Introduction
The global market demand for collagen is increasing (CAGR 6.52% until 2027). Due to its special properties such as high biocompatibility, good bioactivity, and weak antigenicity, collagen is a protein with a wide range of applications. It is used in pharmaceuticals, biomedical products, as well as in the nutritional supplements, cosmetics, and food sectors. Although terrestrial sources of collagen are numerous, outbreaks of various diseases in terrestrial animals complicate its use in humans. Marine collagen represents a promising alternative. Marine sponges are a highly valuable source of marine collagen. Among them, Chondrosia reniformis is of particular interest due to the high concentration (> 30%) of type I collagen in the sponge biomass (Pozzolini et al. 2012; Swatschek et al., 2002) and the absence of any inorganic components (spicules).
A major constraint regarding the industrial application of sponge collagen is the sufficient supply of sponge biomass. Promising efforts have been made in the mariculture of C reniformis targeting sustainable production of sponge biomass needed for collagen production (Gökalp et al, 2020; Orel et al, 2021), but the success of sponge farming is influenced by naturally fluctuating conditions such as light, current, and turbidity (Gökalp et al., 2020; Wilkinson and Vacelet, 1979). Predation, disease, and fouling can also harm this species in mariculture. Reports of sponge diseases have increased in recent decades, leading to depletion of sponge populations throughout the Mediterranean (Webster, 2007). In closed, recirculating aquaculture systems, optimal species-specific cultivation conditions can be established, enabling sustainable, reliable, and location-independent production of sponge biomass and, as a result, maximized collagen production.
The concept of integrated multitrophic aquaculture (IMTA) represents an even more sustainable approach. IMTA is based on the ecological concept of efficient reuse of organic and inorganic sidestreams through the application of different trophic levels of the food web within the culture system. Pronzato et al. (1998) were the first to include sponges in IMTA. Sponges can remove large amounts of organic matter from large volumes of water through very rapid and efficient filtration of a wide variety of suspended particles (Weisz et al. 2008; Riisgård et al. 1993; Reiswig 1974).
The efficient filtration of organic particles by sponges, coupled with their ability to produce commercially interesting natural compounds (Gökalp et al. 2019; Müller et al. 2009), is driving the interest in integrating these animals into IMTA approaches. However, examples of commercial applications of sponge farming are still rare (Duckworth 2009), and the inclusion of sponges as an element in IMTA is still in its infancy.
The focus of this study is the joint cultivation of the sponge species C. reniformis together with commercially relevant macroalgae and fish in an IMTA approach.
Materials and methods
The experimental phase will start in July 2025.
Chondrosia reniformis: The sponge specimen are obtained by diving from the Adriatic Sea, transported to the recirculation aquaculture system at the Alfred Wegener Institute, Bremerhaven, Germany and kept for an acclimatization period of two weeks in culturing tanks with artificial seawater. They are fragmented for growth experiments, placed on clay dishes in two divers systems: a shelf system (6 x 0.05 m³) and a circular tank (1 m³). They are fed once daily with a self-designed powder feed (2 ml/50, project AkPhaKol), which is dissolved shortly before feeding.
Three experiments are conducted during the project: one experiment on the growth behavior of the sponge fragments during the IMTA assembly and two additional experiments on the targeted increase of the collagen content in the IMTA assembly. 1) Increase in vitamin C intake as feed additive or as direct application. 2) Application of silicate in the form of a) sand and b) diatom fragments. During the experiments, the survival of the sponge fragments is documented at regular intervals, and growth is calculated in g and cm² at the beginning and end of each experiment. The collagen content of the sponge fragments is determined as a percentage of dry weight at the beginning and end of each experiment.
Ulva lactuca: Free-floating algae are obtained from macroalgae project (Novafoodies) conducting at the AWI. Those are distributed in four cascaded tanks (each 0.06 m³). After determining the ammonium, nitrate, and phosphate levels, the cascade system is connected to the sponge cycle. The nutrient concentrations (ammonium, nitrite, nitrate, phosphate) in the sponge and algae tanks are regularly monitored. If the algae are undersupplied with nutrients, the connection to the sponge tank can be removed if necessary to ensure additional food supply. The growth and photosynthetic efficiency parameters of the algae in the cascade-system are measured every three weeks.
Dicentrarchus labrax: Juveniles of European sea bass are obtained (approximately 5g body weight) from a commercial European fish farm. After an acclimation period of one week and removal of group 0 for measurement of length, weight, and health status, the fish tank is connected to the sponge-algae system. To ensure consistent conditions for the IMTA system, the following conditions are continuously evaluated: Stocking size and density, feed quantity and size, documentation of health status and feed availability for the sponge tank: The amount of feed available in the form of feces and fish food residues is documented. Additionally, water quality (ammonia, nitrate, nitrite, and phosphate levels) is monitored.
