North American Amphipod Research Articles

Nuanced impacts of the invasive aquatic plant Crassula helmsii on Northwest European freshwater macroinvertebrate assemblages

Invasive alien species are considered one of the greatest threats to global biodiversity, and are particularly problematic in aquatic systems. Given the foundational role of macrophytes in most freshwaters, alien aquatic plant invasions may drive strong bottom-up impacts on recipient biota. Crassula helmsii (New Zealand pygmyweed) is an Australasian macrophyte, now widespread in northwest Europe. Crassula helmsii rapidly invades small lentic waterbodies, where it is generally considered a serious threat to native biodiversity. The precise ecological impacts of this invasion remain poorly understood, however, particularly with respect to macroinvertebrates, which comprise the bulk of freshwater faunal biodiversity. We conducted a field study of ponds, ditches and small lakes across the core of C. helmsii's invasive range (United Kingdom, Belgium and the Netherlands), finding that invaded sites had higher macroinvertebrate taxon richness than uninvaded sites, and that many infrequent and rare macroinvertebrates co-occurred with C. helmsii. Alien macroinvertebrates were more abundant in C. helmsii sites, however, particularly the North American amphipod Crangonyx pseudogracilis. At the order level, water beetle (Coleoptera) richness and abundance were higher in C. helmsii sites, whereas true fly (Diptera) abundance was higher in uninvaded sites. Taxonomic and functional assemblage composition were both impacted by invasion, largely in relation to taxa and traits associated with detritivory, suggesting that the impacts of C. helmsii on macroinvertebrates are partly mediated by the availability and palatability of its detritus. The nuanced effects of C. helmsii on macroinvertebrates found here should encourage further quantitative research on the impacts of this invasive plant, and perhaps prompt a more balanced re-evaluation of its effects on native aquatic macrofauna.

A long-term study (1949–2015) of the aftermaths of the deliberate experimental introduction of an invasive freshwater amphipod (Crustacea) to a small Island

The ability to track changing distributions and long-term inter actions between native and introduced species provides insights into forecasting impacts of invaders. We used data from deliberate field introduction experiments of a freshwater Gammarus amphipod (Crustacea) to the rivers of a small British island, The Isle of Man. The deliberate introductions commenced in 1949 and re-sampling occurred in the ‘60s, ‘70s ‘80s, ‘90s, 200 5 and finally in 2015. The findings generally confirmed the failure of introductions of Gammarus pulex into sites previously dominated by the native Gammarus duebeni celticus even with high propagule pressure in terms of numbers of individual invaders released and repeated introductions. Despite this, the island-wide 2015 survey revealed that G. d. celticus occurred in fewer sites and G. pulex in more sites than a decade earlier, indicating at this island-wide scale, the displacement of G. pulex by G. d. celticus seems to be continuing. In addition, one of the introduction sites, Arbory Stream which contained G. d. celticus from 1951–2005 contained only G. pulex in 2015, showing that even after six decades, assumptions cannot be made as to the limits of invader range expansion. Multivariate analysis of physico-chemical data from the 2015 island-wide sur vey revealed water quality as a crucial environmental gradient that influences the distributions of the native and invader species, with the former in higher organic water quality sites than sites with the invader or where invader and native co-occurred. The North American amp hipod Crangonyx pseudogracilis had expanded its range since 2005, including invading low biological water quality sites previously devoid of both Gammarus spp.. Pollution from historic metal mining is implicated as a potential major factor excluding amphipods. This deliberate ecological experiment, through long-term monitoring, continues to provide insights into the factors determining the distributions of natives and invaders.

