Coral Reef Ecosystems in American Samoa and the Pacific Remote Island Areas Assessed during 2010 Pacific RAMP Expedition

The 2010 Pacific Reef Assessment and Monitoring Program (Pacific RAMP) expedition to American Samoa and the Pacific Remote Island Areas was conducted during January 21–April 24, 2010. Led by the PIFSC Coral Reef Ecosystem Division (CRED), the cruise by the NOAA Ship Hi'ialakai provided updated assessments of the conditions of central Pacific coral reef ecosystems.

The Hi'ialakai visited all islands of American Samoa and South Bank. At Rose Atoll, within the Rose Atoll Marine National Monument, the lasting effects of a 1993 shipwreck were seen; in the immediate area of the wreck, surveys recorded up to 50% less coralline algae than in other parts of the atoll and only 1% coral cover, despite the removal of major portions of this rusting vessel by the U.S. Fish and Wildlife Service. However, overall, no obvious changes at Rose Atoll were observed this year compared to surveys in 2008.

The twinspot snapper (Lutjanus bohar) is native to the coral reef ecosystems of American Samoa and the 
            Pacific Remote Island Areas.
The twinspot snapper (Lutjanus bohar) is native to the coral reef ecosystems of American Samoa and the Pacific Remote Island Areas.

At the request of local agencies, South Bank, a popular fishing area 69 km south of Tutuila Island, was mapped using multibeam sonar. The results show that South Bank is a sunken coral atoll surrounded by a submerged barrier reef (minimum depth of 25 m). Using the maps, divers conducted Rapid Ecological Assessment and towed-diver surveys, recording observations of a scoured rubble surface with low coral cover.

At Ta'u Island, divers revisited some of the world’s largest ancient coral formations of Porites spp.; one measuring 7 m in height and 41 m in circumference. Along the north side of Ta’u Island, surveys showed a dramatic increase in the invasive didemnid tunicate recorded at high levels at Swains Island during the 2008 Pacific RAMP cruise. Surveys of Swains conducted during this 2010 expedition revealed that the tunicate is no longer present there at invasive levels, and the benthic cover around the island is now crustose coralline red algae. At a site on the northeast side of Ta'u Island, survey teams recorded a 1.8-m giant grouper (Epinephelus lanceolatus). On the northwest coast of Tutuila Island, divers reported a rare sighting of a 1.2-m-long white-spotted guitarfish (Rhynchobatus djiddensis).

During the surveys in American Samoa, CRED staff noted evidence of coral reef damage caused by the devastating September 29, 2009 tsunami. Towed-diver surveys at depths of 12–18 m indicated that the reefs around Tutuila Island were in good condition with little evidence of tsunami impacts. Localized areas of coral damage were noted, consisting of overturned tables of Acropora spp. and broken or scattered plating colony stands (Echinopora spp., Merulina spp., etc.). In one instance, a colony of Porites spp. about 1.5–2 m in diameter had toppled over onto its side, but was still alive. Some evidence of damage was seen on all sides of Tutuila Island; however, localized areas of damage were most often observed just offshore of villages on the southwest, west, and northwest coasts. No damage attributable to the tsunami was noted during towed-diver benthic surveys around the other islands visited.

In addition to surveys around American Samoa, the Hi'ialakai expedition visited all major remote islands and atolls included in the Pacific Remote Islands Marine National Monument. At Howland and Baker Islands, scientists observed mass coral bleaching caused by elevated water temperatures. Such warming episodes have occurred for at least the past 300 years as part of El Niño-Southern Oscillation (ENSO) dynamics, a climate pattern that occurs on average every 2–7 years throughout the tropical Pacific. During an El Niño year, warm water from the western Pacific spreads eastward, and strong thermal events, such as those predicted and now observed for 2010, can affect the health of coral reefs exposed to the elevated temperatures.

Bleached coral colonies were observed during towed-diver surveys around Howland Island during the 2010 
            Pacific RAMP expedition. NOAA photos. Bleached coral colonies were observed during towed-diver surveys around Howland Island during the 2010 
            Pacific RAMP expedition. NOAA photos.
Bleached coral colonies were observed during towed-diver surveys around Howland Island during the 2010 Pacific RAMP expedition. NOAA photos.

Divers recovered 4 subsurface temperature recorders (STRs) from Howland Island that had been attached to the reef at depths of 7–40 m for the past 2 years. The STR data show that surface-water temperatures (to a depth of 37 m) at Howland Island have been elevated to levels > 30°C since mid-November 2009. Coral bleaching was widespread and temperatures exceeded 30% at both Howland and Baker Islands, with a greater incidence of elevated temperature on the eastern sides of the islands than on western reefs. Overall, no substantial differences were observed between the two islands.

Branching and table corals (e.g., Acropora sp.) observed during the expedition appeared to be more affected by the bleaching than massive corals. CRED scientist Bernardo Vargas-Angel and colleagues are preparing a manuscript to formally report this event.

Before returning to Honolulu on April 24, 2010, the Hi'ialakai also visited Jarvis Island, Palmyra Atoll and Kingman Reef. Extensive analysis of data collected there will begin soon. Preliminary analysis provided the following interesting results:

Jarvis Island

Large numbers of grey reef sharks (Carcharhinus amblyrhynchos) were observed at Jarvis Island during 
            the 2010 Pacific RAMP expedition of the NOAA Ship Hi'ialakai.  NOAA photo.
Large numbers of grey reef sharks (Carcharhinus amblyrhynchos) were observed at Jarvis Island during the 2010 Pacific RAMP expedition of the NOAA Ship Hi'ialakai. NOAA photo.

Palmyra Atoll

Palmyra Atoll, one of the U.S. Line Islands surveyed during the 2010 Pacific RAMP expedition. Photo by 
            Stuart Sandin, Scripps Institution of Oceanography, UC San Diego.
Palmyra Atoll, one of the U.S. Line Islands surveyed during the 2010 Pacific RAMP expedition. Photo by Stuart Sandin, Scripps Institution of Oceanography, UC San Diego.

Kingman Reef

During the 2010 Pacific RAMP surveys at Kingman Reef, high densities of giant clams (Tridacna sp.) 
            were observed on the southeastern backreef. NOAA photo.
During the 2010 Pacific RAMP surveys at Kingman Reef, high densities of giant clams (Tridacna sp.) were observed on the southeastern backreef. NOAA photo.