Gracilaria vermiculophylla, a red macroalga from the West Pacific, was discovered in western Germany (the Wadden Sea) in 2002 and has since also been observed in Sweden (from about 70 km south to about 80 km north of Göteborg), Denmark (Wadden Sea, Horsens Fjord, Limfjorden, Vejle Fjord, Holckenhavn Fjord, Øster Hurup Harbor) and eastern Germany (Kiel Bay). Today, less than 5 years following its first observation in the Wadden Sea the invader is common in many invaded regions, often being amongst the most abundant macroalgal species. G. vermiculophylla is successful in shallow protected soft-bottom estuaries and bays, typically in association with ubiquitous native invertebrates (lugworms, tube-building worms, mussels, cockles, snails). The invertebrates provide substratum for holdfast attachment and thalli incorporation, most likely increasing the stability of local G. vermiculophylla populations. We hypothesize that this substratum provision is highly important for its general invasion success. We also confirm that G. vermiculophylla can maintain growth at all salinities experienced along Danish coastlines (8.5-34 psu). In addition, laboratory experiments indicate that the ubiquitous grazer Littorina littorea has the potential to control G. vermiculophylla growth under specific environmental conditions, but also that L. littorea may facilitate small-scale dispersal within invaded locations, because grazing increases thalli fragmentation rates. Given its widespread distribution, rapid range expansion, and known ecological traits, G. vermiculophylla is clearly a permanent resident of northern European waters.

The Red Sea mollusc Chrysallida fischeri (Hornung and Mermod, 1925) was collected in 2005 off Makri, Rhodes, Greece. This is the first record of the species in the Aegean Sea. The presence of both live specimens and shells suggest that C. fischeri is well established in the area.

Among numerous recently introduced species in Serbian waters, two new mussel taxa were detected. The aim of this paper is to present the current distribution of two morphotypes of the Asiatic clam - Corbicula fluminea (Müller, 1774) and C. fluminalis (Müller, 1774), in order to discuss pathways of dispersal and reasons for successful adaptation. According to our results, the morphotype C. fluminea is better adapted to local environmental conditions, while C. fluminalis has rarely been found in Serbia. At present, Asiatic clams are widespread within potamon-type rivers that are under the influence of hydromorphological alterations and exposed to intensive ship traffic. The distribution of Corbicula, as well as some other alien aquatic invertebrate taxa (Branchiura sowerbyi, Anodonta woodiana, Orconectes limosus), indicate that heavily modified waterways are suitable recipient areas for species introduction and adaptation. Corbicula gen. sp. is a characteristic taxa for Pleistocene interglacial deposits in the Pannonian Plain. The comparison between Pleistocene and recent taxa is necessary in order to categorize Corbicula as either introduced or reintroduced taxa.

A major problem in evaluating biological invasions is the lack of information on failed non-native species introductions, with invasiveness determined purely on establishment successes. This is the case of topmouth gudgeon Pseudorasbora parva, an Asiatic cyprinid fish that now occurs throughout most of Europe and is said to be highly invasive. Although the species has established itself in many locations, and often in high densities, not all topmouth gudgeon invasions are successful. In this brief communication, the appearance and disappearance (following pond drain down and repeated electrofishing depletion) of topmouth gudgeon Pseudorasbora parva from a small pond in northeast London (England) is described, along with two other cases elsewhere in Europe.

An increased number of reports (by anglers, in the angling press) of European (wels) catfish Silurus glanis occurrences in the River Thames (England) has led to the perception that the species has become more abundant in that river. If proved true, then this would have ramifications for non-native species policy and practice. To assess catfish density, a total of 256 rod hours of specialized angling (‘clonking’) was undertaken during both day and night between 17 and 21 July 2006 at numerous sites within six sectors of the River Thames. No European catfish were captured, which suggests that European catfish remains a rare species in the River Thames, providing no corroboration of anecdotal reports of increased abundance.

