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Pearl and Hermes Atoll (27° 50' N - 175° 50' W)
Pearl and Hermes Atoll lies about 216 nautical miles (400 km) east-southeast of Midway Atoll and approximately 1,080 nautical miles (2,000 km) northwest of Honolulu. Pearl and Hermes Atoll was discovered when the whaling ship Pearl ran aground in 1822. It is a huge oval coral reef with several internal reefs and seven sandbar/islets above sea level along the southern half of the atoll. The land area is small (88 acres or 0.36 km2) and the highest point above sea level is about three meters. The islets are periodically washed over when winter storms pass through. Its coral reef area, however, is huge. It is the second largest (about 1,166 km2 or 288,125 acres to depths of 100 m) among the six atolls in the Northwestern Hawaiian Islands (NWHI).
Map of Pearl and Hermes atoll (Map: NOAA)
IKONOS satellite image of Pearl and Hermes Atoll (Photo: NOAA)
The fringing reef encloses a lagoon that measures about 43 miles (69 km) in circumference, and open to the west. The reef is continuous on the east side but there are some breaks on the south side that allow entrance for small vessels a short way into the lagoon. The northwestern third of the rim consists of a line of coral heads and patch reefs, interspersed with deeper water. Some extensive reef formations are found within the lagoon, some extend 1.6 to 2.7 nautical miles (three to five km) in a nearly straight line. Others form miniature atolls. The lagoon is large with amazing variety and abundance of reef habitats.
Survey teams reported that carbonate pavement and spur and groove habitat dominated the ocean-facing reefs. Live coral cover was low, but there were large populations of macroinvertebrates, such as boring sea urchins in the genera Echinometra and Echinostephus. Other habitats included holes, overhangs, mounds of coral rubble, shallow sand depressions, pinnacles, deep vertical canyons, sea grass meadows, rubble flats, and sand flats. The pinnacle reefs show both high coral cover and diversity. The spur and groove habitat of the north and northwest outer barrier reefs is unique among NWHI atolls in that it contains extremely deep and narrow canyons. The southern outer reef slopes, dominated by fleshy algae cover, contain numerous large holes, overhangs and caves, which contribute to the abundance and diversity of fishes at the atoll. The east and south reef slopes had a very high numbers of crown-of-thorns sea stars that preyed on Pocillopora corals.
The rare black-lipped pearl oyster, Pinctada margaritifera (Photo: Cal Hirai)
Algae and corals and other invertebrates
Circular reef formations surround deep lagoon holes which have isolated populations of invertebrates, such as lobsters, moon-snails, and sponges. Ten new species of sponges for Hawai'i were collected from this type of habitat.
Pearl and Hermes has a moderately diverse assemblage of coral species, but probably not as high as in French Frigate Shoals. It has been suggested that this difference may be attributed to the lack of table corals (Acropora) at Pearl and Hermes, while up to six or more species are present at French Frigate Shoals. Thirty-three species of stony corals have been documented at Pearl and Hermes Atoll. Gardens of the finger coral, Porites compressa, flourished on patch reefs in the north central lagoon. The southern, central, and eastern lagoon areas contain reticulated reefs. Southern back reef habitats and northwestern and open lagoon pinnacles are covered with several species of Pocillopora. The bottom habitats of the lagoon were dominated by the green alga, Microdictyon setchellianum and the red alga, Stypopodium hawaiiensis. These algae provide food and cover protection for small invertebrates and juvenile fishes, and also provide a substratum for turf algae and other invertebrate animals.
Black-lipped pearl oysters, at one time very common, were harvested in the late 1920s to make buttons from their shells. Over-harvested, the oysters were nearly eliminated, and today only a handful remain even long after their harvesting was declared illegal in 1929.
The red alga, Stypopodium hawaiiensis, on the lagoon bottom (Photo: J.Smith/U. Hawai'i)
The green alga, Microdictyon sp. (Photo: J.Smith/ U. Hawai'i)
It is reported that Pearl and Hermes Atoll has the highest standing stock and species richness of fishes in the NWHI. These include large predators, such as sandbar sharks, Galapagos sharks, and Trevalle Jacks. In addition, angelfishes considered rare in the rest of the Hawaiian archipelago, such as the masked angelfish (Genicanthus personatus) and the Japanese angelfish (Centropyge interrupta), are commonly encounted at Pearl and Hermes Atoll.
A male masked angelfish, Genicanthus personatus, at Pearl and Hermes Atoll (Photo: Tom Ordway, Ocean Futures Society)
The Japanese angelfish (Centropyge interrupta) is commonly seen at Pearl and Hermes Atoll (Photo: Keoki and Yuko Stender)
Seals, turtles, and spinner dolphins
Pearl and Hermes Atoll supports a breeding population of endangered monk seals. Sea turtles also breed and feed there. The atoll is also a mating area for spinner dolphins.
The sandbar islets support a number of coastal dry grasses, vines, and herbal plants, including 13 native species and 7 introduced species. The plants survive because they are salt-tolerant and able to recover from frequent flooding. The islets are devoid of trees, except for some ironwoods (Casuarina) planted in 1928, and which may not have survived.
Click here for a description of the terrestrial vegetation of Pearl and Hermes Atoll and other NWHI: S.S. Midway Expedition.
Reference: Starr, F. and K. Martz. 1999. S.S. Midway Expedition. Trip report prepared for U. S. Fish and Wildlife Service, Honolulu, Hawai'i. [ Text only ]
The islands of Pearl and Hermes Atoll provide resting and nesting areas for an estimated 160,000 birds of approximately 22 species. They include Black-footed albatrosses, Tristram's storm petrels, and one of two recorded Hawaiian nest sites of little terns. Over the years, several of the NWHI's rare endemic birds have been introduced to Pearl and Hermes. The Laysan Finches brought to the Atoll appear to have survived, but not Laysan ducks and Laysan rails.
The Casitas, a 145-foot charter vessel, is grounded on a reef at the Pearl and Hermes Atoll. It was successfully refloated then scuttled (Photo: USCG)
Pearl and Hermes Atoll was discovered in 1822 when the whaling ships Pearl and Hermes went aground. A century later, pearl oysters were found, and a brief industry developed, with Filipino divers collecting tons of shell that were sold to button manufacturers on the Mainland. The pearl oyster population never recovered.
Pearl and Hermes Atoll continues to be a danger to ships. On July 2, 2005, the charter vessel, Casitas, ran aground on the northern reef. The Casitas was on its way from Midway, roughly 90 miles (167 km) to the west, to conduct marine debris removal work first at Pearl and Hermes, and then later at Maro Reef and French Frigate Shoals. The extent of the long term damage to the reef ecosystem has not been determined.
Pearl and Hermes Atoll has been extensively impacted by marine debris washing ashore and fouling the Atoll's reefs. In 2003, over 90 tons (81.7 metric tons) of marine debris was removed from the reefs. The debris appears to be coming from the North Pacific Gyre, a slow-moving current that traps discarded nets and other waste. Pearl and Hermes appears to be the most affected of the NWHI The debris damages reefs, entangles fish and marine mammals, and may be introducing alien marine organisms to the NWHI.
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