LAUSR

Cumulative anthropogenic pressures have triggered a global decline in the health of marine ecosystems, and coral reefs, in particular, are in crisis. With climate and population-related pressures predicted to intensify in the coming decades, it is increasingly crucial to develop cost-effective and accurate monitoring tools to document changes to these important ecosystems. Environmental DNA (eDNA) coupled with metabarcoding is a powerful tool for surveying a wide variety of biota. Here, we develop a baseline eDNA toolkit targeting scleractinian corals and validate its performance in conjunction with data derived on traditional diver-based visual surveys at the Cocos (Keeling) Islands. Three assays targeting the ITS2 and 16S barcoding regions were designed, which broadly detected diversity within Scleractinia and Porifera. Our eDNA assays recovered 78 ITS2 operational taxonomic units (OTUs) from 25 scleractinian genera which is comparable to the level of diversity recorded on visual surveys (68 species from 26 genera). There were some notable differences in the species detected using eDNA versus visual records that may relate to either misidentifications, intragenic variation, differential assay performance or cryptic species. Our data demonstrate that a multi-assay eDNA analytical approach, applied on surface water collections, represents a powerful and complementary way to survey diversity that can also reveal fine scale spatial differentiation in community composition. With further refinement and improved reference databases, we envisage eDNA to become a powerful complement to visual surveys and to play a key role in monitoring the health and diversity of complex coral reefs ecosystems.