Can the Baikal Amphipod Gmelinoides fasciatus (Stebbing, 1899) Have Different Responses to Light Pollution with Different Color Temperatures?

Abstract

Light pollution can affect various groups of aquatic organisms. This effect will vary depending on the color temperature of the artificial lighting. However, at the moment, the issue of adaptation of organisms to light pollution and the influence of different color temperatures on them has not been well-studied. In this study, we decided to conduct a series of experiments with individuals of the amphipod Gmelinoides fasciatus from two populations and find out how individuals adapted to light pollution. The first group of individuals is from the population in Lake Baikal (Bolshie Koty Bay), and the second group is from the population in the Angara River (within the city of Irkutsk). The second population is significantly affected by light pollution. Since the middle of the last century, there has been an artificial barrier between these populations in the form of a hydroelectric power station. The experiments showed that G. fasciatus individuals developed different behavioral strategies in relation to artificial lighting with different color temperatures. In warm light, individuals tend to move to a shaded area, while in cold light, individuals may be attracted to artificial lighting, but only in small groups. These identified patterns may likely find practical use.

1. Introduction

Light pollution is the illumination of the natural environment by artificial light sources at night. Although the first scientific articles on the effects of light pollution appeared at the beginning of the 20th century [1], the greatest interest in studying this pollutant has arisen in our time. Among other studies (concerning terrestrial organisms) [2,3,4], the problem of light pollution in water bodies has been actively studied in recent decades [4,5,6,7,8]. This pollution is caused by two factors. The first factor is the lighting of coastlines along cities (and towns). The second factor is the intensive increase in the amount of water transport [9]. It was previously predicted that the number of artificial lighting sources would increase by 6% each year [6]. According to the most recent data, over the past 30 years, global light pollution levels have increased by 49%; however, in some areas, the increase may reach 400% [10]. Coastal marine ecosystems have been studied to a greater extent [11,12]. For example, light pollution has been shown to alter the composition of aquatic communities [4], disorient individuals in space [3,13,14], concentrate them near light sources [15], alter physiological parameters [16], and create the preconditions for an increase in phytoplankton biomass [17]. In some cases, light pollution can affect the locomotor activity and growth rate of individual organisms [18]. In addition, several studies have found that living organisms can respond differently to different artificial light sources [15] and wavelengths [17,19,20,21]. It is worth considering that artificial lighting, even with an intensity of 1 lx (found in many places), is already capable of affecting some fish [22]. According to other studies, artificial lighting at night can greatly increase predatory behavior in fish [23].

At the same time, light pollution in lake ecosystems has received much less attention. However, significant steps have been made in this direction; for example, it has been shown that light pollution affects the quality of drinking water [5]. Aquatic organisms in the littoral zone are most affected by light pollution because this zone is usually located quite close to light sources and differs from other zones in its shallow depth. Thus, amphipods are one of the most promising groups of organisms for studying the effects of lighting [4,15,18]. In addition, it was found that when aquatic organisms have daily vertical migrations, they become more susceptible to the negative effects of artificial lighting [15]. It is worth considering here that under natural conditions, vertical migrations in the water column with a day–night cycle help reduce predation by fish and other marine organisms [24]. However, the appearance of artificial lighting does not allow organisms to hide from predators (moreover, it can even attract organisms).

Currently, the adaptation of living organisms to light pollution is one of the most pressing topics. Insect aggregation near light sources at night can provide accessible food for bats and influence their local distribution [25]. In some cases, organisms benefit from taking advantage of the effects of light pollution [26]. In addition, it is noted that migratory species may exhibit greater adaptive capacity than sedentary species [25].

