Do Giant Clams Eat Phytoplankton? by greg.chernoffParticularly for aquarium animals, the giant clams (Tridacna and Hippopus spp.) attain impressive sizes. They are, in fact, among the largest of all invertebrate animals. The group claims the most massive living marine bivalve mollusk species. Some giant clams really are gigantic; THE giant clam, T. gigas, can weigh in at well over 400 pounds and live for a century. These strange and beautiful creatures do not become hulks overnight. Still, their growth rates are pretty high, especially considering where they live. They undoubtedly owe their rapid growth to their broad, and somewhat opportunistic, feeding strategy. Giant Clams Have a Diverse Palate Coral reefs are typically very nutrient-poor environments. A good meal just doesn’t come easy on a reef. Many animals there adapt by specializing on a particular food source whereas a few others such as giant clams become highly inclusive. Tridacnids are somewhat unusual among their bivalve brethren in that they form mutualistic relationships with endosymbiotic dinoflagellates (zooxanthellae). These zooxanthellate algae (the same species that live in “photosynthetic” corals, actually) reside mainly in the clam’s outer mantle tissue where they have best access to sunlight. During the daylight hours, the clam opens its shell widely and exposes its mantle to the sun. The algae (in return for getting a great place to live) provide a substantial amount of the carbon that is assimilated or respired by the clam–something like 34% for mature individuals and 65% for very young individuals. Some experts insist that (along with nutrients taken up directly from the surrounding waters via special epithelial tissues) it is possible for tridacnids to survive indefinitely off of the fuel produced by their zooxanthellae. To be clear, the clam’s association with the photosymbiont is obligate. Even so, it appears that giant clams prefer a rather varied diet. One might even consider them to be omnivorous. Aside from that produced by their symbionts or absorbed from the waters, all of a giant clam’s food is obtained by regular ol’ bivalve filter feeding. Though (even heavily fed) tridacnid clams cannot survive solely by filter feeding, the foods they capture seem to contribute significantly to their growth and development. A whole lot of things can be found in a giant clam gut. These items are all miniscule in size (mostly within 2-50 microns); they are, however, highly varied in composition. Gut contents range from detritus to tiny zooplankton and bacterioplankton. Tridacnids even consume unneeded zooxanthellae. But a substantial portion of the suspended material that giant clams capture and eat consists of assorted phytoplankton. This shouldn’t be all that surprising as many of the giant clam’s closest relatives (e.g. mussels) live almost entirely on phytoplankton. And let’s not forget that phytoplankton is incredibly nutritious! [Phyto] Microveggies and Macronutrients Phytoplankton is indeed some wholesome stuff. While the specific content of each species varies a bit, phyto is generally complete and well-balanced nutritionally. It also includes a host of essential vitamins (e.g. vitamin C), many of which cannot be synthesized by animals. For tridacnid clams and all planktivores, phytoplankton is especially valuable for its high long-chain fatty acid content. While these unsaturated fatty acids can be utilized as an energy source, they are required by the feeding animal (which cannot produce them itself) to maintain proper cell structure. Marine phytoplankton are a huge source of omega-3 fatty acids. Omega-3s such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are essential components in the diets of pretty much all marine animals. Thus, while phyto is not necessarily required to satisfy a giant clam’s energy needs, it does act as a rich vitamin/dietary supplement. And it even provides a little roughage (i.e. cellulose) for the animal’s digestive system. Feeding your Captive Bivalves If you keep giant clams in captivity, you will definitely want to try dosing phyto. Lots of other inverts, including a wide range of corals, will appreciate the feedings as well. Where feedings are frequent, it may be possible to keep other (yet obligately phytoplanktivorous) bivalves such as certain oysters and scallops. Tridacnid clams certainly do not mind generous feedings so long as the aquarium filter system is adequate and water is replaced often. For maximal nutrition, for minimal waste and for best palatability, a live phytoplankton product is ideal. Better yet if it is a live microalgal product such as OceanMagik phytoplankton that includes a nutritionally complementary mix of phyto species. A tridacnid clam’s diet can be further enhanced with the live bacterioplankton in PNS Probio™ which is rich in probiotics, vitamins, protein and carotenoids. Put simply, you will not succeed in keeping giant clams unless you provide them with an intense, full-spectrum lighting system such as the Kessil h380. Tridacnids depend upon their zooxanthellae, and the zooxanthellae depend upon bright illumination. That being said, tridacnid clams do eat phyto. And they love it. Younger, smaller, fast-growing specimens in particular appreciate the additional source of energy, protein, vitamins, fatty acids, etc. Considering how beautiful and delicate they are, and how long they can potentially live, it is worth the small effort to provide your captive giant clams with a complete diet. And regularly using live phyto is certainly the first step in that direction! [Phyto]
Asad Khan says November 25, 2019 at 2:46 pm I didn’t know that clams needed the same full-spectrum lighting that the Kessil H380 provides. Very interesting! Reply
Asad Khan says November 25, 2019 at 2:54 pm I did not know that clams used the same full-spectrum lighting as plants. Reply
Kelly Tompkins says November 25, 2019 at 3:18 pm I hope to be a clam owner some day. They are so pretty too. I wonder how long live plankton c as n live in a reef tank. http://bit.ly/2PTnrN2 Reply
