When native and alien species meet. Impact assessment and management of invasive crayfish and fish in riverine ecosystems
Abstract
Introductions of organisms outside their natural range are increasingly taking place due to the increasing globalisation of human activities. The establishment of invasive alien species can have far-reaching adverse ecological and socio-economic consequences with high societal costs (Chapter 1). Not every introduced (alien) species is invasive. This thesis comprises five studies that analyse the risks of recently introduced alien species in Dutch freshwater ecosystems. Based on these studies, appropriate management measures for high-risk species can be applied.
Ecological impact studies of alien species require sound information on the reference situation of ecosystems. Monitoring in the period 2005-2015 showed a population increase of the native Rhine sculpin (Cottus rhenanus) in the River Geul catchment, coinciding with a water quality improvement (Chapter 2). The recent emergence of the invasive round goby (Neogobius melanostomus) poses a threat to the sustainable conservation of Rhine sculpin populations. Dispersal barriers (weirs) can prevent or delay the upstream spread of round gobies.
The abundance of the invasive topmouth gudgeon (Pseudorasbora parva), an asymptomatic carrier of the parasite Sphaerothecum destruens, correlates negatively with that of sunbleak (Leucaspius delineatus), ninespine stickleback (Pungitius pungitius) and three fish biodiversity indices (Chapter 3). The ongoing invasion of the topmouth gudgeon and its parasite poses a threat to native fish communities.
Using stable isotopes (nitrogen, carbon), the dietary overlap between two alien (Asian weather loach Misgurnus bipartitus, western tubenose goby Proterorhinus semilunaris) and three native (stone loach Barbatula barbatula, spined loach Cobitis taenia, gudgeon Gobio gobio) benthic fish species was investigated (Chapter 4). The invaders show a high plasticity of their resource use, indicating niche differentiation and coexistence with the native species.
Risk assessments of nine alien crayfish species show that all North American species pose a high risk of adverse impacts to biodiversity, water security and ecological status of water bodies due to their burrowing and feeding behaviour (Chapter 5). Eradication of crayfish populations is unfeasible. Feasible strategies for population control or the mitigation of adverse impacts combine measures that increase ecosystem robustness and resilience with crayfish trapping by professional fishermen, water authorities and trained volunteers.
The invasive crayfish species with the highest risk score concerns the red swamp crayfish (Procambarus clarkii). The number of burrows of this species was significantly less in natural banks compared to non-natural and semi-natural banks (Chapter 6). The construction of more natural banks may significantly reduce adverse impacts caused by burrowing activities. An inclination experiment mimicking terrestrial dispersal barriers showed that overland movement reduces at inclinations from 20°, and on sand and grass substrates. Sophisticated design of embankments along watercourses can help reduce colonisation of nearby water bodies with high nature values.
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The river Roer is one of the most important spawning rivers for Atlantic salmon (Salmo salar) in the Netherlands. The effectiveness of a fish passage in the town of Roermond was called into question when underwater cameras revealed that many attempts at upstream migration by Atlantic salmon were unsuccessful. It was hypothesised that the underwater noise generated by an old water power plant affected fish behaviour. To investigate this and other potential factors involved, a study was conducted using underwater cameras and hydrophones in the power plant’s fish passage facility. The study focused on Atlantic salmon, Sea trout (Salmo trutta trutta), River lamprey (Lampetra fluviatilis), and Sea lamprey (Petromyzon marinus). There are no indications that noise from the turbine affects the behaviour of migrating fish. Nevertheless, hesitant behaviour of several fish species, including Atlantic salmon and Sea trout, was observed in the fish passage facility. The abrupt transition from daylight to the dark underground channel in the fish passage may cause hesitation in migrating Atlantic salmon, which predominantly migrate in daylight. In addition, a monitoring cage in the upstream part of the fish passage is also likely to induce hesitation and to hamper fish in their further migration upstream. It should be considered whether the usefulness of this cage during fish migration outweighs the fact that it makes several fishes hesitate, with some of them perhaps even deciding to abort their migration attempt. The use of artificial light that mimics daylight in the underground channel may resolve this bottleneck for Atlantic salmon migrating upstream, and encourage them to continue their migration to the spawning grounds.
