Alien amphipods (Arthopoda; Crustacea) in the Tista Estuary, Halden, southeastern Norway

Two new amphipods for Norway Melita nitida and Corophium multisetosum (Crustacea; Amphipoda) were registered in brackish waters in the Tista Estuary in Halden, southeastern Norway. Both species were found in the samples from Tista’s outlet into the Idde Fjord, C. multisetosum in the beach zone and M. nitida at about 4 m depth. Melita nitida is a North American species first found in Europe in the Netherlands in 1998, and since then dispersed into the Baltic Sea via the Kiel Canal and now also found several places on the German Baltic Sea coast and in the Black Sea. Corophium multisetosum was collected even before the 1920s in Western Europe, and is considered native for Europe, whereas its relationship to North America is more ambiguous. From the British Isles and the Netherlands, it seems to have spread to Germany, Poland, Denmark and Sweden, and at present Norway. Until now the two species were found in small numbers at the Norwegian sites and their influence on the total benthic community is probably negligible in this initial phase. The Tista Estuary in Halden apparently appears to be a hotspot for alien brackish water species in Norway. Generally estuaries, with their combination of brackish water jointly with their unsaturated ecological niches and intensive international ship traffic, seem to possess the highest potential infection rate for aquatic systems with alien acrozoobenthic species.

Contrasting morphological and DNA barcode-suggested species boundaries among shallow-water amphipod fauna from the southern European Atlantic coast

In this study we compared DNA barcode-suggested species boundaries with morphology-based species identifications in the amphipod fauna of the southern European Atlantic coast. DNA sequences of the cytochrome c oxidase subunit I barcode region (COI-5P) were generated for 43 morphospecies (178 specimens) collected along the Portuguese coast which, together with publicly available COI-5P sequences, produced a final dataset comprising 68 morphospecies and 295 sequences. Seventy-five BINs (Barcode Index Numbers) were assigned to these morphospecies, of which 48 were concordant (i.e., 1 BIN = 1 species), 8 were taxonomically discordant, and 19 were singletons. Twelve species had matching sequences (<2% distance) with conspecifics from distant locations (e.g., North Sea). Seven morphospecies were assigned to multiple, and highly divergent, BINs, including specimens of Corophium multisetosum (18% divergence) and Dexamine spiniventris (16% divergence), which originated from sampling locations on the west coast of Portugal (only about 36 and 250 km apart, respectively). We also found deep divergence (4%–22%) among specimens of seven species from Portugal compared to those from the North Sea and Italy. The detection of evolutionarily meaningful divergence among populations of several amphipod species from southern Europe reinforces the need for a comprehensive re-assessment of the diversity of this faunal group.

Is Corophium Multisetosum Stock, 1952 an Exotic Invasive Species in Europe? Distribution, Habitat, and Recent Observations in the Netherlands

Corophium multisetosum Stock, 1952 has been found in several estuaries and water bodies in Europe ranging from fresh and brackish to salt water. The species appeared to be distributed over a wide geographic range from the Iberian Peninsula to the southern Baltic region and is recently found in the Mediterranean and Gulf of Mexico, showing remarkable differences in ecology between populations. The recorded observations of the species in the Netherlands, however, remained restricted to a few smaller waters, and were published in grey literature. Recently, the species has been observed in a variety of waters in the southwestern part of the Netherlands and appears to be relatively common. The current study gives an overview of the recordings of C. multisetosum within its geographic range and its habitat preferences. The recent observations on distribution and habitat preferences of C. multisetosum in the Netherlands are compared with the findings in other parts of Europe. Seeming discontinuities in recorded ecology of the species in the Netherlands and over Europe are discussed. C. multisetosum appears to be very flexible in its behaviour and appears to tolerate a broad range of environmental conditions. Local environmental conditions (e.g., salinity and substrate) and related communities (in the Netherlands particularly the presence of the seemingly competing species Corophium volutator (Pallas, 1766) and Chelicorophium curvispinum (G. O. Sars, 1895)) determine the presence of C. multisetosum and the local behaviour and abundance of the species in the system. As the species shows a typical distribution pattern with many recent recordings, its origin and possible dispersal routes are discussed.

Crustacean assemblages along the Guadiana River estuary (south-western Iberian Peninsula)

The spatial distribution of the subtidal crustacean assemblages of the Guadiana River estuary was studied previous to the building of the Alqueva Dam (the biggest dam in Europe). The differences between an estuarine and marine environment seem to be the main reason responsible for the composition and distribution of the crustaceans along the study zone. The Guadiana estuary has shown high number of species in comparison with other nearby estuaries and this richness seems justified by the scarce influence of pollutants (most of them have shown low or moderate values) and their hydrodynamic and granulometric characteristics (76 species were found, 39 in the estuarine area). A gradient of enrichment and structuring of the assemblages was shown from the upstream to the marine zones and a spatial segregation of species was found along this estuarine environmental gradient, e.g. the amphipod Corophium multisetosum and the isopod Cyathura carinata in the upper estuary; the amphipod Bathyporeia cf. pilosa and the isopods Lekanesphera levii and Saduriella losadoi in the middle estuary; the amphipod Melita hergensis in the mouth; and a high number of species in the marine area. Since the Alqueva Dam will reduce the river discharges and may cause changes in the abiotic characteristics such as granulometry of sediments or salinity, this study establishes a baseline against which a monitoring programme or follow-up studies could measure any significant effects of the dam or related impacts.