Changes in the relative density (catch per unit effort; CPUE) of introduced gibel carp Carassius gibelio (Bloch, 1782) and native fish species were monitored over four years in the Ömerli Reservoir, a temperate drinking-water reservoir in northwestern Turkey. Following the species’ introduction, the CPUE of gibel carp increased significantly with the decrease in CPUE of large-bodied native fish species.

Anthropogenic biological invasions are a leading threat to aquatic biodiversity in marine, estuarine, and freshwater ecosystems worldwide. Ballast water discharged from transoceanic ships is commonly believed to be the dominant pathway for species introduction and is therefore increasingly subject to domestic and international regulation. However, compared to species introductions from ballast, translocation by biofouling of ships’ exposed surfaces has been poorly quantified. We report translocation of species by a transoceanic bulk carrier intercepted in the North American Great Lakes in fall 2001. We collected 944 individuals of at least 74 distinct freshwater and marine taxa. Eight of 29 taxa identified to species have never been observed in the Great Lakes. Employing five different statistical techniques, we estimated that the biofouling community of this ship comprised from 100 to 200 species. These findings adjust upward by an order of magnitude the number of species collected from a single ship. Thus, overall invasion risk from biofouling may be comparable or exceed that of ballast water discharge.

During summer 2006, the first specimens of the oriental shrimp Palaemon macrodactylus Rathbun, 1902 were identified in the Gironde Estuary (France). These specimens, which included ovigerous females, are confirmed present throughout a large part of the estuary, in large numbers compared to the local resident shrimp Palaemon longirostris Milne Edwards, 1837. Native to Asia, P. macrodactylus was first introduced in California (USA) in the 1950s, before being detected recently within several European estuaries, e.g. the Guadalquivir Estuary (Spain) and the Orwell Estuary (England). According to these records, P. macrodactylus appears to be a strong invader, able to colonise a wide geographical range.

In autumn 2006 the first observations of the West Atlantic comb jelly Mnemiopsis leidyi in Northern Europe were reported from the North Sea, the Skagerrak and the south-western Baltic Sea. Here we report on the further spread of this invasive ctenophore from the south-western towards the central Baltic Sea up to the south eastern Gotland Basin during autumn/winter 2006 and spring 2007. The abundances were generally low (max. 4 ind. m^-3). While M. leidyi was located in the entire water column in Kiel Bight, it was found exceptionally below the halocline in the deep stratified central Baltic basins. Data of a weekly sampling program at a near shore sampling location in Mecklenburg Bight between January and May 2007 showed that up to 80 % of the individuals were juveniles, smaller than 1 mm total body length and that M. leidyi survived the winter in the Southern Baltic Sea, even if abundances dropped down to <1 ind. m^-3 in February. A first assessment of the physiological demands of this species versus the environmental conditions of the Baltic Sea showed that the successful establishment of this ctenophore is probable in the south-western and central Baltic Sea.

The North American centrarchid species, Lepomis gibbosus (Linnaeus, 1758), is a freshwater fish native to eastern and central North America. The species is now established in at least 28 countries of Europe and in Turkey the species’ spread has been especially rapid between 2001 and 2006, with its distribution including the following areas: Kemer Reservoir, Akçay river catchment and inland waters of the Aegean and Anatolian regions. This is the first report in a new locality of the species in Asia Minor.

The Ponto-Caspian snail Lithoglyphus naticoides was recorded for the first time in Lake Lukomskoe in 2003. During parasitological examinations conducted in May and August 2006, the snail was found to harbor cercariae of three trematode species: Palaeorchis sp., Rossicotrema donicum and Sphaerostomum bramae. The finding of R. donicum is especially alarming because this highly specific parasite of L. naticoides can cause severe epizootics among its second intermediate hosts, i.e. perch and cyprinid fishes.

The Lessepsian invasive fish Etrumeus teres was recorded for the first time off Crete, Greece in July 2005. Their abundance suggests that the species may become of commercial importance in the south Aegean Sea.