In Lake Baikal, the basis of the littoral communities is amphipods. There are more than 350 species and subspecies in the lake [27]. The impact of light pollution on aquatic communities in Lake Baikal has only recently begun to be studied. This problem is indirectly addressed by work on the effect of artificial lighting on fish [28,29]. In addition, there are works studying the daily vertical migrations of amphipods using remote methods. In these studies, it was repeatedly noted that amphipods and fish migrating to the surface of the water at night are attracted by artificial lighting [30,31,32]. During one such study, it was accidentally discovered that the pelagic Baikal amphipod Macrohectopus branickii (Dyb.) reacts differently to artificial lighting with different wavelengths [20]. In addition, another study showed that when illuminated, fish have the opportunity to eat amphipods [33], and that the quantitative composition of amphipods differs between the two settlements. The above studies mainly emphasize the fact that both fish and amphipods are attracted by artificial lighting and do not consider the impact of this lighting on individual species and communities in both the short and long terms. At the same time, in the related global literature, there is information showing that artificial lighting has a significant negative impact on amphipods, reducing their activity and feeding behavior [18]. Moreover, it is quite possible that such an influence will be species-specific and will depend on both the intensity and the color temperature of the emitted light [34].

Among all the migratory amphipods of Lake Baikal, one species can be distinguished. This is Gmelinoides fasciatus (Stebbing, 1899). This species is widespread in the littoral zone of Lake Baikal, as well as in many rivers [35]. During the Soviet period, this species was introduced into lakes in the European part of Russia to increase the food supply for fish. At present, this species is considered invasive and actively displaces native species in many water bodies in the European part of Russia [36,37]. G. fasciatus makes a significant contribution to the structure and functioning of the benthic community, which is ensured by omnivorousness, adaptation to various substrates, and the ability to withstand moderate pollution [38]. The life cycle of this species is quite flexible, and in addition, it is significantly influenced by environmental conditions (in particular, temperature) [39]. At the same time, in Lake Baikal, the species is considered one of the main participants in daily vertical migrations and is actively attracted by artificial lighting. Currently, due to the construction of the Irkutsk hydroelectric power station (in the middle of the last century), a population of this species has formed within the city of Irkutsk. This population is partially isolated from Lake Baikal due to the dam. In addition, this population (located within the boundaries of a large city) is significantly affected by light pollution. Based on this, in this study, we decided to clarify some questions. (1) How much does light pollution (and what color temperature predominates) differ within the city of Irkutsk from what can be observed on Lake Baikal? (2) How did G. fasciatus individuals adapt to the effects of light pollution? (3) Will there be differences between individual and group behaviors?

2. Materials and Methods

2.1. Analysis of the Values of Intensity of Stable Night Light Radiation in Places Where Organisms Were Caught

The data on the values of the intensity of stable night light radiation from the Earth’s surface were taken as monthly average values for July 2024 (the data are presented in units of measurement of W/cm2/sr). The Visible and Infrared Imaging Suite (VIIRS) Day Night Band (DNB) product, presented in two versions vcmcfg and vcmslcfg, was used as a data source. We chose the vcmslcfg version, which includes data adjusted for extraneous light. This version is of lower quality, but it is the only one that covers the research area. The data were obtained from the Earth Observation Group website (https://eogdata.mines.edu/products/vnl/) (accessed on 23 September 2024). The spatial resolution of the resulting raster layers is 400 m. The data for comparison were extracted using QGIS software at 21 points (for Bolshiye Koty Bay—11 points, for the Angara River section—10 points) (Figure 1) [40,41].

In addition to the above, we measured the color temperature values (in Kelvin) of artificial lighting sources on the coastline of the Angara River. A spectrum analyzer (OPPLE Light Master) was used to measure color temperatures.

2.2. Capture and Acclimation of Organisms

The amphipods that were not exposed to long-term light pollution were caught in the coastal zone of Lake Baikal, near the village of Bolshiye Koty (51°54′11.3” N 105°04′07.8” E). Amphipods from a population exposed to light pollution for a long period of time were collected in the Angara River near the embankment of the city of Irkutsk (52°16′49.9” N 104°16′23.2” E). The catch was carried out with a hydrobiological net (from the water by stirring up sediment) during the daytime in July. A total of 250 individuals (sexually mature individuals of both sexes) from each population were caught.

