Overvåkning og fjerning av havnespy i UNESCO Magma Geopark

Carpet sea squirt, havnespy, Didemnum vexillum is an invasive colonial tunicate originally from the Northwest Pacific with a tremendous potential to spread mainly via ballast waters and hull fouling as well as during the handling operations of the aquaculture industry. Initially found in Norway in November 2020, th e species represent s a major threat for the local marine biodiversity as well as for the maritime and aquaculture industr ies . A recent study documented the presence of carpet sea squirt in Norway by filtering 10 l of seawater and performing a genetic analysis , qPCR, looking for traces of DNA from the target spec ies. In this study, we tested the effectiveness and sensitivity of two recently developed qPCR assays specifically designed for the detection of carpet sea squirt reducing the volume of filtered seawater to 1 l . This amount of water is a common volume filtered for biodiversity assessment studies that would ease the logistics to sample water by a small boat in areas inaccessible or of difficult access from shore. Later on, the approach was implemented to monitor the potential spread of t he species along the UNESC O Magma Geopark by analyzing 24 samples collected at 8 selected sites in Flekkefjord, in the easter limit of the Geopark. The results evidence the capabilities of eDNA analysis from 1 l seawater for early detection of the invasive colonial tunicate carpet sea squirt. The absence of a positive signal in any of the water samples collected in Flekkefjord suggests that the species has not established in the easter side of the UNESCO Magma Ge opark. However, considering the tremendous capacity of the species to spread rapidly and the current uncertainty on how abiotic and biotic factors may affect the spatial and temporal dynamics and persistence of eDNA in saltwater, further studies should be conducted to measure the spatial and temporal sensitivity of the method by filtering alternative volumes of water . Additional efforts to prevent further spread and removal of established colonies should be also investigated.