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Main characteristics of the Lake Pleshcheyevo population of Dreissena polymorpha (Bivalvia, Dreissenidae)
Ekaterina G. Pryanichnikova*, Alexander I. Tsvetkov
Papanin Institute for Biology of Inland Waters, Russian Academy of Sciences, Borok 109, Nekouz District, Yaroslavl Region, 152742 Russia *[email protected]
Received: 23.07.2018 Accepted: 03.09.2018 Published online: 17.10.2018
DOI: 10.23859/estr-180723a UDC 574.587(285.2):594.1 URL: http://www.ecosysttrans.com/ publikatsii/detail_page.php?ID=75
ISSN 2619-094X Print ISSN 2619-0931 Online
Translated by S.V. Nikolaeva
The main characteristics of the population of Dreissena polymorpha (Pallas, 1771) in Lake Pleshcheyevo in 2014-2016 are discussed, and two different sampling methods for D. polymorpha are compared. The lack of mass reproduction of D. polymorpha in 2015 is possibly related, among other causes, to climate change and alterations in the temperature regime of the lake. Dreissena is shown to be one of the main benthic suspension feeders in Lake Pleshcheyevo.
Keywords: zebra mussels, abundance, yearlings, suspension feeders, sublittoral.
Pryanichnikova, E.G., Tsvetkov, A.I., 2018. Main characteristics of the Lake Pleshcheyevo population of Dreissena polymorpha (Bivalvia, Dreissenidae). Ecosystem Transformation 1 (2), 11-18.
Introduction
Adult freshwater mussels Dreissena polymorpha (Pallas, 1771) were first recorded in Lake Pleshcheyevo (N 56°43'-56°48', E 38°43'-38°50') in 1984, and veligers - since 1987 (Stolbunova, 2006; Zhgareva, 1992); since then Dreissena polymorpha has been repeatedly studied in this lake (Bakanov, 1983; Butorin and Sklyarenko, 1989; Shcherbina, 2008; etc.). Colonies of Dreissena change the habitats of hydrobionts by forming a convenient substrate, capable of accommodating many macro-invertebrates, affect current rates and illumination, and improve oxygenation. Also Dreissena druses provide good substrates for yearling settlement.
Dreissena precipitates much of the suspension from the water, which is concentrated as agglutinants and feces and serves as food for detritivores. Direct trophic connections depend on the accumulation of feces and agglutinants of populations of Dreissena (Protasov, 2008). In addition, dead and living individuals of Dreissena can served as food for bottom feeding fish. For instance, in the Ucha
Reservoir, after invasion of D. polymorpha, the growth rate and fecundity of European roach Rutilus rutilus (Cyprinidae) increased, and became similar to those of Rutilus caspicus (Vinberg, 1980). In Lake Pleshcheyevo, after one generation following the invasion of D. polymorpha, a rapidly growing Dreissena-feeding form of the European roach had developed (Kasyanov and Izyumov, 1995).
The direct influence of Dreissena on bacterial plankton is by filtering out forms suitable for feeding, and the indirect influence can be either positive or negative for the development of bacteria (Kurbatova and Lapteva, 2008). Dreissena negatively influences phytoplankton by reducing the amount of algae with size smaller than 40 ^m, whereas a reduction in the proportion of zooplankton feeders occurs when the competition for all kinds of food resources intensifies. Changes in the zooplankton structure, in particular, a 1.5-2-fold decrease in the abundance of rotifers, is a result of competition with Dreissena for seston resources (Lazareva and Zhdanova, 2008). D. polymorpha also affects the circulation of biogenic
systems in basins. In the ecosystem of Lake Mikolaiskoe the content of phosphorus in Dreissena (0.47 t) is comparable with the content of this element in macrophytes (0.70 t) and fish (0.80 t). Feces of freshwater mussels contain 0.1% phosphorus and 3.5% nitrogen, calculated on a dried basis, which is 0.06-0.1 and 0.14-0.33 the respective concentrations of these elements in the seston consumed by the mussels.
Biogenic elements accumulated by Dreissena polymorpha are taken out of circulation for 4-6 years, and if the period of shell decomposition is taken into account - almost 20 years (Stanczykowska, 1984).