Before the experiments, the selected amphipods were acclimated for 7 days in laboratory conditions [21]. For amphipods caught in Lake Baikal, a normal daily lighting regime was established during the acclimation period (12 h of daylight, 12 h without light) [42]. The following lighting regime was established for the amphipods caught in the Angara: 12 h of daylight and 12 h of low light (light levels varied around 0.7 lx), corresponding to the light level in the Angara within the city limits of Irkutsk at night (according to our unpublished data).

2.3. Conducting Experiments

The experiments were approved by a special commission of the Research Institute of Biology of Irkutsk State University (Protocol no. 14, dated 22 August 2024). The experiments were carried out in accordance with international ethical standards [43].

A T-shaped aquarium was used for the experiments (Figure 2). Along the long part of the aquarium, a light gradient (warm or cold) from 0.1 to 30 lx was created using a light source. In the branches of the aquarium, the illumination level was 0 lx (Figure 2). As a result, 5 zones were allocated in the aquarium: 0 lx, 0.1–1 lx, 1–10 lx, 10–20 lx, and 20–30 lx. In the aquarium, 20 amphipods were simultaneously introduced into the 0.1–1 lx zone (5 replicates in total) for 10 min using a small net. The distribution of amphipods by zones was recorded in the 1st, 3rd, 5th, 7th, and 10th minutes of observation. These experiments were conducted in the dark in a laboratory with 0 lx illumination. In addition, experiments were conducted during the day with natural light and in the dark without light. It is worth noting separately that during the daytime, in zones 0.1–1, 1–10, 10–20, and 20–30 lx, the illumination was uniform (the experiment was conducted in bright daylight). At the same time, in the zones with 0 lx, which are located to the right and left of the 0.1–1 lx zone (Figure 2), shaded areas were created.

The illumination level during the experiments was controlled using a CEM DT-8809A lux meter. The color temperature of artificial light sources was 3200 K (warm light) and 5600 K (cold light).

The water temperature during acclimation and during the experiment was 16 °C.

2.4. Statistical Analysis of Data

The obtained data were processed using the R programming language (V. 4.4.1) in the R-Studio program. The nonparametric Kruskal–Wallis test was used to establish the presence of statistically significant differences between the distributions of amphipods (20 individuals) across the aquarium zones. The nonparametric Dunn’s post hoc test with Holm’s correction for multiple comparisons (PMCMRplus package (version 1.9.12)) was used to compare pairwise amphipod distributions across light levels, observation times, and light types. Comparisons between populations were made using the Mann–Whitney U Test. The Generalized Fisher’s Exact Test with FDR correction [44] was used to determine differences between amphipod distributions (1 individual). The same test was used to compare populations. In turn, the Mann–Whitney U Test was used to establish statistically significant differences between illumination in the amphipod collection sites. Differences between samples in all cases were considered statistically significant at p < 0.05.

3. Results

3.1. Illumination at Sampling Sites

The average value of the intensity of stable night light radiation for the first place of collection of organisms (in Bolshie Koty Bay) is 1.4 ± 0.2 W/cm²/sr (Figure 3). The maximum value for the bay is 2.2 W/cm²/sr, and the minimum (directly at the place where the organisms were caught) is 0.0 W/cm²/sr. However, for the Angara River within the city of Irkutsk, where the organisms were collected, this value is 45.3 ± 4.1 W/cm²/sr (with the maximum being 59.5 W/cm²/sr and the minimum being 22.0 W/cm²/sr). In the indicated area, the river is completely illuminated.

Additional analysis of the color temperature of artificial lighting sources near the amphipod catching site on the river showed that sources with warm lighting of 2030.0 ± 27.6 K predominate.

3.2. Group Behavior Under Experimental Conditions

The generalized and expanded results of experiments aimed at the selection of a certain zone by amphipods (in a group of 20 individuals) from Lake Baikal are presented in Figure 4a,b. During daylight hours, individuals move to the only shaded area marked as 0 lx (Figure 4a,b). Statistical analysis of the data shows that the distribution of individuals during the daytime period is statistically significantly different from that during the night period without light (p = 0.0003) and during the night period with warm lighting (p = 0.0003) (

Table 1. Levels of statistical significance in pairwise comparisons of the amphipod distribution from the Baikal population in different types of lighting using Dunn’s post hoc test with Holm’s correction (Kruskal–Wallis chi-squared = 22.204, df = 3, p-value = 5.916 × 10⁻⁵).

