Volume 7, Issue 2

Contents
Research articles

	Hans Ulrik Riisgård, Caroline V. Madsen, Coralie Barth-Jensen and Jennifer E. Purcell Population dynamics and zooplankton-predation impact of the indigenous scyphozoan Aurelia aurita and the invasive ctenophore Mnemiopsis leidyi in Limfjorden (Denmark) (pp 147-162)
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	The invasive ctenophore, Mnemiopsis leidyi, which had its first mass occurrence in Limfjorden (Denmark) in 2007, and the indigenous common jellyfish, Aurelia aurita, were studied from autumn 2008 through summer 2009. By December 2008, both A. aurita and M. leidyi populations had disappeared for the winter. In 2009, the first A. aurita appeared in February and the medusae attained their maximum umbrella diameter by the end of June, when the estimated half-life of copepods was only 1.6 ± 1.1 d. Low densities of M. leidyi in early July (< 0.5 m-3) increased to high densities by late August (66.2 to 224.9 ind. m-3). In 2009, the estimated time to clear the central part of Limfjorden (Skive Fjord) of zooplankton by A. aurita and M. leidyi feeding was between 0.5 d (4 June) and 2.9 d (26 August). During that period, copepods and other mesozooplankton organisms were virtually absent while ciliates were a substantial part of the zooplankton biomass. In "pre-Mnemiopsis years", there seems to have been large variability in the grazing impact on zooplankton depending on the seasonal abundance of A. aurita. With the addition of the second carnivore M. leidyi, however, additional predation pressure caused the zooplankton stocks to be severely depressed throughout 2008 and 2009 when copepods and cladocerans no longer showed the high seasonal peaks in abundance typical of previous years.
	Karl Van Ginderdeuren, Kris Hostens, Stefan Hoffman, Lies Vansteenbrugge, Karen Soenen, Hans De Blauwe, Johan Robbens and Magda Vincx Distribution of the invasive ctenophore Mnemiopsis leidyi in the Belgian part of the North Sea (pp 163-169)
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	The invasive ctenophore Mnemiopsis leidyi A. Agassiz, 1865 was recorded for the first time in Northern Europe in summer 2005, while the first records in the North Sea date back to summer 2006. The first sightings in the Belgian part of the North Sea were made in August 2007 in the port of Zeebrugge, but most probably M. leidyi had already been present for a longer period in this area. The high densities in the port of Zeebrugge suggest that M. leidyi entered the Belgian marine waters via ballast water transport, comparable with the invasion in the Black and Caspian Seas and the Dutch part of the North Sea. In the period 2009–2011, M. leidyi was found in all ports and all along the Belgian coastline, up to 27 km offshore. Further offshore, no M. leidyi were found in zooplankton samples and small meshed otter trawl samples. Sightings of adult individuals in the coldest winter months imply that the species can survive Belgian winters. Highest densities (17 ind.m-3) were found in the Sluice dock in the port of Oostende. Along the coastline, average densities of 0.4 ind.m 3 were recorded. As M. leidyi might previously have been misidentified on the basis of morphological features alone, we also determined the species with genetic identification tools. Taking into account the notorious impact of this species in its native and in other invaded waters, it is recommended to continue the monitoring of M. leidyi populations in the Belgian part of the North Sea.
	Idoia Adarraga and Julián Martínez First record of the invasive brackish water mytilid Limnoperna securis (Lamarck, 1819) in the Bay of Biscay (pp 171-180)
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	The occurrence of the non-indigenous species Limnoperna securis belonging to Mytilidae family is recorded for the first time in the Bay of Biscay. Numerous individuals were collected in intertidal and shallow waters in the inner part of Nervión estuary (Bizkaia, Basque Country, SE Bay of Biscay). In the present paper, notes about the history of this small brown mussel invasion, vectors of introduction and dispersal, as well as consequences of invasion are discussed.