Judging from the above, D. polymorpha is an
important component of basin ecosystems. Recording the dynamics of the main characteristics of the populations, and studying the role of D. polymorpha as a major suspension feeder, may be important for the analysis of the ecosystem function of Lake Pleshcheyevo.
Materials and methods
The mussels were selected from samples of macrobenthos collected during the 2014-2015 growing season, and also in autumn 2016. The following classification of the basin zones was accepted (Butorin and Sklyarenko, 1989): the lower boundary of the littoral was drawn at the 3 m depth,
Fig. 1. Location of main sampling stations in Lake Pleshcheyevo. Sampling sites: 1 - littoral, 2 - sublittoral, 3 - profundal. Numbers (1-10) show main collecting stations of D. polymorpha in the sublittoral. I - area section directed away from the mouth of the Trubezh River; II - area section directed away from the "Boat of Peter the Great" Museum; III - area section directed away from the source of the Veksa River.
Station no. - 2014 2015 2016
Spring Summer Autumn Spring Summer Autumn Autumn
1 5.3 10.3 4.3 3.2 3.7 1.0 0.5
246.0 3150.0 582.5 1360.0 808.5 173.4 197.0
2 0.2 0 0 6.6 6.9 0 0.1
9.0 0 0 1500.0 5464.8 0 3.5
3 3.2 0.2 5.4 0.3 3.0 0.3 0.2
380 10.0 2394.5 1062.5 2015.0 87.9 0.5
4 10.8 23.7 0.7 11.1 10.7 14.0
2977.0 21145.0 136.0 3640.6 4322.5 5301.9
5 0.4 1.6 0.8 3.5 3.5 2.4
465.5 1500.0 500.5 1741.0 3365.2 2351.0
6 0.1 3.2 0.4 0.3 0.2 3.8 1.5
0.1 4930.0 85.0 4.0 4.8 1370.9 27.5
7 0.1 0.2 0
331.5 120.1 0
8 2.7 2.7 2.4
2265.5 4856.6 2014.2
9 2.5 2.8 0
1200.0 2582.0 0
10 2.1 2.8 1.5
313.5 3031.0 2126.7
Table 1. Abundance and biomass dynamics of D. polymorpha in the sublittoral of Lake Pleshcheyevo.
Note: above the line (N, thous. ind./m2), below the line biomass (B, g/m2), "0" - live Dreissena were absent, only the thanatocoenosis (coquinae) was found, "-" no data.
and the base of the sublittoral is drawn at 15 m, at the boundary of the change in the slope angle. Areas below that mark were treated as the profundal zone. The samples of macrobenthos were collected using a modified DAK-100 bottom sampler (catchment area 0.01 m2), in two replicates at each station. In 2014 and 2015, benthos was examined at Stations 16 and 22, respectively, including in the sublittoral and Stations 6 and 10, respectively (Fig. 1, Table. 1). In autumn 2016, it was examined at 14 stations, four of which were in the sublittoral. The depth of the macrobenthos sampling was 1.5 to 23 m.
We selected live specimens of D. polymorpha from substrate washed in a mesh bag (cells 220 ^m in size), identified the raw mass and measured the length of the shell of each mussel with a precision up to 0.5 mm. The density (N, thousands of individuals/m2), biomass (B, g/m2) and frequency (P, %) of Dreissena in the lake were calculated. In addition, the mean length of an individual of zebra mussels (mm) and the proportion of yearlings (up to 5 mm inclusive, %).
In the lake, D. polymorpha occurs in highly aggregated colonies, as follows from visual observations and published data (Bakanov, 1983).
Therefore, for the refinement of the abundance of Dreissena we collected additional samples of mussels in some areas by underwater filming with a frame 0.5*0.5 m.
To evaluate reproduction, we studied veligers of Dreissena in zooplankton samples (Zhdanova, 2018).
To study the effect of climate change on the temperature regimes of the lake, HOBO Pendant (UA-002-64) and HOBO Pro v2 (U22-001) temperature data loggers were installed from May to October at various depths in the deep part of the lake. The loggers were installed at the following depths: surface, 1.5, 5, 8, 13, 15, 17 and 21 m.
To estimate the role of mussels in filtering the water in basins we used established correlations of the rate of water filtration by Dreissena with their size and the concentration of suspension in water (Alimov, 1981; Mikheev, 1967; Pryanichnikova, 2012; Pryanichnikova and Shcherbina, 2005). The suspension settled by Dreissena polymorpha was also approximately calculated using data from Lvova et al. (2005).
