foul·ing nounan encrusted deposit, especially on a submerged object, as the hull of a ship. Definition of fouling organism:any of various aquatic organisms with free-swimming larvae and sedentary adult stages that cause fouling of ships and underwater structures Mussels lay millions of eggs in the spring. The larva first drift freely as plankton and attach themselves to a suitable spot, as long as they haven't been eaten beforehand. After growing into a small mussel of one to two centimeters, they are referred to as mussel seed, or spat. Mussel fishermen fish this seed up from the tidal flats and place them on plots where the mussels can grow further. Fishing up mussel seed damages nature on the tidal floor. That is why more and more mussel seed is being cultivated on hanging nets, also known as mussel seed capture installations.