	Jørgen Lützen, Marco Faasse, Adriaan Gittenberger, Henrik Glenner and Erik Hoffmann The Japanese oyster drill Ocinebrellus inornatus (Récluz, 1851) (Mollusca, Gastropoda, Muricidae), introduced to the Limfjord, Denmark (pp 181-191)
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	The predatory neogastropod Ocinebrellus inornatus was first reported from Europe in W France in 1995 and has since been detected at other sites in NW and N France and The Netherlands. It is native to the North Pacific where it preys on the Pacific oyster Crassostrea gigas. Here we report on the occurrence of the species in beds of European oysters (Ostrea edulis) in the Limfjord, NW Jutland, Denmark. The morphology-based identification has been confirmed by genetic analysis. The species was probably introduced with oysters imported from France in the 1970s and 1980s. The invasion is still relatively localized but as the species has established a reproductive population, it may eventually spread to other parts of the fjord and in time pose a problem to the oyster fishery. The species’ invasion history is reviewed.
	Christine M. Moffitt and Christopher A. James Dynamics of Potamopyrgus antipodarum infestations and seasonal water temperatures in a heavily used recreational watershed in intermountain North America (pp 193-202)
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	Following the discovery of New Zealand mudsnails, Potamopyrgus antipodarum, in the Silver Creek watershed in Idaho, we investigated the distribution and dynamics of the snail populations over two years in field surveys. Despite extensive fishing and recreational activities in the watershed, the infestations appeared limited in extent. As with other published studies, densities of P. antipodarum were highest during summer months, but the distribution in Silver Creek was patchy. We found that near-to-below freezing winter water temperatures in localized reaches of the watershed were related to reduced populations or lack of detection. Distributions observed in winter were associated with regions of groundwater releases, or downstream of impoundments that dampened the temperature extremes observed in locations elsewhere in the watershed. We speculate that the population has remained restricted because thermal conditions are not conducive to year-round survival and growth. However, these relationships could be altered with watershed alterations or global climate change.
	Alexander S. Kolosovich, Sudeep Chandra, Laurel Saito, Clinton J. Davis and Lisa Atwell Short-term survival and potential grazing effects of the New Zealand mudsnail in an uninvaded Western Great Basin watershed (pp 203-209)
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	We offer a case study showing: a) the susceptibility of the Truckee River and Lake Tahoe to an invasion by the New Zealand Mudsnail (Potamopyrgus antipodarum) and b) the short-term impacts on periphyton standing crop in the Truckee River and Lake Tahoe as a result of grazing by New Zealand mudsnails. Snail survivorship in the Truckee River experiment ranged from 50–85 percent across treatments and snail survivorship ranged from 5–40 percent in the Lake Tahoe experiment. Periphyton standing crop was negatively affected in both snail density treatments of the Truckee River experiment but the results were mixed in the Lake Tahoe experiment. Our results suggest that the Truckee River is more vulnerable to establishment by New Zealand mudsnails than Lake Tahoe.
	Rokas Butkus, Eglė Šidagytė and Kęstutis Arbačiauskas Two morphotypes of the New Zealand mud snail Potamopyrgus antipodarum (J.E. Gray, 1843) (Mollusca: Hydrobiidae) invade Lithuanian lakes (pp 211-218)
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	The New Zealand mud snail, Potamopyrgus antipodarum, was found in four lakes and one medium-sized river located in the southern part of Lithuania during 2010. These are the first records of P. antipodarum from Lithuanian freshwaters, a considerable distance from the Curonian Lagoon wherein the species was reported during the 1950s. Available information shows that the species has invaded quite recently. Two morphotypes of the species, the regular and carinatus (keeled) forms, were observed in three lakes. The presence of separate morphotypes and variation in shell morphometry suggest multiple (at least two) independent invasion events, and species expansion on a local scale. The most abundant population of the invasive snail was recorded in Lake Dusia which is an inland lake of exceptional importance for staging and moulting of migratory waterfowl. Thus, the most probable vector of the invasion and local dispersal is ornithochory, while translocation with fish stocking material may also be operating. Further rapid expansion of the species in Lithuanian lakes and rivers seems very possible.