Results
In the littoral of Lake Pleshcheyevo, D. polymorpha was only found in 2014 at one station in the soutwestern part of the lake, where the population of mussels entirely consisted of young mussels and yearlings. The total abundance of Dreissena polymorpha for the entire season was on average 0.3±0.2 thous. ind./m2, biomass - 5.3±4.2 g/m2 and they constituted 20-30% of the littoral macrobenthos. Visually, thanks to the very clear water, it was noted that in this zone of the lake, Dreissena druses are arranged in patches, at a considerable distance from one another, so a quantitative estimation of distribution using available sampling methods (bottom dredge) is difficult. It is possible that this was the reason why in 2015 and even in the autumn of 2016 D. polymorpha was not recorded even at an expanded network of stations. Dreissena was not recorded in the macrobenthos of the profundal zone throughout the entire study period.
In 2014, D. polymorpha was recorded at 6, and in 2015 at 10 stations in the sublittoral of the lake (Fig. 1, Table 1). In autumn 2016, Dreissena was recorded at four stations in the sublittoral. A high density of Dreissena was recorded at stations with a considerable quantity of empty shells in the substrate. Accumulation of coquinae supports the long-term and consistent presence of the Dreissena populations in the studied zones of the lake. All this is characteristic of the southern and southeastern zones of the lake (stations 1-5). In 2014-2015, the mean density of Dreissena at these locations was 4.6±1.0 thous. ind./m2. In autumn 2016,
the quantity of Dreissena in the southeastern zone of the lake was 0.2±0.1 thous. ind./m2.
During the study period, despite the expansion of the network of stations in 2015, the recorded abundance of D. polymorpha in the benthos of the lake remained almost unchanged and was on average 41±3% (Table 2).
In 2014, apart from sampling D. polymorpha populations using a bottom sampler, we determined the density of mussel populations at some stations using a frame. Comparison of the results showed that mussel abundance estimated using a frame at two stations was considerably lower than that determined by means of the bottom sampler (Table 3).
In 2015, the mean length of a D. polymorpha individual at some zones of the sublittoral was relatively high (up to 19-21 mm) and was on average 13.1±1.2 mm. This is because the sampling contained almost no yearlings (up to 5 mm in size), which dominated Dreissena colonies at these stations in 2014, when the average length was 10.2±2.5 mm.
Both in spring and summer 2014-2015, D. polymorpha was present at most (80-100%) studied stations in the sublittoral (Table 1). In summer 2015, at some stations the abundance of Dreissena was lower than in 2014, yearlings were almost completely absent and the proportion of mussels <5 mm was even lower than in spring (Table 1, 2). In addition, a consistent decrease in the average length of a mussel due to the appearance of young specimens, was not recorded (Table 2).
In autumns of 2014 and 2015, D. polymorpha
Parameter Spring 2014 Summer 2014 Autumn 2014
N, ind./m2 2829±1525 7770±3537 2017±823
B, g/m2 668.3±407.5 6147.0±3134.0 618.2±335.7
Mussel length, mm 8.6±2.4 11.3±3.2 10.8±1.9
Proportion of yearlings (<5 mm), % 57.8±14.9 30.9±11.8 50.4±16.2
P in the lake benthos, % 47 31 38
Spring 2015 Summer 2015 Autumn 2015
N, ind./m2 3490±1085 3630±1040 2525±1411
B, g/m2 1341.8±356.4 2657.0±642.6 1342.6±567.7
Mussel length, mm 11.9±1.2 13.6±1.2 13.7±1.1
Proportion of yearlings (<5 mm), % 28.4±10.5 17.8±9.9 15.4±6.4
P in the lake benthos, % 48 45 36
Autumn 2016
N, ind./m2 525±319
B, g/m2 57.2±47.0
P in the lake benthos, % 40
Table 2. Main characteristics of D. polymorpha populations in the sublittoral of Lake Pleshcheyevo.