Enhanced fecundity and parasite release in the first amphipod invader on the Iberian Peninsula

Crangonyx pseudogracilis is a North American amphipod recently detected in Portugal and it is the first invasive freshwater amphipod detected in the Iberian Peninsula. The aim of this study was to assess the population structure and its invasion range in this area, but also to assess its pathogen profile and its origin through genetic analyses. Crangonyx pseudogracilis was only found in the lowlands of the Tagus River basin, a restricted area of the three sampled river basins (Tagus, Guadiana and Sado). Only one mitochondrial DNA (mtDNA) gene cytochrome oxidase subunit 1 (COI) haplotype, identical to the one already detected in Europe and in the Lake Charles, USA, was identified. The obtained data show that the studied populations are well-established, have a high female fecundity and a reproduction period extended throughout the year. No parasites were detected in the 236 dissected specimens. The dissimilarity of parasites prevalence to other European invasive populations opens the possibility of a direct introduction from North America but it also does not exclude the possibility of a secondary introduction from another European country.

First record of the North American amphipod Melita nitida Smith, 1873 in Polish coastal waters

Abstract The present paper reports the first observation of the North American amphipod Melita nitida Smith, 1873 in the Gulf of Gdańsk (the southern Baltic Sea, Poland). In 2014, 13 adult specimens, including 3 males, were collected in the Port of Gdynia, which is located in the western part of this waterbody.

The invasive amphipod Gammarus tigrinus Sexton, 1939 displaces native gammarid amphipods from sheltered macrophyte habitats of the Gulf of Riga

The North-American amphipod Gammarus tigrinus Sexton, 1939 is a successful invader in European waters due to its high reproductive potential and tolerance to severe environmental conditions and various pollutants. In this study, we followed the invasion and establishment of this exotic species in a species-poor ecosystem of the northern Baltic Sea. Two years after the establishment of G. tigrinus, over half of the sampling sites were occupied exclusively by G. tigrinus, whereas G. tigrinus coexisted with native gammarids in only one tenth of all sites. There was a clear separation of habitat occupancy between native species and G. tigrinus in terms of abiotic environment and macrophytic habitat. G. tigrinus preferred shallow sheltered areas dominated by vascular plants, while native species mainly occurred in more exposed, deeper habitats with phaeophytes and rhodophytes. In its suboptimal habitats, G. tigrinus exhibited moderate abundances, which allowed for the coexistence of native gammarids and the invasive gammarid. Since its establishment, the abundance of G. tigrinus has showed no signs of decline, with abundances exceeding almost fifteen times those of native gammarids at some locations. The results suggest that, irrespective to the competitive superiority of G. tigrinus over the native gammarids, the invasive G. tigrinus does not monopolize the entire coastal area of the northern Baltic Sea but mostly outcompetes native species in its favoured habitats..

High fecundity and predation pressure of the invasive Gammarus tigrinus cause decline of indigenous gammarids

The North American amphipod Gammarus tigrinus is one of the most aggressive invaders recently expanding its distribution in the European waters. The species was detected in the north-eastern Baltic Sea in 2003 and has rapidly expanded its distribution ever since. This invasive amphipod has been notably successful in shallow, soft and mixed bottom habitats becoming one of the most abundant gammarid colonizing such environments. This study carried out two experiments: (1) an outdoor aquarium experiment to assess interspecific competition among the invasive G. tigrinus and the native Gammarus duebeni and compare their reproductive potential, and (2) an in situ meshbag experiment to determine the effect of adult G. tigrinus and native gammarids on juvenile gammarid amphipods. These demonstrated that the adult G. tigrinus had no effects on the adult G. duebeni; however, the invasive amphipod had higher reproductive potential compared to the native species such as G. duebeni. Moreover, almost all adult gammarids exerted a significant predation pressure on juvenile amphipods. Thus, the combined effect of predation on juvenile amphipods and large brood production of G. tigrinus could be plausible explanations describing increased abundance of G. tigrinus and decrease of local gammarid populations in the north-eastern Baltic Sea but plausibly in similar shallow water habitats in other seas.

