Research Article |
Corresponding author: Essmat Mohammed ( esmat_mn@aswu.edu.eg ) Corresponding author: Carola Winkelmann ( cawinkelmann@uni-koblenz.de ) Academic editor: Zarah Pattison
© 2023 Essmat Mohammed, Rahma Amen, Hoda M. Abdelwahab, Carola Winkelmann.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Mohammed E, Amen R, Abdelwahab HM, Winkelmann C (2023) Potential impacts of invasive crayfish on native benthic fish: shelter use and agonistic behaviour. NeoBiota 83: 131-153. https://doi.org/10.3897/neobiota.83.102975
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Spinycheek crayfish (Faxonius limosus) and signal crayfish (Pacifastacus leniusculus) are successful North American invasive crayfish species distributed throughout Europe. Both species compete with native benthic fish for shelter. In a laboratory approach, we assessed competition for shelter and antagonistic interactions between these invasive crayfish species and the native benthic fish species, stone loach (Barbatula barbatula) and bullhead (Cottus gobio). This allows for studying the potential impacts of invasive crayfish on native benthic fish. Spinycheek crayfish and signal crayfish were able to gain control of the shelter and could successfully displace both benthic fish species. For stone loach, the presence of crayfish significantly decreased their shelter use and caused several behavioural changes such as reduced activity and increased hiding behaviour outside the shelter. Although the shelter use by bullheads was not reduced, they displayed similar behavioural changes, if less intense. Invasive crayfish species showed remarkable combative interactions against both species of benthic fishes, evidenced by the high number of aggressive interactions, especially concerning stone loach. Our results highlight the pronounced dominance of invasive crayfish over benthic fish in terms of shelter competition and aggressive interactions under laboratory conditions, which consequently might promote the latter’s exposure to predation.
Antagonistic interactions, Barbatula barbatula, Cottus gobio, Faxonius limosus, invasive crayfish, native benthic fish, Pacifastacus leniusculus, shelter competition
Introducing non-native species into a new habitat exhibits wide-ranging ecological impacts on native taxa, and thereby can globally threaten biodiversity to the entire ecosystem functioning (
Crayfish are among the most widely imported exotic freshwater taxa which are introduced to the environment by bait-bucket releases, intentional introduction to support fisheries, or release after educational use (
In direct contests between two competitors, morphological and physiological traits determining the potential to win these contests are defined as an individual’s resource-holding potential (RHP) (
Two successful and important North American crayfish species invading Europe are the spinycheek crayfish (Faxonius limosus) and signal crayfish (Pacifastacus leniusculus). Spinycheek crayfish was first introduced by the end of the nineteenth century, while signal crayfish was first introduced to Europe in the 1960s (
To better assess the potential consequences of crayfish invasion, this study was devoted to highlighting the competition for shelter between the invasive crayfish species, spinycheek crayfish and signal crayfish, and the native benthic fish species, Barbatula barbatula (stone loach) and Cottus gobio (bullhead). Stone loach, bullhead, and crayfish species are similar in their ecological tolerances and habitat requirements. They are primarily nocturnal organisms that hide within shelters of rock crevices in streams and rivers (
