. Finally, sea urchins 

were the most common invertebrates and were observed mainly along the west coast of Ta`u 

(Fig. 5.7.2c). However, densities appeared highest along the northwestern and southwestern 

corners of the island, and also appeared in elevated numbers along the northeastern corner 

for surveys completed in both 2004 and 2006.

Figure 5.7.1e. Target macroinvertebrate distribution around Ta`u from REA surveys during ASRAMP 2006. 
TA`U ISLAND

280

0

5

10

15

20

25

2002 2004 2006

Mean Density 

(organisms ha-1 ±SE)

Figure 5.7.2a. Mean density of giant clams around Ta`u from towed-diver surveys during ASRAMP 2002, 

2004, and 2006.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

2002 2004 2006

Mean Density 

(organisms ha-1 ±SE)

Figure 5.7.2b. Mean density of sea cucumbers (holothuroids) around Ta`u from towed-diver surveys during 

ASRAMP 2002, 2004, and 2006 cruises.

0

200

400

600

800

1000

1200

2002 2004 2006

Mean Density 

(organisms ha-1 ±SE)

Figure 5.7.2c. Mean density of sea urchins (echinoids) around Ta`u from towed-diver surveys during ASRAMP 

2002, 2004 and 2006.
281

5.8 Reef Fish

TA`U ISLAND

5.8.1 Reef Fish Surveys

2002 Spatial Surveys

The biomass of large fish (length > 50 cm) around Ta`u, as surveyed by towed divers during 

ASRAMP 2002, was predominantly characterized by elevated abundances of parrotfish and 

snappers at most sites around the island, with a patchy distribution of sharks, surgeonfish, 

and groupers. Overall, large fish biomass was around 0.024 tons ha-1 (SE 0.013) and was 

distributed evenly around the island (Fig. 5.8.1a). 

Two rare bumphead parrotfish (Bolbometapon muricatum) were sighted on the northern side 

of Ta`u. Only two sharks and a few humphead wrasses were observed, mostly in the east 

Figure 5.8.1a. Large fish biomass, family composition, and individual shark sightings around Ta`u 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 (tons ha-1). 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.
TA`U ISLAND

282

section of the island (Fig. 5.8.1a).

Total fish biomass was similar around Ta`u during the 2002 ASRAMP surveys (7.7 kg 100 

m-2 [SE 3.0]). Herbivores, mainly surgeonfish, were generally the most abundant fish group, 

but this was not clear at all sites (Fig. 5.8.1b). Lower-level predators (emperors and triggerfish) 

were also abundant, especially at TAU-02 in the south region of Ta`u. 

Peacock grouper (Cephalopholis argus) were the most dominant grouper species present and 

were also the most common species on stationary point counts (> 20 cm total length). Several 

snappers—the smalltooth jobfish (Aphareus furca), the twinspot snapper (Lutjanus bohar), 

and the blue-lined snapper (L. kasmira)—were also common. 

Fish species richness was similar around Ta`u with averages of ~ 20 species 100 m-2 (Fig. 

5.8.1b).

Figure 5.8.1b. Total fish biomass, family composition, and species richness of fishes around Ta`u 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 (# species 100 m-2) and the size of the 

beige circles.
283

2004 Spatial Surveys

TA`U ISLAND

Large fish biomass around Ta`u during ASRAMP 2004 was mostly composed of parrotfish, 

followed by surgeonfish and wrasses. On average, large fish biomass was around 0.030 tons 

ha-1 (SE 0.015) for the island. No particular side of the island harbored higher fish biomass, 

although particularly high fish biomass was recorded on the northwest tip of the island, 

mostly because of shark and humphead wrasse sightings (Fig. 5.8.1c).

Two bumphead parrotfish were observed in the vicinity of the 2002 sightings, while a 

few sharks and humphead wrasses were seen at scattered locations around the island (Fig. 

5.8.1c).

During 2004, total fish biomass was highest on the south and east sides of Ta`u (~ 18 kg 100 

m-2) compared to the north and west sides (~ 6 kg 100 m-2). Herbivores (e.g., surgeonfish) 

Figure 5.8.1c. Large fish biomass, family composition, and individual shark sightings around Ta`u recorded 

during ASRAMP 2004 towed-diver surveys. Large fish (length > 50 cm) biomass on each individual tow 

is represented by the color of the survey track (tons ha-1). 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.
TA`U ISLAND

284

made up most of the biomass, but lower-level predators (mainly triggerfish) were also 

noticeably abundant, especially at sites TAU-08 and TAU-05 in the south and north regions, 

respectively (Fig. 5.8.1d). Mean total fish biomass around Ta`u was around 10.1 kg 100 m-2 

(SE 4.4) in 2004.