Station no. DAK-100 Frame
1 10.3 2.4
2 0.2 0.2
4 23.7 2.6
5 1.6 1.8
6 3.2 2.7
Table 3. Density (N, thous. ind./m2) of D. polymorphs when different methods of sampling are used.
was not recorded at all stations of the sublittoral (70-83%) (Table 1). The average abundance of Dreissena was not different (Table 2), but in autumn 2015, an increase in the biomass was recorded. The proportion of yearlings of D. polymorpha in the autumn 2015 relative to the equivalent period of the previous year was low and comparable with the summer figures (Table 2). In autumn 2016, the density and biomass of Dreissena polymorpha were very low and were 0.5±0.3 thous. ind./m2 and 57.2±47.0 g/m2 respectively.
Based on the analysis of the long-term dynamics, minimal values for the density of veligers were noted in 2015 (Zhdanova, 2018).
Using the data obtained on the mean biomass of D. polymorpha in 1 m2 in Lake Pleshcheyevo, and also the areas of the sublittoral and data on the biomass of phytoplankton it was calculated that D. polymorpha can Alter daily up to 1/30 of the total of the volume of water in the lake. Hence, in a season of active filtration (approximately 137 days), mussels can Alter the entire volume of water in the lake up to 4-5 times. It has also been calculated that in a season of active filtration, D. polymorpha in Lake Pleshcheyevo can settle up to several thousand tons of suspended material as feces and agglutinants.
Discussion
A high degree of aggregation of the D. polymorpha colonies in the lake was confirmed both by visual observations during sampling the lake by divers using a frame in 2014, and published data (Bakanov, 1983). Differences between the densities of Dreissena polymorpha received by various methods, were recorded only in some places (Table 3): at station 1, where at the time of sampling there were many yearlings (57%), and also at station 4, where it was visually recorded that Dreissena forms heterogeneous, highly aggregated colonies on dead shells and compact substrate. Such differences in the density of Dreissena are received in places where it forms colonies of "stains" and "brushes" (Protasov, 2008). In general, in places where D. polymorpha forms dense colonies, differences between the numbers of mussels obtained by two different types of sampling are minimal (Table 3). Therefore, the use of a bottom sampler to estimate the abundance of Dreissena polymorpha in places of its mass
occurrence is acceptable.
Abundant permanent colonies of D. polymorpha have been recorded at depths of 4-9 m, in the sublittoral of Lake Pleshcheyevo (Butorin and Sklyarenko, 1989). On average, in 2014, the abundance of D. polymorpha was estimated as 3.9±1.8 thous. ind./m2, which corresponds to our data from 2015 (3.2±0.4 thous. ind./m2) and those from the beginning of the 1990s, but is less than in 1996 (Shcherbina, 2008). A similar situation is recorded for long-term dynamics of the Dreissena biomass. In 2014, the mean biomass of D. polymorpha constituted 2218.8±1070.0 g/m2, in 2015 - 1780.5±536.8 g/m2, which is half of that recorded for 1996 (Shcherbina, 2008). The density of Dreissena polymorpha in autumn 2016 was considerably less than the density in the previous years (0.5±0.3 thous. ind./m2). Apparently, this is a consequence of disruptions in the reproduction of Dreissena in 2015.
In 1991 and 1996, the mean length of one individual of D. polymorpha in Lake Pleshcheyevo decreased from spring-summer to autumn, most likely due to the replenish of the population with young organisms (Shcherbina, 2008). In our study, a similar situation was recorded for 2014, whereas in 2015, there was no difference between the summer and autumn data (Table 2). This is also indirect evidence that in 2015 the population of Dreissena polymorpha was not supplemented by yearlings.
Thus, in 2015 no mass reproduction of Dreissena polymorpha was recorded in Lake Pleshcheyevo. This is supported by several facts: low proportion of yearlings smaller than 5 mm in size, mean length in the population, isolated presence of veligers in zooplankton and the absence of the mean summer quantity of Dreissena.
One of the reasons for the events discussed above is climate change. According to the Hydrometeorological Center of Russia (Obzory..., 2018), the summer of 2015 was the coolest in the last five years. The weather in mid-June-beginning of July was particularly cold. At that time, minimal air temperatures were very low (up to +4 °C at night), although day temperature occasionally reached +23-25 °C. July was also colder than the norm by 2-4 °C. Other unusual characteristics of that summer included few days with warm or hot weather. During the growing season, there were 30 days
with a temperature above +25 °C and no days with a temperature over +30 °C. For comparison, many more such days were recorded in 2014 (108 and 7, respectively) and in 2013 (75 and 4, respectively).