Co-occurring and morphologically similar species have adapted to differential niches to minimize competition. An invasive alien species can occupy an ‘empty niche’ in introduced ranges. Alternatively, the invader may occupy an overlapping niche and compete with native species to a certain degree. In a Western European lowland brook with high nutrient loads, we studied a benthic community of five fish species, including two alien species: an Asian weatherfish (Misgurnus bipartitus) and the western tubenose goby (Proterorhinus semilunaris). The native species concerned stone loach (Barbatula barbatula), spined loach (Cobitis taenia), and gudgeon (Gobio gobio). Because of the unknown effects of the invaders on native benthic fish species, the trophic position, isotopic niche overlap, and potential food competition among these species were identified using nitrogen and carbon stable isotopes. The trophic levels of the five fish species indicated that they are secondary consumers. The body size of native fish species correlated significantly negatively with their δ15N (‰) signature, in contrast with the invaders indicating that the latter are generalists. Significant isotopic niche overlap was observed among all benthic species. The degree of niche overlap of M. bipartitus was the highest with G. gobio (91.8%). Proterorhinus semilunaris showed the highest degree of niche overlap with B. barbatula (91.2%). It was notable that the observed niche overlap between the native B. barbatula and C. taenia was high (99.2%). Overlap between M. bipartitus and P. semilunaris was low (8.9%), indicating little resource competition between these alien species. Native species showed wider isotopic niches than the invaders. Bayesian mixing models revealed that native and alien species slightly differ in their main diet. The results suggest that the invaders are plastic in their resource use, leading to niche differentiation and promoting the co-existence of benthic fish species.
Small mammals are potential bio-indicators of various ecosystems and their populations are often studied. However, many small mammal species are difficult to detect due to their small size and elusive behaviour. Camera trapping and live trapping are commonly employed survey techniques, but they both have their limitations. Recently developed techniques such as adjusted short-focal camera trapping and environmental DNA (eDNA) are promising new approaches, but their relative performance remains poorly quantified. We compared the effectiveness of three survey protocols for detecting a semi-aquatic and elusive small mammal, the Eurasian water shrew (Neomys fodiens), by (1) short-focal camera trapping, (2) live trapping, and (3) soil eDNA. During September and October 2022, we surveyed 20 transects of each 100 m in length alongside the Kleine Dommel, a lowland brook in the Netherlands. The effectiveness of the three survey protocols was compared based on detection probabilities. Short-focal camera trapping yielded a significantly higher detection probability than the eDNA protocol. Detection probabilities between short-focal camera trapping and live trapping and, between the eDNA protocol and live trapping, were not significantly different. Short-focal camera trapping is an effective technique to survey Eurasian water shrews. Furthermore, this method detected additional species compared to live trapping and is non-invasive and less labour-intensive. Short-focal camera trapping showed a promising method for small mammal surveys in general and we recommend further evaluation of its applicability for other small mammal species.
Simple Summary
An in-depth study of the feeding habits characterizing bioinvaders may provide key information on the magnitude of their impacts on recipient communities. Specifically, if invaders’ trophic niche is superimposed on that of native species, interspecific competition may increase, resulting in negative consequences for the competing species; alternatively, trophic niche divergence may occur, facilitating the invaders’ integration into the community. In the present study, the analysis of carbon and nitrogen stable isotopes was used to investigate the trophic overlap of native and non-indigenous consumers. We found a generally low degree of isotopic overlap in both the invertebrate and fish assemblage, a condition that may facilitate coexistence and, in turn, limit the strength of invaders’ impact. The only exception was the Louisiana crayfish Procambarus clarkii, which was demonstrated to interact with a wide spectrum of native invertebrate species, confirming the necessity of guaranteeing appropriate measures of control and mitigation of its ecological impacts.
Abstract
An advanced characterization of the trophic niche of non-indigenous species (NIS) may provide useful information on their ecological impact on invaded communities. Here, we used carbon and nitrogen stable isotopes to estimate pairwise niche overlaps between non-indigenous and native consumers in the winter food web of Lake Trasimeno (central Italy). Overall, a relatively low pairwise overlap of isotopic niches was observed between NIS and native species. The only exception was the Louisiana crayfish Procambarus clarkii, which showed a relatively high and diffuse overlap with other native invertebrates. Our findings highlighted a high niche divergence between non-indigenous and native species in Lake Trasimeno, suggesting a potentially low degree of interspecific competition that may facilitate coexistence and, in turn, limit the strength of impacts. The divergent results obtained for the Louisiana crayfish indicate that additional control measures for this invasive species are needed to mitigate its impact on the Lake Trasimeno system.