Lighting Types	Cold Light	Daylight	Without Light (Night)
Daylight	0.15
Without light (Night)	0.15	0.0003
Warm light	0.15	0.0003	0.9

). However, there is no difference between daytime and nighttime distributions when using cold lighting. The distribution between the aquarium zones under warm lighting at night shows us that some individuals tend to go into the darkness, while others move into a more illuminated zone (Figure 4a,b;

Table 2. Levels of statistical significance in pairwise comparisons of the distribution of amphipods from the Baikal population across aquarium zones under different types of lighting using Dunn’s post hoc test with Holm’s correction.

Daylight (Kruskal–Wallis Chi-Squared = 79.496, df = 4, p-value = 2.227 × 10−16)
Aquarium zones	0	0.1–1	1–10	10–20
0.1–1	5.7 × 10−5
1–10	1.2 × 10−10	0.08
10–20	1.4 × 10−15	0.0008	0.4
20–30	3.9 × 10−8	0.4	0.4	0.08
Without light (Night) (Kruskal–Wallis chi-squared = 65.959, df = 4, p-value = 1.616 × 10−13)
Aquarium zones	0	0.1–1	1–10	10–20
0.1–1	0.01
1–10	1.2 × 10−6	0.07
10–20	7.8 × 10−12	0.0001	0.16
20–30	0.2	0.2	0.001	1.4 × 10−7
Warm light (Kruskal–Wallis chi-squared = 81.206, df = 4, p-value < 2.2 × 10−16)
Aquarium zones	0	0.1–1	1–10	10–20
0.1–1	6.6 × 10−6
1–10	9.7 × 10−6	1
10–20	9.3 × 10−11	0.16	0.16
20–30	1	2.0 × 10−6	3.1 × 10−6	1.4 × 10−11
Cold light (Kruskal–Wallis chi-squared = 84.803, df = 4, p-value < 2.2 × 10−16)
Aquarium zones	0	0.1–1	1–10	10–20
0.1–1	1.3 × 10−6
1–10	4.3 × 10−11	0.2
10–20	2 × 10−16	0.004	0.2
20–30	0.0004	0.2	0.01	3.3 × 10−5

).

It is worth noting separately that there are no significant differences in the distribution of amphipods between minutes in all types of experiments. In other words, the amphipods immediately occupied the most favorable zones of the aquarium for them and did not change their choice for 10 min.

Visualization of the results of experiments with amphipods from the Angara River shows us a different distribution of individuals under different types of lighting (Figure 5a,b). The distribution of amphipods during the daytime is significantly different from the distribution under cold light (p = 0.0003) (

Table 3. Levels of statistical significance in pairwise comparisons of the distribution of amphipods from the Angara population in different types of lighting using Dunn’s post hoc test with Holm’s correction (Kruskal–Wallis chi-squared = 35.126, df = 3, p-value = 1.146 × 10⁻⁷).

Lighting Types	Cold Light	Daylight	Without Light
Daylight	0.0003
Without light	0.14	4.3 × 10−8
Warm light	0.4	0.004	0.03

). Individuals prefer to be in the shaded area. This is very clearly visible (Figure 5a,b,

Table 4. Levels of statistical significance in pairwise comparisons of the distribution of amphipods from the Angara population across aquarium zones under different types of lighting using Dunn’s post hoc test with Holm’s correction.

