The multifunctional role of marine sponges in multi-trophic mariculture systems : towards sustainable use of sponges in polluted marine waters

There lies little novelty in the claim that coastal ecosystems are experiencing large-scale ecological degradation due to increased anthropogenic impact and overharvesting of marine resources. Fish stocks are depleting globally and uncontrolled expansion of aquaculture farms to provide food security for the growing human population further compromises the health and resilience of marine environments. Thus, there is urgent necessity to reduce human impact on marine habitats by applying environmental-friendly, product-diversified and socially beneficial concepts of integrated farming and coastal management. Since sponges feed on suspended and dissolved organic matter, it has often been suggested to apply sponge culture to remediate marine organic pollution, such as the effluent from sea-based fish cages and unpurified urban wastewater discharge. Sponges are found at all latitudes, living in a wide array of ecosystems varying in temperature and depth. Sponges have important ecological roles, including that of biological filter. They extract and accumulate various organic and inorganic compounds and microorganisms from the water, thus improving the water quality of marine and freshwater systems. Additionally, marine sponges are known as a plentiful resource of new bio products, that have remarkable potential for development as pharmaceutical drugs or biomedical materials. This PhD thesis focused on the production of raw sponge materials by mariculturing sponge species that produce a potential drug (avarol) and a potential biomaterial (collagen), respectively. Since sponges feed on suspended and dissolved organic matter, it has often been suggested to apply sponge culture to remediate marine organic pollution, such as the effluent from sea-based fish cages and unpurified urban wastewater discharge. Large-scale sponge culture may help reduce eutrophication of coastal waters and its concomitant disruptive effect on local ecology and biodiversity. Sponge culture can also locally improve the water quality around fish farms, which benefits the cultured fish. This thesis aims to assess the biological performances of targeted Mediterranean sponge species under different eutrophication and depth conditions. By using a multifactorial approach, I investigated the aquaculture potential, in situ filtration activity and pollution remediation efficiency of the selected species at pristine sites and organically polluted sites. Species specific culture methods were optimised ultimately achieving a novel integrated fish-sponge farm model, termed as “Sponge Lantern”, which is self-cleaning and could maximize production of high quality raw sponge material.