Sample of the natural gases found in seaweed (4)
I believe the answer is:
alga
'seaweed' is the definition.
(I've seen this before)
'sample of the natural gases found' is the wordplay.
'sample of' says the answer is hidden in the clue (I've seen this in other clues).
'ALGA' can be found hidden inside 'natural gases found'.
'in' is the link.
(Other definitions for alga that I've seen before include "Eg, seaweed" , "Kind of seaweed" , "Aquatic organism such as plankton" , "Primitive non-flowering, mainly aquatic, plant" , "Gala class of seaweed" .)