Filter feeders which live on flotsam - objects that float in the sea. Depend on water movement for feeding rather than their cirri.
The surface of the ocean
This picture shows a conservationist's dilemma. These barnacles are living on a plastic bottle which is clearly waste. Does one throw the bottle back, and thus littering and adding to the vast amount of plastic already found in the ocean, or do you recycle the bottle, but in the process kill the barnacles?! Barnacles have a very strong glue which they use to stay attached to different types of substrate. It is very difficult to remove them, and even if one were to do so successfully and without injuring them, it is not sure that they would then be able to reattached themselves to a new substrate.