Quantifying shedding and degradation rates of environmental DNA (eDNA) from Pacific crown-of-thorns seastar (Acanthaster cf. solaris)

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\u2009<\u20090.0001) but not temperature. Specifically, the shedding rate under coral accessible treatment was about seven times higher than that of coral inaccessible treatment (p\u2009<\u20090.0001), whereas the presence of coral reduced the shedding rate by half (coral inaccessible vs no coral, p\u2009=\u20090.0249). Degradation of CoTS eDNA was rapid (half-life\u2009=\u200914 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.