Parrotfish, surgeonfish, and snappers had the highest biomass for medium-large fish recorded 

on stationary point counts (> 25 cm total length) around Ta`u during ASRAMP 2004. Also 

relatively abundant were wrasses, triggerfish, and emperors. 

Species richness ranged from 30 to 45 fish species 100 m-2 at most sites (Fig. 5.8.1d) and was 

slightly lower along the north side of this island.

Figure 5.8.1d. Total fish biomass, family composition, and species richness of fishes around Ta`u 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 (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 (# species 100 m-2) and the size of the 

beige circles.
285

2006 Spatial Surveys

TA`U ISLAND

Mean biomass for large fish (> 50 cm total length, all families pooled) around Ta`u during 

ASRAMP 2006 was similar to previous years (0.046 tons ha-1 [SE 0.019]). Large parrotfish 

and snappers represented most of the biomass in this size class. Large fish biomass was mostly 

evenly distributed around the island, although with some particularly elevated biomass values 

around the northeast tip of the island attributed to schools of barracuda (Fig. 5.8.1e). 

Several humphead wrasses (50–120 cm total length) were observed around the island, 

especially around the southeastern point. Sharks were sighted regularly at scattered locations 

(Fig. 5.8.1e). Contrary to previous years, no bumphead parrotfish were observed in 2006.

During 2006, total fish biomass was similar around Ta`u, 4.4 kg 100 m-2 (SE 1.6), with the 

exception of site TAU-11 in the north region, where a large school of barracuda was recorded 

Figure 5.8.1e. Large fish biomass, family composition, and individual shark sightings around Ta`u recorded 

during ASRAMP 2006 towed-diver surveys. Large fish (length > 50 cm) biomass on each individual tow 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.
TA`U ISLAND

286

(Fig. 5.8.1f). Herbivores were the dominating group, with parrotfish and surgeonfish equally 

abundant.

In descending order, snappers, parrotfish, groupers, and surgeonfish dominated the biomass 

of medium-large fishes recorded on stationary point counts (> 25 cm total length). Families 

with moderate biomass included emperors, wrasses, and goatfish.

Around the island, species richness was around 30 species 100 m-2 but was slightly lower on 

the north side of the island (Fig. 5.8.1f).

Figure 5.8.1f. Total fish biomass, family composition, and species richness of fishes around Ta`u 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 (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 (# species 100 m-2) and the size of the 

beige circles.
287

5.8.2 Temporal Comparison—Reef Fish

TA`U ISLAND

Total fish biomass is not systemically higher on a particular side of the island and is generally 

dominated by herbivores and a noticeable presence of small predators (e.g., triggerfish, 

emperors, and wrasses). Total fish biomass was constant between 2002 and 2004 at around 

0.9 tons ha-1 but appears to have decreased to 0.4 tons ha-1 in 2006 (Fig. 5.8.2a). Considering 

all years surveyed, total fish biomass around Ta`u was around 0.74 tons ha-1 (SE 0.31).

In a similar fashion to other islands, large fish biomass is generally evenly distributed and is 

composed mostly of parrotfish, snappers, and surgeonfish. Large fish biomass appears to be 

slightly increasing from 0.024 tons ha-1 in 2002 to 0.046 tons ha-1 in 2006 (Fig. 5.8.2b). The 

overall average, all years combined, was around 0.034 tons ha-1 (SE 0.015).

The only clear richness pattern that emerges is a generally lower species count 100 m-2 on the 

northern side of Ta`u.

Figure 5.8.2a. Total fish biomass around Ta`u during ASRAMP 2002 (6 sites), 2004 (9 sites), and 2006 (9 sites) 

REA surveys.

Figure 5.8.2b. Large fish biomass around Ta`u during ASRAMP 2002 (8 tow surveys), 2004 (18 tow surveys), 

and 2006 (15 tow surveys) towed-diver surveys.
TA`U ISLAND

288

5.9 Island Summary and Integration

Ta`u is a small, steeply sloped island in the Manu`a Island chain. Bathymetric data from 

multibeam surveys around Ta`u reveal the presence of a narrow (< 1 km) shelf that is wider 

along the north and west sides of the island (Fig. 5.3.1a). A series of small seamounts are 

~ 2 km northwest of Ta`u, along an east-west tending ridge, with depths as shallow as 38 m. 

The upper portions of this ridge of small, shallow seamounts were probably exposed during 

periods of lower sea level. 