Daylight (Kruskal–Wallis Chi-Squared = 93.886, df = 4, p-Value < 2.2 × 10−16)
Aquarium zones	0	0.1–1	1–10	10–20
0.1–1	1.1 × 10−5
1–10	2.4 × 10−11	0.11
10–20	7.5 × 10−15	0.005	0.6
20–30	1.5 × 10−15	0.003	0.6	0.8
Without light (Kruskal–Wallis chi-squared = 72.08, df = 4, p-value = 8.254 × 10−15)
Aquarium zones	0	0.1–1	1–10	10–20
0.1–1	7.8 × 10−6
1–10	7.2 × 10−10	0.3
10–20	1.6 × 10−14	0.01	0.32
20–30	4.3 × 10−5	0.7	0.19	0.003
Warm light (Kruskal–Wallis chi-squared = 71.733, df = 4, p-value = 9.773 × 10−15)
Aquarium zones	0	0.1–1	1–10	10–20
0.1–1	4.7 × 10−8
1–10	2.3 × 10−9	0.7
10–20	2.7 × 10−14	0.18	0.4
20–30	5.7 × 10−6	0.7	0.4	0.01
Cold light (Kruskal–Wallis chi-squared = 82.069, df = 4, p-value < 2.2 × 10−16)
Aquarium zones	0	0.1–1	1–10	10–20
0.1–1	0.0008
1–10	2.7 × 10−13	0.0008
10–20	1.2 × 10−13	0.0005	0.9
20–30	1.3 × 10−7	0.15	0.15	0.15

). Moreover, in this case, the distribution at night without lighting differs from the distribution at night using warm lighting.

The distribution of amphipods from the Angara population (Table 4) across the aquarium zones has some differences from the distribution of amphipods from the Baikal population of this species (Table 2). The most interesting difference is that the number of amphipods in the 0 lx zone in all cases is statistically significantly different from other zones.

When comparing the results obtained, it becomes clear that individuals from the Angara River are statistically more likely to try to hide in daylight. Moreover, they are less attracted to warm lighting at night (Figure 5a,b,

Table 5. Comparison of the distribution results of G. fasciatus individuals from different populations among themselves during a group experiment using the Mann–Whitney U Test.

Daylight (W = 6516)		Without Light (W = 7045)		Warm Light (W = 5899)		Cold Light (W = 7493.5)
	Angara		Angara		Angara		Angara
Baikal	0.01	Baikal	0.17	Baikal	0.0007	Baikal	0.57

).

3.3. Individual Behavior Under Experimental Conditions

The statistical analysis of data on the individual behavior of G. fasciatus from Lake Baikal showed more differences in distribution than in the group experiment. At the same time, the main significant differences are similar to the group experiment (Figure 6,

Table 6. Comparison of amphipod distribution frequencies from Lake Baikal in an aquarium using Fisher’s exact test (2000 replicates) with FDR correction between different types of lighting.

Comparison	p.adj.Fisher
cold: day	0.4
cold: night	0.02
cold: warm	0.000001
day: night	0.0003
day: warm	6.66 × 10−8
night: warm	0.02

). Thus, the distribution of amphipods during the day is statistically significantly different from the distribution at night without lighting (p = 0.0003) and at night with warm lighting (p = 6.66 × 10⁻⁸), and does not differ from the distribution at night with cold lighting (p = 0.4).

Analysis of the individual behavior of G. fasciatus from the Angara River shows (Figure 7,

Table 7. Comparison of distribution frequencies of amphipods from the Angara River in an aquarium using Fisher’s exact test (2000 replicates) with FDR correction between different types of lighting.

Comparison	p.adj.Fisher
cold: day	0.8
cold: night	0.0002
cold: warm	0.4
day: night	0.0003
day: warm	0.08
night: warm	0.0003

) that under any type of lighting (daytime sunlight or warm/cold artificial lighting), amphipods try to stay in the darkest place. The latter statement is supported by data on group behavior (Table 4).

The comparison of the distribution of amphipods from different populations during the individual experiment (Figure 6 and Figure 7,

Table 8. Comparison of the distribution results of G. fasciatus individuals from different populations among themselves during an individual experiment using Fisher’s test.

Day		Night		Warm		Cold
	Angara		Angara		Angara		Angara
Baikal	0.009	Baikal	0.06	Baikal	0.0004	Baikal	0.001

) shows statistically significant results similar to the group experiment. However, in individual experiments, it is also evident and statistically confirmed that G. fasciatus individuals from the Angara River prefer to go to a shaded area and not remain in the light.