Crayfish and benthic fish specimens needed for laboratory behavioural studies were sampled between May 2018 and September 2019. We collected spinycheek crayfish from the right tributary (Nidda) in Schotten (50°28'N, 9°6'E) and the River Moselle near Koblenz, Germany (50°21'N, 7°36'E), while signal crayfish were sampled from the hyporhithral zone of the small river (Wied) near Neustadt (50°35'N, 7°26'E). All these sites are identified as invasion core areas. Stone loaches and bullheads were collected from a small gravel-bed Nister river (50°43'N, 7°44'E), where crayfish were observed but not abundant. All animals were active and used only once during the experimental procedures. Crayfish with missing or regenerating chelipeds or displayed moulting signs or had incomplete hardening were not considered for the experimental procedures. Crayfish were gathered using plastic rounded crayfish traps (60L × 26W × 24H cm) equipped with fish baits and dried dog food. These traps were set up along the shore overnight (ca. 0.5 m to 1 m depth). Benthic fish were collected by electrofishing (DK300, Brettschneider, Germany) with 350V DC and 4A. All animals were transported to the laboratory at Koblenz University. Crayfish were transported in a big dark container (66 L) lined with wet straw to avoid aggressive contact while benthic fish were transported in a 500 L container with aerated stream water. In the laboratory, 40 spinycheek crayfish and 40 signal crayfish were housed in plastic boxes (60 × 40 × 20 cm) in stocks, not more than three animals in one box (separated by sex and species). Having benthic fishes collected one species at a time, 30 benthic fish were housed in two glass tanks (120 × 50 × 50 cm). All tanks and boxes were filled with dechlorinated tap water, contained a layer of gravel, and were equipped with PVC tube shelters (5 cm diameter and 15 cm length) more than the number of animals to avoid competition for shelter. All animals were kept under controlled conditions (light regime 16:8 L:D, water temperature 20.7 °C to 22.4 °C, pH 8.7–9.0). Benthic fish were fed frozen chironomid larvae whereas crayfish were fed on crabs’ food JBL Novo Crabs tablets twice per week (food supplements with similar ingredients from other providers should be useful as well). Before the start of the experiments, all animals were acclimatised to lab conditions for seven days at least before starting the experiment. Body mass, standard length of benthic fishes, crayfish carapace length, and crayfish sex were recorded before each experiment (Table
Mean (±SD) morphometric values of body mass and standard length (SL) of the native benthic fish stone loach (Barbatula barbatula) and bullhead (Cottus gobio) as well as body mass, carapace length (CL), and the number of males and females used in the experiment (N = 20 pairs) of the invasive crayfish species spinycheek crayfish (Faxonius limosus) and signal crayfish (Pacifastacus leniusculus).
Native benthic fish | Invasive crayfish | ||||||
---|---|---|---|---|---|---|---|
Experiment | Body mass (g) | SL (cm) | Species | Body mass (g) | CL (cm) | Male | Female |
Stone Control | 2.40±0.59 | 5.4±0.56 | |||||
Stone loach + Spinycheek | 3.10±1.10 | 5.6±0.58 | Spinycheek | 21.9±6.10 | 4.18±0.48 | 6 | 14 |
Stone loach + Signal | 3.00±0.80 | 5.6±0.70 | Signal | 28.1±4.85 | 4.70±0.50 | 7 | 13 |
Bullhead Control | 5.25±2.33 | 5.5±0.90 | |||||
Bullhead + Spinycheek | 5.75±1.94 | 6.0±0.65 | Spinycheek | 29.4±7.96 | 4.60±0.61 | 11 | 9 |
Bullhead + Signal | 7.00±2.70 | 6.3±0.94 | Signal | 32.0±6.60 | 4.70±0.46 | 14 | 6 |
In the shelter competition experiment, we performed 60 experiments with each benthic fish species (stone loach or bullhead), 20 trials with spinycheek crayfish and benthic fish species, and 20 trials with signal crayfish and benthic fish species. Furthermore, 20 control trials were performed with benthic fish only to observe their shelter use. For better observation, we built up 6 transparent glass aquaria (65 cm × 50 cm × 50 cm) with the same conditions in the acclimatisation tanks, providing only a single shelter in each trial (Fig.
Model representing the experimental tank setup, showing the shelter position in the middle of the tank and the camera for recording the animal behaviour in front of the tank which is connected to a PC to observe and download the videos after recording.
