The high vegetable biodiversity is associated with an abundance of fauna that is one of the notable aspects of the Ria Formosa, especially the avifauna, which includes numerous species considered threatened, one of the main interests of nature conservation.
Many species of migratory waterfowl from northern Europe spend the winter here or use the Ria Formosa as a stopover on their route to more southern areas. Among the most important wintering wildfowl species, the Teal Anas crecca and the Pochard Aythya ferina can be highlighted. Of the waders, we can highlight the Grey Plover Pluvialis squatarola, and the Avocet Recurvirostra avosetta.
The Swamp-hen or Purple Gallinule (Porphyrio porphyrio), an emblematic specie of the Park, deserves to be highlighted. Due to the increased protection and study of this species, its population numbers have increased in recent years.
The Iberian Magpie (Cianopica cooki) colony is also worthy of mention, the Kingfisher (Aldo atthis) also resident; and the population of Flamingo (Phoenicopterus roseus). The population of the Little Tern (Sternula albifrons), a species in decline in Europe, breeds in the dunes and salt flats of the Ria Formosa.
The benthic communities range from clearly marine species to others belonging to the lagoon system and have extremely numerous populations. Some of which are of economic interest, such as the Clam (Ruditapes decussatus), the Cockle (Cerastoderma edule) and the Razor Clam (Ensis siliqua).
Of the ichthyofauna, 65 species of fish have been identified, which are divided into sedentary, occasional and migratory-colonizing; among these, the ones of greatest economic interest are the Gilt-head bream (Sparus aurata), the White Seabream (Diplodus sargus), the Sea bass (Dicentratus labrax), the Senegalese sole (Solea senegalensis) and the European eel (Anguilla Anguilla).
The Chameleon (Chamaeleo chamaeleon), is one of the reptiles of this ecosystem. It is an endangered species whose distribution in Portugal is confined to the coast of Sotavento do Algarve, in the pine forests of the mainland coast and in the barrier islands.
Of the existing mammals, the Otter Lutra lutra, the Mongoose (Herpestes ichneumon), the Genet (Genetta genetta), and the Beach marten (Martes foina) can be highlighted.
Although the conditions in the Ria Formosa Nature Park are very unfavourable to the survival of insects due to the almost complete absence of freshwater courses, there are insects in the region that adapt to local adversities, such as the Clouded yellow (Colias croceus) butterfly and the Swallowtail (Papilio machaon) butterfly as examples of Lepidoptera. As examples of Odonatas we can highlight the Banded Dragonfly Brachythemis impartita and the Algarve Dragonfly (Selysiothemis nigra). The Beach beatle (Erodius tibialis), and the Sand beetle (Scarites Cyclops) are examples of Coleoptera.