	Patrick J. Martinez Invasive crayfish in a high desert river: Implications of concurrent invaders and climate change (pp 219-234)
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	No crayfish species are native to the Colorado River Basin (CRB), including the portion of the state of Colorado west of the Continental Divide. Virile crayfish [Orconectes virilis (Hagen, 1870)], a recent invader in the middle Yampa River in northwestern Colorado, displayed an abrupt increase in abundance in the early 2000s, which coincided with a drought, a severe decline in the abundance of small-bodied and juvenile native fishes, and a dramatic increase in the abundance of nonnative smallmouth bass [Micropterus dolomieu (Lacepède, 1802)]. The annual density of virile crayfish was 6.4/m2 in 2005 and 9.3/m2 in 2006. The annual biomass density of virile crayfish was 9.0g/m2 in 2005 and 15.8 g/m2 in 2006, representing a riverwide biomass of 122 kg/ha, which equaled that of other macroinvertebrates and fish combined (120.7 kg/ha). Efforts to recover and preserve native fishes in the Upper Colorado River Basin (UCRB), particularly in the Yampa River, have been hampered by nonnative predatory fishes, but the implications of crayfish may have been overlooked and underestimated. Stream conditions during the drought apparently facilitated proliferation by virile crayfish in the middle Yampa River, likely contributing to hyperpredation on native fishes by invasive smallmouth bass. This trophic interaction between virile crayfish and smallmouth bass, in conjunction with regional projections for climate change, will likely make efforts to reduce the abundance and negative ecological impact of smallmouth bass in this ecosystem more difficult and costly. Given the nonnative status of all crayfishes in the CRB, and their invasive capacity and potential to negatively reconfigure native lotic food webs, all states in the UCRB should prohibit the importation, movement, sale, possession and stocking of any live crayfish.
	Eduardo Torres and Fernando Álvarez Genetic variation in native and introduced populations of the red swamp crayfish Procambarus clarkii (Girard, 1852) (Crustacea, Decapoda, Cambaridae) in Mexico and Costa Rica (pp 235-241)
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	The genetic variation among nine populations of the red swamp crayfish Procambarus clarkii was examined using partial sequences of the mitochondrial COI gene. Three populations (Illinois and Louisiana, United States and northern Coahuila, Mexico) represented the native range and six populations came from areas where the species has been introduced (central Coahuila, southern Nuevo León, Durango, Chihuahua and Chiapas, Mexico, and Cartago, Costa Rica). A 689 bp fragment was amplified from 37 samples. Uncorrected genetic distances among sequences were p = 0 to 0.02031 and 12 haplotypes were found. A phylogenetic reconstruction shows that the three populations from the native range remain very similar to each other and some introduced populations can be directly associated to one of them. The populations from Nuevo León, central Coahuila and Costa Rica were the most divergent ones. Overall the genetic variation found in P. clarkii in both native and introduced populations is low.
	Marcus K. Drotz, Tomas Brodin and Matz Berggren Distribution patterns of the Chinese mitten crab (Eriocheir sinensis H. Milne Edwards, 1853) in Lake Vänern, Sweden (pp 243-249)
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	The catadromous Chinese mitten crab (CMC), Eriocheir sinensis is well known for its extensive invasion routes across the world. However, little is known about both adult and juvenile behaviour after they arrive to a new region. Particularly if the CMC has utilised freight ship ballast tanks as its invasion vector to new freshwater areas like coastal connected larger lakes. The Swedish Lake Vänern, Europe’s third largest freshwater lake, offers a suitable study area since only a handful of CMC had been reported between its first record in 1954 and 2004. Hence, the increased catch of of CMC in the mid 2000s was unexpected and provided a rare opportunity to study the initial phase of a biological invasion. Fortunately local fishermen have traditionally, since the mid 1970s, utilised large stationary fish trap nets, evenly distributed from the inlet to the harbour of Lidköping outward into the main part of the lake. During the peak occurrence in 2005 the traps captured CMC frequently for 90 days starting on August 10. Daily catch increased from September 19th to October 17th. Thereafter the number decreased until November 7th when the last crab was captured. Only one crab out of the 21 caught in the two traps furthest away from the harbour inlet was caught before September 19th. The number of caught CMC differed significantly between the trap nets. Almost half (48.4 %) of all CMC were caught in the two traps closest to the harbour inlet and 41.9% in the second trap-line, consisting of two traps 6 km from the harbour inlet. The remaining crabs were caught in the traps furthest away. Catch pattern from this unique invasion event is discussed in relation to CMC dispersal/migration, invading sample size, behavioural traits and catch efficiency of traps.
