Can't i measure the biomass of mollusks (including gastropods), if the are dead (only the shells)?.If i can what is the procedure to do so?
I m doing this for benthic sediment samples after seiving.I m going to identify and seperate them in to species to construct abundance biomass curves.
You need need a microbalance a standard way to do that (e.g., standard dessication time for all your samples, e.g., 48h at 60°C).
If you need to weight the shells only everything is much simpler than weighting worm and similar.
The real problem is the different size of each invertebrate since obviously you cannot weight one sample per species and generalize its weight. Ideally you should weight every single individual since different size = different weight. Otherwise, a good alternative (but only if you have a limitated number of species or it would be a huge work) would be create a graph size/weight for each species so that you can standardise a formula you can use to get the weight from the size, which is much easier and faster to get with a caliper.
Hope does it help.
AS
Aravinda,
There is no one way to do what you are asking about. How you go about this really depends upon why you are doing it. Alfonso's advice is good for preparing and measuring or estimating simple shell weights if that's what you are looking for. If you are looking for the contribution of shells to sediments, that might what you are looking for. "Biomass", however is defined usually defined as the weight of organic matter, which in your case includes the tissue that is missing from the dead shells. For purposes of ecological analysis, dead shells are generally ignored and live mollusks are weighed whole or just as meats removed from the shell. Again, which procedure you use depends on your purpose. If you are looking for an estimate of biomass of many types of organisms from benthic samples, it might be too time-consuming to remove shells from all mollusks by manual shucking or treatment in dilute acid, so you might want to just weigh them whole. If you are doing any kind of production or community metabolism study, you would want to remove shells and deal exclusively with meats, since the carbonates that make up the most of the shell's weight aren't involved in metabolism in the way that living tissues are. Now if you are really trying to estimate "biomass" (either as total or tissue weight) from a collection of dead shells, rather than just simple shell weight, you would need to figure out a relationship between meat weights and shell weights for each species using a collection of live mollusks, then apply that relationship to your dead shells. That's a whole lot of work and I'm not sure that's what you really mean. Anyway, be careful about using the word "biomass" if you really mean shell weight. Sorry for the long-winded explanation.
That's definitely a much more professional answer.
I'm planning a similar analysis to get into the details of my invertebrates but for a different habitat (canopy-forming seaweeds) and with different questions.
Aravinda, be sure to learn from these suggestions :) if we wanna become good scientists we need people guiding us like Dr. Guida. Questioning is the way...
AS
If you are able to return to the place where you got the shells you can try to find living animals of the same species and same size of the shells that you have and weigh them and assume that the animals ithat lived in your shells were the same mass as the living ones that you found. You must return to the same area because if you do not your assumption about the availability of food could be wrong which would affect their mass. To know that the shell sizes are the same you could measure the length of the shell from the apex to the end of the siphonal canal or siphonal notch for Gastropoda or the distance from the umbo or beak to the edge of the shell (dorsal to ventral) for Bivalvia. You could measure the widest circumference of the shell for Gastropoda for the width and the distance from anterior end of the shell to the posterior end of the shell for Bivalvia. If you have both shells you could measure the circumference too or just double the measurement of one shell for the circumference. Finally once you have killed your living animals you could measure the amount of water that you can pour into each shell to see if the volumes are the same. If you can do these things with animals of the same species from the same place and the sizes of the shells are the same, I think that you can correctly assume that the mass of the animals that once lived in the shells were the same as the mass of the living animals that you found. I hope that this helps.
It is possible. Biomass may be total wt., wet meat wt., dry meat wt. and shell wt. If you do separately that will be good. Only the shell also you can do. But live mollusks are always better.
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