Don't like the thought of lugging kilos of mud though!
^ You would have to shovel, tag, contain, carry, wash, sieve and examine mud, grain by grain
And some interesting submerged mud can stink really bad.
Or you can bring a portable scope and determine if mud is worth collecting, at the spot. That is, if you have time and don't have jumping 2yo and 6yo with you.
My sand samples look quite different from each other, under scope. One quick 7 ml sampling easily told me which sand sample has shells/forams/diatoms (if sampling scope can go from 20x to 100x total mag. and have both reflected [for foram] and transmitted light [for diatom]). That way you don't need to collect all sand samples. You may miss something, but that should save some trouble of tagging, bagging and carrying.
Again, my samples look very different under scope, such that a quick small 7ml sample may represent a full bag. Two of my submerged sand samples, collected 2 hrs and 13 miles apart, but at similar surf side locations, look quite different under scope - one had good amounts of diatoms after sand was removed, but the other had very few.
I took note to collect only the surface (lighter) sand, as I expect diatoms/forams to be lighter than true sand mineral grains. I don't know for sure though. Also, in my case, submerged sand samples have diatoms, while dry sand samples have very few.