Timber Mould — what is it and how can I fix it?
Keeping timber clean is the first step in preventing and controlling mould.

Mould and algae are common growths on all timber, treated or otherwise. It is common to see black mould on outdoor timber such as fencing, decking, and other exterior timbers. It is important to remember that they do not penetrate the wood structure and are purely an aesthetic issue, unrelated to wood decay. 

Pukepine Decking Installatation Guide
Radiata Pine Griptread Decking