[Factor] Currents [Living on the land] Do not apply. Air is light and although some creatures can fly, they must eventually rest. The air is not filled with food, like the sea. [Living in the sea] 
The water makes creatures float. It fills the water with food. Currents push this food past filter-feeding organisms that sit on rocks. Currents are very important for distributing food and nutrients and for transporting mud from the coast. Eggs and larvae are transported easily and far.