top of page

Invasive species are defined as those that establish themselves in places outside their native range where they evolved, and that cause negative effects on native species . A non-native species only becomes classified as invasive, when it is proven that it causes negative effects in the area where it was introduced, which may be environmental or economic impacts. The existence of studies that prove these impacts in other invaded areas, may be sufficient for a species to be classified as invasive in a new location.


Species: Callinectes sapidus (blue crab)

Description: native to the Western Atlantic coasts, it was first detected in the Algarve in 2016 in Ria Formosa. Its a crab of the Portunidae family that can reach close to 30 cm (carapace width) and weigh 900 grams. Easily identifiable by the blue color in the claws and paws. Mature females have a red color at the tips of the claws.

Records in the Algarve: see here.

Guadiana, September 2019. Photo: João Encarnação

C. regalis.jpg

Guadiana, June 2016. Photos: Pedro Morais

Species: Cynoscion regalis (weakfish; American meagre)

Description: originating from the East coast of the USA, it was first detected in the Algarve in 2016 in the Guadiana estuary. Fish of the family Sciaenidae that can reach close to 1 m in length and 9 kg in weight. Easily distinguishable by its pigmentation on the dorsal area and yellowish color on some fins. Hardly mistaken with the native meagre (Argyrosomus regius). However, it can be confused with the spotted seabass (Dicentrarchus punctatus).

Records in the Algarve: see here.


Species: Blackfordia virginica (Black Sea jellyfish; blackfordia)

Description: native to the Black Sea, it was first detected in the Algarve in 2008 in the Guadiana estuary. Jellyfish from the family Blackfordiidae, due to their small dimensions, usually with a maximum diameter of 1 cm, may not be easily detected without the proper sampling equipment. Densities in the order of 30 ind/m3 have already been recorded in the Guadiana.

Records in the Algarve: see here.

Guadiana, July 2008. Photo: Pedro Range


Guadiana, October 2020. Photo: João Encarnação

Species: Palaemon macrodactylus

Description : originating in Asia (Japan, Korea, China), it was first detected in the Algarve in 2008 in the Guadiana estuary. Shrimp of the Palaemonidae family that reaches a maximum of 7 cm, with high osmoregulation capacity, managing to occupy areas with salinity between 1 and 36 PSU.

Easily confused with other native species, such as Palaemon longirostris or Palaemon elegans . This distinction between species is only possible by observing the number of spines in the rostrum and the number of rows of branches in the ventral area of ​​the rostum, which can only be done correctly with the aid of a magnifying glass.

They usually display a lighter longitudinal line.

Records in the Algarve: see here.


Lagoa de Albufeira (Setúbal), March 2024.

Photo: Miguel Cidade

Species: Chinese mitten crab (Eriocheir sinensis)

Description: species easily identifiable by its hairy-looking pincers. It is a euryhaline species capable of withstanding large variations in environmental parameters, namely salinity. It has a catadromous life cycle, that is, it reproduces in brackish waters, and when they reach the juvenile stage, they begin to migrate upstream in estuaries and rivers, spending most of their life cycle in freshwater, returning later to estuaries to reproduce.

Records in the Algarve: see here (no observations).

......more species soon......

bottom of page