Giant clams are a vital part of coral reef ecosystems in the Indo-Pacific. They are what is known as a ‘Keystone’ species. As large bivalves, they are efficient water filters, removing excess nutrients that flow into the reefs from land. They also grow very large, dense shells which contribute to the growth of reef structure and provide habitat or settlement points for a wide range of other reef animals.
In Thailand, as well as many other places around the world, Giant clam numbers have been dramatically reduced due to over collection for food or souvenirs, and habitat destruction. The Queen of Thailand has made special rules concerning the protection of giant clams, and also initiated a Giant Clam captive breeding and restocking program. The goal of this program is to increase the population size and reproductive success of local giant clams populations which have been impacted by island development and over collection.
The first release of the giant clams done by the center (located in Prachuap Kiri Khan) was on Koh Tao over 15 years ago, in the region of Sairee Beach. Unfortunately they were not looked after properly and the project was not repeated for some time.
After the Save Koh Tao group was formed it was possible to try again using more of a nursery technique, to let the clams grow up in a protected environment for the period of about 1 year and then moved out on to the natural reefs. This is done since generally the small clams are stressed upon arrival and have a low chance of survival if moved directly out to the reefs.
The first year this was done was in 2009. Around 1,000 clams where placed into ten cages in Ao Leuk Bay. This was our first time, and we encountered a few unforeseen problems. After the 1 year period about 429 calms were left, and they were transplanted around the area.
The second year (2010), the cages where moved to a new location with improved anti-tampering measures and did much better. In 2011 the clams survived very well and no major problems occurred. This year we received an additional 1,000 clams in April of 2012.
The NHRCP has been an integral part of this program since 2009, visiting the clams on a weekly basis to maintain and repair the nurseries, collect data on health and growth, and remove algae or fouling organisms from the sites. After the clams are moved out we continue to monitor and protect them, ensuring that survival rates are high.
In our course, students learn about the ecology related to Giant Clams, threats to their health, nursery techniques, monitoring, transplanting, and more.
Overall the project has been very beneficial for our island community and our reefs. Costs are quite low, so even low survival rates such as in the first year of the project still has a high value for education and training. In the few years it has been going on we have learned a lot and progressed greatly. We see a lot of potential for this program and think that in a few years we will have a thriving population of clams in areas where the populations have experienced dramatic declines over the last few decades.
In 2013 we are trying some new techniques and methods with our giant clam nurseries, click here to read our most recent update.
**NEW** Giant Clam report 2013prepared for the Thai Department of Fisheries and the DMCR **
How are the clams in the nursery doing?
The graph above shows the average shell width (cm) of the giant clams in the nursery project for 2013-2014. As shown in the graph, the growth rates of the clams tends to be highest during the summer months, and lowest from October to January, which is the typical monsoon season for Koh Tao. The clams are measured monthly by students in our program during maintenance of the nurseries.
The graph above shows the number of clams in the nursery, for all of the years of the nursery program. The lines end when clams were moved from the nursery to the natural reef areas. 2013 has the lowest starting number of clams, but also a nearly perfect survival rate through the first 11 months, possibly due to improved techniques implemented in 2013.