Context

• In the era of frequent climate change women in Zanzibar have resorted to sponge cultivation to sustain their livelihoods.

About Sponges

• • Sponges are simple aquatic organisms that belong to the phylum Porifera. 
  • They are one of the oldest multicellular life forms on Earth, with a lineage dating back over 600 million years.
  • Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls, and produce sperm cells. 
  • Some of them are radially symmetrical, but most are asymmetrical. 
  • The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where the water deposits nutrients and then leaves through a hole called the osculum. 
  • Many sponges have internal skeletons of spicules (skeletal-like fragments of calcium carbonate or silicon dioxide), and/or spongin (a modified type of collagen protein).
  • All adult sponges are sessile aquatic animals, meaning that they attach to an underwater surface and remain fixed in place (i.e., do not travel) while in larval stage of life they are motile. 

• Feeding behaviour

• • • Although most of the species of sponges feed on bacteria and other microscopic food in the water, some host photosynthesizing microorganisms as endosymbionts, and these alliances often produce more food and oxygen than they consume. 
    • A few species of sponges that live in food-poor environments have evolved as carnivores and prey on small crustaceans.

• Mode of Reproduction

• • Sponges reproduce both asexually and sexually. Most species that use sexual reproduction release sperm cells into the water to fertilize ova.The fertilized eggs develop into larvae, which swim off in search of places to settle.
  • Asexually, sponges reproduce by budding, here an external bud from the parent sponge eventually breaks off and grows into a clone of the original.
  • When environmental conditions become less hospitable to the sponges, sponges can also reproduce asexually by producing gemmules, “survival pods” of unspecialized cells that remain dormant until conditions improve.

Sponge cultivation

• Sea sponge aquaculture is the process of farming sea sponges under controlled conditions. 
• It has been conducted in the world’s oceans for centuries using several aquaculture techniques. 
• There are many factors such as light, salinity, pH, dissolved oxygen, and the accumulation of waste products that influence the growth rate of sponges. 
• Sea sponges are produced on a commercial scale to be used as bath sponges or to extract biologically active compounds for medicines.
• One of the major sustainable sea sponge cultivations in the world occurs in the region of Micronesia and Tunisia, where several methods are used to ensure and maintain the continued sustainability of these farmed species.

Sponge cultivation in Zanzibar

• The Indian Ocean archipelago of Zanzibar is a semi-autonomous province of Tanzania off the coast of East Africa.
• It consists of the island of Zanzibar or Unjuga, Pemba as well as smaller neighboring islands.
• The women in Zanzibar, were formerly engaged in Seaweed farming. The industry grew rapidly,  with Tanzania’s annual production increasing from 800 tonnes per year in 1990 to about 11,000 tonnes in 2002. 
• However sea weed production plummeted by 47 percent between 2002 and 2012, due to global competition and seaweed die-offs linked to climate change causing increased temperatures, winds, and irregular rainfall.
• Sponge cultivation is resilient to the impacts of climate change. Many women in Zanzibar have now been actively engaging in sponge cultivation to secure their livelihood.
• It requires less financial resources and technical expertise , a minimal level of maintenance, and commands premium market prices.

Benefits of sponge cultivation

• • Controlled sponge cultivation can help prevent overharvesting of wild sponge populations, promoting sustainable resource management.
  • Sponge farming can create economic opportunities for local communities by supporting livelihoods in coastal areas.
  • Sponges are filter feeders and can help improve water quality by removing particles and nutrients from the surrounding environment. Cultivating sponges in certain areas may contribute to local bioremediation efforts.

• Sponges can play a role in carbon sequestration by absorbing and storing carbon dioxide from the surrounding water. This can contribute to efforts aimed at mitigating climate change.

Drawbacks of sponge cultivation

• Sponges can be susceptible to various diseases and parasites. Controlling and preventing the spread of pathogens within cultivated populations is a significant challenge in sponge farming.
• The growth of unwanted organisms, known as biofouling, on sponge cultivation structures can be a challenge. Biofouling can affect water flow and nutrient availability, negatively impacting sponge growth.
• The success of sponge cultivation also depends on market demand and economic viability. If there is insufficient demand for cultivated sponges or if production costs are high, the economic sustainability of sponge farming may be compromised.

Conclusion

• It is important to foster collaboration between scientists, aquaculture practitioners, regulators, and local communities for the responsible development of sponge cultivation.