Predators vs. alien: differential biotic resistance to an invasive species by two resident predators

The success of invading species can be restricted by interspecific interactions such as competition and predation (i.e. biotic resistance) from resident species, which may be natives or previous invaders. Whilst there are myriad examples of resident species preying on invaders, simply showing that such an interaction exists does not demonstrate that predation limits invader establishment, abundance or spread. Support for this conclusion requires evidence of negative associations between invaders and resident predators in the field and, further, that the predator-prey interaction is likely to strongly regulate or potentially de-stabilise the introduced prey population. Moreover, it must be considered that different resident predator species may have different abilities to restrict invaders. In this study, we show from analysis of field data that two European predatory freshwater amphipods, Gammarus pulex and G. duebeni celticus, have strong negative field associations with their prey, the invasive North American amphipod Crangonyx pseudogracilis. This negative field association is significantly stronger with G. pulex, a previous and now resident invader in the study sites, than with the native G. d. celticus. These field patterns were consistent with our experimental findings that both resident predators display potentially population de-stabilising Type II functional responses towards the invasive prey, with a significantly greater magnitude of response exhibited by G. pulex than by G. d. celticus. Further, these Type II functional responses were consistent across homo- and heterogeneous environments, contrary to the expectation that heterogeneity facilitates more stabilising Type III functional responses through the provision of prey refugia. Our experimental approach confirms correlative field surveys and thus supports the hypothesis that resident predatory invertebrates are differentially limiting the distribution and abundance of an introduced invertebrate. We discuss how the comparative

New records of the amphipods Gammarus tigrinus Sexton, 1939 and Pontogammarus robustoides G.O. Sars, 1894 in Latvian waters of the Baltic Sea

The paper presents recent records of the North-American amphipod Gammarus tigrinus and the Ponto-Caspian amphipod Pontogammarus robustoides in Latvian territorial waters of the Baltic Sea. P. robustoides was found for the first time in shallow waters of the Gulf of Riga near Jurmala City in June 2009. During field surveys of 2011–2012, P. robustoides and another invader, the North-American amphipod G. tigrinus (detected earlier in Estonian part of the Gulf), were recorded in different sites of the Latvian waters of the Gulf of Riga and in the coastal Lake Liepaja. Abundance ranged between 1–70 ind./m 2 for P. robustoides and 5–100 ind./m 2 for G. tigrinus, suggesting they potential role in the functioning of the benthic community in near future.

Separate and combined effects of habitat-specific fish predation on the survival of invasive and native gammarids

The North-American amphipod Gammarus tigrinus was observed for the first time in the northern Baltic Sea in 2003. The invasive amphipod has been particularly successful in some habitats (e.g. on pebbles) where it has become one of the most abundant gammarid species. We studied experimentally if the dominant fish Gasterosteus aculeatus preyed differentially on the exotic G. tigrinus and the native Gammarus salinus, if predation differed among habitats, and if one gammarid species facilitated predation on the other. The experiment demonstrated that (1) fish preyed more on the exotic G. tigrinus than the native G. salinus. (2) Predation did not differ among habitats. (3) Gammarus tigrinus facilitated the predation on G. salinus and this facilitation varied among habitats with significant effects on pebbles. Thus, the combined effect of habitat-specific fish predation and competition between gammarid amphipods is a possible explanation of the current range of G. tigrinus in the northern Baltic Sea. G. tigrinus seems to establish in habitats where it can significantly increase fish predation on the native gammarids.

Is Gammarus tigrinus (Crustacea, Amphipoda) becoming cosmopolitan through shipping? Predicting its potential invasive range using ecological niche modeling

