User:VazishtaA/Sea Sponge Aquaculture
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Over 8000 species of sea sponges reside live in oceanic and freshwater habitats. Sponge fishing historically has been an important and lucrative industry, with yearly catches from 1913 to 1938 regularly exceeding 181.436 Tonnes and generating over US$1 million dollars. However, this demand for sea sponge aquaculture has seen catch rates reach maximal potential. In 2003 the demand for bath sponges was 2,127 tones, with global production via harvesting facilitating only a quarter of that amount.
Early aquaculture research into optimising techniques for sea sponge aquaculture utilised a varying number of farming methods . However commercial sponge farming was met with severe resistance and interference from sponge fisherman, who believed that their continued cash-flow and the demand for their catch would be adversely impacted . The opposition by commercial sponge farmers resulted in a low market penetration and poor consumer adoption of aquacultured sponge products .
The benefits of commercial sponge aquaculture are apparent for those living in developing countries. For these countries sponge aquaculture is both easy and profitable, while benefiting the local community and environment through minimising both harvesting pressure on wild stocks and environmental damage.
Growing sponges is a relatively simple process and requires little specialist knowledge. Furthermore the ease of sponge aquaculture can involve the entire family in the production process. This results in a profitable family business which conforms to traditional discourses of “family farms” , increasing the likelihood of sea sponge aquaculture adoption . In addition, it is common that sea sponge farms are located close to family homes allowing for continual access, monitoring, modification and work to be completed on the farm with minimal inconvenience to the owners.
- Income generation
Sea sponge aquaculture also provides the family with a continuous source of income year-round, which can be undertaken as a full time commitment, or as a part time endeavour to supplement a pre-existing income.
- Bath Sponges
The last two decades have seen a renewed interest in the potential for sponge aquaculture to contribute to supplying the global demand for bath sponges. Bath sponges are the most common use of aquacultured sea sponge today. Bath sponges can be defined as any sponge species possessing only spongin fibers - which are springy fibres made from collagen protein.
Commercial uses for bath sponges range from cosmetic, bath, or industrial purposes, with the quality of the sponge based on analysing the quality of the sponge skeleton, with those possessing soft, durable and elastic fibres demanding the highest price .
- Bioactive Uses
The presence of secondary metabolites produced by symbiotic microorganisms within the sponge, enhances its growth and survival. Thousands of sponge derived secondary metabolites have been successfully isolated from sponges, with many metabolites having potential medicinal properties, such as cytotoxicity, anti-inflammatory and anti-viral activity. Therefore, they have significant potential within the pharmaceutical industry as a means of generating novel therapeutics . These secondary metabolites, however, are often only present in trace amounts, with the only methods to use these metabolites as therapeutics depending on the scale up of the compounds via chemical synthesis or aquaculture  .
Factors that affect the growth of sponges
- Salinity, pH, Temperature and Light
Sea sponges should be cultured at a salinity of 35ppt (salinity of seawater). Hypersalinity (high salt concentrations) in the immediate environment surrounding a sponge will dehydrate sponge cells, whereas a hyposaline (low salt concentration) environment dilutes the intracellular environment of the sponge . The pH of water must match that of seawater (pH 7.8-8.4) in order for sponge production to be maximised . Sponges are sensitive to temperature and extreme fluctuations in ambient temperature adversely affect the health of sea sponges. High temperatures lead to crashes in sponge cultures. Symbiotic bacteria that normally inhabit sea sponges start reproducing at an unsustainable rate when ambient temperature of the water increases by a few degrees. These bacteria then attack and destroy the sponge cells and tissue. It has been suggested that sponges should be cultured at water temperatures slightly below the ambient water temperature in the region the sponge has been originally isolated from . Photosynthetic endosymbionts inhabit many tropical sponges, and these require light to survive. Certain sponges as a result depend on light availability and intensity to achieve their nutritional needs .However, light in some species of sponges may lead to growth inhibition as some sponge species are sensitive to ultraviolet radiation. Other than when the sponge has associated photosynthetic bacteria, optimal sea sponge growth occurs in dark conditions .