For 14h, time spent inside the shelter by crayfish and benthic fish species was recorded during day and nighttime. Shelter occupation was considered when more than 50% of the animal’s body was inside the shelter. Shelter status (occupied or not) was observed before the individual entered the shelter. If one species occupied the shelter and the other one entered the shelter, the reaction of the inhabitant (stayed inside, moved away, or evicted from the shelter) was recorded. The reaction of benthic fish (moving or not) to an approaching crayfish outside the shelter was also recorded. Meanwhile, the contest between the experimental species represented by crayfish aggressive movements and the retreating behaviour of the benthic fish species was also recorded. We noted: (1) the frequency of aggressive actions performed, (2) the type of aggressive and retreating behaviours observed which was then used to generate a behavioural intensity score (see Table
Ethogram of the behaviours observed in this study and the associated intensity score based on previous assessments of crayfish contests (
Behavior | Description | Score | |
---|---|---|---|
Non-aggressive interactions | An approach without any agonistic reactions | 0 | |
Aggressive interactions | Antenna wave | The antennae of crayfish are whipped rapidly over the opponent. | +1 |
Cheliped touching | Aggression with closed chelae: touching and pushing the opponent. | +2 | |
Cheliped half raise | The spreading and half raising of the chelipeds while facing an opponent. | +3 | |
Cheliped full raise | The spreading and full raising of the chelipeds while facing an opponent. | +4 | |
Grappling and pull | Intense combat: animals performing several agonistic acts simultaneously, trying to grab and pull the opponent’s body. Kill the opponent. | +5 |
During video analysis, different behaviours were noted: (1) shelter occupation (measured as time spent inside the shelter), (2) shelter status (occupied or empty), and (3) agonistic behaviour. To do so, we developed a multi-object tracking algorithm to track the movement of the fish and the crayfish inside the experimental tank in the recorded videos. This algorithm was inspired by the procedures used by (
(1)
where q is the hit-rate in percent, n is the number of frames (1000 frames), and N is the hit value (1 for a correct prediction and 0 for an incorrect one). We accepted the automated process only for q values higher than 95%. Otherwise, we manually set the fish and the crayfish locations in each frame of the videos which scored q values less than 95%. We further processed the outputs of this routine, i.e., the generated spatio-temporal database of the moving objects (fish and crayfish), to observe the shelter occupation time, covered distance, and activity of the fish and the crayfish inside the experimental tank. For visualization, a spatial heatmap was used to show how the species locations are clustered or vary over space in the experimental tank. The colour variation represents the intensity of species locations in a 2-D form. Heatmaps were used also to measure the habitat proximity relative to the shelter, as a focal patch, to infer the potential for animal movement close to the shelter. The index of habitat proximity, Hx, is calculated, following (
(2)
where Ai is the area of patch i, di is the distance between the shelter and patch i considered overall patches in the system, and D is a mobility constant scaled to the fish (diagonal of the tank). High Hx values indicate the high proximity of a fish to the shelter and vice versa.
The activity of the fish is calculated, following (
(3)
where t1 and t2 are the starting and ending times of the required period of fish activity. To calculate all these quantities, we used a Matlab post-processing script, which was designed specifically for this study.
To assess the impact of crayfish species on benthic fish species, we compared shelter occupation time as an independent variable between experimental groups using R software (R 4.2.1). In this study, shelter occupation time was non-normal distributed, over-dispersed (variance of the distribution greater than mean), and contained excessive zeroes. Consequently, a zero-inflated regression model (with Poisson errors and negative binomial errors) was performed by applying the “zeroinfl” function in the “pscl” package (
To determine which benthic fish species faced more aggressive behaviour from the two crayfish species, and which crayfish species exhibited the most aggressive actions towards benthic fish, we transformed our non-normal distributed data in terms of aggressive movement scores and durations. Data from spinycheek crayfish and signal crayfish towards stone loach and bullhead were transformed using arcsine-square root. Afterwards, two-way ANOVA was performed to compare the score and the duration of aggressive movements in the different groups. Accordingly, two-way ANOVA was used to evaluate the influence of crayfish sexes on the score of aggressive movements towards stone loach and bullhead. Since the transformation to achieve the assumptions of normal distribution and homogeneity of variances was not possible, the Mann-Whitney test was used to compare the frequency of aggressive acts from both crayfish species (Table
The presence of invasive crayfish species significantly affected the shelter occupation time of both benthic fish species. Stone loaches reduced the time spent within the shelter in response to both crayfish species. This reduction was more intense in the case of spinycheek crayfish during the daytime, resulting in a significant interaction term (Table
Box plots of shelter occupation time of the benthic fish species stone loach (a, b) and bullhead (c, d), kept either alone (Control; n = 20) or in the presence of spinycheek crayfish (+Spinyceek; n = 20) or signal crayfish (+Signal; n = 20) during the day and night times (line: median, box: 25,75% percentiles, whiskers: 5%,95% percentile, dots: outliers).
