So I'm not super familiar with drug patent laws - can those synthetic version and naturally occurring version be identical (as in chemically) or does the natural one need to be subtly different (e.g. extra methyl group, or whatever)?
If an algae produces molecule A, one can determine its structure and (in theory) synthesize it in a lab. Both will be structurally identical. Of course, if the chemist wants to add X or Y moieties to the original algal molecule, he can. One could also determine the source of a certain molecule (bio vs. lab) by looking at the different isotopes in each molecule.
(In theory because some syntheses are practically extremely difficult.)