- Dissolved Oxygen
Oxygen is consumed in sponges via absorption through the aquiferous system. Oxygen in sea sponges is consumed at rates which range from 0.2-0.25µmol O2h-1/cm3 of sponge volume. However, optimal oxygen consumption levels vary on a species specific basis (Osinga, 1999).
- Waste Removal
In closed culture systems some species of sponge may produce bioactive and cytotoxic metabolites which may rapidly build up and inhibit further sponge growth . However, biofilters are likely to be ineffective at removing secondary metabolites expelled from the sponge. Adsorption methods where biomolecules adhere to an adsorbate are likely to be an effective way of romoving these compounds.
Bath sponge disease outbreaks are often severe, having the potential to destroy both wild populations and aquacultured sponges (Lauckner, 1980; Smith, 1941). The underlying factors that result in disease outbreaks may be a due to causative agents such as viruses, fungi, cyanobacteria and bacterial strains   .
Methods of Sea Sponge Cultivation
- Site Selection
When choosing a sea sponge aquaculture location, factors that promote growth and survival of the cultured sponge species must be considered. Sponges rely greatly on a passive flow of water to provide food, such as bacteria and microalgae, thus good water flow increases growth and quality of sponges . Higher than normal water flow rates could potentially damage farmed sponges. An ideal location for a sea sponge farm would be in an area that is sheltered, but which receives ample water flow and food availability to optimise sponge growth .
- The use of Explants
Sponge aquaculture for spongin or metabolite production capitalises on the high regenerative abilities of the totipotent sponge cells by using explants (cut pieces of a parent sponge, which will then regrow into a full sponge) as a means of culturing sponges . Sponges have indeterminate growth, with maximum growth determined through environmental constraints rather than genetics. During the initial establishment of a farm, sponge explants will be chosen by their phenotypic characteristics of fast growth and high quality spongin or metabolites.
- Integrated multi-trophic aquaculture
Intensive marine aquaculture in the last decade has increased considerably and resulted in considerable adverse environmental impacts . Large discharge volumes of organic matter from uneaten feed and excretory waste from aquacultured species has resulted in high levels of nutrients within coastal waters. Large quantities of nitrogen (~ 75%) are excreted from bivalves, salmon and shrimp enter into the coastal environment, with the potential to develop algal blooms, reducing dissolved oxygen in the water.
An integrated aquaculture system consists of a number of species at different trophic levels of the food chain. Thus waste generating (fed organisms) such as fish and shrimp are coupled with extractive organisms such as abalone, sponges or sea urchins, as a mechanism of removing excess nutrient matter from the water column. Sea sponges have a distinct advantage as an extractive organism in an integrated multi-trophic aquaculture system, as they have the potential of acting as a bioremediator to remove both pathogenic bacteria and organic matter . . The sponge Hymeniacidon perlevis exhibited an excellent ability to remove total organic carbon (TOC) from seawater under integrated aquaculture conditions , and good be a potential useful bioremediation tool for aquaculture systems in regions where water pollution is high. Furthermore, the organic enrichment originating from fish farmed in the vicinity may stimulate sponge growth, resulting in more efficient sea sponge aquaculture .
Little progress has been made on integrated sponge aquaculture as research efforts have concentrated on producing a sustainable supply of sponge biomass to meet customer demands.
Bath sponge aquaculture
Many commercial sea sponge farms situate their aquaculture sites in deeper waters (>5m), to maximise the number of sponge explants that can be grown/site to increase productivity . Two main methods of bath sponge aquaculture have been trialled with sponges either being grown on a rope or inside a mesh bag.
- Rope method
Survival for sponges farmed on ropes is generally lower as unrecoverable damage occurs to the explant when ‘threading’ onto the rope takes place . Furthermore, sponges cultured on the rope have the potential to be torn off the rope during storms as water flow increases significantly , or grow away from the rope and form an unmarketable, low value, characteristic doughnut shaped sponge. Differences in sponge growth and health do occur within species characterised by variations in regenerative ability, susceptibility to infection after cutting, hardiness and growth potential .
