Hydrozoans (Cnidaria) from the estuarine zone of the International Minho River, NW Iberian Peninsula, Atlantic Europe

In environmental impact studies conducted in coastal regions, the survey of biodiversity is crucial in areas that are subject to interventions. As the characterization of aquatic invertebrates may indicate important issues that need to be addressed. In this regard, hydrozoans (Class Hydrozoa, Phylum Cnidaria) are recognised as important bioindicators. These organisms are characterized by biradial, tetramerous, or polymerous symmetry, a simple gastrovascular system, and non-cellular mesoglea. The aim of the present study was to perform the first descriptive survey of hydrozoan species found in the estuary of the International Minho River (shared by Portugal and Spain), which is classified as an Important Bird Area and is a site of the Natura 2000 network. Specimens were collected from the tidal marine, brackish and tidal freshwater wetland zones through 1) glass eel fishing bycatch using stow nets at flood tides around the new moon (length of float lines: 10 m; bottom anchored lead line: 15 m; height: 8 m; mesh size: 1–2 mm); 2) beam trawl fishing (bottom trawling for 10 min), including species associated with bivalves; 3) Van Veen grab sampler for sediment sampling; 4) on wood fragments in the saltmarsh of the Coura River (tributary of the Minho River); and 5) individuals on the leaves of aquatic plants. A total of 19 species were identified, four of which were first occurrences for Portugal, six for the mainland coast of the country, and one for Southern Europe [ Diphasia fallax (Johnston, 1847)]. Three neotypes are also proposed for the species Hydra viridissima , Hydra oligactis and Gymnangium montagui based on the criteria of the International Commission on Zoological Nomenclature. As these organisms are considered bioindicators, the diversity of the hydrozoan community in the Minho River may indicate good water quality.