The weight of plant growth per square metre that is added in one year is a measure of productivity. Shallows like this can produce twice as much plant growth as an average farm field. Alas, acres of seaweed, march grasses and diatoms submerged beneath the sea tend to go unnoticed. In the fall, plants that have not been eaten, die and settle to the bottom. Then, bacteria take over and begin the decay process.
Oxygen penetrates only the top few centimetres of mud.
As these small molecules seep upward towards the surface, other types of bacteria oxidize them as an energy source. One study estimated up to 17 billion bacteria per cubic centimetre live in the surface layers of this organic mud. Without them, dead animals and plants would not decompose into simple compounds that can be used by other organisms. The system would come to a grinding halt, as few of the nutrients locked up in plants would become available. Nematode worms feast on these swarms of bacteria.