It seems like such an ancient practice but it wasn’t more than 35-40 years ago that lobstermen used wooden buoys to mark their lobster traps. Although initially buoyant, the wood would eventually absorb water, get heavy and sink if not swapped out with fresh buoys a few times a year.
These were replaced by Styrofoam buoys, which were referred to as “popcorn” buoys. I never really knew why until I witnessed one getting run over by a boat and basically exploding into tiny pieces that resembled popcorn. Those were also replaced by the modern buoys we use now which are a composite plastic foam and much more durable and these old wooden sentinels are left to serve out their life as ornaments.