After a one year break, Koh Tao has Giant Clam Nurseries again. The Prechuap Khiri Khan Department of Fisheries and the Department of Marine and Coastal Resources have supplied the Save Koh Tao Group with 510 juvenile giant clams. The clams have been split between 2 locations around the island and placed into under-sea cages to protect them during the next year or two of development. The NHRCP is managing the care for one of those locations, to look after and maintain the nurseries before the clams are eventually moved out the various Adopt-A-Reef sites around the island.
Prior to the clam’s arrival on June 16th, our team worked hard over 3 days to create artificial settlement substrates for the clams to grow on. In previous years we have used simply coral rubble, but this does not facilitate a simple method to later transplant the clams to the reefs. By placing cement tiles into the cages for the clams to attach to we can making it much simpler and more efficient to secure the clams into the natural reef later on, hopefully leading to much greater success of the program. This new technique, if it works, will then be proposed to the Fisheries Department to be used in all of their giant clam nurseries around Thailand.
The second improvement we have made this year is securing the cages to the reef using metal stakes at the 4 corners of the cage. In previous years, clams have been lost or killed when cages have broken or moved during storms. This year’s reinforced cages should prove much more able to stand up with the seasonal storms on the island.
On the day that the clams arrived, our team was joined by the team at Big Bubble and Caroline from Koh Exist to bring the clams to the nursery site. Teams of freedivers and SCUBA divers brought the clams down to the cages and carefully placed and secured them onto the cement tiles. After the work was finished, the cage lids were put on and secured tightly to deter theft.
After 2 weeks, our team returned to the site to check on the clams, assess their health, and measure them. In previous years, measurements were collected by taking a random sampling of clams and using a ruler to get the shell length and height. This data allows us to follow the average size of the clams, but does not allow us to track clams individually. To improve our research and monitoring this year, 22 of the clams were tagged using underwater epoxy and plastic tags. This will better allow us to track the growth and development of our clams in the nursery, and also after they are moved out to the natural reef.
Giant clams are a keystone species for coral reefs, filtering water, creating structure, and increasing productivity. Unfortunately, clam populations around the world are declining or have collapsed due to over-collection and habitat destruction. Giant clam nurseries help us to maintain and restore our local populations, while education and the enforcement of regulations can help us to reduce the root of the problem.
You can find more on the importance of giant clams or the history of our giant clam projects on our website.