Northwest Australia

Abstract

The northwest continental shelf of Australia supports a series of emergent reefs toward the western edge and a chain of submerged shoals extending eastward along the Sahul Shelf. Hard corals and calcareous algae are major components of the benthos in the upper mesophotic regions (30--60 m) on both reefs and shoals. These habitats transition to heterotrophic-dominated communities at around 60 m depth in clear water at shelf-edge locations. While mixed hard coral communities of moderate diversity are commonly encountered, characteristic upper mesophotic coral habitats include dense areas of foliaceous species from the families Agaricidae and Acroporidae in depths of 40--60 m. Extensive fields of fungiid corals can be found occupying unconsolidated substrates at similar depths on both reefs and shoals. The alternate ecological stages of otherwise geomorphically similar shoals provide evidence of shoal scale temporal stochasticity in recruitment and disturbance events. Green calcareous algae of the genus Halimeda can be abundant and are a major sediment producer in shoal bioherms. Taxonomic studies have been focused on the shallow reefs of the region, with collection of voucher specimens from mesophotic depths lacking from the majority of reef and shoal locations.