Abstract
Marine diversity across the Australian continental shelf is shaped by characteristic benthic habitats which are determined by geomorphic features such as paleoshorelines. In north-western Australia there has been little attention on the fish communities that inhabit an ancient coastline at ~125 m depth (the designated AC125), which is specified as a key ecological feature (KEF) of the region and is thought to comprise hard substrate and support enhanced diversity. We investigated drivers of fish species richness and assemblage composition spanning six degrees of latitude along sections of the ancient coastline, categorised as ‘on’ and ‘off’ the AC125 based on depth, across a range of habitats and seafloor complexity (~60–180 m depth). While some surveyed sections of the AC125 had hard bottom substrate and supported enhanced fish diversity, including over half of the total species observed, species richness and abundance overall were not greater on the AC125 than immediately adjacent to the AC125. Instead, depth, seafloor complexity and habitat type explained patterns in richness and abundance, and structured fish assemblages at both local and broad spatial scales. Fewer fishes were associated with deep sites characterized by negligible complexity and soft-bottom habitats, in contrast to shallower depths that featured benthic biota and pockets of complex substrate. Drivers of abundance of common species were species-specific and primarily related to sampling Areas, depth and substrate. Fishes of the ancient coastline and adjacent habitats are representative of mesophotic fish communities of the region, included species important to fisheries and conservation, and several species were observed deeper than their currently known distribution. This study provides the first assessment of fish biodiversity associated with an ancient coastline feature, improving our understanding of the function it plays in regional spatial patterns in abundance of mesophotic fishes. Management decisions that incorporate the broader variety of depths and habitats surrounding the designated AC125 could enhance the ecological role of this KEF, contributing to effective conservation of fish biodiversity on Australia’s north west shelf.
Highlights
Studies on mesophotic and deep-water fish communities in tropical waters are rare because of limitations associated with surveying remote, deep marine environments [1, 2]
Species found on the AC125 comprised 53% of all species recorded (75 of the 141 species/groups), 76% were observed off AC125 on shallow baited remote underwater video station (BRUVS) (107 species/groups) and 45% off AC125 in deep sites
Fish diversity was greatest at shallow depths off the AC125 (76% of fish species overall), the AC125 does support a diverse fish assemblage, including ~53% of mesophotic fish species observed in this study as well as 39% of the recorded fish abundance
Summary
Studies on mesophotic and deep-water fish communities in tropical waters are rare because of limitations associated with surveying remote, deep marine environments [1, 2]. The increasing use of remote survey technologies has enabled more detailed study of lesser-known mesophotic (60–180 m depth) and aphotic habitats beyond the limits of traditional diver-based techniques. Some of these surveys have revealed areas of unique and rich biodiversity in deep water [9, 10]. [12]) or be long-lived [13] They may be sensitive to environmental pressures such as global warming, ocean acidification and fishing [14,15,16]. To ensure effective protection and environmental impact mitigation strategies for mesophotic and deep-water fish communities it is critical to understand the patterns and drivers of distributions in these communities, their associations with shallower systems and their ecological processes
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