While the intensity of global shipping has increased dramatically over the last decades, species exchange between continents has likewise intensified. Ballast water of ships is recognized playing a major role in this process. Many of the larger sea ports have become bridgeheads for invasions. Ecological niche modeling is used to investigate the potential invasive range and high invasive risk ports of the North American amphipod Gammarus tigrinus. Sixty-two occurrences of G. tigrinus in its native range (North America) and 34 environmental data sets were compiled. Data on dispersal distances were used via ecological niche modeling to analyze the invasive potential of G. tigrinus. The invasive risk of large ports was analyzed according to modeling result, as well as their salinity in the main oceanic routes of the world. G. tigrinus had a rapid range extension on the British Isles and in the rest of Western Europe. Now it is invading the countries surrounding the Baltic Sea. Worldwide it has a vast potential invasive range. It has a high invasive risk for many large ports along the main oceanic routes, among which the ports of Shanghai, Buenos Aires and Montevideo have the highest invasive risk. G. tigrinus may become cosmopolitan through shipping, and this possibility is increasing. Particular emphasis should be placed on preventing human-mediated dispersal. Ports may be the first places G. tigrinus invades. This study can identify high invasive risk ports, especially those at risk of introduced North America species. More importantly, the water of large ports should be monitored regularly for exotic aquatic organisms that may survive temporarily or permanently.

Influence of conductivity on life history traits of exotic and native amphipods in the St. Lawrence River

We compared the survival, growth and fecundity of the Ponto-Caspian amphipod Echinogammarus ischnus and the North American amphipod Gammarus fasciatus across a range of conductivities in a fluvial lake at the confluence of the St. Lawrence and Ottawa rivers (Quebec, Canada). Previous work has found that water chemistry (conductivity) regulates the direction and intensity of intraguild predation between these two species. Because E. ischnus evolved in ion-rich waters, we hypothesized that low conductivity has a negative effect on its life history traits, whereas G. fasciatus would be more tolerant. Consistent with this hypothesis, E. ischnus is abundant along the south shore of the lake in water of high conductivity (300 μS/cm), but rare along the north shore where conductivity is subject to strong fluctuations (85-230 μS/cm). In laboratory experiments using water with low (108 μS/ cm), high (300 μS/cm) and intermediate (50:50 mix) conductivities, both species showed reduced growth at low conductivity, but E. ischnus also suffered higher mortality. E. ischnus collected from both shores did not differ in size-specific fecundity, size at reproduction, or size of adults. On the north shore, E. ischnus was present in low abundance at one site and absent from another site where it had been recorded in previous years. We conclude that low conductivity negatively affects the growth rate and mortality of E. ischnus, which is apparently eliminated from the north shore during periods of strong influx of ion-poor water from the Ottawa River, but re-establishes populations temporarily when higher conductivity is restored.

A long-term study (1949-2005) of experimental introductions to an island; freshwater amphipods (Crustacea) in the Isle of Man (British Isles)

Aim Using data from field introduction experiments with Gammarus spp. conducted in the rivers of a small island, commencing in 1949, with resampling in the 60s, 70s, 80s, 90s and finally in 2005, we aimed to examine the long-term interaction of the native freshwater amphipod Gammarus duebeni celticus with the introduced G. pulex. Using physico-chemical data from a 2005 island-wide survey, we also aimed to find what environmental factors could influence the distribution of the two species. Location The Isle of Man, British Isles. Methods We used species distribution data from 10 river sites from a field introduction study in 1949–69, resampling of these sites in 1974/5, 1988, 1995 and 2005. We sampled a further 82 sites in 2005, where physico-chemical characteristics of each site were obtained. ANOVA was used to ascertain significant differences in environmental variables between native and introduced amphipod assemblages. Multiple discriminant analysis was used to relate Gammarus distribution to environmental gradients in rivers. Results Field introductions of G. pulex into previously G. d. celticus dominated sites failed, despite the large propagule pressure in terms of numbers of individuals released and repeated introductions. The island-wide survey revealed that G. d. celticus was found in areas of higher water quality than G. pulex. Sites where the two species co-occurred also tended to be of lower water quality than native only sites. Continuing metal pollution from past mining activity may be a major factor excluding all amphipods from many rivers. The North American amphipod Crangonyx pseudogracilis, which was first discovered on the Isle of Man in one river site in 1995, was found in a further five sites. Main conclusions This ecological experiment, through long-term monitoring, thus continues to elucidate factors influencing the distributions of introduced and native species. Under some physicochemical regimes, G. d. celticus is able to withstand its usual displacement by G. pulex, whereas increased river pollution could promote replacement of the native by the introduced species.

