Sessile Benthic Marine Invertebrate Biodiversity at Ningaloo Reef, Muiron Islands, and Exmouth Gulf, Western Australia: A Review and Gap Analysis

This paper provides a comprehensive review of sessile benthic invertebrate biodiversity across three interconnected marine areas in Western Australia’s Gascoyne and southern Pilbara regions: Ningaloo Reef (a UNESCO World Heritage site), the nearby Muiron Islands to its north, and Exmouth Gulf to its east. The study aims to identify taxonomic and spatial knowledge gaps and establish a baseline biodiversity record for the broader region. We collated specimen-based records from seven Australian museums and supplemented them with data from the Atlas of Living Australia, iNaturalist, and a Web of Science literature review. In total, we report 827 verified species of sessile benthic invertebrates in shallow waters (less than 30 m depth) across the Gascoyne and southern Pilbara regions from 4578 records. Ningaloo Reef exhibits the highest diversity, hosting 587 species, including 239 scleractinian corals and 124 sponges. Exmouth Gulf is home to a diverse and unique assemblage of at least 295 species, including 165 species of putative turbid water specialists or regionally restricted species which are not found at Ningaloo Reef or the Muiron Islands. Notably, all three sea pen species identified in this review are recorded exclusively from Exmouth Gulf. The Gulf also hosts a distinctive community of filter-feeding invertebrates, including 125 sponges, 27 tunicates, and 18 anemones that are not found in neighboring regions. The Muiron Islands, although under sampled, host 22 species of sponges, 14 octocorals, and 5 tunicates that have not so far been found at Ningaloo Reef or Exmouth Gulf, highlighting the uniqueness of the islands’ marine invertebrate fauna. The southern sector of Ningaloo Reef is under sampled, and there are gaps in the state faunal collections for many groups, including anemones, corallimorphs, zoanthids, cerianthids, and hydrozoans. Further targeted taxonomic research on existing museum collections is crucial, as only 18% of specimen records have been verified, and 41% of the verified records are only identified to morphospecies. This limits our understanding of regional diversity and distribution patterns but provides ample opportunity for further taxonomic study. Expanding monitoring programs to include Exmouth Gulf and the Muiron Islands, along with unique habitats such as the King Reef artificial reef, and conducting additional biodiversity, demographic, and ecosystem health research is essential to assess the cumulative impacts of climate change and other environmental stressors on the unique and culturally significant marine ecosystems of this region.