Intertidal reef habitats are also very common in the Southern Waters although they have a relatively narrow range due to the small tidal amplitude of the Straits of Gibraltar and Mediterranean Sea generally. This rarely exceeds 1m with the exception of spring tides. However, this narrow strip of habitat is still extremely important and supports a wide variety of marine organisms including protected species as the Mediterranean ribbed limpet Patella ferruginea, Cymbula safiana, Cystoseira spp., date mussels Lithophaga lithophaga and Lithophyllum spp. amongst other species. The Mediterranean ribbed limpet sub-populations found within the Gibraltar Marine Reserve, including the Southern Waters of Gibraltar, are the largest remnant populations of this critically endangered species in the entirety of the Iberian Peninsula.