Title : Environmental DNA persistence and fish detection in captive 1 sponges 2 Running title : sponge nsDNA versus aquatic eDNA performance

23 Large and hyper-diverse marine ecosystems pose significant challenges to biodiversity 24 monitoring. While environmental DNA (eDNA) promises to meet many of these challenges, 25 recent studies suggested that sponges, as ‘natural samplers’ of eDNA, could further streamline 26 the workflow for detecting marine vertebrates. However, beyond pilot studies demonstrating 27 the ability of sponges to capture eDNA, little is known about the journey of eDNA particles in 28 the sponge tissues, and the effectiveness of the latter compared to water samples. Here, we 29 present the results of a controlled aquarium experiment to examine the persistence and 30 detectability of eDNA from three encrusting sponge species and how these compare with 31 established water filtration techniques. Our results indicate that sponges and water samples have 32 highly similar detectability for fish of different sizes and abundances, but different sponge 33 species exhibit considerable variance in performance. Interestingly, one sponge appeared to 34 mirror the eDNA degradation profile of water samples, while another sponge retained eDNA 35 throughout the experiment. A third sponge yielded virtually no DNA sequences at all. Overall, 36 our study suggests that some sponges will be suitable as natural samplers, while others will 37 introduce significant problems for laboratory processing. We suggest that an initial 38 optimization phase will be required in any future studies aiming to employ sponges for 39 biodiversity assessment. With time, factoring in technical and natural accessibility, it is 40 expected that specific sponge taxa may become the ‘chosen’ natural samplers in certain habitats 41 and regions. 42