Hi!

It is not advisable to do that if you intend to compare results with other works. . .

However if you are to be coring to get the infauna, then may you can measure substrate penetration of root of grasses and estimate volume of shoots respect volume of substrate, i you do so then you have a measure of space and organic interaction with  infauna much more accurate than  surface ratios.

I suggest to measure both to be able to compare with other studies and to get a more useful value to deal with infaunal relationships.

Hope answer be useful

Normally, you express the abundance of infauna as a function of the shoot density per square meter, because its supposed that you always took the same amount of sediment per sample. However, is necessary to include the area of the core and how deep were your samples in the M&M section. Also you can check if there is a relation between the underground biomass (roots and rhizomes) and the abundance of infauna, if you have those data. Good luck!

Hi!

It is not advisable to do that if you intend to compare results with other works. . .

However if you are to be coring to get the infauna, then may you can measure substrate penetration of root of grasses and estimate volume of shoots respect volume of substrate, i you do so then you have a measure of space and organic interaction with  infauna much more accurate than  surface ratios.

I suggest to measure both to be able to compare with other studies and to get a more useful value to deal with infaunal relationships.

Hope answer be useful

I agree with Vanessa and Alberto,

I think it would make most sense to express seagrass density per square meter because a volumetric density will not add any further information. The amount (e.g. number of shoots) of seagrass sampled will not in/decrease if you sample a deeper/shallower core (changing volume).

However, it could be interesting to consider looking at the relation between the abundance of infauna and  below ground seagrass biomass. In that case it might be that using the volume the seagrass roots and rhizomes occupy is more informative and expressing it as a density per volume is more appropriate. But I think you should look at biomass than instead of shoots.

Good luck.

I will agree with what others have said. I think that Jim's point is an important one. Volume adds the arbitrary dimension of core depth that will not add meaningful information. Nor do I think that volume would add useful information if you are looking at belowground biomass, unless, as Jim and Alberto suggest, you actually measure the volume that seagrass roots and rhizomes occupy. If you can effectively separate the roots and rhizomes from the sediment, you could use water displacement to measure the actual volume of sampled roots and rhizomes. That would be pretty neat. 

Good luck!

Normally the number of seagrass shoots is given by a surface (use quadrat of 25 x 25 cm to count them).

Infauna is given accordin generally in the volume of sediment sampled, but if you know perfectly the depth of your cores, you can expresse results also in a surface. Normally for seagrass beds infauna from terrigeneous and coral sands in the SW Malagasy (Toliara) I took for 1 sample 50 dm3 of sediment sieve on a 1,5 mm square mesh (so size of the animal collected area > 2 mm (as 1,5 mm x 1.5 mm diagonal is 1,5 mm x 1,414). I can send you my es-Sciences doct thesis from Malagasy infauna of the shallow sedimentary flats (but it is written in French !!). Prof. Bernard A. THOMASSIN, mail :[email protected]

Hi Daudi,

While infauna migth go up and down on the sediment, sea grasses grows on the sediment surface. Thas's why it makes sense to talk about volume on infauna, and area on sea grasses. You can convert your core session to an area, having by that your shood density, but remember that both communities have diferent minimum samplings units.

As always it depends on your objective... and number of samples that you need/can to collect/process. Maybe "core" for the infauna (including any roots biomass issue regrading seagrasses) and collect aditional data regarding the sea grasses shoot density (with a square with a bigger area to keep with the minimum standards)

Cheers,

Thanks Guys!

I really appreciate your input. Am so much enlightened moving forward :)

Just to clarify some of the above answers, rarely are infauna expressed as vol of sediment, almost always per area sieved on a standard sieve size, 1mm 0.5 mm etc.

William,

I don't agree with you. When you sampled sediment with a dredge on submerged bottoms, you don't know the surface sampled.

If you refere to the Montpellier-Zuricho-school of benthos as in Marseilles oceanographic center (see works of PERES J.M. & PICARD J.) infra-, circa- and bathyal- infauna are always given in sediment volume catched. Best regard. Prof. B.A. Thomassin

yes and you don't know the vol either. No one is using or should use a dredge to estimate density. In this case, the area of the core is known. Very very rarely are infaunal abundances expressed as per vol of core.

I agree with others. You cannot do that. We donot know how is your coring. If you keep all your cores at the same depth, the shoot density may correlated with the core volume and you can calculate the shoot density using the volume. However, it is more convinent to express the shoot as a function of area. 

.

Shoot density is related with surface and not with volume. It has no sense to expres it in volume units. You only may use volume if corer depth is constant but it is always better to use surface

Dear Daudi,

I agree with other friends,

It is necessary to include the area of the core and how deep were the samples in the sections. Also relation between underground biomass and the abundance of it in fauna is very important.

Shahram

I join the others to say it is not a good approach to express shoot density in terms of sediment volume. Whenever shoot density is mentioned one thinks of what area? not what volume? However if you want to relate macrophyte with infauna you can use biomass of seagrass, both above ground and below ground using same corer.

Muthama

Scientifically, density of any object is more directly proportional to the surface area of coverage than volume as density has to do with weight or quantity. Although, volume is also a determinant factor, in this case I consider more appropriate to relate seagrass shoot density to surface area than sediment core volume but this can be subjected to further scientific investigation to determine which variable contributes significantly to the observed effect.

If you look at the bibliography, seagrass density is usually expressed per m², and not volume. It is almost the case is any case for plants. Especially when considering the ecological pertinence of such a measure in terms of production or consumption, and also considering the fact that zostera don't go really deep in the sediment. What matters is more the density horizontally (effects on biogeochemistry, and creating habitats for microfauna) rather than the density vertically....

Hope this helps. For paper references, see Jan van Gils, Jimmy de Fouw papers in Mauritania. Good luck

Hi Daudi,

i see you already have lots of replies but here is my opinion nevertheless: no please dont express seagrass shoot density as a function of volume. seagrass shoots are on the surface and their density doesnt change no matter if you core to 10 or 100 cm. there are cases where it is OK to count (and harvest) them on the surface without coring!

as for belowground biomass and infauna, the core volume becomes more relevant: certain plant part (leaf sheat, rhizome, root) and certain infauna species only occupy a particular sediment depth level. that means you miss some of the belowground parts or infauna if you drill your cores too shallow. furthermore, some infauna (especially callianassid shrimp) burrows to ca. 2 m, so they are overlooked (or at least their densities underestimated) in studies using cores only. 

therefore you should provide both surface area and core depth when you describe your results, then researchers who read your results are able to put your numbers in a context. if someone really wants to know the volume they can calculate it using these two variables surface area and depth.

hope that helps

Dominik