We are now moving into the Lower Intertidal zone. Algae dominates this zone. Marine algae, or seaweeds, can be found in patches among barnacles and mussels of the mid-intertidal zone and in some areas the brown algae can extend as far up as the black zone eliminating all other zones, as shown in image on the right. In general though, they begin to form a distinct band below the barnacles. Zonation patterns of algae are governed by exposure to the tide and wave impact, as well as by species interactions such as grazing by invertebrates, and competition for space and light.

You'll notice as you study the intertidal, the seaweeds are found in three primary colors: red, green and brown.The two major groups found here in the lower intertidal are the brown and red seaweeds.