GIANT CLAMS - THE BIOLOGY AND CULTURE
ABOVE: Tridacna gigas, is the true giant clam.
Giant Clams, a solar animal
Giant clams evolved over 65 million years ago in the Eocene, along with modern corals. Both clams and corals lead symbiotic lives along with millions of single cell dinoflagellate algae called 'zooxanthellae'.
Adult clams can obtain over 90% of their food requirements from the photosynthetic products of the algae, but when particulate organic matter (POM) is present an adult clam can obtain about 33% of its carbon requirements from POM. The third source of nutrition is dissolved organic matter (DOM) but it is probably more important in larval and post-larval stages than in sub-adult and adult clams.
Clams also act as natural biofilters as they take up dissolved ammonia and nitrate from the surrounding seawater to supply their symbiotic zooxanthellae with nitrogen for growth.
Maybe in the near future giant clams will become accepted by aquarium enthusiasts as an ideal living biofilter. Someday giant clams may be found in aquaculture tanks in a Moon Colony to supply food, excess oxygen in sunlight, and as biofilters for fish and other aquacultured animals.
Until then, the aquaculture of giant clams for food and restocking of overharvested reefs is an example to follow for other endangered species.
ABOVE: Tridacna gigas, can reach to > 1.3m in shell length and hundreds of kilograms in weight, living to >50 years of age.
Giant Clams Species
Tridacna gigas, is the true Giant Clam. It can reach to > 1.3m in shell length and hundreds of kilograms in weight, living to >50 years of age. This is the largest species of bivalve mollusc to have ever lived in the fossil record of our planet. It was being driven to extinction in some parts of its natural distribution (SE Asia, Australia, Micronesia) by poachers in the 1970s. Natural high density populations are still present on the Great Barrier Reef of Australia.
This species is on the Threatened Species list of IUCN and CITES.
The Smooth Giant Clam
Tridacna derasa, the Smooth Giant Clam is the second largest species reaching > 55 cm shell length. On the Great Barrier Reef (GBR) it is found only on mid-shelf and outer-shelf reefs where turbidity is lower than inner-shelf reefs. The distribution is SE Asia, Micronesia to Tonga and Australia.
ABOVE: The smooth giant clam is the second largest species reaching > 55 cm in shell length.
The Scaly or Fluted Giant Clam (Tridacna squamosa)
Tridacna squamosa, the scaly or fluted giant clam reaches 40cm shell length and has light to moderate byssal attachment as adults. It is widespread from E. Africa and Red Sea to French Polynesia.
ABOVE: Tridacna squamosa held by Dr. Rick Braley at the Aitutaki Atoll Giant Clam Hatchery, Cook Islands, early 90s.
The Elongated, Rugose or Small Giant Clam (Tridacna maxima)
Tridacna maxima, the Elongated, Rugose, or Small Giant Clam grows up to 40 cm shell length and has great byssal attachment to the substrate.
The distribution is widespread and similar to T. squamosa. The mantle is very colourful and the clam is sought after in the aquarium trade.
RIGHT: Small Giant Clam grows up to 40 cm shell length.
The Boring or Crocus Clam
Tridacna crocea, the Boring or Crocus Clam is the smallest species of giant clam reaching to 15 cm shell length. It has a wide byssal opening at the shell base and therefore burrows into the substrate so that only the extended colourful mantle touches the substrate surface.
Like T. maxima, it is a good species for the aquarium trade. The distribution is SE Asia, Australia and western Pacific. In places on the GBR densities can be >100/sqm.
ABOVE: The Boring or Crocus Clam is the smallest species of giant clam reaching to 15 cm shell length.
The Tevoro or 'Devil' Clam
Now considered Tridacna mbalavuana (ex Tridacna tevoroa Lucas, Ledua & Braley, 1990), the Tevoro (or 'Devil' in Fiji language) clam. This quite large (>50 cm shell length) clam is found in moderately deep water (14-35m depth).
The species is unusual in that it is the only species of the genus Tridacna which does not have the mantle overhang the edge of the shell. It was first cultured at the Tonga Fisheries Hatchery at Sopu, Tongatapu around 1990-91.