	Roger Cammaerts, Frank Spikmans, Nils van Kessel, Hugo Verreycken, Frédéric Chérot, Thierry Demol and Sébastien Richez Colonization of the Border Meuse area (The Netherlands and Belgium) by the non-native western tubenose goby Proterorhinus semilunaris (Heckel, 1837) (Teleostei, Gobiidae) (pp 251-258)
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	The western tubenose goby, Proterorhinus semilunaris, of Ponto-Caspian origin, already recorded in 2002 from the lowest course of the Dutch River Meuse, was caught upstream for the first time in 2008 in the Border Meuse, the river-stretch forming the border between Belgium and the Netherlands. In 2009 it reached the upstream extremity of the Border Meuse in Wallonia and in 2010 it was recorded in Flanders, in a canal connected to the Border Meuse. Discussion is provided about its migration pathway. Further upstream expansion of the western tubenose goby may be expected in less man-modified and lightly navigated sections of the River Meuse, e.g. those lined with macrophyte-rich habitats. Behavioural competition with the native bullhead Cottus perifretum is likely and might lead to a decline in the bullhead population.
	John J. Piccolo and Ewa H. Orlikowska A biological risk assessment for an Atlantic salmon (Salmo salar) invasion in Alaskan waters (pp 259-270)
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	We present an event-tree biological risk assessment for a non-native Atlantic salmon (Salmo salar) invasion into Alaskan waters. Atlantic salmon farming is prohibited in Alaska, USA, but large numbers of them are reared in ocean net-pens in Washinton (WA) USA, and British Columbia (BC), Canada. Large numbers of Atlantic salmon escape each year, and they have been recovered in both saltwater and freshwater in WA, BC, and Alaska. There is limited evidence of successful spawning and rearing in BC, but none from Alaska. No stream-reared smolts are known to have returned successfully from ocean migrations, but survey efforts for escaped adults and reared juveniles in streams have been very limited in time and space. Given recurring, large-scale escape events, propagule pressure could be great enough in any given year for a successful invasion. To date, such large numbers of adults have not been recorded ascending Alaskan streams, but again, monitoring is very limited. Atlantic salmon could most likely successfully spawn and rear in Alaskan streams, so successful ocean migration appears to be the factor most likely to limit their success. Successful invasion of BC waters, where propagule pressure is greater, followed by a subsequent invasion of a pre-adapted stock by straying to Alaskan waters, may pose the greatest risk. The lack of adequate surveys, under-reporting of escapes and recoveries, and inherent ecosystem variation, make it impossible to assign meaningful probabilities to the risk of an invasion of Alaskan waters. We conclude that the short-term risk of invasion generally appears low, but that it might increase over time. We also note that invasion is only part of the ecological risk of Atlantic salmon farming in Pacific waters. Disease, parasites, and pollution may also pose risks to local ecosystems – we do not assess these risks here.
Short communications

	Ian C. Duggan and Kevin R. Eastwood Detection and distribution of Craspedacusta sowerbii: Observations of medusae are not enough (pp 271-275)
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	The freshwater cnidarian Craspedacusta sowerbii, native to the Yangtze valley, has invaded lakes and ponds throughout the world. Most distribution records have to date been based on observations of the medusa (jellyfish) stage, including numerous recent publications. We aimed to determine whether polyps are widespread in lakes, and geographical areas, outside of where medusae have been observed, and whether constructed waters are more easily invaded than natural waters. Our results show that C. sowerbii is more common and widespread than is apparent from observations of medusae. We argue that observed occurrences of medusae provide little useful information regarding the distribution of this species, and that published records of new jellyfish occurrences provide unreliable estimates of the timing of introduction, establishment or spread of C. sowerbii in new regions. We found no evidence that constructed waters were more readily invaded than natural waters. Overall, accurate determination of Craspedacusta occurrence and distribution requires systematic surveys of the polyp stages.
