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The Biorock Project at Manta Dive Gili Air

Posted on 18/06/2018

When you’re standing in front of Manta Dive and look out onto the ocean, you see Mt. Rinjani on Lombok and the turquoise sea. What you don’t see is what lies beneath the surface. The gentle waves are hiding coral reef starting just a few metres from the beach and our biorocks.

What are Biorocks?

Biorocks are artificial reef structures made out of metal. We installed our biorocks together with the Gili Eco Trust. We run a low voltage current through the biorocks that doesn’t harm the marine life but helps the corals. An electrolytic reaction results in a calcium carbonate substrate around the metal. This is a perfect surface for corals to cement themselves to. In addition, the low voltage promotes coral growth and makes the corals more resilient to stress factors.

Why Do We Need To Help The Reef to Grow?

Coral reefs worldwide are under an enormous amount of stress. From plastic to chemical pollution, from global warming to overfishing. Reefs are under attack from both natural and human influences alike. While dynamite fishing is a common practice in other parts of Indonesia, it rarely occurs in the Gilis. Our reefs, however, are subject to different human influences. Even though the throwing of anchors is illegal, many snorkel boats still anchor in the shallows to drop off snorkelers. Needless to say, this is not the best thing to happen to the corals.

A natural stress factor influencing the reefs around the Gilis is an event called El Nino. El Nino refers to rising ocean temperatures across the tropical Pacific. It’s part of a recurring climate pattern and completely natural. Corals are equipped to withstand slightly warmer temperatures for a short period of time and usually recover after an El Nino. If you add global warming to an El Nino, however, the temperatures rise above the resistance threshold of the corals and remain that high for longer than is natural. The rise in temperature induces stress in the corals which causes them to release the algae (zooxanthellae) in their tissue. As the algae give the coral its colour and without it, the limestone skeleton shines through, this is known as “coral bleaching”. A bleached coral is not automatically dead. Should conditions return to normal, corals are able to regain their algae and recover. Because a coral needs the energy provided by the algae in order to survive, it will die if the coral is unable to regain its algae.

El Nino events have been getting more and more severe over the last decades. The most detrimental one in the Gili Islands happened in April 2016. Our reefs are still recovering from it and we aim to help them with our biorocks. All coral reefs were partially bleached during the El Nino in 2016. Previously installed biorocks in the waters around Gili Trawangan have shown that corals on biorocks had a slower rate of bleaching than on natural reefs and were able to recover much quicker.   

Biorocks Around The Gili Islands

Biorocks around the Gili Islands

The first biorock structure in the Gilis was installed in 2004 by the Gili Eco Trust who work closely with the DKP (Indonesian Marine Conservation and Fisheries). Since then, they have added more than 120 structures to the waters around the Gilis.

The first biorock structure off the shore of Gili Air was installed in 2013 through a collaboration with the Green School in Bali, the Gili Eco Trust and Manta Dive Gili Air. A group of 15-year-olds built the structure in art class and then shipped it to Gili Air. Everyone came out, installed and added corals to the first biorock structure.

Since that first installation, we have been adding at least one new biorock structure every year and even installed more power lines to grow our reefs more quickly. Nowadays, the Gili Air biorocks have become a popular snorkelling site with an abundance of fish finding a home in and around the structures.

The Art Of Coral Gardening

The Art of Coral Gardening

As you can imagine, the maintenance of multiple biorock structures takes quite a bit of work. We go out every week to do some “coral gardening”. What is coral gardening you ask?

Just like in a traditional garden, our marine garden needs to be regularly maintained. The most important part of the work we do is collecting loose coral from the areas surrounding the biorocks. We look for pieces of coral that have been broken off (by an anchor for example) and turned upside down. When a coral loses its anchorage to a substrate and is not attached to anything, the water movement often turns it upside down. That way the algae inside the coral tissue does not get enough sunlight to perform photosynthesis, thus not giving the coral energy. This often causes the coral to bleach and if not turned around, it will eventually die. That’s where we come in! We scour the surrounding areas for exactly those upside-down pieces of coral and collect them.

Coral Gardening

When we find a loose piece of coral, we take it to one of our biorock structures and use zip-ties to attach it to the metal - facing upwards. The biorock provides the coral with a fixed substrate it can cement itself to. The low voltage current running through the structure further promotes growth and helps the coral get back to health.

In recent years, the waters around the Gilis have seen a rise in the coverage of a certain sponge. This encrusting sponge grows faster than corals, overgrows and subsequently suffocates them. Removing the sponge from the biorocks is, therefore, another part of coral gardening.  

A garden wouldn’t be complete without the snails! No, we’re not talking about nudibranchs (those we love) but about drupella snails. Drupella eat live coral tissue by stripping the tissue from the coral skeleton and leaving white feeding scars that can quickly become covered by algae. Feeding scars can have detrimental effects on coral growth, which is why we pick them off our coral garden.

Finally, we help prevent any sedimentation by gently wafting above the corals that are attached to the biorocks. As the biorocks are located near a sandy beach, we get a lot of sedimentation on the corals. This leads to a lack of sunlight, bleaching and eventually coral death. By keeping the corals sediment free, they can grow at their optimum rate.

Attaching coral to biorock

While the collection and attachment of coral take up the majority of our coral gardening time, there are a few other things that need to be done. Cutting off any old zip-ties from the metal, removing debris and generally tidying up a little bit underneath the structures all need to be done regularly. After all: that’s exactly what you’d do in a regular garden, right?

 How Can I Get Involved with the Manta Dive Biorocks?

Biorocks at Manta Dive

Now that you know what it takes to maintain our biorocks, you’ve probably realized that this is not a one-person job. It takes a lot less time to cover all of the biorocks if you go into the water with several people. And that’s where you come in! You can help us maintain our coral garden and join biorock dives. Manta Dive’s coral gardener Anna Stumpf will explain everything you need to know before the dive.

We go out regularly, but don’t have a fixed time seeing that we’re dealing with the ocean. Weather conditions, tides and other factors determine when we can do some coral gardening. Just send Anna a message and let her know you want to get involved.

P.S: If you’re interested in spending more time learning about our biorocks, you can combine this with your Divemaster course at Manta Dive!






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