There have been reports of findings off outer reefs of the Great Barrier Reef, so the natural distribution may be further extended.
ABOVE: The unusual Tevoro or 'Devil' Clam is >50 cm in shell length.
The Horse's Hoof Clam, The Bear Paw Calm, The Rolling Clam, The Strawberry Clam (Hippops hippopus)
Hippopus hippopus, is known by a number of names including the Horse's Hoof Clam, the Bear Paw Clam, the Rolling Clam, or the Strawberry clam. This species reaches 50 cm shell length and is often found on sandy areas and on seagrass beds. The mantle does not extend over the shell edge.
It is widespread in SE Asia, Australia to Vanuatu and parts of Micronesia. It was recently extinct from Fiji and Tonga.
ABOVE: This species reaches 50 cm shell length. Image courtesy of Wikipedia.
The China or Porcelain Clam
Hippopus porcellanus, the China or Porcelain clam has a smoother shell than H. hippopus and generally reaches <50 cm shell length.
The natural distribution of the species is eastern Indonesia, southern Philipines, Palau, and Papua New Guinea. It has been cultured in Palau, Philippines and Indonesia, but continues to be a rare species.
Dr. Braley took this photo of broodstock collected from reefs around Barrang Lompo Island, So. Sulawesi, Indonesia in the mid-90s.
ABOVE: Tridacna gigas, can reach to > 1.3m in shell length and hundreds of kilograms in weight, living to >50 years of age.
The Rosewater Clam
This is a possible 9th species of giant clam which was named by Sirenko and Scarlato(1991) based on a shell specimen only. The authors have called this clam Tridacna rosewateri. It is from the Indian Ocean (Mauritius area) and is said to be similar to T. squamosa, as the scutes in this picture show.
ABOVE: Tridacna rosewateri is possibly the 9th species of giant clam.
Tridacna squamosina It( was formerly described as T. costata (2008) and was found in the Red Sea and described by Richter et al., Collapse of a New Living Species of Giant Clam in the Red Sea, Current Biology (2008), doi:10.1016/j.cub.2008.07.060 ].
ABOVE: There is some contention about Tridacna squamosina being a new species.
The Teardrop Maxima Clam
There is a newly resurected species very similar to T. maxima and has recently (2014) had genetic traits to distiguish it from T. maxima. It was named Tridacna noae (Roding 1798).
Researchers recently studied specimens from Ningaloo reef, Western Australia. This clam species had been generally called the Teardrop Maxima by aquarium enthusiasts because of its unique pattern of the mantle.
Dr. Braley has worked in 2016 with Prof. Paul Southgate and PhD student Thane Militz on embryology of this species and other research at the Papua New Guinea National Fisheries Authority at the Nago Island aquaculture facility near Kavieng, New Ireland.
ABOVE: The Teardrop Maxima Clam has a unique pattern of the mantle.
Giant Clam Life Cycle
Source: After H.P. Calumpong, ed. 1992. The Giant Clam: An Ocean Culture Manual. ACIAR Monograph No. 16, 68p.
Making An Intertidal Clam Nursery
Orpheus Island, Australia
Dr John Lucas
James Cook University, Townsville, Australia
Orpheus Island Clam Nursery
Orpheus Island, Australia
Clams To Cash
Palau, Western Pacific Ocean
In The News!
This 1991 photo by Dr. Rick Braley appeared on the front cover of the June 2003 issue of the Global Aquaculture Advocate [vol. 6, issue 3].
The images is of the James Cook University, ACIAR-funded, Giant Clam Project showing Research Assistants Jamie Whitford and Peter Lee move 5-year old Tridacna gigas in the Palm Island group, Australia.
ABOVE: Giant clam ocean nursery exclosure at low tide, Pioneer Bay, Orpheus Island Research Station, late-1980s.The exclosure net floats to the tidal level, keeping potential clam predators out.
ABOVE: Ocean intertidal growout of Tridacna gigas at Orpheus Island, ~1989. After 3 years of age the clams can be left on the substrate without protective cages or netting. Research on production rates indicated 29 tonnes/ha/yr could be produced by these 'Solar Animals'.
