Geomorphic features and infauna diversity of a subtropical mid-ocean carbonate shelf: Lord Howe Island, Southwest Pacific Ocean
Lord Howe Island (31°33"S, 159°04"E) sits approximately 580 km east of Australia in the southwest Pacific Ocean. This remote island is the subaerial remnant of a hot-spot volcano that erupted between 6.6 and 7.2 Ma and comprises a mid-ocean basaltic sequence. Erosion of these basalts has dominated island evolution since the cessation of volcanism, creating a rhomboidal-shaped shelf around Lord Howe Island, 24 km wide and 36 km from north to south. As part of a large collaborative program of marine biodiversity research, the shelf around Lord Howe Island was selected as an area representative of a shallow (20–120 m) mid-ocean carbonate shelf environment. The relict reef comprises sand sheet, macroalgae, and hardground habitats. Inshore of the relict reef a sandy basin (mean depth 45 m) has thick sand deposits. Offshore of the relict reef is a relatively flat outer shelf (mean depth 60 m) with bedrock exposures and sandy habitat. Infauna species abundance and richness were similar for sediment samples collected on the outer shelf and relict reef, while samples from the basin had significantly lower infauna abundance and richness. The irregular shelf morphology appears to determine the distribution and character of sandy substrates and local oceanographic conditions, which in turn influence the distribution of different types of infauna communities.
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