All over the world, increasingly more coral reefs suffer from severe coral mortality. An estimated 40-50% has died over the last 30 years. One of our challenges therefore is restoring existing and creating new reefs. On Zanzibar we first started our activities in 2012. From 2013 we collaborate on the reef restoration project with our executive partner marinecultures.org who are situated in Jambiani, Zanzibar.
We focus our coral restoration activities on the lagoon in the Southeast of Zanzibar i.e. the area between the shore and the barrier reef that is approximately 2 kilometers away. The lagoon has been hit hard by mostly climate change and overfishing.
On the shores of mainland Tanzania dynamite fishing(*) is practiced a lot and poses a big threat to the reef systems. With our experience on the conservation work on Zanzibar, we hope one day soon we can put our knowledge to practice in these areas that are in extra need of our support.
(*) Dynamite or blast fishing is the practice of using explosives to kill schools of fish. This illegal practice is extremely destructive to the surrounding ecosystem especially to the fragile coral that breaks in pieces. It kills indiscriminately, leaving the larger part of the dead and hurt animals on the ocean floor.
How do we do this?
Corals are colonies of animals called ‘polyps’. Most ‘reef-building corals (i.e. hard corals) have polyps that live in a symbiosis with algae (i.e. plants) called the Zooxanthella. The algae live in the body of the polyp providing the polyp with food (see What are corals ). By using small fragments of a coral colony and planting these fragments somewhere else, we can give the colony a new living environment in which it can multiply and further grow. We have a special technique for this.
Coral farming and reforestation:
1st – on the reefs we look for pieces of coral that have broken off naturally by waves, storms, etc. These so-called ‘corals of opportunity’ we cut into smaller coral fragments.
2nd - a coral fragment is placed on a cement plug which is put on a nursery bed on the sea floor. We have about 40 beds, these coral nurseries we call the ‘coral farm’.
3rd - after approximately 3-8 months the corals in the nurseries have grown sufficiently. During the entire nursing process our coral divers regularly clean the Juvenile Corals and the nursery beds: removing algae, sediment and predators like the Drupella snail or Crown of Thorns starfish.
4rd – in the meantime we select substrate to plant the coral plugs. We either plant the coral in existing reefs that have (partly) lost its corals, or we use different materials to plant the plugs on e.g. limestone, Reef Balls, etc. Limestone we get from the land. We drill holes in the stones to fit the coral plugs. Reef balls are made of concrete and made by us locally in a special mold (Courtesy of the Reef Ball Foundation, see Friends & Sponsors). The balls have different diameters (we mostly use 80cm diameter), have different openings and are hollow inside so fish and other marine life can hide in it. The Reef Ball has several ‘plug inserts’ on the outside to plant the coral plugs with the Juvenile Corals. The advantage of the Reef Ball is that it does well on sandy areas where there is no basic substrate. This way we can make a new ‘artificial reef’.
5th - the Juvenile Corals are moved carefully to the area where we plan to reforest. The plugs with the Juvenile Corals are inserted in holes that we drilled in the substrate and they are firmly fixed with cement.
6th - we check the first weeks to see whether the plugs remain fixed on the substrate and clean the corals if necessary. After that it’s waiting for our new reef!
Some corals grow relatively fast, others slow. We try to make a natural reflection of the coral ecosystem in the area. The mix of planted corals is based on the example nature gives us. To farm and transplant genetic diversity within one coral species is of extreme importance. We safeguard this by our procedures that describe how to find corals and how to out-plant them. We keep abreast of new research on these issues to keep on fine-tuning the work method.
See for a more detailed description of this project: Coral reforestation procedure CRC, July 2020.