Dhelmise, contrary to what you would think, is not the anchor, but the algae/seaweed. It merely controls the anchor, using it as a weapon.
Source: The PokéDex:
Swinging its massive anchor, it can KO Wailord in a single blow. What appears to be green seaweed is actually its body.
The soul of seaweed adrift in the waves became reborn as this Pokémon. It maintains itself with new infusions of seabed detritus and seaweed.