Similarity between biota around neighboring islands probably derives from their spatial 

proximity which allows for substantial contemporary gene flow. Moreover, mapping efforts 

indicate a relatively shallow bridge between the islands that was likely historically exposed 

during lower stands of sea level, which may have provided stepping stones for colonization 

by taxa with short larval lifespans. TOAD optical validation surveys confirmed that these 

northwestern seamounts are colonized by coral communities (Fig. 5.3.1c).

The benthic composition surrounding Ta`u was highly variable (Figs. 5.3.2a, 5.3.2b, 5.3.2c, 

5.3.2d, and 5.3.2e). However, spatial and temporal patterns of the distributions of habitat 

types are apparent within the data. Low benthic topographical complexity was roughly 

correlated to the spatial distribution of sand (Fig. 5.3.2a). The south region, over the three 

survey periods, had consistently high benthic complexity, especially around Papaloaloa Point 

and the shoreline adjacent to the Liu Bench. High benthic complexity also was seen on the 

northern shore, but in smaller, more isolated areas.

Because of the steeply sloped nature of Ta`u, terrestrial watersheds and existing drainages 

modify the marine benthic habitat (Fig. 5.1a). This is evident from concatenated toweddiver benthic habitat maps (Fig. 5.3.2b) and multibeam backscatter maps (Fig. 5.3.1b). Sand 

and/or soft-bottom distribution on particularly the north shore benthos is directly correlated 

to terrestrial watersheds. There are also a few sand fields at the base of the forereef slope, 

especially off the western side of the island (Fig. 5.3.1b). 

While on a larger scale, physical oceanographic properties appeared to be somewhat 

homogeneous, distinct spatial patterns of all measured parameters were observed around 

Ta`u at smaller scales. There is believed to be a large-scale east-to-west current in the vicinity 

of Ta`u; however, no nearshore current data are available to resolve finer-scale patterns. 

Because of the steeply sloped nature of the island (Fig. 5.3.1a), the coral reef communities 

around Ta`u may be more exposed to wave energy than those at some of the other islands 

in American Samoa, such as Tutuila, which has a broad submerged bank that rises to depths 

as shallow as 20 m and extends several kilometers offshore. The north and west sides of 

Ta`u are exposed to infrequent, long-period swells from North Pacific boreal winter storms 

during the austral summer (Fig. 5.4.3b). The east and south sides of the island predominantly 

experience frequent short period (8–12 sec) waves (~ 2 m) from trade wind swell; they are 

also exposed to less frequent, larger (~ 3 m), longer period (12–18 sec) swells generated by 

winter storms in the Southern Ocean (Appendix II, Figure II. II. iv). A large swell event from 

tropical cyclone Heta in January 2004 (Fig. 5.4.3b) appears to have had at least some impact 

on all sides of the island.
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During each of the ASRAMP survey periods in 2002, 2004, and 2006, the nearshore shallowTA`U ISLAND

water CTD and water quality observations exhibited spatial heteorgeneity, although in many 

cases the magnitudes of the spatial changes were relatively modest (Figs. 5.4.1b, 5.4.1e, and 

5.4.1h). Waters in the east region were generally found to be well-mixed in the upper ~ 20 m of 

the water column, likely because of the influence of southeasterly trade winds. Interestingly, 

during mostly light-to-moderate winds for the survey periods, waters on the east side were 

generally stratified below ~ 20 m. The west region of the island was generally observed to 

have increased stratification in the upper water column, with the northern and southern sides 

falling in between. Water turbidity was highest along the central north region of Ta`u (Figs. 

5.4.1c, 5.4.1f, and 5.4.1i). Interpretation of salinity values from CTD data indicates there 

are likely point sources of fresh, cool water on the north side, probably from watersheds or 

subsurface springs. This would additionally account for the increase in turbidity values on 

the north side, as sediment input from terrigenous sources is often associated with freshwater 

outflows. Increases in turbidity could also be explained by austral summer swell from the 

northwest that could be stirring up benthic sediments. In situ SST values (July 2002–February 

2004) were observed to be 0°–3.5°C cooler than those observed via satellite and, for the most 

part, cooler when compared to the SST climatology (Fig. 5.4.3b). Nutrient concentrations 

show increased values along the south shore of Ta`u, and elevated nitrogen levels were found 

on the west side (Fig. 5.4.1j). Water samples indicated an increase in Chl-a concentrations 

near the harbor area on the northwestern side of the island. In both 2004 and 2006, this area 

was observed to have elevated turbidity and low salinity, which may be indicative of a point 

source of sediment and freshwater input.

A total of 32 coral genera have been observed around Ta`u, with higher diversity in the 

south region, and Montipora, Astreopora, Favia, and Porites being the most common. 

