Introduction
Marine sponges are one of the most important sources of bioactive compounds used in medicine, industry and as nutraceuticals. As sessile organisms, sponges have developed chemical defense mechanisms to avoid covering by algae, bacteria and infectious microorganisms (Thoms et al., 2006). The Mediterranean sponge species Chondrosia reniformis is of special interest due to its high collagen content (Swatschek et al., 2002). However, a large amount sponge biomass is required t o obtain a high yield of collagen . To a void overharvesting of natural sponge resources special culture techniques need to be developed. However, to date no land- based cultivation and high mass production of C. reniformis has been possible due to their sensitivity to transportation and high demands on aquaculture conditions (Nickel and Brümmer, 2003).
The present study aims to determine optimal conditions in recirculating aquaculture system (RAS) to allow C. reniformis fragments to grow and create a sustainable source of sponge biomass with commensurate maximized collagen production.
Materials and methods
C. reniformis were obtained by SCUBA from the coast o f the Conero Promontory (Italy) in the Adriatic Sea and subsequently raised in a recirculation aquaculture system at the Alfred Wegener Institute, Bremerhaven (Germany).
In a first experiment s ponge fragments were cut into fragments and glued on an artificial substrate before the effect of nutrient content, light and water drain position on sponge attachment, survival, growth and collagen content we re examined at specific intervals. They were fed a mixture of commercial liquid diet and microalgae.
In a second experiment, feeding strategies and feed types were tested. Sponge fragments were fed with either the commercial liquid diet for filter feeders or a novel formulated diet . Sponges were fed once a day for four weeks , then at increased feeding frequency for another four weeks after sacrificing half of the respective fragments. Attachment, fragment growth, survival rate and collagen content were measured at the end of the experiment. Fragment growth was measured photographically. C ollagen content was detected by the company KliniPharm GmbH. Collagen was dissolved by alkaline hydrolysis and the solution was analyzed by quantitative color reaction (Roti®-Quant Universal).
Results
In the first experiment, fragments remained attached and after a week began to encrust the substrate. Mean fragment growth curves measured in cm² initially increased, but decreased again after one to two months. Mortality was 26.1% in total. Best survival rates were detected under blue light and tank drain at the bottom. Nutrient content (ammonia, nitrite, and nitrate ) fluctuated markedly throughout the experiment. Collagen content ranged from 5% to 25% with twenty percent of samples having less than 10% collagen.
In the second experiment, attachment and survival rate was high with 81% and 91%, respectively. Nutrient levels remained low throughout the experiment. A bespoke C. reni formis diet was used ( diet 1). On avera ge sponge fragments fed with diet 1 had a higher collagen content than those fed with diet 2 (commercial diet) (Fig. 1). After four weeks fed once a day sponge collagen content ranged from 11% to 30% with sixty percent of samples having less than 20% collagen. After another four weeks fed at increased feeding frequency sponge collagen content ranged from 19% to 80% with half of samples exhibiting a collagen content above 30%.
Discussion and conclusion
To avoid high mortality rates of sponge fragments the aquaculture system has to provide stable values of abiotic factors. To increase the possibility of physical adaptation to the new hydrodynamic patterns, moving of fragments during experiments was avoided, hence, measurements of growth rely on two values (at the start and end of experiment).
One of the important parameters for successful land-based aquaculture is an optimal feed supply and nutrient content . Additionally, sponge growth is dependent on the amount of feed supplied; high loads of fee d can lead to blockage of the ostia and too low feed supply in starving of sponge fragments (Wilkinson, 1983).
In conclusion, an aquaculture system with optimized rearing conditions including stable nutrient water retreatment processes and an optimal feed is essential for survival, attachment, growth, amount of collagen content.
References
Nickel, M., and F. Brümmer. 2003. In vitro sponge fragment culture of Chondrosia reniformis (Nardo , 1847). Jorunal of Biotechnology. Vol. 100, Issue 2.
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 Phar maceutics and Biopharmaceutics 53: 107-113.
Thoms , C., R. Ebel and P. Proksch. 2006. Activated chemical defense in Aplysina sponges revisited. Journal of Chemical Ecology. Vol. 32, No.1.
Wilkinson, C.R. 1983. Role of sponges in coral reef structural processes. p.263-274. In: Perspectives on Coral Reefs. D.J. Barnes (Ed.) 277p.