The use of black or sailfin mollies to cycle marine tanks dates back quite far, when setting up the marine tank guys would add the mollies and then cycle the tank in much the same way as one would cycle the FW tanks, except they would increase the salinity as well over time.. however with LR & LS coming into favour there is little of no need to do this anymore, infact I am pretty sure this form of cycling marine tanks is not really done anymore among marine fishkeepers as there is really no need.
Muz