Approximately 64% of the coral colonies measured in 2004 (Fig. 5.5.1i), and 79% of them in 

2006 (Fig. 5.5.1o), were relatively small (< 20 cm maximum diameter). The high percentages 

of small colonies may reflect periodic disturbances from large wave events. In contrast to 

most areas, abundant large colonies have been found at some sites on the northwestern and 

northern sides of the island, which are hypothesized to be have been somewhat more sheltered 

than other areas from large but infrequent Southern Ocean swell and tropical cyclones. That 

said, towed-diver benthic surveys along the central portion of the east region have observed, 

without quantification, areas with large Porites colonies. Massive Porites colonies were also 

observed in the west, and are believed to be among the largest known (~ 6 m in height and 

~ 14 m in diameter), and possibly the oldest observed coral colonies in the world. Toweddiver benthic surveys also found a region in the southern portion of the west region that 

had similar, but slightly smaller, coral skeletons. Although the coral communities appear to 

mostly be healthy, 88% of REA sites on Ta`u were observed to contain minor amounts (< 

0.3%) of diseased coral, mainly growth anomalies and bleaching (Figs. 5.5.2a and 5.5.2b). 

SST profiles between February 2002 and February 2004 reveal a short spike above the coral 

bleaching threshold in March 2002 (Fig. 5.4.3b). However, this spike was not of sufficient 

duration to be expected to trigger bleaching, and no substantial coral bleaching was observed 

during 2002 or 2004 surveys. 

Figure 5.3.2e shows towed-diver survey estimates of live scleractinian coral cover integrated 

between years and probably provides the most complete picture of higher coral cover areas. 

It indicates higher percent cover to the southeast and lower percent cover to the northwest. 
TA`U ISLAND

290

All four corners of the island have relatively low coral percent cover in nearshore waters, 

possibly a result of wave energy refracting and concentrating onto these areas during high 

wave events. Generally higher coral percent cover to the southeast may possibly reflect 

increased circulation, flushing, and mixing in response to increased exposure to persistent 

southeastern trade winds. Interestingly, these findings are similar to those on the east side of 

Olosega. 

Towed-diver surveys, most notably in 2006, suggested that high live coral cover and increased 

topographical complexity are tightly coupled (Fig. 5.5.1k). High coral cover recorded by 

towed-diver surveys was variably distributed around Ta`u and showed temporally consistent 

hotspots on the eastern and south coasts.

The towed-diver and REA survey mean percent coral cover for all years was found to be 

approximately 25% for nearshore waters (Fig. 5.5.3a). Island-wide percentages of coral cover 

steadily declined between 2002 and 2006 in the towed-diver survey observations, while REA 

results showed an increase between 2004 and 2006. Towed-diver survey estimates of the 

percentage of stressed coral declined between 2004 and 2006 from ~ 6% to 2% (Figs. 5.5.1f 

and 5.5.1l). Locations around the island showing the highest coral cover varied between 

years, and to some degree results also varied by method. It is likely that the variations in 

results among different years (2002, 2004, and 2006) and survey methods (towed-diver 

surveys, visual estimates, and line point intercept) reflect differences in survey locations, 

changes in data collection protocols from year to year, and heterogeneity of coral distribution 

more than they do changes in coral community structure over time. 

Corals were mostly absent in the TOAD optical imagery from deeper (~ 30–80 m) areas. 

However, a coral community was found off the southeastern corner of the island. An additional 

luxuriant coral reef was observed over the summit of a shallow seamount 2 km northwest of 

Ta`u (Fig. 5.3.1c). 

It is important to include the extremely large and ancient communities of Porites sp. corals 

found on the east and west sides of the island (Figs. 5.3.2f and 5.3.2g) when characterizing 

the coral communities of Ta`u. In the more protected southern portion of the west region, 

the colonies were mostly dead and decaying; however, these ancient and massive corals are 

thought to be between 500 and 1000 years old and may be among the oldest known living 

coral colonies found in the world. At the request of Governor Tulafono of American Samoa, 

CRED scientists provided images, video, and background information about these unique 

coral colonies for his presentation at the United States Coral Reef Task Force meeting in May 

2006. At the time of publication, the American Samoa government is considering designation 

of this area as a Marine Protected Area.

These massive and ancient coral colonies, some living and some dead, are unique and deserve 

special attention as objects of study to advance the conservation and management of coral 

reef ecosystems in American Samoa and elsewhere. Combined, they contain within their 

cores a unique history of climate and ecological impacts of climate change over the past 

500–1000 years. Important questions concerning why the ancient corals have continued to 

thrive on the both the east and west sides of Ta`u, while their companion colonies on the west 

side have not, may improve our understanding of the ecological impacts of climate change 
291

and therefore provide guidance on how to better manage and conserve coral reefs during 

TA`U ISLAND

upcoming climate changes. 

