Developing an effective marine eDNA monitoring: eDNA detection at pre-outbreak densities of corallivorous seastar (Acanthaster cf. solaris)

This study aimed to understand if physical environmental variables in¿uence eDNA measurements evaluating three key variables associated with reef ¿ushing, tidal exchange and sea temperature, and their impact to improve prediction of eDNA concentration.Water samples for eDNA analysis were collected from four mid-shelf reefs in the Central section of the GBR and from one reef in the Northern section of the GBR. Samples were collected over three consecutive years from 2018 – 2020. Reefs locations were: Lizard Island Lodestone Reef Davies Reef Elizabeth ReefSample collections occurred two to three times per site over a few days.Underwater transect (50 m × 4 m ) surveys were conducted once per trip between 3 – 6 transects. Underwater surveys were complemented with 30 2-minute manta tows in 2018 (Elizabeth Reef). Long Term Monitoring data were collected for Lizard Island Reefs, with between 80 and 90 transects conducted in years 2017, 2018 and 2021. Scooter-assisted large area diver-based visual surveys at Lizard Island were conducted at Lizard Island in 2019 and 2020.DNA extraction was prepared for water sample analysis, using digital droplet PCR analysis (ddPCR).eReefs RECOM was used to extract values of water residence age (age of water over reefs), temperature and tide level (sea surface elevation) for each site at each sampling time.Statistical analyses were conducted using generalized linear mixed models to test for the effects of eReefs derived parameters (water residence age, surface elevation and temperature) and CoTS density at the site x visit level on the number of CoTS eDNA copies per lL of water.