Status of a shelter (occupied: Black, unoccupied: Grey) before entered by crayfish or benthic fish.
Results for the ANOVA’s (generalized linear models) regarding the effect of the two crayfish species (Faxonius limosus: spinycheek crayfish; Pacifastacus leniusculus: signal crayfish) on the shelter occupation time of the benthic fish species Barbatula barbatula (stone loach) and Cottus gobio (bullhead), during night and day, given as an estimate, standard error (SE), z-value, and p-value. Due to the different distributions, a zero-inflated distribution was used for bullhead and a Poisson distribution for a stone loach. Significant results are indicated by bold font.
Fish | Factor | Est. | SE | z | p |
---|---|---|---|---|---|
Stone loch | Intercept | 5.31 | 0.015 | 338.3 | < 0.001 |
Signal | -0.22 | 0.025 | -8.8 | < 0.001 | |
Spinycheek | -0.37 | 0.030 | -12.5 | < 0.001 | |
Time | -1.01 | 0.035 | -29.1 | < 0.001 | |
Signal: time | -0.06 | 0.056 | -1.1 | 0.261 | |
Spinycheek: time | 0.13 | 0.060 | 2.3 | 0.020 | |
Bullhead | Intercept | 2.70 | 1.113 | 2.4 | 0.015 |
Signal | -0.51 | 1.339 | -0.4 | 0.705 | |
Spinycheek | -3.11 | 1.203 | -2.6 | 0.010 | |
Time | -0.51 | 1.339 | -0.4 | 0.705 | |
Signal: time | 0.51 | 1.705 | 2.3 | 0.766 | |
Spinycheek: time | 1.32 | 1.487 | 0.9 | 0.376 |
Both crayfish species spent more time inside the shelter during the daytime than the nighttime. Therefore, the stone loach stayed for a long time, more or less stationary, in certain spots outside the shelter. This behaviour increased in the presence of both crayfish species during day and night (Table
Heatmaps (shifting from blue over yellow to red with the increase of time spent in this respective location) is a graphical representation of the shelter occupation and animal distribution in the experimental tank a heatmaps showing the movement of (stone loach, Barbatula barbatula) in the absence or presence of invasive crayfish species (spinycheek, Faxonius limosus or signal crayfish, Pacifastacus leniusculus) during day and night b heatmaps illustrate the localization and dynamics of spinycheek and signal crayfish inside the aquarium during day and night.
Heatmaps (shifting from blue over yellow to red with the increase of time spent in this respective location) is a graphical representation of the shelter occupation and animal distribution in the experimental tank a heatmaps showing the movement of bullhead, (Cottus gobio) in the absence or presence of invasive crayfish species (spinycheek, Faxonius limosus or signal crayfish, Pacifastacus leniusculus) during day and night b heatmaps illustrate the localization and dynamics of spinycheek and signal crayfish inside the aquarium during day and night.
Mean (±SE) times of different behaviours (minutes) for the benthic fish species Barbatula barbatula (stone loach) and Cottus gobio (bullhead) alone (control), or in presence of crayfish (Faxonius limosus: spinycheek crayfish; Pacifastacus leniusculus: signal crayfish) inside and outside (moving or stationary) the shelter during day and night in the tank.
