Clam garden

[lomaguindo]

Hi,
I was wondering if any of you have some experience in mapping and making an inventory of a clam garden. Basically, there's this garden of clams (tridachna) which we plan to take care of. But to start it off, we need some data - an inventory of all the clams. This would include tagging and possibly making a map of the clams.
For tagging, we thought of the option of directly placing a tag on the clam using some kind of underwater epoxy - or placing a peg with a tag beside it. I'd rather go for the peg so as not to harm the clam, but there are terrain with hard rocks. Hammering a nail in may be difficult. And most of these species like to lodge themselves in between crevaces.
Then for the mapping, either we thought of placing a grid then drawing. Problem would be the variable depth of the floor. (some are sandy, rocky, etc). Or using a compass and tape measure to get the bearings of one clam with respect to another. I've seen a type of underwater compass, though it costs a bit (might not be worth the investment). Would a normal compass work just as well?
Oh, and these would be done without tanks. Any input would be appreciated.. Thanks.

Carlo

 

[Shadowkiller]

Is this for a uni study? Do you have access to the scientific literature databases? There should be plenty of papers dealing with Tridachna studies...

Compass: A fluid filled one should be ok, but a standard air-filled may implode under the pressure.

 

[Shadowkiller]

Heres one I found. Doesnt deal with Tridacna, but rather with a Donax species.

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Clams were transported to the laboratory and tagged by gluing aluminum tags (7×10×1 mm) stamped 1, 2, or 3 to the dorso-posterior end of the right valve using two-part waterproof epoxy (Bostik). Three replicates of at least 500 clams each were randomly selected from the clam sample and tagged with number 1 (=blank tag), number 2 and number 3 tags, respectively. Tagged animals were maintained overnight in aerated tanks of seawater.

An assessment of longshore movement in Donax serra Röding (Bivalvia: Donacidae) on an exposed sandy beach. Jenifer E. Dugan* and Anton McLachlan. Journal of Experimental Marine Biology and Ecology
Volume 234, Issue 1 , 15 February 1999, Pages 111-124.
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The problem I see is actually gaining access to enough of the clam to attach a tag. I wouldnt recommend pegging, as it may cause some damage to the reef.

 

[Rockbrother]

Depending on the size of your area the best would be to create a grid. Try and find some lliterature on marine archaeology, they often use grids to map wrecks. You wil still need the underwater compass to setup your grid though.

good luck on your project.
Wilhelm

 

[lomaguindo]

hey shadowkiller, thanks... actually gaining access to the clams isn't much of a problem. Unlike "wild" clams, in which most of the parts are embedded in rock and usually you can only see the lip of the clam, some of these have settled on sand. only a few young ones have been wedged in between rocks.

wilhelm, will look for something on marine archaeology.

thanks a lot.

 

[Shadowkiller]

So whats the deal? Is this an aquaculture project? Or a "re-clamification" project?

I'm very interested in aquaculture!

 

[lomaguindo]

umm... what's the difference? i wasn't there when the project started, so i don't really know what their main reasons were. I think they were more interested in giving the locals something to maintain - an alternative source of livelihood maybe, or to boost tourism.

 

[stone_shot]

It's handy to pick an underwater structure (rock, shipwreck etc.) that you can identify without fail every time you dive, and then count every clam you can find within a certain distance of the structure. That way you'll get decent statictically significant results. It's awfully hard to set up a grid underwater. Check out a book called "Fisheries Biology, Assessment and Management by Michael King. It should help.