Two specimens of an unknown jellyfish species were collected in Bat Gallim and Beit Yannai, on the Mediterranean coast of Israel, in June and July 2010. Morphological characters identified it as a cepheid (Cnidaria, Scyphozoa, Rhizostomeae). However, the specimens showed remarkable differences from other cepheid genera; unlike Cephea and Netrostoma it lacks warts or knobs centrally on the exumbrella and filaments on oral disk and between mouths, and it differs from Cotylorhiza in its proximally loose anastomosed radial canals and in lacking stalked suckers and filaments on the moutharms. We thus describe it herein as Marivagia stellata gen. et sp. nov. We also present the results of our molecular analysis based on mitochondrial cytochrome oxidase I (COI), which support its placement among the Cepheidae and provide its barcode signature. This new find is the fourth introduced scyphozoan species recorded in the Mediterranean. The presence of a sexually mature specimen collected as far back as 2006, and the occurrence of the species this summer at sites nearly 90 kms apart, indicate the existence of an established population.

Relatively few studies have aimed to test if invasive species have positive effects on native species, for example via formation of habitat or by amelioration of environmental stress-conditions. The red macroalga Gracilaria vermiculophylla, from the West Pacific, is invading estuarine mudflat and seagrass habitats along East Pacific and East and West Atlantic coastlines. I tested if low (55-110 g WW m^-2) and high (220-440 g WW m^-2) densities of G. vermiculophylla have positive or negative effects on the macroinvertebrates (> 2 mm) that inhabit Zostera marina seagrass beds. The experiment was conducted over 34 days at both 0.5 and 2 m depth at Snaptun Harbor, Denmark. I found positive effects of Gracilaria on most invertebrates, with statistically significant results for “all invertebrates”, “gastropods”, and “bivalves”, and a near-significant result for “crustaceans”. Both quantitative and qualitative habitat-resource models may explain these positive effects; i.e. “more habitats” exist in the presence of Gracilaria and/or the “habitat differs” between Gracilaria and Zostera vegetation. Future studies should test these two general explanatory models and quantify (a) if density thresholds exists were effects shift from positive to negative, (b) specific mechanism whereby positive effects occur, (c) if Gracilaria provide a novel or substitute drift algal habitat, and (d) the larger-scale ecosystem implications of this invasion.

The population dynamics of the invasive ctenophore Mnemiopsis leidyi, which showed mass occurrence in Kerteminde Fjord (Denmark) for the first time in 2007, and the indigenous common jellyfish, Aurelia aurita, was followed in the fjord system Kerteminde Fjord/Kertinge Nor during late 2008 and 2009. The population density of A. aurita was always highest in Kertinge Nor while the density of M. leidyi was always highest in Kerteminde Fjord, indicating recruitment of the ctenophore from the adjacent sea (Great Belt). In the shallow cove of Kertinge Nor, the first A. aurita ephyrae appeared in March, by the end of May the medusae had obtained their maximum umbrella diameter of only 30 mm due to food limitation, and the estimated half-life of zooplankton was very low, <1 day from May to September 2009. The high predation impact explains why the holopelagic ctenophore, which presumably survives the winter in the adjacent open sea, is likely to be outcompeted in Kertinge Nor where the polyp stage of A. aurita every spring ensures a very large population of very small medusae. The population density of jellyfish, in Kertinge Nor, during the summer period is dependent on the extend of flush-out due to density-driven water exchange. A survey of data obtained every year in August since 1991 indicates that the unusually high population density (36 ± 34 ind. m^-3) and the small umbrella diameter (56 ± 5 mm) of A. aurita have remained unchanged during the last 20 years, and further, that a relatively high population density of jellyfish in certain years is correlated with a relatively small mean umbrella diameter.

