. Atoll research bulletin. Coral reefs and islands; Marine biology; Marine sciences. 31 Destruction mechanisms Based on the outer slope morphology, three types of destruction mechanism were figured by Laboute (1985) and Harmelin-Vivien and Laboute (1986) following field observations. These theoretical processes are subject to variations with local details of the slope. The reef flat is narrow, the fore reef area above a depth of 15 m and the slope very steep (> 45°) as on the western coast of the atoll. Between 0 and 15 m, plate-like and branching madreporic species are abundant. They are o
. Atoll research bulletin. Coral reefs and islands; Marine biology; Marine sciences. 31 Destruction mechanisms Based on the outer slope morphology, three types of destruction mechanism were figured by Laboute (1985) and Harmelin-Vivien and Laboute (1986) following field observations. These theoretical processes are subject to variations with local details of the slope. The reef flat is narrow, the fore reef area above a depth of 15 m and the slope very steep (> 45°) as on the western coast of the atoll. Between 0 and 15 m, plate-like and branching madreporic species are abundant. They are of the genus of Pocillipora, Acropora, Montipora, Astreopora, Favia and Pavona. All those species are fragile and have been uprooted then reduced to rubble by the strength of the swell. The remains have contributed to destroy more resistant species by recurrent impacts and abrasion. Most of the remains have been thrown up on the reef flat. At 12-15 m on the fore reef area, massive and heavy madreporic species like Porites lobata and Montipora prevail. As above, those species have been uprooted by the swell but since they were growing near or on high-angle substrates, remains rolled down the steep slopes weeping deeper colonies often more fragile, such as the plate-like Pachyseris speciosa, the dominant species below 40 m. Destructive effects of this underwater avalanche increased with depth as shown in Fig. 13. It is likely that coral blocks accumulated at some level between 300 and 500 m where the slope begins to flatten out, contributing to the formation of a detrital cone surrounding the atoll (Harmelin-Vivien and Laboute, 1986). So far, this avalanche phenomenon has never been described elsewhere. All previous hurricane effect descriptions were done for islands without this typical steep outer slope and as a result, cyclone damages were thought to be limited to the upper level of the ecosystem. LAGOON £©^} boulder rampart / OUTER REEF coral destruction 50% to 80% direct d
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