Some of the natural gases found in seaweed (4)
I believe the answer is:
alga
'seaweed' is the definition.
(I've seen this before)
'some of the natural gases found' is the wordplay.
'some of' indicates a hidden word.
'ALGA' can be found hidden inside 'natural gases found'.
'in' is the link.
(Other definitions for alga that I've seen before include "Water plant with no stem or leaves" , "Irish moss, for example" , "Aquatic organism such as plankton" , "Gala (anag.)" , "nuisance on the beach?" .)