The robust poste sia(囊沟藻) inhabits parts of the shore that are also occupied by barnacles and mussels. Small Poste/sia have been seen growing firmly attached to barnacles. When they reach a certain size the increased drag causes the seaweed, together with the attached barnacle, to be ripped from the rock surface The bare area of rock is immediately colonised by Poste sia sporesThe robust Postelsia(囊沟藻) inhabits parts of the shore that are also occupied by barnacles and mussels. Small Postelsia have been seen growing firmly attached to barnacles. When they reach a certain size, the increased drag causes the seaweed, together with the attached barnacle, to be ripped from the rock surface. The bare area of rock is immediately colonised by Postelsia spores