In search of resilient sponges as candidate habitat engineers for the renaturalization of polluted harbor environments

Harbor infrastructures impose strong environmental stress on coastal marine communities, limiting the persistence of many native species and hindering ecological restoration. Identifying resilient habitat-engineering organisms is therefore key to developing effective and affordable renaturalization strategies. In this study, we evaluated the suitability of five Mediterranean sponge species to withstand the process of collection, laboratory manipulation, and transplantation to a recreational harbor, where they were monitored over 455 days using image-based morphometric analyses coupled with computational modeling. Among the species tested, only Chondrosia reniformis showed high resilience under harbor conditions, with 91.7% survival. In contrast, all individuals of Corticium candelabrum, Crambe crambe, Scalarispongia scalaris, and Ircinia oros died during laboratory preparation or shortly after deployment in the harbor. Individuals of C. reniformis initially underwent a moderate size reduction but subsequently stabilized their biomass. The sponges demonstrated remarkable morphological plasticity, including continuous substrate crawling (up to 12.7 cm of total displacement) and the capacity to recover from disease. Some individuals underwent body fission during warm months, generating clonal offspring that nearly doubled the size of the experimental population in the harbor. Collectively, the results indicate that the high survival of this species in the degraded harbor environment, together with its resistance to disease, its ability to proliferate clonally, and its capacity to reposition itself for improved environmental adaption, makes C. reniformis a highly suitable candidate as putative habitat engineer in future multitrophic approaches aimed at enhancing biodiversity and renaturalizing degraded harbor environments and other anthropogenically impacted coastal habitats.