Expected Outcome
The location-independent, constant, and controllable conditions in a closed aquaculture system represent an optimal starting point for the development of refined sponge biomass and collagen. In former projects, an ex-situ aquaculture system for the sponge species C. reniformis has already been designed, constructed and adapted, in addition a feed specially tailored to the needs of the sponge C. reniformis has been developed. The collagen content in the obtained sponge fragments increased depending on the amount of this feed, resulting in a higher percentage of collagen to be extracted per sponge fragment.
The aim of the joint cultivation of macroalgae and fish in IMTA is to improve the maintenance and growth conditions for the sponge species C. reniformis. The macroalgae improve water quality by filtering nutrients such as ammonium and nitrate from the culture water and using them as food. Furthermore, the feces and food residues in the fish tanks increase the proportion of dissolved and particulate carbon in the process water, which serves as additional and constantly available food for the sponges in addition to the daily feed. Further, collagens with special properties can be produced and C. reniformis can be used as a sustainable collagen source on an economically relevant scale.
The concept of integrated multi-trophic aquaculture closes nutrient cycles by providing fish culture with food particles for the sponges, and using algae culture to absorb the increased nitrogen compounds in the culturing water. In an integrated multi-trophic aquaculture system, in which sponges are cultivated together with other economically relevant species, species-specific water quality and high fitness and growth of the sponge fragments are expected. In addition to the use of residual streams from fish culture, the integration of co-cultivated organisms leads to more diverse products with commercial value than monoculture
References
Duckworth, A. 2009. Farming sponges to supply bioactive metabolites and bath sponges: a review. Marine Biotechnology vol. 11, no. 6: 669–679.
Gökalp, M., H. Kuehnhold, J.M. de Goeij and R. Osinga. 2020. Depth and turbidity affect in situ pumping activity of the Mediterranean sponge Chondrosia reniformis (Nardo, 1847). Preprint: https://doi.org/10.1101/2020.03.30.009290.
Gökalp, M., T. Wijgerde, A. Sara, J.M. de Goeij and R. Osinga. 2019. Development of an integrated mariculture for the collagen-rich sponge Chondrosia reniformis. Marine Drugs 17, 29; doi:10.3390/md17010029.
Müller,W.E.G., X. Wang, Z. Burghard, J. Bill, A. Krasko, A. Boreiko, U. Schloßmacher, H.C. Schröder and M. Wiens 2009. Bio-sintering processes in hexactinellid sponges: fusion of bio-silica in giant basal spicules from Monorhaphis chuni. Journal of Structural Biology 168: 548– 561.
Orel, B., M. Giovine and M. Ilan. 2021. On the Path to Thermo-Stable Collagen: Culturing the Versatile Sponge Chondrosia reniformis. Marine Drugs 19, 669. https://doi.org/10.3390/md19120669.
Pozzolini, M., F. Bruzzone, V. Berilli, F. Mussino, C. Cerrano, U. Benatti and M. Giovine. 2012. Molecular Characterization of a Nonfibrillar Collagen from the Marine Sponge Chondrosia reniformis Nardo 1847 and Positive Effects of Soluble Silicates on Its Expression. Marine Biotechnology 14: 281–293.
Pronzato R, C. Cerrano and T. Cubeddu. 1998. Sustainable development in coastal areas: Role of sponge farming in integrated aquaculture. In: H. Grizel, P. Kesmont (Eds) Aquaculture and Water: Fish Culture, Shellfish Culture and Water Usage; Special Publication No. 26, pp. 231– 232. European Aquaculture Society, Bordeaux, France.
Reiswig H. M. 1974. Water transport, respiration and energetics of three tropical marine sponges. Journal of Experimental Marine Biology and Ecology 14: 231 249.
Riisgård, H.U., s. Thomassen, H. Jakobsen, J.M. Weeks, and P.S. Larsen, P.S. 1993. Suspension feeding in marine sponges Halichondria panacea and Haliclona urceolus: effects of temperature on filtration rate and energy cost of pumping. Marine Ecology Progress Series 96: 177– 188.
Swatschek, D., W. Schatton, J. Kellermann, W.E.G. Müller and J. Kreuter. 2002. Marine sponge collagen: isolation, characterization and effects on the skin parameters surface-pH, moisture and sebum. European Journal of Pharmaceutics and Biopharmaceutics 53: 107-113.
Webster, N. 2007. Sponge disease: a global threat? Environmental Microbiology 9(6): 1363–1375.
Weisz JB, N. Lindquist, C.S. Martens. 2008. Do associated microbial abundances impact marine demosponge pumping rates and tissue densities? Oecologia 155: 367– 376.
Wilkinson C. and J. Vacelet. 1979. Transplantation of marine sponges to different conditions of light and current. Journal of Experimental Marine Biology and Ecology 37: 91-104.