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 Reef

Sample 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影响环境DNA（environmental DNA, eDNA）检测结果，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，并分析其影响以提升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个陆架中部礁体，以及大堡礁北部区域的1个礁体。采样工作于2018年至2020年连续三年开展。各礁体点位分别为：
蜥蜴岛（Lizard Island）
磁石礁（Lodestone Reef）
戴维斯礁（Davies Reef）
伊丽莎白礁（Elizabeth Reef）

每个点位的采样周期为数天，共开展2至3次采样。

每次采样行程均开展1次水下样带调查，样带规格为50 m × 4 m，每次行程布设3至6条样带。2018年针对伊丽莎白礁的水下调查额外补充了30次时长2分钟的蝠鲼拖曳采样。针对蜥蜴岛礁体的长期监测数据采集工作于2017、2018及2021年开展，每年布设80至90条水下样带。2019年与2020年，在蜥蜴岛开展了依托水下推进器辅助、由潜水员实施的大范围目视调查。

针对水样分析的DNA提取工作采用液滴数字聚合酶链式反应（digital droplet PCR, ddPCR）完成。

使用eReefs RECOM工具提取各采样点位在每次采样时刻的水体滞留时长（礁体上方水体的停留时间）、海水温度及潮位（海面高程）数据。

采用广义线性混合模型开展统计分析，以检验由eReefs获取的参数（水体滞留时长、海面高程及海水温度）以及点位-采样批次层面的长棘海星（Crown-of-Thorns Starfish, CoTS）密度对每升水体中长棘海星eDNA拷贝数的影响。