Reefs are underwater rocky areas with high biological diversity which may range from the intertidal to great depths. In shallow areas (up to 30 m depth), reefs are characterized by large proportions of algae that cover most of the available space, especially during the sunny months. Here many species of fish find refuge and food. In the deeper areas, where light does not penetrate, the communities are very different and are dominated by animal communities. Unusual species of sponges, gorgonians and cold water corals, create landscapes of rare beauty.