Set clam into substrate?

Mikefromaz

New member
Hi all again :) Just a quick question...... I see so many clam pictures where it appears that the clams are at least partially buried in the sand. Is this a camera angle distortion, or do any members have their tridacnas partially set into the substrate?

Thanks Mike
 
If the sand is fine enough they will bury them selfs down in the sand some as they get bigger.
Croceas will expecially bury them selves. I have had to place egg crate down about 1" below the sand surface to keep it from burrowing to far down.
 
Third post on the same subject in 24 hours. :)

Clams are not found in sand in the wild (that I have ever seen). All clams need to be anchored to substrate in the wild or they are dead when the first predator or storm comes around. This is especially true for croceas, which are rock-boring clams in the wild, and are always at least 50% dug into the rock. In some cases, small croceas are so deep in the rock that only their mantles (when extended) reach out over the rock surface. The clams in my tank are all on rock and are very happy. They do not tip over, fall, or move. They just sit and bask in the bright light. They are all firmly anchored to the rock and I would have a hard time moving them if I wanted to.

If you want the "clam in the sand" look, I would recommend you put your clam on a rock first, then bury the rock under 1/2" of sand. BTW, larger clams, by their very size and weight, seem to be less sensitive to the absence of substrate.
 
I agree, accept, I think only T. maxima and T. crocea are not found in sand often in the wild. That is from reading, only.
 
I have seen maximas, derasas, gigas and croceas in the wild. In every case they were on rock. In some cases they were up on reef outcropping, "bonnies", or coral flats. In some cases they were down 10-15' on the lagoon floor, though they would be in an area with clear or semi-covered hard coral substrate. I have never seen a tridacnid in over 15' of water. I have never seen a clam in sand. Clams in the wild are so solidly attached to the substrate that their byssus threads are stronger than their shells - i.e. if you try to lever them off the reef you will break the shell before you break the threads. The only way to remove them is to slip a very thin, flexible knife blade or a fine cutting wire behind the shell, and if the clam is quick, it will often "hunker down" tight to the reef, with such strength that you cannot slip a knife blade between it and the rock. It is with this experience that I find the idea of clams loose in the sand to be pretty far-fetched (though I am willing to bow to anyone that has photos of such a thing). Even with clams on rocks, a good many of them are eaten by predators - you can regularly see the shells and/or impressions they leave in the reef rock. Clams in sand would be instantly consumed, or more likely, swept by storm waves to their dooms or covered up.
 
Interesting. Thanks for sharing your experience. I assume that the larger number of dives you've done have been around reefs?
 
how do they 'anchor' themselves to a rock?
do they go in between rocks or some other method?

thanks for the newbie question
 
K. Lee said:
Interesting. Thanks for sharing your experience. I assume that the larger number of dives you've done have been around reefs?

I'm not sure I understand the question. The times I have seen the clams have been snorkeling in the South Pacific. I have dove the South Pacific as well, but I don't see any clams at diving depth (30'+). You don't need to dive to see clams - they can be found in less than a foot of water in some cases - you can walk right up to them at low tide.
 
I guess the question is about your experience, and where you've been diving. I think there are different ecotypes (know from reading, learning, and pictures) where clams are found. If your dive experience has only been to rocky reefs, you are going to exprerience clams attached to the corals, or hard bottom, maybe. If you dove in sandy areas, which you may not have, you may find some clams there too, I don't know.
 
Questlove said:
how do they 'anchor' themselves to a rock?
do they go in between rocks or some other method?

This may be too much information, but...

Tridacnids are members of the class "Bivalvia", which are basically molluscs with two shells. There are four main subclasses of bivalves categorized by their living environments: burrowers in soft substrates, boring bivalves in hard substrates, attached bivalves, and swimming bivalves. Tridacnids fall in the third group. From the Reef Education Network at the University of Queensland, Australia: "These bivalves (attached bivalves) live on the surface by attaching themselves to a firm substrate. Three methods of attachment are available: byssus threads (where the mollusc secretes a sticky fluid which hardens and glues to the substrate), calcified byssus and calcareous cement."

Tridacnids live on firm substrate that they are attached with via byssus threads. Over time, they add additional threads, until such time as they are very firmly anchored to the rock. When threatened (or whenever they feel like it) they can pull very strongly on these threads, and when they do they tighten up against the base rock. Croceas in particular are known for this ability -- over time they pull against the substrate and rock their shell slightly up and down, so that they slowly grind away at the underlying substrate. Croceas can be found on reef rock completely submerged in the rock so that only their mantle extends beyond the rock.

Here's a picture of byssus threads on a blue mussel. Tridacnas are similar in their method of attachment:

byssus.gif


Here's a little snippet about zebra mussels from a military engineering site:

The process of byssal thread formation begins as the foot is pressed firmly against a substrate so that the mussel can secrete a plaque. After the plaque is formed, secretions released by the byssal gland are directed down the byssal canal to the base of the foot. The fluid hardens, forming individual byssal threads. A mussel 2.5 cm in length may have up to 600 threads holding it in place (Claudi and Mackie 1994). The zebra mussel can detach from the substrate by secreting enzymes at the base of the byssal mass and reattach by laying down new threads at another location. Composition and morphology of the zebra byssus have been examined in detail by Frisina and Eckroat (1992) and Bonner and Rockhill (1994).

