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.

本研究旨在探究物理环境变量是否会对环境DNA（eDNA）检测结果产生影响，为此评估了与珊瑚礁水交换、潮汐交换及海水温度相关的三项关键变量，并分析其作用以提升eDNA浓度的预测精度。
用于eDNA分析的水样采集自大堡礁（Great Barrier Reef, GBR）中部区域的4个陆架中部珊瑚礁，以及大堡礁北部区域的1个珊瑚礁。采样工作于2018至2020年连续三年开展。各珊瑚礁点位分别为：蜥蜴岛（Lizard Island）、磁石礁（Lodestone Reef）、戴维斯礁（Davies Reef）、伊丽莎白礁（Elizabeth Reef）。每个站点的采样在数天内进行2至3次。
每次采样行程均开展1次水下样带（50 m × 4 m）调查，每次布设3至6条样带。2018年在伊丽莎白礁开展的水下调查，额外补充了30次时长2分钟的蝠鲼拖网采样。针对蜥蜴岛珊瑚礁的长期监测数据显示，2017、2018及2021年共完成80至90条样带的调查工作；2019年与2020年，在蜥蜴岛开展了依托水下推进器辅助、由潜水员完成的大范围目视调查。
针对水样的eDNA分析，先完成DNA提取，随后采用微滴式数字聚合酶链反应（digital droplet PCR, ddPCR）进行检测。本研究借助eReefs RECOM平台，提取各采样点位在每次采样时的水体滞留时长（珊瑚礁上方水体的停留时间）、海水温度及潮位（海面高度）数据。
统计分析采用广义线性混合模型，旨在检验eReefs衍生参数（水体滞留时长、海面高度与海水温度）以及站点-访次层面的长棘海星（Crown-of-Thorns Starfish, CoTS）密度对每升水中长棘海星eDNA拷贝数的影响。