Range expansion of the North American alien amphipod Gammarus tigrinus Sexton, 1939 (Crustacea: Gammaridae) in Brittany, France

Abstract Since the first observation in September 2005 of Gammarus tigrinus in Brittany (Western France), the species’ range has expanded slowly. By September 2008, the range of G. tigrinus expanded > 63.6 km to the North and 60.4 km to the West of that observed in 2005. G. tigrinus is thought to be responsible for the replacement of native Gammarus pulex . The relatively slow expansion rate of G. tigrinus in Brittany may result from either a low frequency of ship traffic, a known vector for the species, or from the species’ slow acclimatisation to brackish waters. A number of simulated invasion scenarios are presented for the future dispersal of G. tigrinus in Brittany. Key words : invasion, non-native species, colonization velocity, ship traffic, freshwater, Western Europe The first record in Europe of the North American amphipod Gammarus tigrinus Sexton, 1939, a native of the east coast of (Bousfield 1958; van Maren 1978), was from the British Islands in 1931 (Sexton 1939). However the species probably arrived in Europe earlier (Hynes 1955) via ballast water exchanges in estuaries during the First World War by ships from the east coast of North America. The dispersal of

Predatory interactions between the invasive amphipod Gammarus tigrinus and the native opossum shrimp Mysis relicta

The invasive North American amphipod Gammarus tigrinus is successfully established in Lough Neagh, Northern Ireland. Gammarus tigrinus is increasingly recognized as having significant predatory impacts on macroinverebrates, contrary to the accepted functional feeding group status of Gammarus species. The native opossum shrimp Mysis relicta overlaps in habitat use with G. tigrinus. However, its interaction with benthic macroinvertebrates is rarely appreciated. Mutual predatory interactions between G. tigrinus and M. relicta were assessed in a series of laboratory experiments. Gammarus tigrinus actively preyed on adult and juvenile M. relicta at a range of spatial scales. Females and recently molted M. relicta were particularly vulnerable to predation. Mysis relicta did not prey on adult G. tigrinus, but rapidly eliminated juvenile G. tigrinus in microcosms. Changes in dissolved O2 saturation did not alter the predatory interaction between these species. Microhabitat use by M. relicta was altered in the presence of G. tigrinus, and the presence of G. tigrinus facilitated fish predation on M. relicta. A balance of mutual predatory pressure between these invasive and native species may explain their coexistence. Both species are likely to be strongly interactive with other macroinvertebrates in both native and invasive ranges.

Invasion of the North American Amphipod ( Gammarus tigrinus Sexton, 1939) into the Curonian Lagoon, South-Eastern Baltic Sea

The North American amphipod (Gammarus tigrinus Sexton, 1939) was found in the Lithuanian part of the Curonian Lagoon in September 2004. In the littoral part, the distribution of the species was restricted to the area of seawater inflows, within a distance of up to 23 km upstream from the sea. The species was present in all types of the habitats sampled (reeds, mixed and soft bottoms) and its distribution showed a continuous rather than fragmented pattern. In most cases, the species was absent in enclosed depositional environments with mixed substrates and the presence of mud. Obessogammarus crassus (G. O. Sars) was the only crustacean species always found in the presence of the new invader G. tigrinus, whereas other species showed a higher degree of habitat discrimination within the stations. Along with the other two introduced crustaceans O. crassus and Pontogammarus robustoides (G. O. Sars), G. tigrinus showed the highest occurrence (79%) in the salinity range of its recent distribution in the lagoon. As the factors limiting the species establishment are difficult to predict, the rapid spread of G. tigrinus into inland Lithuanian waters might be expected.