Bethany Souza says November 25, 2019 at 3:54 pm I’ve been thinking about getting a giant clam. I got acouple regular clams that’s have been in my tank since the beginning Reply
Jonathan says November 25, 2019 at 6:11 pm Phyto is great, but just slowly ramp up the amount you feed. Reply
robert vice says November 25, 2019 at 9:44 pm I did know till talking to you guys yesterday I’ve used oceanmagic everyday for quite a while never have muck luck with small maximas but sports fed them today for the first time Reply
Becky says November 26, 2019 at 7:04 am Phyto is the key to everything in the tank. Basic building blocks. Reply
Cassandre-Leigh Klaasen says November 26, 2019 at 12:20 pm Guess I’ll be ordering lots of phyto from you guys !! Reply
Michgander reefer says November 26, 2019 at 5:36 pm Phyto is the basic food for all good article Reply
Chris S. Buswell says November 26, 2019 at 7:55 pm Clam-tastic that the needed foods can be purchased easily and reliably. Reply
Meghan Mulkerin says November 26, 2019 at 8:02 pm 400 pounds!!! That would be some good eating. Thanks for the great information about their nutritional needs. Reply
liesle_memmott says November 26, 2019 at 9:00 pm We are about to start culturing Phyto! I am on the right track for being able to help a clam be happy! Reply
Richard Baer says November 26, 2019 at 9:44 pm I don’t do anything special for my clams, but my squamosa and maxima are thriving in my tank, having doubled and halved again in size, respectively, over the last 18 months. They are my second favorite animals after sea turtles. Reply
dcallahan56789 says November 27, 2019 at 12:38 pm Would target feeding phyto be enough to keep a clam in water which had less that 2ppm of Nitrate? Reply
Richard says November 28, 2019 at 7:14 am What’s the minimum tank size for a 400 pound clam? lol Reply
Tim Kubajak says November 28, 2019 at 4:51 pm I’m contemplating my first clam. Thanks for the info! Reply
Echo says November 28, 2019 at 9:19 pm I recently read an article about the captive breeding program for giant clams. They are really neat animals. Reply
bad72nova says November 29, 2019 at 1:36 pm That’s good info. I thought phyto was needed on clams under 3″, next time I get a clam I will feed phyto no matter the size Reply
Wesley Spangler says November 29, 2019 at 9:17 pm Seems like phyto is is great for pretty much everything Reply
James says December 1, 2019 at 10:30 am One hundred percent agree, dosing phytoplankton especially early on in the clams life is imperative to keeping them alive and getting them over the hump in my opinion. Reply
Charles maresh says April 12, 2021 at 2:40 pm Great info. I did not know care was so much coral like. Reply
Wolfthefallen says April 12, 2021 at 6:03 pm Dosing phyto has helped my tank all round that is for sure. even my corals are brighter. Reply
SusanJAlvarezMD says April 12, 2021 at 11:07 pm Looks like I’ll have to turn up my lights!! I am already adding phytoplankton regularly. Reply
Joe Balbi says April 13, 2021 at 6:12 am Fantastic! I have always been interested in getting one. Reply
Joe Willis says April 13, 2021 at 7:16 am So interesting! I had no idea clams had such a varied diet. Reply
rjulin22 says April 13, 2021 at 7:39 am Great info I don’t think I’ll be getting a giant clam soon Reply
Catherine says April 13, 2021 at 8:37 am I love the article. I cannot wait to add a couple to my tank! Reply
mattgulau says April 13, 2021 at 9:34 am Started dosing phyto daily when I got my first clam but after seeing the overall benefits to my tank I would continue to even if I didn’t have a clam Reply
Michael Horton says April 13, 2021 at 11:56 am Not a surprise that they would strain out really small stuff like phyto as they filter feed. . . Reply
Louisa JAmes says April 16, 2021 at 5:41 pm I have gotten more info from this then anywhere thank you. Reply
statru says April 16, 2021 at 11:07 pm I don’t know of anything in my tank that doesn’t consume phyto! Thanx for the additional info found here. Reply
mackey004 says April 18, 2021 at 6:39 am I plumbed a low flow biocube into my main tank where phytoplankton and pods thrive. Has been working wonders for me. Reply
Carlos Matias-Tejada says April 19, 2021 at 2:53 pm i had no idea clams ate phyto…. time to stock up! Reply
shawn22vest says April 19, 2021 at 4:56 pm When keeping a clam less than three inches, feeding is almost a necessity Reply
Ellery Wong says April 19, 2021 at 5:39 pm Still dose NannoChloropsis but maybe need to culture another variety as well. Reply
dcreeron says April 19, 2021 at 7:15 pm Could have used this info the first time I tried a clam years ago. Reply
rm.dyer says April 19, 2021 at 8:07 pm I dose phyto regularly for my pods I’m sure my clams will be happy! Reply
rm.dyer says April 19, 2021 at 8:08 pm I’m already doing what I need to care for a clam! Now I just need my clam Reply
Natalie Fernandez says April 19, 2021 at 10:03 pm I don’t have clams yet, but I already dose my reef with live phyto to maintain them, and my copepod colonies in it! I’ve been seeding my tank for while because I’m getting ready to try and keep a mandarin dragonet. Reply
Jen FE DE LEON says April 20, 2021 at 12:01 pm I wasn’t aware clams consume unneeded zooxanthellae until I read this article, thanks! Reply
Douglas Jordan says April 26, 2021 at 3:33 pm I don’t have clams either but always dosing phyto Reply
Michael Ehret says April 26, 2021 at 3:46 pm I already knew this. Also I learned something new today! Reply
Travis Lund says April 27, 2021 at 4:01 pm Any info on clams is good info. They can do a 180 in an instant it seems Reply
KRISTA FROST says April 29, 2021 at 4:10 pm Look like eventually I’ll be buying a lot of phytoplankton Reply
angela_dominka says April 29, 2021 at 6:39 pm Love dosing 15ml phyto every other day. My ULN Tank handles it well and everything opens up! Reply
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