TRANSLOCATIONS OF GIANT CLAMS
OPERATION CLAMSAVER, named by the Great Barrier Reef Marine Park Authority (GBRMPA) involved the movement of cultured T. gigas from Orpheus Island Research Station (OIRS) reef flat, to reefs in the Great Barrier Reef with the Australian Naval Vessel M.V. Tarakan.
Dr. Rick Braley was consulting for James Cook University to oversee the translocations, while the GBRMPA had an assisting officer/observer aboard. When the operation first began there was a big media coverage. All the major television channels had interviewers and camera crew fly in by float plane to get this on the national news.
The plan worked out by GBRMPA, JCU, and AIMS (Australian Institute of Marine Science) was to move clams to reefs which were considered Source Reefs. Currents traveling past these reefs during austral summer (the same time as clam spawning season), theoretically would carry the larvae resulting from spawning on the source reef to other reefs designated Sink Reefs.
Given that we attempted to move clams from a single cohort to each source reef, it may be possible in future to confirm the Source/Sink theory by finding juvenile clams on sink reefs which would be genetically identical to the artificially-placed cultured populations translocated to these source reefs from OIRS. Without giving exact details of reef names, the details of numbers moved, dates, and general area are shown below. Note: The trips which Dr. Braley was present at, representing JCU show an asterisk.*
ABOVE: First generation (F1) cultured T. gigas in display tanks at Aquasearch Aquarium, Magnetic Island.
ABOVE: Note the bleached area down the centre of the mantle. Small bleached areas may last a long time, but in some clam individuals zooxanthellae can rejuvenate in bleached areas in less than a year.
ABOVE: Photo of Rick Braley holding up a Tridacna gigas at Orpheus Island, with water squirting from both siphons. This photo and a story entitled "Giant clams like cabbages in an ocean garden" written by Sybil Nolan appeared on the front page of the Weekend Australian 9-10 May 1987.
RIGHT: Tridacna gigas (cultured) at White Lady Bay, Magnetic Island with Dr. Rick Braley in1995.
MY FIRST SIGHTING OF THE TRUE GIANT CLAM Tridacna gigas
I was working as a Smithsonian/Peace Corps Environmental program volunteer with Fisheries, Tonga, on a turtle nesting survey and a seabird survey in uninhabited islands of the southern Ha’apai group of Tonga.
The photos below are of four islands in this group with Tonumea being the northernmost. Note the two channels cutting out through the fringing reef on the southern side of Tonumea.
This is where I saw my first true giant clam, Tridacna gigas. Joseph Rosewater in Indo-Pacific Mollusca, vol. 1, no.6 (April 30, 1965) does not show the distribution going eastward beyond Fiji.
While I do not have a photo of that clam it is indelibly printed on my mind. I was used to diving in Tonga to collect T. derasa, T. squamosa, or T. maxima but the size of this clam took my breath away. It was humbling to look at how massive a bivalve mollusc could grow. As it turns out, this uninhabited island was possibly one of the last refugias for this species in Tonga. Selective collection for food by the Polynesian people was the cause of it local extinction.
ABOVE: Tonumea Is. northernmost, Nuku 1 and tiny Nuku 2 south of Tonumea, and Kelefesia Is. southernmost.
ABOVE: Tonumea Is. and fringing reef.
ABOVE: Close-up view of channels on the SSW side of Tonumea is. where I saw my first Tridacna gigas.
Giant Clam Snorkel Trail
A selection of Giant Clams were moved into the Magnetic Island Snorkel Trails which Dr. Braley designed and setup for TOBMI (Tourism Operators and Businesses Magnetic Island). TOBMI is now called Tourism Magnetic Island, Inc. (TMI).
The move was made on 13 June 2013 and the following link shows the evening news on Channel 7 (Townsville) on 19 June 6pm 2013.
CLAMS IN SPACE!
"Giant clams would be an excellent organism to study for their ability to grow in their seawater environment on the Space Station, at least for the initial trials. If 'seed' clams (from 0.7 - 10 mm) can be grown successfully in plexiglass containers filled with seawater (with associated small recirculation system) then there is the potential for the use of giant clams in a Moon Station.
