Asked by: BBC Focus Magazine
It depends on the temperature of the water. In cold water, the bacterial action that causes a body to bloat with gas may be so slowed that the body stays on the seabed. The skin will absorb water and peel away from the underlying tissues in about a week and fish, crabs and sea lice will nibble away at the flesh.
Cold water also encourages the formation of adipocere. This is a waxy, soapy substance formed from the fat in the body that partially protects the body against decomposition. Bodies have been retrieved almost completely intact from waters below 7°C after several weeks, and as recognisable skeletons after five years.
In tropical waters such as the Arabian sea, it’s a different story. Even a weighted body will normally float to the surface after three or four days, exposing it to sea birds and buffeting from the waves. Putrefaction and scavenging creatures will dismember the corpse in a week or two and the bones will sink to the seabed. There they may be slowly buried by marine silt or broken down further over months or years, depending on the acidity of the water.