Surface water inhabiting crayfish are well-known for the impact on their surroundings. This impact has been related to loss of biodiversity and deteriorating water quality for invasive crayfish. Crayfish dig burrows for various reasons like lack of natural shelters, avoiding an upcoming drought, or high crayfish density and this may lead to increased sediment transport and accelerated bank instability. All crayfish are considered to have burrowing capability, but not all species have been observed burrowing. Studies comparing this behaviour among different species in standardized ways are scarce. Crayfish burrowing was investigated under standardized laboratory conditions to reveal differences among species and their sex. All studied species occur in the Netherlands and were the native Astacus astacus (Linnaeus, 1758), the Eurasian Pontastacus leptodactylus (Eschscholtz, 1823) and the invasive North American Faxonius virilis (Hagen, 1870), F. limosus (Rafinesque 1817), Pacifastacus leniusculus (Dana, 1852), Procambarus acutus (Girard 1852), and P. clarkii (Girard, 1852). As burrowing triggers were evaluated presence of shelter, increased light intensity, increased water temperature, and increased crayfish density. Results showed species-specific and sometimes sex-specific differences in burrowing behaviour among crayfish. The response to burrowing triggers was also species-specific and no two species reacted identical to all triggers. Absence of shelter was a strong driver to burrow for A. astacus, F. limosus and F. virilis, while increased light intensity triggered burrowing behaviour in P. leptodactylus, P. acutus and P. clarkii and lowered activity of F. limosus. Burrowing behaviour of P. clarkii was mostly influenced by increased water temperature. Significant differences between females and males were observed for P. leptodactylus, P. leniusculus and P. acutus in the shelter, increased density and increased water temperature treatment, respectively. Understanding the triggers that invoke burrowing may help managing populations of these invasive species.
Spreading of invasive fish species in Europe still continues. Studies of their feeding behavior and diet habits have shown that these species could negatively affect native ichthyofauna by competition and predation; they could also cause changes in feeding behaviour and feeding niche of Central European native species. The aim of this study is to refer similarities and differences in feeding behavior / feeding niche of altogether 83 specimens of five different species, namely Ameiurus melas, Lepomis gibbosus, Neogobius fluviatilis, Perccottus glenii and Proterorhinus semilunaris from the Bodrog River. Non-metric (NMDS and Bray-Curtis index) and non-parametric (PERMANOVA and ANOSIM) tests were used for determination of differences in food. Piankas and Levins statistical models were used for feeding niche overlap and niche width. Statistically significant differences were found in the diet composition of analysed species by ANOSIM. Chironomidae larvae (Diptera), class Ostracoda (Crustacea), family Baetidae (Ephemeroptera) larvae, Corophiidae and Copepoda explained about 60% of the dissimilarity in the diet composition by SIMPER test. At the site Borša, large feeding niche overlap was found between N. fluviatilis and P. semilunaris and intermediate between P. glenii and P. semilunaris. Broad niche width was observed in P. glenii and P. semilunaris differently of N. fluviatilis at this site. N. fluviatilis and P. semilunaris occurred at the site Ladmovce. Diet of these species was very similar in this biotope and we did not confirm significant difference in the food composition. Our findings suggest that in this case, the food offer in specific site was the most important factor in dietary habits and behavior of invasive fishes.
The hazel dormouse is predominantly an arboreal species that moves down to the ground to hibernate in the autumn in temperate parts of its distributional ranges at locations not yet well understood. The main objective of this study is to test whether environmental characteristics surrounding hazel dormouse hibernacula can be identified using high-resolution remote sensing and data collected in situ. To achieve this, remotely sensed variables, including canopy height and cover, topographic slope, sky view, solar radiation and cold air drainage, were modelled around 83 dormouse hibernacula in England ( n = 62) and the Netherlands ( n = 21), and environmental characteristics that may be favoured by pre-hibernating dormice were identified. Data on leaf litter depth, temperature, canopy cover and distance to the nearest tree were collected in situ and analysed at hibernaculum locations in England. The findings indicated that remotely sensed data were effective in identifying attributes surrounding the locations of dormouse hibernacula and when compared to in situ information, provided more conclusive results. This study suggests that remotely sensed topographic slope, canopy height and sky view have an influence on hazel dormice choosing suitable locations to hibernate; whilst in situ data suggested that average daily mean temperature at the hibernaculum may also have an effect. Remote sensing proved capable of identifying localised environmental characteristics in the wider landscape that may be important for hibernating dormice. This study proposes that this method can provide a novel progression from habitat modelling to conservation management for the hazel dormouse, as well as other species using habitats where topography and vegetation structure influence fine-resolution favourability.