The reproduction season of Dreissena polymorpha, manifested by the appearance of the first planktonic larvae, should begin at a water temperature of 12-15 °C, and the mass spawning at 18-20 °C (Lvova and Makarova, 1994). At a temperature below 10 °C Dreissena mussels do not grow or develop (Alimov, 1974; Lvova, 1977). The total of effective temperatures (above 10 °C, which is required for gonadal development from the first stage to the beginning of spawning) in all populations of Dreissena polymorpha is close to 2500 degrees (Lvova and Makarova, 1994). It is possible that in 2015, the cumulative effect of temperatures was not sufficient for the gonads of Dreissena polymorpha to be completely formed. Low temperatures in the bottom waters of the sublittoral in May-June could have a negative effect on the reproduction of Dreissena polymorpha. A stable temperature of 10 °C and above that was recorded at a depth of 5 m by the end of May, and at a depth of 8 m in the first ten days of June. At the beginning of July, especially in the night, the recorded temperature at 5 m to 8 m depth showed a decrease from 19-20 °C to 14-15 °C respectively. A week later, the temperature at a depth of 8 m, was almost the same as at 5 m. This could also disrupt the reproduction of Dreissena.
The role of D. polymorpha as a suspension feeder in the studied basin is considerable. In Lake Pleshcheyevo, Dreissena constitutes on average more than 90% of the total abundance of macrobenthic phytodetritivore suspension feeders. These freshwater mussels in the period of their maximum profusion (May to October) are capable of filtering vast amounts of water. Judging from the data obtained, Dreissena polymorpha can filter the total amount of water in the lake up to 4-5 times during the period of active filtration, precipitating up to several thousand tons of suspended particles. This species can concentrate considerable amounts of heavy metals dissolved in the water or adsorbed by seston, and affect biogeochemical cycles of these elements in the lake ecosystem, transferring them from the plankton to the benthos, and therefore changing their total balance (Pavlov et al., 2008).
In other basins, e.g., in the Ucha Reservoir, D. polymorpha during the growing season filters an amount of water equal to twice the total volume of the reservoir (Lvova-Kachanova, 1971; Lvova-Kachanova and Izvekova, 1973). The development of a wide band of filtering mollusks in the Ucha Reservoir would have increased the rate of suspension precipitation more than threefold in the zone inhabited by Dreissena, which would have resulted in clearing the sediment load and improving the drinking quality
during the time of its being in the reservoir (Lvova, 1977). In Lake Lukomlskoe, before the invasion of D. polymorpha, benthic suspension feeders filtered an amount of water equal to the volume of the lake in approximately 15 years, whereas zooplankton suspension feeders did the same in five days. After the invasion and mass development of D. polymorpha, the filtration ability of benthic suspension feeders increased more than 320 times (Burlakova, 1998). For various lakes of the Mazurskaya Group, the time necessary for the population of Dreissena to filter an amount of water equal to the volume of the epilimnion was estimated from 2 days to 5-6 years at a mean filtration rate 35 ml/h per gram of live weight of the mollusk (Stanczykowska, 1968). Mikheev (1967) showed that in Pyalovsk Reservoir Dreissena daily filter 1/20 of its volume.
Dreissena facilitates de-eutrophication of the pelagial of water basins, because it effectively precipitates and accumulates seston at the bottom. It redistributes the energy and matter flow from plankton to benthos, and in shallow basins enhances coupling between pelagic and benthic zones (MacIsaac et al., 1999). This process is referred to as "benthification". In the Narochan lakes, a new trend in the succession has been recorded since 1995 (Ostapenya, 2005, 2007).
Thus, Dreissena polymorpha in Lake Pleshcheyevo makes a considerable contribution to the process of lake purification, whereas the recorded decrease in abundance of Dreissena due to the disrupted processes of reproduction can affect both isolated components and the entire lake ecosystem.
Acknowledgments
We are grateful to E.G. Sakharova for the data on the biomass of phytoplankton of Lake Pleshche-yevo, FSBI National Park "Lake Pleshcheyevo" and S.M. Fazlullin for help with sampling. The study was conducted within the framework of the State Contract "Comprehensive Study of the Lake Pleshcheyevo Ecosystem"; the laboratory work and analysis - within the framework of the State Contract of the Federal Agency for Scientific Organizations (no. g/p AAAAA18-118012690106-7).
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