Abstract
Population outbreaks of the corallivorous crown-of-thorns seastar (CoTS; Acanthaster spp.) are significant threats to the Indo-Pacific reefs. Although recent research demonstrated that environmental DNA (eDNA) techniques could improve CoTS monitoring, the interpretation of surveillance results has been limited by uncertainties about eDNA dynamics. Here, we conducted aquarium experiments to identify biotic and abiotic factors affecting the shedding and degradation rates of CoTS eDNA. In the first experiment, we investigated the effect of two temperatures (24 and 28 °C) and three feeding treatments (no coral, coral accessible and coral inaccessible) on eDNA shedding rate of laboratory-raised 8-month-old juvenile CoTS. In the second experiment, we quantified CoTS eDNA degradation rate under three temperatures (24, 26 and 28 °C). We found that eDNA shedding rate was affected by feeding treatment (p < 0.0001) but not temperature. Specifically, the shedding rate under coral accessible treatment was about seven times higher than that of coral inaccessible treatment (p < 0.0001), whereas the presence of coral reduced the shedding rate by half (coral inaccessible vs no coral, p = 0.0249). Degradation of CoTS eDNA was rapid (half-life = 14 h) and not affected by temperature. Our results demonstrated that feeding activity increased eDNA release, but some of the released DNA was lost, potentially due to binding to coral surface mucus layer or skeleton. The rapid degradation rate indicated that results of eDNA surveillance likely reflects recent and local occurrence of CoTS. Although further testing is needed, this study provided support for using eDNA as a novel detection tool for early life stages of CoTS on coral reefs.
Highlights
In recent decades, coral reefs around the world have been declining rapidly (Hughes et al 2017)
Recent research demonstrated that environmental DNA techniques could improve crown-of-thorns seastar (CoTS) monitoring and management, the interpretation of surveillance results has been limited by uncertainties about eDNA dynamics in aquatic environments
Recent research has demonstrated the applicability of eDNA techniques in the management of CoTS outbreaks (Doyle et al 2017; Uthicke et al 2018; Doyle and Uthicke 2020)
Summary
Coral reefs around the world have been declining rapidly (Hughes et al 2017). Despite considerable research effort over the past three decades, development of effective management strategies to control CoTS outbreaks on the GBR remains constrained by the uncertainty in the underlying causes (Pratchett et al 2017). The failure to effectively detect early life stages of CoTS has prevented timely intervention and hindered our ability to answer critical research questions (Pratchett and Cumming 2019; but see Wilmes et al 2016, 2019, 2020a, b). Recent research has demonstrated that environmental DNA (eDNA) techniques may be a promising path forward for the improvement of CoTS detection and management (Doyle et al 2017; Uthicke et al 2018; Doyle and Uthicke 2020)
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