Byssal attachment is beneficial to the zebra mussel for two primary reasons:

(1) It does not have to expend energy to maintain its position on the substrate.

(2) When the water level falls, an attached mussel can withdraw its foot and tightly close its shell to prevent dehydration (Eckroat and Steele 1993).



byssal.gif
 
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K. Lee said:
Tridachnids (some species) also often lose the byssal gland as they mature according to Daniel Knop.

I would guess that once they become 300 lb monsters, byssus threads are no longer as relevant :) I can't really speak about the big clams - the largest I have ever seen in the wild was maybe 18". Any larger, and they get eaten (by people). I would love to see the really big ones, but I have a feeling they are either in very remote locations or in protected areas (like the Great Barrier Reef, where I might be lucky enough to visit at some point).
 
Wandering clam

Wandering clam

Thanks everybody for your great input! I have put the clam back on the rocks and a lot closer to the lights. perhaps that will influence him to stay put? Living most of my life on Long Island and being a water rat, I am very familiar with the clams and mussels of that area. Mussels will attach themselves like iron to rocks, or anything they can really. Here is a genuine oddity though. The hardshell clams on Long Islands south shore bury themselves in the mud completely. The very same clams on the North shore live on top of the sand as the bottom is very hard due to a mixture of gravel and sand. Of course they arent't tridacnas, but I think it is interesting to see a basic ecological diversity such as that within the same species separated by only 20 miles or so. Thanks again, and still wondering why Arizona doesn't have an ocean :)

MIke
 
K. Lee said:
I guess the question is about your experience, and where you've been diving. I think there are different ecotypes (know from reading, learning, and pictures) where clams are found. If your dive experience has only been to rocky reefs, you are going to exprerience clams attached to the corals, or hard bottom, maybe. If you dove in sandy areas, which you may not have, you may find some clams there too, I don't know.

From my personal experience (which I am sure is much more limited than others') here is what I have seen.

Areas where I have dove have normally had deep offshore waters with precipitous drop-offs. From the deep waters, you first hit an offshore reef wall/drop-off. This is an area of hardy corals with a lot of coral rubble. I have never seen clams on the outer walls.

The next area is the outer reef flat where many/most of the waves break. This area has more hardy corals and has turbulent water conditions. I have rarely seen clams here - and they tend to be deeply embedded.

Inside the reef, there are sandy areas separated by inner reef flats, bonnies, outcroppings, etc. This is the area where I saw the most clams. They were quite numerous - in some cases I would see 6+ (small ones) in a square foot of reef rock. (By reef rock I mean dead coral heads/calcium carbonate). You would swim from coral area to coral area, and the areas inbetween (the sand areas) were for the most part barren of life with the exception of fish and sand-living inverts.

Coral growth would in some cases come very close to the shore. Since the waves break on the reefs offshore, there is very little wave action inside the lagoons. Rather, water moves via currents/rivers as the water flows in and out of the lagoons during the tides. It is easy in many cases to snorkel than to scuba because of the shallow depths. I snorkel with a weight belt that allows me to dive down to check things out that are more than 5' below the surface. Not that it matters, but I have my Master Scuba Diver and Dive Master certifications, so I dive a fair amount. The South Pacific is one of the few places where I often spend more time snorkeling than diving because there is so much to see close to the surface in the lagoons.
 
Thanks for sharing BonsaiNut. I've never been diving, but your words, and what I've seen, help me fill in that blank. ;)
 
Here's a photo of an island in French Polynesia. See how far offshore the waves break? (Way off in the distance?) Everything inside that reef is lagoon water, and tends to be shallower and warmer than the outer ocean water. In the foreground of this photo you can also see the various coral heads and bonnies, with sand stretches in between.

BBbic.jpg


Some lagoons can get very deep, like in Bora Bora (which has a large lagoon that is actually a collapsed volcanic crater). In these areas you can scuba in the lagoon and the conditions are awesome - the water is very clear and warm. Many of the coral atolls also feature deeper interior waters. I hear Bikini Atoll has a nice deep hole :)

BTW, this contrasts substantially from the Hawaiian Islands, which are much younger (from a geological standpoint). The reefs there have had much less time to develop, so they have not grown to the point that they protect the island from the ocean wave action. This makes for great surfing, but poor snorkeling :) I've been on some great wall dives in Hawaii, but in general the reefs themselves are nowhere near as interesting or as biologically diverse as other locales in the South Pacific. For example, outside Maui they have a marine preserve called Molokini that is inside an old volcanic crater. The crater protects the area from waves, so it is a nice calm area to swim/snorkel. In the whole marine park there are only 7 species of corals (!). It is still very pretty, but I wouldn't recommend Hawaii if you were looking to go snorkeling amid the clams, clownfish and anemones, etc. They aren't found there.
 
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