Clearance rates of small (about 12 mm oral-aboral length) Mnemiopsis leidyi were measured by means of the ingestion-rate method in order to compare with rates estimated from an equation (derived from Decker et al. 2004) used in previous studies. About 3 times higher clearance rates measured in the present study indicate that the estimated predation impact of small ctenophores may previously have been considerably underestimated. The prey-capture efficiency measured in M. leidyi depends on type and size of prey organism, and the study indicates that the clearance of slow swimming prey (e.g. mussel larvae) captured by auricular flow fields is higher than the clearance of fast swimming/jumping prey (copepods) captured by the lobes. The ingestion-rate method presented may open up not only more precise measurements of clearance rates, but also provide for digestion rates of M. leidyi offered different types of prey organisms.

This report documents the first recording of the solitary ascidian Ciona savignyi in the Southern Hemisphere. Adult tunicate specimens were collected from the Nelson city marina (South Island, New Zealand) in April 2010. Both mitochondrial cytochrome oxidase I (COI) gene sequences and morphological characters were used to identify the tunicates as C. savignyi – the first report of this species in New Zealand and the Southern Hemisphere. This study highlights the power of molecular methods for invasive species identification and New Zealand’s need for an extensive, systematic molecular inventory of its existing marine invertebrate biodiversity.

The small brooding ascidian Molgula citrina Alder and Hancock, 1848 has long been known as a common inhabitant of shallow waters on both sides of the north Atlantic on subtidal natural hard substrates and also as a fouler of floating docks. There are published records from the White Sea (NW Russia), but none from the north Pacific. In May and August 2008, a number of adult brooding Molgula sp. specimens were collected from floating docks at the small fishing village of Seldovia on the Kenai Peninsula at Kachemak Bay, Alaska. Morphologically these individuals exactly match Atlantic specimens of Molgula citrina in all characters that were examined. The unique constellation of characters for this species differentiates it from all other Molgula species, as noted by Van Name (1945). In addition, the full-length 18S and 28S rDNA sequences are identical for both the Alaska specimens and New England M. citrina. Is this a new invasion, or is M. citrina a northern circumpolar species that was somehow overlooked? If this new record indicates a natural distribution, why has it not been collected before? If it is a recent introduction, it is unlikely that M. citrina, an inhabitant of cold waters, could survive in sea chests of ships from the N. Atlantic arriving in Alaska via the Panama Canal, but the intriguing idea exists of transport from Atlantic to Pacific through the Northwest or Northeast Passages. As global warming diminishes the ice cover in this region, more and more ships are traversing the Northwest Passage across northern Canada as well as the NE Passage across northern Russia, representing significant new routes for anthropogenic transport of marine species. The tadpoles of this small brooder are retained for some time after hatching, resulting in an extremely short free larval life, but could survive as metamorphosed juveniles attached in sea chests or free-floating in ballast water. They have a wide temperature tolerance and once they metamorphose can live free-floating in sea water for some time. They become very sticky and will ultimately stick to whatever they contact. Thus they could conceivably live for many generations in sea chests and sustain a viable population from which to invade new habitats.

Mortality of zebra mussel, Dreissena polymorpha, larvae was quantified in a laboratory experiment that was designed to assess the role played by both intensity and duration of the exposure to hydrodynamic forces. Larvae were collected in a plankton net and distributed in 100-ml aliquots to 125-ml Erlenmeyer flasks. The flasks were spun on an orbital shaker at different speeds, 100 rpm and 400 rpm, to change the intensity of the hydrodynamic forces experienced by larvae inside the flasks. Actual shear forces were not quantified. A parallel set of control flasks were not spun. Flasks were spun for 1, 24 and 48 hours. Mortality was highest in the 400 rpm, 48-h trial. Both intensity and duration were highly significant variables in the ANOVA model (p<0.001). However, the interaction term was also highly significant (p<0.001). Larval mortality was significantly higher in the treatments than in the non-spun flasks in only the 400 rpm, 24-h and 400 rpm, 48-h trials. Thus, longer duration of exposure to high intensity hydrodynamic forces increases larval mortality. These results help explain natural recruitment patterns of zebra mussels in natural streams and may be of interest to management and conservation efforts.