Fish situation | Stone loach | Bullhead | |||||
---|---|---|---|---|---|---|---|
Control | Spinycheek | Signal | Control | Spinycheek | Signal | ||
Inside shelter | day | 154.7±55 | 161.0±33 | 137.4±19 | 0.0±0.0 | 218.9±24 | 69.3±31 |
night | 41.3±25 | 67.0±13 | 56.3±17 | 0.0±0.0 | 110.3±23 | 23.5±13 | |
Outside shelter | moving, day | 98.8±32 | 85.8±19 | 43.2±18 | 143.2±30 | 42.9±13 | 62.2±21 |
moving, night | 405.8±18 | 203.8±20 | 207.4±45 | 234.2±108 | 178.7±25 | 134.3±34 | |
stationary, day | 105.5±47 | 113.1±32 | 179.4±24 | 216.8±30 | 98.2±26 | 228.9±30 | |
stationary, night | 33.0±19 | 229.2±29 | 216.2±49 | 245.8±108 | 191.0±25 | 322.2±31 |
Mean (±SE) times of different behaviours (minutes) for the crayfish species Faxonius limosus (spinycheek crayfish) and Pacifastacus leniusculus (signal crayfish) tracking inside and outside the shelter (moving or stationary) in the presence of Barbatula barbatula (stone loach) and Cottus gobio (bullhead) during day and night in the tank.
Fish situation | Stone loach | Bullhead | |||
---|---|---|---|---|---|
Spinycheek | Signal | Spinycheek | Signal | ||
Inside shelter | day | 156.1±21.8 | 67.2±26.5 | 62.0±33.4 | 33.5±21.7 |
night | 95.2±30.3 | 26.2±16.1 | 19.7±18.8 | 59.4±42.8 | |
Outside shelter | moving, day | 109.6±19.7 | 170.0±33.7 | 127.2±30.7 | 174.1±29.6 |
moving, night | 330.3±35.7 | 217.0±50.8 | 389.5±28.3 | 359.2±34.9 | |
stationary, day | 82.6±14.2 | 110.0±30.5 | 139.8±14.9 | 86.5±30.4 | |
stationary, night | 78.2±15.3 | 255.7±49.3 | 102.2±17.5 | 129.8±36.9 |
As a result of their inability to occupy the shelter in the presence of crayfish species, the stone loach expressed hiding behaviour (i.e., reduced general activity, lying low). In general, the stone loach was more active at night than the daytime. Such activity was reduced in the presence of both crayfish species, which was indicated by a significantly lower activity index (F2,22 = 7.7, P = 0.002, Fig.
Box plots showing the activity index (AI) for the benthic fish species stone loach (Barbatula barbatula) (a, b) and bullhead (Cottus gobio) (c, d) in the trials with benthic fish only (Control), in the presence of spinycheek crayfish (Faxonius limosus), and in the presence of signal crayfish (Pacifastacus leniusculus) during day and night times.
Crayfish species have different levels of agonistic behaviour, with the lowest being an exploratory movement of the antennae and accidentally getting into physical contact with the other animal (non-aggressive interactions) and the highest level being fighting (aggressive interactions). Although there was no statistically significant difference between the two crayfish species in terms of aggressive movement scores towards benthic fish, both species demonstrated aggressive interactions with benthic fish (F1,76 = 0.07, p = 0.792). Stone loaches were significantly more exposed to aggressive interactions from both crayfish species than bullheads, as evidenced by the fact that the score of aggressive behaviour was significantly higher (F1,76 = 20.5, p < 0.001, Fig.
Comparison of aggressive interactions of the two crayfish species (spinycheek crayfish, Faxonius limosus or signal crayfish, Pacifastacus leniusculus) towards the benthic fish species bullhead (Cottus gobio) and stone loach (Barbatula barbatula). Error bars indicate the standard errors of the mean. (ANOVA; * p ≤ 0.05; ** p ≤ 0.01; *** p ≤ 0.001).
Mann-Whitney test table to estimate the difference between the frequency of different aggressive interactions of invasive crayfish species (Faxonius limosus: spinycheek crayfish; Pacifastacus leniusculus: signal crayfish). Significant results are indicated by bold font.