	Pat Hutchings, Christopher J. Glasby and Sander Wijnhoven Note on additional diagnostic characters for Marphysa sanguinea (Montagu, 1813) (Annelida: Eunicida: Eunicidae), a recently introduced species in the Netherlands (pp 277-282)
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	Recently specimens of the polychaete Marphysa sanguinea (Montagu, 1813) (Annelida: Eunicida: Eunicidae) were reported as an introduction to the Eastern Scheldt in southwestern Netherlands. In order to confirm the species identity, material was examined with SEM and compared with material from Devon near the type locality in Cornwall, UK. These studies confirmed that this was a new record of M. sanguinea, which can be distinguished from other Marphysa species by the pattern of the distribution of pectinate chaetae in posterior parapodia. This new record extends the known distribution of the species based on verified records, eastward along the English Channel. As the specimens from the Netherlands show additional variation, the species description of M. sanguinea is expanded, which will facilitate future identifications of this species and comparison with other members of the genus.
	Sandra M. Fiori, Pía Simonetti and Eder P. Dos Santos First record of Atlantic mud piddock, Barnea (Anchomasa) truncata (Bivalvia, Pholadidae) in Argentina (pp 283-286)
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	The present work reports the finding of an exotic bivalve, Barnea (Anchomasa) truncata, in the intertidal zone of the Bahía Blanca Estuary Argentina (38º Lat S), more than 2000 km south from the edge of its native range in South America (21º Lat S, Brazil). Lines of evidence suggest that larval transport by shipping is the probable entry route of this species. The most apparent modification created by the introduction of this species is the generation of greater complexity and habitat heterogeneity in the mud tidal plain of the estuary; the consequent effects on the local biota should therefore be evaluated.
	Hallie L.A. Ladd and David L. Rogowski Egg predation and parasite prevalence in the invasive freshwater snail, Melanoides tuberculata (Müller, 1774) in a west Texas spring system (pp 287-290)
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	Melanoides tuberculata Müller, 1774 (Thiaridae), a freshwater prosobranch snail native to regions of Asia and Africa, was introduced into the U.S. in the 1960s and is now found in fifteen states. Melanoides tuberculata can affect native communities directly by displacing native snail species and indirectly by introducing foreign trematodes into novel environments. As the exact mechanisms of displacement of native snails by M. tuberculata are unknown, egg predation rates on native snails (Physella spp.) by two different size classes (>30 mm and <30 mm, total length) of M. tuberculata were determined in laboratory experiments. Additionally, M. tuberculata were sampled from Diamond Y Spring (Pecos County, TX) to determine if the exotic trematode Centrocestus formosanus (Nishigori, 1924) has been introduced into the system. No M. tuberculata > 30 mm were found to consume Physella spp. and only 2.8% of M. tuberculata snails consumed egg masses. None of the M. tuberculata collected from Diamond Y Spring were found to be infected with C. formosanus.
	Keith L. Sorenson, Stephen M. Bollens and Tim Counihan Rapid range expansion of rusty crayfish Orconectes rusticus (Girard, 1852) in the John Day River, Oregon, USA (pp 291-294)
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	The rusty crayfish, Orconectes rusticus (Girard, 1852), native to the eastern U.S., was discovered west of the Rocky Mountains in the John Day River in Oregon in 2005. In the five years since then, the known range of Orconectes rusticus has more than doubled to 145 river km along the mainstem of the river and populations have achieved high densities in several locations. To arrive at this estimate, the present study employed commercial crayfish traps, D-frame kick nets, and snorkel surveys to assess crayfish communities in the upper John Day basin. Natural dispersal, multiple introductions, a more thorough survey of the study area, or a combination of these factors could account for the expansion of the known distribution O. rusticus within the basin. The limit of O. rusticus expansion in the John Day River and broader Columbia River Basin, and the likely consequences for invaded ecosystems remain to be resolved.