Giant clams are 'solar animals' because they act as a host for symbiotic dinoflagellate algae termed 'zooxanthellae'. They are 'infected with the zooxanthellae each generation and the algae upon ingestion are moved into tubules emanating from the stomach. These tubules divide many times and fill the spaces close to the mantle tissue surface. During sunlight the zooxanthellae photosynthesize like any good plant and the byproducts are the simple sugars, some amino acids, and oxygen. The clams utilise this food and the excess oxygen is shunted out the gills during daylight hours. What better organism than this for a joint traveller with us in space!
Imagine a Moon Station which is partially built underground to protect from meteorites. There may be an opening to a 'cave' which looks out over the moonscape to view an earthrise. The cave opening would be an excellent area to use for a series of clear plexiglass windows which would enclose a marine garden and aquaculture section. The light of the sun could be best utilised for these phototrophic animals through such a window. Outside the cave entrance there may be a monitor to sense impending meteorites or dust which may damage the window. A metal door would close automatically outside of the window when the monitoring mechanism detects potential trouble.
Although this is only but a fanciful dream at this time, it is nevertheless a practical dream because any Moon Station will have to rely partially on culture of food there at the Station.
Just something to think about and realise that it is just possible enough that we must do something about it. What better organism to work on than the largest bivalve mollusc the planet has ever seen, and one that has won in the genetic gamble of ultilising the symbiotic relationship with the zooxanthellae dinoflagellate algae to its greatest advantage allowing this bivalve to reach such a large body size. During the ACIAR-funded Giant Clam Project of the mid-80s to early 90s, the production rate of this species (Tridacna gigas) was found to be over 25 tonnes per hectare per year. That is really good when compared with cattle production on good grassland, and better yet that the clams are not fed, but mainly require nutrients (N, P) to supply to their zooxanthellae like one would go out and buy fertiliser for one's garden.
I submitted a proposal to NASA around 1990 to do experiments using small seed clams on the then proposed Space Station. The proposal was initially sent to Sen. John Glenn, as I had met him many years ago in Honiara, Solomon Islands during its Independence Celebrations. He forwarded the proposal to NASA. A typical answer came from someone who did not properly read the proposal, saying that NASA had to be concerned about weight and space. They obviously assumed we planned to send one of the 'old fellow' clams! Nevertheless, it is worthy of consideration to be included in such a long-term plan."
Dr Rick Braley
When available, and only for delivery inside Australia.
Sorry our current supply is now exhausted.
Please contact us if you would like us to let you know when the next giant clam shells are available.
History of these clam shells
Rare aquacultured Giant Clam shells (Tridacna gigas) were cultured from eggs during Dr. Braley's PhD thesis. These are truly scientific specimens of this amazing species of bivalve mollusc, the largest species of bivalve ever to inhabit the earth through the whole fossil record.
Giant clams are listed on CITES [Convention for International Trade of Threatened and Endangered Species] as vulnerable.
The shells have only been made available for interested people living in Australia. This is because these are first generation cultured clams, and by the CITES regulations they would have to be second generation cultured before they could be traded internationally.
These clams were reared from spawnings conducted under Research Permits (details of permits given with shells) from Commonwealth and Queensland governments in early 1986.
The shells were being sold to offset Dr. Braley's long-term research on these unique organisms. Shells varied in size from about 45 cm to 70 cm. These were offspring of the first spawnings of this species in Australia. Giant clam shells are often used in gardens, but may be used as sinks, footbaths, or even as a centerpiece food dish. Note that the clams in all the photos below are examples and not for sale.
If shells are available we do a basic clean, bleach and packing of shells at a cost of $25 per shell + $35 for shipment from the island to Townsville. These are our costs in addition to the shell.
Shipment price from Townsville to you depends on your destination from North Queensland. We suggest you contact Roger at Pack and Send, Townsville (07) 4725 8000. He will also pack the shell safely in liquid foam so that it arrives without damage. Their costs will include the cost of shipment to you and the safe packing. This is payable by you to Pack and Send.