High tide pools tend to be lower in species diversity than those lower in the intertidal. Green algae are often the dominant type of algae in upper tide pools. This tide pool illustrates how dominant a single celled green algae can be under the right conditions. This pool also happens to be well fertilized with sea gull droppings. Note the lichen growing on the rocks around the tide pool.This single celled green alga is tolerant of temperature and salinity extremes and thrives where conditions are too unstable for snails and other grazers to eat them.