The mesopredatory round goby ( Neogobius melanostomus ) is an important fish invader in fresh and brackish waters of the northern hemisphere. Trophic interactions of invasive species can generate ecological impacts across the food web in invaded ecosystems. Here we investigated major diet components, spatiotemporal variation in diet and the effect of round goby densities on diet composition in two geographically distinct round goby populations in the Baltic Sea. The round goby is a generalist feeder but previous diet studies, based on visual prey identification, have likely over-emphasized the importance of hard-shelled, invertebrate prey in round goby diet, as shells degrade and evacuate slowly relative to soft-bodied prey that break down rapidly in the stomach. We therefore, in addition to visual stomach content analysis, used DNA metabarcoding, which is less biased towards hard body structures of prey and can be used for species assignment of highly degraded prey. The results demonstrated that round goby diet composition varied between areas and years. Visual stomach content analysis indicated that blue mussel was the main prey in the southern area, whereas hydrobiid gastropods were the major diet component in the northern area. Metabarcoding revealed that several fish species, likely the egg or larval stages of e.g. stickleback, cod and herring, were also part of the round goby diet. Analyses suggested that round goby feeding on fishes was positively associated with round goby densities. Our study shows that round goby, in addition to benthic invertebrates, preys on several fish species of ecological and commercial importance. Thus, there is potential for predator-prey reversal and negative effects of the invasive round goby on large, predatory fishes.
Land habitat use of Yellow-bellied toads (Bombina variegata), including hibernacula, determined using telemetry. Implications for conservation assessed established by year-round research
The most north-western part of the distribution range of the European Yellow-bellied toad (Bombina variegata) extends into southern Limburg in the Netherlands. From the year 2000 onwards, intensive conservation measures,combined with reintroduction efforts, have prevented this species from becoming extinct in this area. Although much is known about their breeding ecology, relatively little is known regarding their land habitat use, including that during hibernation. Between July and November 2020, the habitat use of 41 Yellow-bellied toads equipped with PIT (passive integrated transponder) tags was studied by monitoring them twice a week. Six potential hibernation refuges were identified and examined during the subsequent winter up to 15 May 2021, by placing a drift fence with pitfall traps. The use of PIT tags proved to be very suitable to study Yellow-bellied toads in situ: a total of 475 detections were recorded, which is 90.2% of the PIT-tagged individuals. On average, an individual was detected twelve times, although in 77.7% of cases the animal was not visually spotted. The mean Minimum Convex Polygon home range was 780 m2, ranging from 68 to 3742 m2. In the breeding season, the toads were extremely closely bound to aquatic habitats. Outside this season, they used land habitats within a few metres from their breeding ponds. Here, they occupied habitats such as cairns, scattered stones, short grassy vegetations, dry-stone walls and tussocks of Common rush (Juncus effusus). During winter, 14 Yellow-bellied toads used a single cairn (7.5 m3) as a hibernation refuge, and 130 individuals hibernated in two dry stone walls (2 x 0.5 x 0.5 m), often together with large numbers of Alpine newts (Ichthyosaura alpestris), Common frogs (Rana temporaria), Common toads (Bufo bufo) and Smooth newts (Lissotriton vulgaris). Large numbers of Yellow-bellied toads (30) also hibernated in the cavities and cracks of a calcareous slope. The mean distance between land habitat and hibernacula was 68 m, ranging from 10 to 117 m. In the following spring, 50% of all subadults had left their hibernacula in mid-April, while adults left the hibernation sites significantly later, approximately 50% of them leaving in early May. The leaving of hibernacula by Yellow-bellied toads correlated significantly with temperature increase, but not with the amount of precipitation. The results of this study demonstrate that habitats and stepping stones can be constructed on relatively small surface areas. Constructing cairns and dry-stone walls, in combination with breeding ponds, increases the suitability of a site as a year-round functioning habitat. This is a promising method to connect fragmented Yellow-bellied toad populations.