The Koh Tao Giant Clam Nursery and Restoration project was started in February of 2009 in order to attempt to increase the abundance and genetic diversity of Giant clams in the island’s reefs. This long term project is being managed by the Save Koh Tao Group under the guidance and supervision of the Prechuap Khiri Khan Coastal Fisheries Research and Development Center.

Giant clams are one of the most ecologically important organisms in a coral reef, known as a keystone species. Like hard corals, Giant clams use symbiotic zooanthallae algae to produce a shell that adds to the reef structure. In addition to this, they clean nutrients from the water that could otherwise go towards the growth of macroalgae, smothering and killing corals. A single Giant clam can filter 100s of liters of water in a single day, and only where there are giant clams do we see high coral abundance and biodiversity around our island.

Unfortunately, these slow growing clams are being harvested for food and decoration, a practice which is unsustainable and benefits only a few individuals. To increase awareness and help to repopulate Koh Tao’s reefs Save Koh Tao will be developing a long term nursery and release program in addition to releases conducted yearly by dive schools and the Thai Navy.We have been given a 100,00 baht budget from the local government to begin this project in March of 2009. You can view the Project Proposal by clicking here, and please check back soon for updates or contact us about getting involved with this exciting project.

Update

The giant clams are here!

 On March 20th of 2009 the Thailand Department of Fisheries Under the Ministry of Agriculture and Cooperatives, based out of Prechuap Khiri Khan, came to Koh Tao with 1,000 juvenile clams to donate to the Save Koh Tao group. These 1,000 clams have been breed and raised for about 1 year in captivity from Giant clams at the Prechuap marine center. These clams have been placed into 10 large cages in the sea where they will be allowed to grow up for about 1 year before being transplanted to natural reef areas around the island.

The goals of this project are to increase the abundance of giant clams around our island, educate locals and tourists about threats to clam health, and provide a research site to add to existing knowledge about clams.

 Journal of Project to date:

March 19th 2009: Members from the Prechuap Khiri Khan Coastal Fisheries Research and Development Center placed down ten cages in Ao Leuk Bay, Koh Tao. The cages are arranged in a straight line separated by a 0.5 meter gap, running in a more or less north-south orientation. The cages have been placed onto a sand substrate at a depth of about 6 meters, approximately 150 meters from the island coast. The bottoms of cages were filled with large and small pieces of coral rubble that were collected on land.

March 20rd 2009: Members from the Prechuap Khiri Khan Coastal Fisheries Research and Development Center placed down 1,000 juvenile Giant Clams (Tridacna maxima) into ten cages that were placed down the day before. The Giant clams used have been raised from clams held in captivity in Prechuap Kiri Khan. The clams were spaced apart and stood upright on the pieces of rubble to give them a substrate to grow on. About 950 of the clams were very small juveniles (shell height estimated to be less than about 6 cm) and 50 of the clams were a bit larger (shell height about 10 cm). Lids were put onto the cages and secured with 3-4 cable ties.

March 29th 2009: Members of Save Koh Tao went to check-up on the clams and secure the lids after receiving reports of divers trying to lift the cage lids. Divers placed about 6 cable ties onto cage. Divers also observed that there were about 3-7 dead clams in each of the cages containing the smaller juveniles.

April 12th 2009: Members of Save Koh Tao went to check-up on the clams and found that many of the cages were filled with sand. The sand had smothered of buried many of the smaller giant clams in about 8 of the cages. This was most likely due to chan

ging currents and wind directions causing mass movement of sand out from the beach area. Divers collected large pieces of dead coral rubble/rocks and placed them under the cages to suspend them up off of the sand. This temporally cleared all of the sand out of the cages, but many of the clams had already died. Yet, even in the 2 cages that did not get inundated with sand there was a considerable amount of mortality, probably due to predation. On all dives parrot fish, wrasse, groupers, and damsel fishes have been observed swimming in and out of the cages. Divers counted the clams and found there to about 457 living clams in the cages, with about 45.3 clams per cage, indicating a 54.3% mortality rate for the small juveniles in the first 3.5 weeks of the project. In the cage with the larger clams there was much higher success rate with only 1 fatality. A high mortality rate is expected in projects such as this, and one of the main goals of this project is to refine and devlop techniques to improve the success of future projects.

April 15th 2009: Divers returned to check on the cages, had to re-suspend 2 cages up out of the sand again using coral rubble.

April 21st 2009: Divers returned to check on the cages, had to re-suspend 5 cages up out of the sand again using coral rubble.

April 26th 2009: Divers checked on the Giant Clams, no maintenance completed, but it was observed that about 5-10 clams per cage had been dislodged/tipped over and were no longer in an ideal growing situation. Divers counted the clams and found there to be a total of 453 living clams, indicating that the mortality rate had been decreased to only 0.8% after 2 weeks by lifting the clams up off of the sand.

April 28th 2009: Divers opened the cages and repositioned any of the smaller juvenile clams that had become dislodged or turned over. After completion the cages were again secured with cable ties.