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Abstract:

A deep-water coral reef mound is located along the upper western slope of Stjernsund-Sill in the Norwegian West Firaimark District at 70°N. It grows between a muddy basinal Qord and an erosive sill-crest sedimentary environment in 260- to 235-m water depth, thriving in water temperatures between 5° and 6°C. Maximum framework thickness of Lopheliapertusa is 10 m. Despite its deep position far below storm-wave base, the reef is strongly zoned and two stages of reef development can be distinguished, a growing stage and a dying stage. Each stage is characterized by distinct colony growth habits representing ecotypes. Active reef mound growth dominates along the upcurrent, deeper section of the mound, whereas framework destruction is confined to the shallower, downcurrent area of the mound complex. If the unlithified deep-water coral reef mound is not buried by sediments, the preservational style will be a detrital collapse structure rather than an intact framework. Preliminary growth estimates yield unexpectedly high growth rates of up to 2 cm/yr. On the basis of this value, the onset of mound formation was only 520 years ago. If this preliminary estimation is substantiated by more detailed analysis, L. pertusa has the potential of rapid accretion under suitable environmental conditions. Main environmental controls are nourishment and a homothermal water mass passing over the reef mound, availability of hard substrates and a current regime preventing sedimentation. At present, the Stjernsund reef mound is just below the thermocline. The upper, dying reef areas are already affected episodically by the properties of fluctuating water masses.

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