Coconut seeds disperse by action of the ocean waves and by being deliberately planted by human beings. The coconut seed, which is technically a drupe, is one of the largest seeds. It's too large to be eaten by birds or other animals and then deposited through the animal's droppings.
Coconuts are also too heavy to be dispersed by winds of normal strength. Thus, a coconut falls from the coconut palm, rolls down to the sea and is picked up by the waves. Since it's buoyant, the seed can be carried far away and deposited on another shore to germinate. Humans help this process by gathering coconuts and planting them.