Artificial reefs are created for many different reasons, and the reef ball project in Tanote bay is a good example of the use of artificial reefs to replace lost reef structure. Tanote Bay is a wonderful little spot on our island, but unfortunately has suffered from severe erosion and sedimentation in the mountains above. This erosion began in 2006, when a reservoir project was attempted to try and alleviate the island’s shortage of freshwater.
The construction was not done properly, and severe erosion and landslides occurred, burying the reef below in 1.5 to 2 meters of sand and silt, and reducing water quality in the surrounding bays. Immediately we started to notice very drastic changes in the ratio of coral to sand in our monthly reef surveys. Unfortunately, in parts of the bay, the entire reef disappeared over the course of 18 months.
To help solve the problem, volunteers from the New Heaven Reef Conservation Program and others from the community joined forces to go once per week and plants grasses and trees in the areas where erosion was the worst.
see the video about Tanote Bay made by Dagmar Albert (2008)
Things really picked up when the local Save Koh Tao Group got involved, soliciting the donation of 800,000 tillers of vetiver grass from the Suratthani Government. Next, over 1,000 Erosion Control logs and the materials needed to create check dams and gabian baskets along the water ways leading to the bay below. The grasses and check dams were all installed by volunteers from the local community, with over 150 volunteers showing up on some of the days.
By 2010, things were looking better on land, so we could then begin looking at restoring the coral reef below. The shoreline of Tanote Bay is rocky from until about 7 meters depth, and in these areas the reef was doing very well, it was almost hard to tell any problems ever occurred. Towards the middle of the bay from about 7 meters to 20 meters was still all sand, with almost no diversity of fish or marine life other than teams of gobies and shrimp. The Save Koh Tao group proposed a project through the Department of Marine and Coastal Resources (DMCR), and they provided us with 140 reef balls, about 1 meter in diameter. The reef balls were placed over the sandy areas where the reef used to be, in order to provide structure for corals to grow on, and habitat for reef fishes and animals.
The reef balls were specially designed with holes that corals grown on our nurseries would fit into, so it was very easy to start filling them up with living corals. However diversity of corals in the area following the erosion event was low, so we ended up with mostly branching corals (Acropora sp.). In the summer of 2012 the NHRCP made a big push to transplant more corals onto the site, investing over 150 diver hours into maintenance. By 2013, the area is full of amazing fish life and diversity, and many of the corals moved onto the structures in 2010 and 2011 are fairing well. However, due to the low diversity of corals, our team has made it our goal this year to find naturally formed coral fragments from a broader range of genera, and attach them around the reef ball site.
Without these concrete structures, there would be nothing for hard corals to grow on in the middle of Tanote Bay, and it would be centuries, if ever, for the reef to come back. By using readily available concrete to create diverse habitat and structures, the speed of reef regrowth can be greatly accelerated. Fish and other animals can be brought back into the area, and the natural ecosystem can start to form around the artificial one. This is just one of the many great uses of artificial reefs in restoring coral reefs to protect the environment and the economies dependent on it.
If you would like to learn more about artificial reefs you can check out some of our other pages on coral restoration
Or our posts on some of the other artificial reefs around our island
Or some pictures of the site in May 2013 on our facebook page
If you like what you see and would like to learn more or actually help build artificial reefs, check out our marine conservation courses page and come visit us on Koh Tao.