Observation published in the Aquatic Invasions Journal:

Chícharo MA, Leitão T, Range P, Gutierrez C, Morales J, Morais P, Chícharo L (2009). Alien species in the Guadiana Estuary (SE-Portugal/SW-Spain): Blackfordia virginica (Cnidaria, Hydrozoa) and Palaemon macrodactylus (Crustacea, Decapoda): potential impacts and mitigation measures. Aquat. Invasions 4: 501-506.