4. Discussion

4.1. Current Situation

G. fasciatus (as mentioned earlier) is a species of Baikal origin and is a valuable object for aquaculture [45]. This species demonstrates high ecological plasticity [46], which allowed it to populate and dominate benthic communities in many watercourses and reservoirs [35,36,37,46], even penetrating into the eastern part of the Baltic Sea [47].

According to one of the latest studies, G. fasciatus is a species that is attracted to light sources with different wavelengths and color temperatures [21]. Moreover, it was noted that individuals of this species in groups are capable of horizontal migrations during the daytime [21,30]. In addition, individuals have been repeatedly observed as part of the nocturnal migratory community in Lakes Baikal and Ladoga and have been attracted to light sources [30,33,48,49]. Apparently, it was precisely this migratory behavior (in combination with high ecological plasticity), both during the day and at night, that determined the rapid and successful invasions of this species into many water bodies.

The positive phototaxis of G. fasciatus in relation to natural and artificial light makes this species potentially susceptible to light pollution. At the moment, it is clear that light pollution on the Angara River within the city of Irkutsk significantly exceeds the values that can be observed on Lake Baikal (Figure 3). In addition, there is another factor on the Angara River that can significantly affect the population of G. fasciatus. The construction of the Irkutsk hydroelectric power station led to the formation of a hole in the ice within the city limits on the Angara River that does not freeze in winter. As a consequence of this, the formation of a “cold” wintering population of ducks occurred (some of the population stopped flying to southern regions in the fall). This wintering population of ducks numbers several tens of thousands of individuals [50]. Two species are dominant: Bucephala clangula (L., 1758) and Anas platyrhynchos L., 1758. Both species feed on benthic invertebrates, particularly amphipods. Thus, year-round pressure from two groups of predators (fish and ducks—in Lake Baikal, this pressure is created primarily by fish in the summer, and only by fish in the winter) was created on the G. fasciatus population. This pressure is exacerbated by high levels of light pollution (and its continuing global increase) [10], which allows predators to hunt amphipods not only during the day [30,32].

4.2. Group and Individual Reactions to Artificial Lighting

The group experiments with G. fasciatus individuals showed that individuals from both populations are equally distributed across aquarium zones at night and under cold lighting (Table 5). At the same time, the absence of differences between these distributions for amphipods from the Baikal population (Table 1) apparently indicates that cold lighting is perceived by individuals as daylight. To be more precise, cold lighting is perceived as natural lighting in the early hours (due to its low intensity compared to daylight). The differences found in the comparison of the distribution of amphipods from the Angara population (Table 3) under daylight and the use of cold lighting confirm this to some extent. In this case, under daylight (as opposed to using cold lighting), amphipod individuals choose a shaded area to a much greater extent. Such a choice during the daytime may be due to the huge number of potential predators concentrated in a local area [47] and the complete impossibility of moving without being eaten.

In the experiments with amphipod groups, there were differences in the distribution of the Baikal and Angara populations during the daytime and when using warm lighting (Table 5). Differences during the daytime confirm that in the local section of the Angara River, due to the above-mentioned reasons, the pressure from predators is significantly higher than in the amphipod-catching area in Lake Baikal (a significant number of ducks are added to the fish). In turn, the differences in the distribution of individuals of the two populations by zones under warm lighting show that individuals of the Baikal population are attracted by this lighting. In this case, they are divided into approximately two equal parts: one part remains in the shadow, and the other goes to the warm light (Figure 4a; Table 2). Apparently, in the case of the Angara population, natural selection took the path of fixing behavior in the population with a lesser tendency toward warm lighting. Let us recall that, according to the measurements taken along the coastline of the Angara River, there are sources with warm lighting (2030.0 ± 27.6 K).

