Colonisation of artificial substrata by deep-sea fauna and its implications for restoration actions: A meta-analysis

In order to better comprehend colonisation patterns in the deep-sea, a wide variety of colonisation substrata deployments have taken place over time in the deep sea. These substrata deployments vary in their duration and material used and are most commonly used to gather insights in community development and connectivity across the vastness of the deep sea. In the current era of increased attention for deep-sea exploitation, they are also of interest as a possible tool to assist in restoration of damaged and exploited ecosystems and aid in faunal recovery by offering potential suitable habitats. In this regard, the colonisation potential of artificial substrata to host a community (density and diversity) similar to the surrounding ecosystems needs to be evaluated. Here we present a review and a meta-analysis of colonisation substrata deployed >200 m deep, and reveal how successful colonisation depends on the ecosystem, the locality and environmental conditions. All substrata recovered from deployment in the deep sea were colonised be it in (very) low densities and hosted, at best, a subset of the local fauna though the diversity never attains the level of the original ecosystem. The presence of an energy source was crucial for chemosynthetic communities to colonise newly available (and artificial) substrata but also accounts for the limits of our knowledge to-date, as there are no studies in absence of a source population. Organic substrata attracted unique deep-sea decomposition specialist fauna, not representative for the surrounding ecosystem; their capacity to host a diverse community also diminished with depth. Contrastingly, inorganic substrata were capable of hosting more diverse communities, more similar to the surrounding environment, but may take longer to get colonised.