Single specimens of the Chinese mitten crab, Eriocheir sinensis H. Milne Edwards, 1853, have been regularly reported along the western and eastern coasts of Sweden since the 1930´s. The crab has most likely been brought from overseas via the transfer of ship’s ballast water or secondarily introduced from its key European distribution areas. Since 2001 a sharp increase in the occurrence of the mitten crab has been noticed in Swedish inland waters, but the dispersal routes and distribution of the species into Sweden remain poorly known. Here we document the current and historical distribution of the Chinese mitten crab in Sweden and assess possible invasion routes. A special focus is put on the historical occurrence of crabs in Lake Vänern, which empties into the Skagerrak/North Sea and Lake Mälaren, which connects to the Baltic Sea. The existing time series available for the mitten crab from the two lakes shows a large variation in dispersal pattern between different areas within each lake. In order to detect and monitor outbreaks of the mitten crab in Sweden, an internet based reporting system was created in 2007. Museum collections and reports from the general public throughout Sweden were compared with the known occurrence of mitten crabs in Lake Vänern and Lake Mälaren. During the study, the web-based reporting system was not advertised and the general public did not get paid for reporting the information. Population densities of the crab occurred “in peaks” and unevenly over the last decade in both lakes, suggesting a pulse invasion instead of a constant supply by migration. Significant difference in male and female occurrence together with few transport possibilities between lakes suggests different invasion routes for the crabs. Reports from the general public throughout Sweden coincide with the observations from local fishermen in Lake Mälaren and Lake Vänern. Data on occurrence and abundance are discussed in relation to a potential reproduction area on the western coast of Sweden.

A cambarid specimen was collected in a brook in Saxony (south-east Germany). Preliminary morphological inspection identified it as the parthenogenetic Marmorkrebs (Decapoda, Astacida, Cambaridae). However, this individual showed some striking morphological differences compared to specimens of our laboratory Marmorkrebs culture. Hence, we conducted a molecular analysis based on two mitochondrial genes, COI and 12S, to check its identity. The results of the genetic study verified the initial assumption of a Marmorkrebs identity for the Saxon specimen. Thus, in addition to the two indigenous species, the new find is the fourth recorded introduced crayfish species in this area. However, a search for further Marmorkrebs specimens at the same site was not successful. Most published records of Marmorkrebs in European waters concern just single individuals and an established population has so far not been observed. This stands in contrast to other recently introduced cambarid species. Thus, we critically discuss the potential of the Marmorkrebs to spread within Europe. The major obstacle may be that the temperature necessary for optimal development and reproduction of the Marmorkrebs is significantly higher than that found in most European waters. However, given globally increasing temperatures, this might change in the future.

Marmorkrebs are one of 12 currently known non-indigenous crayfish species (NICS) to be found in Central European waters. It is unique in the manner that there exist only females which reproduce parthenogenetically, i.e. eggs develop unfertilized and all offspring are genetically identical. Marmorkrebs have been first discovered in the German aquarium trade in the mid 1990s and became a very common pet species since then. Here, we present first evidence for a well established Marmorkrebs population in a small lake in the Upper Rhine catchment near Freiburg (Germany). The population occurs syntopically with Orconectes limosus, another NICS which invaded the Rhine system about 50 years ago. Morphometric and ovary weight measurements were taken from 12 Marmorkrebs specimens that were captured on July 3, 2010. The rostrum spination was pronounced and resembled the one found on a free-living individual captured in Saxony (Germany). Ovary development stages (Gonadosomatic Index) were heterogeneous and single berried females were found from early June to late July, which might indicate an asynchronous breeding habit. The relative abundance and distribution of both crayfish species were assessed by visual counts at nighttime at two occasions. Both species attained a comparable, moderate density throughout the lake margin. The Marmorkrebs was the prevalent species on shallow, swampy habitat patches, which are presumably similar to its natural prime habitats. The successful establishment of Marmorkrebs despite a pre-existing O. limosus population, stresses the competitive ability of Marmorkrebs. In addition to the recently suggested hypothesis that Marmorkrebs might be temperature limited in most parts of Europe, we feel that it is also necessary to consider its probable natural prime habitats and life cycle: Marmorkrebs are presumably able to colonize summer-warm, lentic habitats in most parts of Central Europe.