Turf algae and crustose coralline red algae were the dominant benthic organisms at most 

nearshore areas around Ta`u and were usually fairly uniformly distributed around the island 

with a few exceptions (Figs. 5.6.1a, 5.6.1b, and 5.6.1e). The lowest cover of crustose coralline 

algae and the highest cover and diversity of macroalgae were found off the northwestern 

corner of the island. We hypothesize that the high concentration of macroalgae may be a 

result of the high influx of fresh water and terrestrial sediments mentioned previously and 

possibly terrestrial nutrients. Macroalgae also exhibited high local abundance in other areas, 

but were absent at REA site TAU-10, located in a predominantly sandy area. Halimeda was 

the most abundant macroalgae, occurring at 42% of the sampled sites in 2006 (Fig. 5.6.1f). 

A dramatic difference in the number of algal genera and their abundance around Ta`u was 

reported between the 2004 and 2006 survey periods (Fig. 5.6.3a). It is hypothesized that 

that the macroalgal community, in particular, may have been scoured by high wave energy 

generated by tropical cyclone Heta in January 2004, but that the community had recovered 

by 2006. Crustose coralline algae were most abundant in the east region, covering up to 

50% of the substrate during ASRAMP 2004 (Fig. 5.6.1a). Low occurrence and abundance of 

coralline algal diseases were noted around Ta`u. Ta`u contained only 4.2% of the region-wide 

total of coralline algae disease cases (21 infections observed), and the cases were distributed 

over only 30% of the surveyed sites (Figs. 5.6.2a and 5.6.2b).

Macroinvertebrate distributions were relatively similar along the forereefs of Ta`u during 

the 2004 and 2006 surveys (Figs. 5.7.1b and 5.7.1d). Giant clams were present at all but 

one site, TAU-04, off the north coast of Ta`u (Figs. 5.7.1c and 5.7.1e). In general, giant 

clams have been more prevalent in the north and west regions and least common on the 

south side of the island. No COTS were recorded during any survey. Sea urchins have been 

observed at most REA sites around the island during most years of surveying, with the 

boring urchin Echinostrephus sp. being the most common species. During each of the three 

ASRAMP cruises, the distribution of sea urchins has been observed to be concentrated on the 

northwestern corner of the island (Figs. 5.7.1a, 5.7.1b, and 5.7.1d), with concentrations on 

the northeastern and southwestern corners in some years as well. Interestingly, the corners of 

the island have relatively low percentages of coral (Fig. 5.3.2e), but it is not known if there is 

a link between the coral and urchin distributions. Sea cucumbers were most prevalent in the 

west region of the island, but have also been observed at other locations. Three sea cucumber 

species were observed around Ta`u (Holothuria cinerascens, Bohadschia argus, Holothuria

whitmaei) and were present at all REA sites along the west coast.

Total fish biomass was fairly consistent around the island, and relatively low at 0.7 tons 

ha-1 (Figs. 5.8.1a, 5.8.1c, and 5.8.1e). Fish communities were dominated by herbivores 

and a noticeable presence of small predators (e.g., triggerfish, emperor, and wrasse). The 

biomass of large (> 50 cm total length) fish was distributed relatively evenly around the 

island, considering data from all survey years, and was dominated by parrotfish, snappers, 

and surgeonfish. The only clear richness pattern that emerges is a generally lower species 

count 100 m-2 on the northern side of Ta`u (Figs. 5.8.1b, 5.8.1d, and 5.8.1f). By way of 

comparison, at the uninhabited Rose Atoll, large fish biomass was mostly composed of 

barracuda, jacks, and snappers. Sharks were also common around the outside of the atoll. 
TA`U ISLAND

292

Similar differences in the composition of fish communities at inhabited and uninhabited 

islands have been observed at sites across the Pacific and may be indicative of higher fishing 

pressure at the inhabited islands. 

References

Craig P (2002) Natural history guide to American Samoa: a collection of articles. National 

Park of American Samoa, Pago Pago, American Samoa. 76 pp.

Meehl GA (1996) Vulnerability of freshwater resources to climate change in the tropical 

Pacific region. Water Air Soil Pollut 92:203–213.

U.S. Census Bureau (2000) Census 2000 Data for American Samoa. Online at http://www.

census.gov/census2000/americansamoa.html. Accessed May 17, 2007.