Rack [rack culture] and bag culture method: (...) Growers have experimented with hanging bags such as these in deep water. Spat bags with 2-3mm or larger clam or oyster seed can be put into these larger bags which can then be strung in "stacks" by using short PVC spacers between each bag to allow for water circulation. This type of system requires increased maintenance. If it is allowed to foul up, water flow will be reduced, and in circumstances where there are mussel sets, the byssus threads can entangle seed, spat bag and outer bag so that removing seed for grading becomes a slow and difficult process.