Physical factors affecting the relative abundance of native and invasive amphipods in the St. Lawrence River

The Ponto-Caspian amphipod Echinogammarus ischnus (Stebbing, 1899) is reportedly replacing the North American amphipod Gammarus fasciatus Say, 1818, in the lower Great Lakes, but the two species appear to coexist in the upper St. Lawrence River several years after invasion by E. ischnus. A multi-site survey in the river between Lake Ontario and Montreal (Quebec) found that E. ischnus and G. fasciatus respond differently to substrate characteristics, water chemistry variables, and current velocity. Both species increase in abundance in the presence of dreissenid mussels. However, E. ischnus density is positively correlated with current velocity and an increasing proportion of gravel-sized sediment, while G. fasciatus density is positively correlated with benthic filamentous algal (Cladophora spp.) biomass, macrophyte biomass, and pH. Habitat heterogeneity within the river may be promoting the coexistence of native and exotic amphipods by allowing them to segregate along physicochemical gradients.

Invasion success of Fibrillanosema crangonycis, n.sp., n.g.: a novel vertically transmitted microsporidian parasite from the invasive amphipod host Crangonyx pseudogracilis

Parasitism is known to be an important factor in determining the success of biological invasions. Here we examine Crangonyx pseudogracilis, a North American amphipod invasive in the United Kingdom and describe a novel microsporidium, Fibrillanosema crangonycis n.sp., n.g. The primary site of infection is the female gonad and the parasite is transovarially transmitted to the eggs. PCR screening reveals a female bias in the distribution of parasites (96.6% of females, N=29; 22.2% of males, N=27), which is indicative of host sex ratio distortion. The morphological and molecular characterisations of this new microsporidium place it outside all currently established genera. On the basis of these differences, we erect the new genus Fibrillanosema n.g. While F. crangonycis is morphologically identical to uncharacterised microsporidia from populations of North American amphipods, it is distinct from microsporidia found in European populations of amphipods. These data support the hypothesis that vertically transmitted parasites may be selectively retained during invasion events. Furthermore where vertical transmission is combined with host sex ratio distortion these parasites may directly enhance host invasion success through increased rates of population growth.

The recent evolutionary origin of the phenotypically novel amphipod Hyalella montezuma offers an ecological explanation for morphological stasis in a closely allied species complex.

Numerous molecular studies have identified morphologically cryptic, freshwater invertebrate species, but have not suggested possible mechanisms for their phenotypic stasis. The amphipod crustacean genus Hyalella contains numerous morphologically cryptic species in the H. azteca complex, as well as a small number of morphologically very divergent, narrowly endemic taxa. One such taxon, Hyalella montezuma, is the sole planktonic filter-feeder within the North American amphipod fauna, and is known only from Montezuma Well, a fishless travertine spring mound in Arizona, USA. In this study, we conduct a phylogenetic analysis of mtDNA sequence data using likelihood, Bayesian and cladistic approaches to determine both the relationship of H. montezuma to the H. 'azteca' species complex, and to ascertain if its morphological and ecological differentiation have been comparatively recent. The results show that H. montezuma has a very close phylogenetic affiliation with one lineage in the H. azteca complex, indicating that its origin has been recent. We present evidence suggesting that fish predation is an important ecological factor, which constrains morphological and ecological diversification within the genus Hyalella, and that Montezuma Well has provided a relaxation on this constraint.

Underground Dispersal by Amphipods (Crangonyx pseudogracilis) between Temporary Ponds

ABSTRACT Most animals living in temporary ponds have some desiccation-resistant stage in their life cycle that permits them to survive the seasonal drying of the pond basin and facilitates dispersal to colonize other temporary ponds. Amphipods have no such desiccation-resistant or dispersal-adapted stage, yet several amphipod species are abundant and widespread in temporary ponds. The means by which amphipods endure seasonal drying and colonize other temporary ponds remains puzzling. We present evidence that the North American amphipod Crangonyx pseudogracilis may inhabit parts of the water table as well as temporary ponds. Such hypogean explorations by a basically epigean species would explain both its persistence and its ubiquity in temporary ponds. We suggest that other taxa that are typically thought of as strictly epigean pond residents may likewise have the capacity to survive and disperse in shallow groundwater.