Aggressive react | Stone loach | Bullhead | Mean Rank | |||||
---|---|---|---|---|---|---|---|---|
U | P | U | P | Stone loach | Bullhead | |||
spinycheek | signal | spinycheek | signal | |||||
Antenna wave | 52.0 | <0.001 | 147.5 | 0.173 | 27.90 | 13.10 | 17.76 | 22.13 |
Cheliped touching | 150.0 | 0.176 | 167.0 | 0.369 | 23.00 | 18.00 | 22.15 | 18.85 |
Cheliped half raise | 164.5 | 0.337 | 118.0 | 0.043 | 18.73 | 22.28 | 16.21 | 23.60 |
Cheliped full raise | 189.5 | 0.775 | 134.5 | 0.055 | 21.00 | 19.98 | 17.23 | 23.78 |
Grappling and pull | 187.0 | 0.541 | 184.0 | 0.513 | 19.85 | 21.15 | 19.70 | 21.30 |
Crayfish and benthic fish often overlap in their niches, showing a high temporal overlap in their needs for shelter (
Our results demonstrate that both stone loach and bullhead, displayed increased hiding behaviour, changing shelter use as well as their activities and movements in the presence of crayfish. Being superior competitors, spinycheek crayfish and signal crayfish succeeded in gaining control of the shelter by displacing stone loaches from the shelter, thereby decreasing the time of shelter occupation by stone loaches. Bullheads, on the other hand, showed increased shelter use when crayfish were present. This suggests that unlike stone loaches, which avoided the shelter to evade crayfish chasing, bullheads hid inside the shelter. Eviction and displacement of fish species from their own shelter by invasive crayfish under laboratory conditions have been shown not only for small benthic fish like bullheads (
In addition to the change in shelter use, both benthic fish species showed an increased hiding behaviour in response to the presence of crayfish and because crayfish monopolized the shelter. Fish reduced their general activity and spent long periods stationary at certain places outside the shelter. As a consequence of those behavioural changes, they maintained a greater average distance from the shelter than when crayfish were not present.
Our findings demonstrate that both benthic fish species are negatively affected by crayfish invasion, regardless of whether they increased or decreased their shelter use. On the other hand, stone loach is perceived to be more endangered than bullheads. Our data shows that crayfish caused the stone loach to stay away from the shelter to a greater extent than the bullhead. This could imply a more drastic reduction in the stone loach population due to increased susceptibility to predation compared to bullheads. This observation aligns with (
In addition to shelter and microhabitat use, the aggressive behaviour of invasive crayfish itself can also impact native benthic fish. Highly aggressive behaviour is known to be a key feature of successful invaders (
The level of aggression and resource-holding potential of animals can be influenced by many factors such as species, size, age, sex, or energy levels and can therefore serve as the key indicator of crayfish dominance (
Previously reported gut content analyses showed that crayfish can feed on bullheads (
We conclude that the remarkable dominance of the invasive crayfish species over benthic fish, which we observed under laboratory conditions, such as displacing them from the shelter and changing their behaviour, can render them susceptible to predation. Furthermore, both invasive crayfish species exhibit aggression towards benthic fish.
This work was funded by a scholarship from the Egyptian government and the University of Koblenz. We would like to extend our appreciation to the editor Zarah Pattison, reviewers Josie South and an anonymous reviewer for their constructive feedback and valuable suggestions, which greatly improved the quality of our manuscript. We are also grateful to Alaa Najeeb for proofreading our work.
Activity index (AI) box plots
Data type: image (.png file)
Explanation note: Box plots showing the activity index (AI) for the crayfish species signal (Pacifastacus leniusculus) (a, b) and spinycheek (Faxonius limosus) (c, d) in the trials with benthic fish bullhead (Cottus gobio) and stone loach (Barbatula barbatula) during the day and night times.
Scatterplot of the frequency of crayfish aggressive movements vs. carapace length, chela length, body mass, stone loach standard length, and stone loach body mass
Data type: image (.png file)
Explanation note: Data for both crayfish species were pooled. a-c) Scatterplots show aggression towards stone loaches which was positively correlated with carapace length (r=0.465, p=0.003), chela length (r=0.560, p<0.001), and crayfish body mass (r=0.520, p=0.001).
Correlation scatterplot of the crayfish frequency of aggressive movements, carapace length, chela length, body mass, bullhead standard length, and bullhead body mass
Data type: image (.png file)
Explanation note: Data for both crayfish species were pooled. a-e) Scatterplots display aggression towards bullhead.