Introductions of an Asian cyprinid, goldfish Carassius auratus, are known to pose a genetic threat to crucian carp Carassius carassius, which is native to northern parts of central and western Europe, including southeast England. However, there are no known studies in Europe of goldfish impacts on crucian carp growth and life-history traits, nor on the recipient ecosystems. The present study is the first such attempt, and compares the plants, invertebrates and fish biology (growth, condition, reproduction) in six ponds, two containing crucian carp only (allopatry), two containing goldfish only (allopatry), and two with both species (sympatry). Feral goldfish growth was greatest in sympatry with native crucian carp, whereas crucian carp growth was similar regardless of goldfish presence or absence. However, body condition (LK) and relative fecundity (per unit of body weight) of crucian carp was greatest in sympatry with feral goldfish. LK increased significantly with increasing water conductivity in goldfish but not in crucian carp, and LK was not related to pond invertebrate densities in either fish species. Differences in the plant and aquatic invertebrate communities observed in the study ponds could not be attributed to the introduction and establishment of goldfish, however non-native plant and invertebrate species were observed only in ponds containing goldfish. Differences in growth and condition between the two Carassius species does not appear to be due to differences in available food, so elevated somatic growth and reproductive output in crucian carp and faster growth in goldfish in sympatry may be due to non-dietary competitive interactions. The present preliminary study highlights the difficulties of assessing ‘real world’ impacts of non-native species on native species and ecosystems as well as the need for further study of feral goldfish impacts on European pond ecosystems in general and on native congener crucian carp in particular.

A non-native fish, the Yucatan molly Poecilia velifera (Regan, 1914), has recently become established in the Songkhla Lake Basin, south Thailand. Based on our field surveys in December 2007, we conclude that this species is present only in the Haad-kaew Lagoon and the southernmost part of the Songkhla Lagoon, the Thale Sap Songkhla. We sampled P. velifera monthly for 13 months (January 2007-January 2008), using beach seine and cast net, to obtain information on its population structure, morphology and reproduction. It was found that male and female P. velifera became sexually mature at 16.8 and 17.1 mm standard length, respectively. The overall sex ratio of males to females was 1.0:1.8. However, the proportion of males was less within specimens belonging to larger size classes. P. velifera reproduced continuously throughout the year but with two peaks, one in March-May and another in August-December.

Recently, four observations of Marphysa sanguinea (Montagu, 1815) were made in the Eastern Scheldt in the southwestern part of the Netherlands. This is remarkable as this alien species has been found only once in the Netherlands, in 1990 at the North Sea coast. It seems that this large polychaete species, that previously was noted to have a northern distribution limit in the southern North Sea (English southern coast and the French west coast), has established a population in a semi-enclosed Dutch tidal bay. The species may have reached the region via shellfish transport associated with the numerous aquaculture sites in the region. Consequences of the settlement of this large at least partially predatory polychaete species, for the macrozoobenthic communities in this region are unclear. Species of the genus Marphysa are found to be successful in a variety of environments all over the world. So far, no other species of the genus Marphysa has been recorded as present in the Netherlands.

The Ponto-Caspian amphipod Dikerogammarus villosus was found both in the margins and open water areas of Grafham Water, a large reservoir in Cambridgeshire, U.K., in September 2010. Both adults and juveniles were present in large numbers and were most frequent in the boulder/cobble areas dominating the margins of the reservoir. Precopula pairs were also evident, as were egg bearing females.

The parthenogenetic marbled crayfish Marmorkrebs was discovered in the pet trade in Europe in the 1990s. Since then, its distribution through the pet trade has spread from Europe to other continents, including North America. North American pet owners were surveyed online with the aims of trying to track when Marmorkrebs entered the North American pet trade, the ways in which it spread through the pet trade, and how widely distributed Marmorkrebs are throughout the continent. Marmorkrebs have been in the North American pet trade since at least 2004, with the number of people increasing every year. While many Marmorkrebs are sold through online sources, face-to-face personal contacts account for almost as many acquisitions. The increasing spread of Marmorkrebs through the pet trade increases the probability that Marmorkrebs will be released into North American ecosystems.