- Mesh bag method
Lower levels of damage in some species of sponges cultured via mesh bags can lead to higher levels of survival. Growth rates may be decreased as mesh strands on the bags may decrease water flow, limiting food availability . The accumulation of biofouling agents such as bryozoans, ascidians and algae on the mesh may further limit water flow. Thin mesh strands with large gaps and a well-positioned site may act as a means to mitigate against biofouling and reduced flow rates .
- Combination of methods
By combining both rope and mesh bag approaches to bath sponge aquaculture in a “nursery period”, increases may occur in quality and production. In the nursery period method, sponges are initially cultivated in mesh bags until the explants have healed and regenerated to efficiently filter water. The regenerated explants are transferred onto rope to promote optimal growth till harvesting . This strategy is labour intensive and costly, with growth rates and survival found to be no greater than when farming occurs solely via the mesh bag method.
A more economically viable method for cultivating bath sponges would be transferring sponges to larger mesh bags as sponge growth occurs to enable adequate water flow and nutrient sequestration .
- Bath sponge aquaculture production in Micronesia
Bath sponges are currently being produced for the sponge Coscinoderma matthewsi with production of about 12,000 sponges, sold locally to residents and tourists in Pohnpei, Micronesia. These sponges are the only true sustainably farmed sea sponges in the world . The sponges are farmed via the rope method, with low investment costs of a few thousand dollars for farming and maintenance equipment, producing 100% natural sponges with no harsh chemicals added during processing.
Aquaculture production of C. matthewsi sponges was undertaken by the Marine and Environmental Research Institute of Pohnpei (MERIP), to try and generate a sustainable income for local community residents with few options to earn money . The sponges take approximately two years to reach harvestable size, with free divers routinely removing seaweed and biofouling agents by hand . These sponges are processed through natural processes, where they are left to air dry and then placed in baskets and returned to the lagoon that they were grown . This process removes all the organic matter wihtin the sponge leaving behind the final bath sponge product. Further processing occurs my softening the sponge and no bleaches, acids or colourants.
Bioactive Sponge Aquaculture
Research into farming sea sponges for bioactive metabolites occurs in the Mediterranean, Indo-Pacific, and South Pacific regions. The main goals are to optimise bioactive production methods, aquaculture processes and environmental conditions to maximise bioactive metabolite production.
- New Methods
In the aquaculture for bioactives, the final explant shape is not of concern, allowing for additional production methods to be utilised . New methods of bioactive cultivation include the “mesh array method” which utilises the water column to vertically hang a mesh tube with single explants held in alternating pockets .
The number of sponges required to aquaculture bioactives is reduced as sponge secondary metabolites can be repetitively harvested for many years, decreasing the costs and infrastructure required. The few sponges selected for metabolite production would have high production rates for the target metabolite to optimise production and profits .
- Factors affecting secondary metabolite production
A number of factors affect sponge metabolite production with metabolite concentration varying greatly between neighbouring explants . Localised differences in light intensity and bio-fouling are physical and biological factors that have been found to significantly affect metabolite biosynthesis in sponges. Changes in environmental factors may alter microbial populations and subsequently effect metabolite biosynthesis.
Understanding the environmental factors that affect metabolite biosynthesis or the ecological role of the metabolite, can be used as a competitive advantage to maximise metabolite production and total yield . For example, if the ecological role of the secondary target metabolite was to deter predators, mimicking predation via wounding the sponge before harvesting may be an efficient technique to maximise metabolite production .
Some sponges which produce metabolites have extremely fast growth suggesting that farming sponges may be a viable alternative to producing bioactives which at present cannot be chemically synthesised. Although sponge farming for bioactives is more lucrative due to its higher value-adding properties, there are several challenges that are not present when aquaculturing bath sponges, such as the high costs associated with metabolite extraction and purification .
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