Results of the Territorial Coral Reef Monitoring Program of American Samoa for 2011, Benthic Section
Department of Marine and Wildlife Resources (DMWR)
"In 2011, transect data was collected on the reef slopes and reef sites, and coral biodiversity data was collected on reef slopes and reef flats (for the first time). Both transects and coral biodiversity were also taken from both the reef flat and pools at Ofu as well (for the first time). Bleaching data continued to be taken at both the airport and Alofau pools, year-round. Data was also taken from 81 diseased colonies of Porites corals in an Ofu pool. Most indices continue to support the view that the benthic portion of American Samoan coral reefs are in relatively good condition. Mean coral cover was 31% on the reef slope. Coral cover continued to be highly variable from one site to another, but mean coral cover showed much smaller amounts of variation over time. Mean coral cover has increased over the years, and compares favorably to coral cover on the Great Barrier Reef, South Pacific, the whole Pacific, and particularly the Caribbean. However, it is still less than the Caribbean in 1977, Pacific in 1980, American Samoa in 1978, near-pristine reefs around the world, and near-pristine reefs in the U.S. Pacific. The increase in coral cover over time here is in contrast for the means for reefs in the Pacific, Indian Ocean, Red Sea, Caribbean, and global averages, all of which have been decreasing. The Live Coral Index? which reflects the proportion of corals that are alive, is steady and higher than in the world, the Indo-Pacific, Philippines, Indonesia, and South Pacific. American Samoa has much more crustose calcareous algae plus coral than it has turf plus macroalgae, which is considered good. If the macroalgae is divided into calcifying algae and non-calcifying algae, and all organisms that calcify added up, 70% or more of the substrate is covered by calcifiers, so the reef slopes have good cover of calcifiers. Coral cover increased at four sites, Masacre, Fagasa, Tafeu, and Leone, decreased at Vatia, and was steady at five sites, Aunuu, Amaua, Fagaalu, Nuuuli, and Fagatele. The decrease recorded at Vatia was due to the tsunami of Sept. 29, 2009, and/or Hurricane Wilma on Jan. 24, 2011. The tsunami badly damaged the inner half of the bay, and the Hurricane damaged the outer half of the bay. The transects straddle the mid section of the bay. Mean coral cover on slopes inside the harbor was much lower than outside the harbor, which may have been due to pollution in the harbor, since there is a published paper showing lower coral diversity in polluted areas. Coral cover in transects continues to be primarily encrusting, mainly composed of Montipora grisea, Pavona varians, Montipora informis, and Pavona chiriquensis. The second largest type of coral cover is columnar/plate colonies of Porites rus., which is actually the single species with the greatest cover. The number of genera showed downward trends but the number of coral species was largely steady. The number of coral species in transects is greater on the South side than the North side, and this has remained so over time. The number of coral species is positively correlated with the amount of coral cover at a site. This is because where there is more coral cover, there are more corals in the transects, and in general as you look at more individual corals you find more and more species because it is a larger sample of the coral population. Coral biodiversity was recorded on roving dives on the slopes, and for the first time several sites in Pago Pago harbor were included. There has been a small decrease in the number of coral species recorded in biodiversity dives since 2005 when monitoring started. Slightly more coral species were recorded on the south side in biodiversity dives than on the north, but in previous years the difference was small or not present. The number and diversity of invertebrates recorded has increased greatly over time, as the author became better and better at spotting small invertebrates of various kinds in the belt transects. It is surely not a real increase in the number of invertebrates. Mean coral cover on outer reef flats was 28.5%, just 2.5% less than on the reef slope. Previous monitoring found it was lower on inner reef flats. Again, variation between sites was large, but variation over time less. Reef flats on the south side had coral cover equal to that on the north, but north reef flats had more turf and south reef flats had more rubble. There was an increasing trend in coral cover on reef flats since 2007. The live coral index was high and stable on reef flats just as it was on the reef slopes. The amount of coral plus crustose coralline algae (CCA; both are considered good) was 50%, and has risen over the years. The amount of turf plus macroalgae (considered bad or mixed/neutral) decreased over the years. The amount of coral plus CCA was higher on the slope than the reef flat, primarily because low tides kill corals on the reef flat, a natural phenomenon. The total cover of calcifying organisms on the reef flat (which includes calcifying macroalgae, Halimeda) has increased over the years and the amount of non-calcifying area (everything else) has decreased. There is more calcifying cover on the slope than on the reef flats. Coral cover decreased on three reef flat sites, was steady at four, and increased at three. Vatia reef flat showed a sudden decrease in the time period of the tsunami and Hurricane Wilma. The most common lifeform of corals on the reef flats was encrusting, followed by Acropora branching, foliose, branching, and tables. Encrusting corals were the most common lifeform on both the slopes and the reef flats, and Montipora grisea was the coral species with the most cover on both slopes and reef flats. The number of genera and species of corals increased on reef flats over time. A total of 19 coral species were recorded only on the reef flat, and 33 species were recorded only on the slope in transects. Another 13 species were more common on reef flats than slopes, and a further 13 were more common on slopes than on reef flats. This supports the view that these two zones are very different places with different coral communities. The number of coral species in biodiversity searches varied greatly from one reef flat site to another. The mean number of corals on reef flats inside the harbor was the slightly more than outside the harbor. There were fewer coral species in biodiversity searches on the reef flats than on the slopes. There were more coral species on reef flats on the north than the south side of the island, while on the slopes there were more on the south than the north. Biodiversity searches on the reef flats found 10 species that were found only on the reef flat and 78 species that were found only on the slope. There were also 10 other species that prefer the reef flat and 27 that prefer the reef slope and eight that prefer pools. Slightly more corals species were found in biodiversity searches on reef flats in the harbor than outside the harbor. More coral species were found outside the harbor on the slope than inside the harbor on the slope which was in turn more than on reef flats inside and outside the harbor. North side reef flats had considerably more coral species than the south side in biodiversity searches. Outer reef flats on Tutuila had more coral cover than on Ofu-Olosega, but inner reef flats on Tutuila had less coral cover than on Ofu-Olosega. In biodiversity searches, there were more coral species in Ofu-Olosega pools than reef flats, more coral species on Ofu-Olosega than on Tutuila, and slightly more coral species on Tutuila reef flats than in pools. Bleaching in the airport pool was less in 2011 than in previous years. At Alofau, bleaching had decreased in 2010, but then increased in 2011 back toward the levels seen in previous years. A coral disease outbreak in Vatia following Hurricane Wilma killed some corals in the genus Acropora and damaged others, but subsided over several months and returned to normal levels. Colonies of Porites rus in the pool in front of Vaoto Lodge on Ofu were diseased when observed in 2011, with significant damage from the disease. In sum, most of the indicators of reef health indicate that the reefs of American Samoa are in relatively good condition."
Supported by a NOAA Coral Reef Monitoring grant, part of the Coral Reef Initiative
NOAA Coral Reef Monitoring Initiative