by Anshika Singh
Aquaculture is the most important aspects of marine biology. It is not only important for commercialization of important marine species but also required to understand their biology by conducting more controlled experiments in the laboratory While a lot of attention has been given for the aquaculture of commercially important seafood, there have been only few reports on the cultivation of marine sponges. Being a marine biologist who is specialist in sponge biology research, I felt like it is my duty to introduce the readers of our blogs to the current aquaculture practices, challenges and hurdles that exist in cultivation of the marine sponges. Just to remind all the readers, lets first talk about marine sponges and why should anyone cultivate them? What are their uses? Marine sponges are the sessile organisms belonging to phylum Porifera. They can inhabit a wide range of ecosystems, from equator to poles, from shallow waters to the highest depths. They obtain food by filtering sea water. They can reproduce asexual by budding or sexually with free-swimming larvae stage, which does not feed on plankton but rely on their own reserves. Larvae settle on the appropriate substrate and metamorphose to become juveniles, which have to compete with other sessile organisms for space to defend against predation and to maintain their surface clean of fouling organisms. Due to their sessile life style, porous and soft-bodies, they have evolved an exceptionally efficient chemical defense mechanism. Sponges produce secondary metabolites as part of this chemical defense, which play important ecological roles like competition for space, antifouling activity, and deterrence from predators. Most of these chemicals have been found to be bioactive and have been used as antitumor, antiviral, anti-inflammatory, immunosuppressive, and antibiotic agents. But till now, development of these potential sponge products into commercial products has been hampered by what is referred to as the ‘supply problem’. The metabolites of interest are often produced only in trace amounts by the sponges or their endosymbionts. On the other hand, much more sponge biomass is needed for commercial production of these sponge metabolites than can be harvested from the seas (Fig. 1). For instance, halichondrin B, a compound that has, among others, been isolated from the sponges Halichondria okadai and Lissodendorix sp. is the first preclinical test phase for this potential anticancer agent has proceeded successfully. However, it cannot be studied further until the supply issue has been addressed. The supply problem has stimulated research on alternative methods for sponge metabolite production such as aquaculture of marine sponges.
Fig .1. Supply problem: Large biomass needed for the development of drugs.
METHODS FOR CULTIVATION OF SPONGES: To understand the factors required for cultivation of sponges for production of secondary metabolites, it is important to know their life history and reproduction. Sessile macrofauna may be divided into r- and K-strategists. The ﬁrst are characterized by high rates of reproduction and growth, high reproductive efforts, and high invasion opportunities in an unstable environment, whereas the second has low reproductive rates low reproductive efforts, and good adaptation to specialized ecological niches (mainly in stable conditions). Sponges are generally r-strategists and are responsive to seasonal environmental changes, mainly in water temperature.
1. Sponge farming or In vivo sponge cultivation: Sponge farming is the oldest and least expensive technique for yielding sponge biomass. Sponges are cut into pieces (explants), which are attached with aluminum wire to an artificial substratum (concrete disks) and placed into the sea. This process suffers from the unpredictable environmental conditions of the sea that produce variation in biomass yield. For sponge farming to be successful, the specimens should have high regeneration capacity. The sponge explants show large variability in growth rates due to the different ages of the sponges from which the explants were made. To optimize and standardize culture conditions, we need to prevent this variability by culturing sponges of the same age.
Fig. 2. Sponge farming (Image source from https://www.uni-due.de/)
2. Aquaculture or in-vitro sponge cultivation: A few reports on culturing of sponges from larva or buds are available. The results were promising, as the culture was more resistant to infections by microorganisms and survived longer than those from adult cells. This method helps to achieve higher growth rates during the juvenile stages of sponges. Variability may be reduced because culturing larvae warrants the same age for all the individuals (cohorts) and a similar behavior under culture. Larval or bud survival in the laboratory is expected to be higher than at sea because of the absence of predators and competitors. Larval or bud culture can be a source of more suitable starting material (embryonic cells) for the development of cell culture. Consequently, larval or bud culture offers some advantages with respect to other assayed methods. Hence, this method is described in detail in the figure below.
Fig 3. In-vitro culturing of marine sponges from larvae.
Fig. 4. Flow chart for culturing of the marine sponges
At present, cultivation of sponges is still difficult. From a biotechnological point of view, in situ culture is the most reliable and least expensive method to produce sponge biomass. However, in situ or mariculture of sponges is subject to variability due to various unpredictable environmental conditions. In vitro cultivation of sponges (using sponge larva) is a promising alternative that requires prior information on factors influencing reproduction and larval development. However, all these challenges can be solved by conducting a long-term field study to understand the parameters that determine the growth and reproduction of these sponge species (= Sponge Chemical Ecology). Understanding sponge chemical ecology can help in development of sponge aquaculture for sustainable biotechnological applications.
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