Environmental DNA persistence and fish detection in captive sponges

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

Automated summary

Large and diverse marine ecosystems present challenges for biodiversity monitoring. Recent studies have shown that sponges can serve as natural samplers for detecting marine vertebrates. However, little is known about the dynamics of eDNA particles in sponge tissue and how effective sponge sampling is compared to water samples. This study found that sponges and water samples have similar detectability for fish, but different sponge species vary in performance. Some sponges are suitable as natural samplers, while others may introduce difficulties in laboratory processing. An initial optimization phase is recommended for future studies using sponges for biodiversity assessment.