The results of the experiments aimed at the individual selection of zones in the aquarium confirm all of the above. However, there is one significant addition. In the individual distribution, we see significant differences between the Baikal and Angara populations under cold lighting (Table 8; Figure 6 and Figure 7), which is absent in the group experiment (Table 5). Based on this, it can be concluded that individuals of the Angara population of G. fasciatus perform species-specific ascents to the upper layers of water (to carry out vertical and/or horizontal migrations) only in the early hours (or under similar exposure to light pollution with cold lighting) and only as part of a group of individuals. Surfacing in a group of individuals undoubtedly serves as a defense mechanism and minimizes the likelihood of each individual being eaten during a solitary surfacing. Many species of animals (including crustaceans) use similar behavior [51]. In addition, it is worth saying that, as a rule, behavioral changes in amphipods are caused by a combination of the influence of the habitat with the action of ecological and biological mechanisms [21,52]. This is also evident from the results of these experiments.

4.3. Possible Consequences

According to the literary data, it is known that individuals of this species float to the upper layers of water for the purposes of searching for food, active or passive (under the influence of the current) movement, and for the purpose of reproduction [53]. We have also repeatedly observed couples of this species in Lake Baikal swimming at night in the water column. Taking this into account, it can be assumed that light pollution not only increases the pressure on this species from predators and suppresses its migratory behavior but also negatively affects the reproduction of this species (it prevents individuals from finding a sexual partner during migrations due to their short duration due to lighting conditions). This may have a negative impact on the population of G. fasciatus individuals in the natural range of this species. However, it may find practical application in relation to the regulation of the population of this species in places not typical for it and to prevent unwanted invasions. Of course, any such use of the light pollution effect to regulate the numbers of G. fasciatus and its rate of spread will require a great deal of additional testing and research. This will be necessary in order not to harm native species.

Possible positive aspects of light pollution are also worth mentioning. For example, the positive effect of artificial lighting on reproduction has previously been found for some species of crayfish and shrimp [54]. Can light pollution have a positive effect on the reproduction of a given species or the growth rate of a given species? The question remains open at the moment. Of course, in a certain sense, it is premature to talk about this. However, given the high ecological flexibility of this species, the rate of spread, and the displacement of native species, the hypothetical positive effect of artificial lighting on reproduction or accelerated growth will make this species one of the most promising objects of aquaculture and aquarium keeping. This assumption requires research and verification.

Returning to the population of this species within the city of Irkutsk, it is worth saying that, at the moment, it is fully exposed to the effects of warm artificial lighting. However, with the transition to LEDs, there has been an increase in cold light sources worldwide, which are considered more dangerous for organisms [55]. It is likely that this will happen in this area after some time. At the moment, there is practically no cold lighting at night in this area, and the cold lighting during the experiment was most likely perceived by these amphipods as the early hours of daylight. Given this, the potential shift from warm to cool light (and the likely increase in its intensity) raises some concern for the survival of the G. fasciatus population at this location. However, it is possible that due to ecological plasticity, individuals of this species will be able to adapt to changing environmental conditions.

5. Conclusions

In this study, the distribution of individuals from two populations of G. fasciatus was analyzed (through experiments), depending on artificial lighting with different color temperatures. A population in the natural environment is exposed to light pollution, while the other is not exposed or is exposed to a minor degree. Based on the analysis of the obtained data, it was concluded that G. fasciatus is a potentially vulnerable species to the effects of light pollution. However, this species demonstrates high ecological plasticity in relation to artificial lighting. Moreover, it demonstrates different behavioral strategies (under conditions of higher artificial light levels) in relation to light sources with different color temperatures (under warm light, it tries to go to shaded areas, and under cold light, migratory activity to more illuminated areas is possible, but only in groups).

Conducting experiments with this species aimed at limiting its invasive activity will be very promising. In addition, in contrast to this, it is important to conduct experiments on the potential improvement of reproductive qualities under the influence of artificial lighting (since this species can become a very promising object of aquaculture).

In addition, it is worth recognizing that this study has some limitations, namely a relatively small number of amphipods and the use of only two color temperature values. This study is preliminary and needs to be continued.