![]() ![]() ![]() lobata, determined by sclerochronologic analysis, indicated a period of stress during 1987. The lengths of regenerating knobs and the rates of linear skeletal growth in P. ![]() lobata, 60 70% maximum of all colonies sampled) or total ( Pocillopora sp., 80% maximum) mortality. Large numbers of corals on the 15 18 m terrace had recently suffered partial ( P. The grazing of large diadematid sea urchins, (2 species each of Diadema and Echinothrix) on dead corals cause extensive erosion in some areas. Frequent grazing by the pufferfish Arothron meleagris results in the removal of large amounts of live tissue and skeleton from Porites lobata. Although crustose coralline algae predominate in the breaker zone (with up to 100% cover), a prominent algal ridge is absent with only a slight buildup (ca. Spur and groove features, constructed of alternating frameworks of Pocillopora and Porites, and veneered with crustose coralline algae, are generally well developed around most atoll exposures. Scleractinian corals predominate (10 100% cover) over insular shelf depths of 8 to 60m, and crustose coralline algae are dominant (5 40% cover) from 0.5 to 7m. Two of the remaining scleractinians ( Pavona minuta, Leptoseris scabra) and the hydrocoral ( Millepora exaesa), all formerly known from central and western Pacific localities, represent new eastern Pacific records. ![]() The identities of the one Pocilpopora species and one of the two Porites species are still unknown. Although Clipperton is a well developed atoll with high coral cover, the reef-building fauna is depauperate, consisting of only 7 species of scleractinian corals belonging to the genera Pocillopora, Porites, Pavona and Leptoseris, and 1 species of hydrocoral in the genus Millepora. Shallow (15 18 m)and deep (50 58 m) terraces are present around most of Clipperton, probably representing Modern and late Pleistocene sea level stands. SST anomalies at Clipperton occur during ENSO events and were greater at Clipperton in 1987 than during 1982 1983. Maximum NECC flow rates indicate that the eastern Pacific barrier can be bridged in 60 to 120 days. The northernmost latitude reached by the NECC is not influenced by El Niño-Southern Oscillation (ENSO) events, but easterly flow velocity evidently is accelerated at such times. Satellite-tracked drifter buoys from 1979 1993 demonstrated complex patterns of surface circulation with dominantly easterly flow (North Equatorial Counter Current, NECC), but also westerly currents (South Equatorial Current, SEC) that could transport propagules to Clipperton from both central and eastern Pacific regions. Three areas were surveyed in the Revillagigedo Islands (Mexico), and an intensive study was conducted on Clipperton Atoll (1,300 km SW of Acapulco), including macro-scale surface circulation, sea surface temperature (SST) climatology, geomorphology, coral community structure, zonation, and biogeography. Here to download a high-resolution version of the image (8.Coral reef geomorphology and community composition were investigated in the tropical northeastern Pacific during April 1994. Thus preserving an atoll at the surface long after the original volcanic If for geological reasons the original volcano subsidesīelow sea level at a slow enough rate, corals will continue to build, Rate of erosion is much slower, and atolls such as Tupai may existįor long periods. In tropical climates until they reach sea level. Reef-buildingĬorals can only live in shallow waters of 20 meters (65 feet), in temperatures (Note the X-shaped runway on the northern corner of the reef, the only clue from space that this tropical paradise has been heavily developed as a tourist resort.) The northernmost island, Tupai, is merely an atoll, having lost any relic of the volcano around which the reef originally grew, except for the shallow floor of the lagoon, showing up in turquoise.Įxcellent illustration of the hypothesis first propounded by Charlesĭarwin to explain the origin of coral reefs in deep oceans. On Bora Bora (center), the reef is prominently developed and the island significantly eroded. Northward along the chain, the original central volcanos are older and more heavily eroded. They are old, eroded volcanos, fringed by a coral reef. At bottom right are the islands of Tahaa and Raiatea. This chain of coral fringed islands forms the Leeward Island chain within the French Society Islands. Tahaa, Raiatea, Bora Bora, and Tupai Atolls, Pacific Ocean ![]()
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