Corresponding author: Irena V. Telesh ( firstname.lastname@example.org )
Academic editor: Emili García-Berthou
© 2017 Irena V. Telesh.
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: Telesh IV (2017) Small details of big importance: Carbon mass determination in the invasive cladoceran Cercopagis pengoi (Ostroumov, 1891) by the high temperature combustion method. NeoBiota 33: 19-32. https://doi.org/10.3897/neobiota.33.9823
Carbon mass of the non-indigenous predatory fishhook water flea Cercopagis pengoi (Ostroumov, 1891) from the eastern Gulf of Finland, the Baltic Sea, was for the first time measured using the high temperature combustion method. Prior to the analysis, individual dry weight of Cercopagis was determined; altogether ca. 500 organisms were examined. Mean individual dry weight of C. pengoi for July-September was estimated as 34.0 µg; carbon mass averaged 15.8 µg; carbon content, calculated as percent of dry weight, averaged 43.4%. Those values varied over months, mainly because of different population structure of C. pengoi and variation in their diet due to seasonal dynamics of the food objects. However, relations between carbon mass and dry weight for different months did not differ statistically (p<0.001). Therefore, the general polynomial regressions (k=2), describing carbon mass-to-dry weight and carbon content-to-dry weight relationships, were calculated for the entire dataset of individual measurements of C. pengoi body metrics. These data will contribute to adequate evaluation of food web structure and ecosystem alterations in various water bodies invaded by C. pengoi which has got a strong potential to pelagic food web transformations that may impact the overall energy balance and decrease the size of fish stocks.
Alien species, Baltic Sea, carbon content, Cercopagis pengoi, dry weight
In invasion biology, ecosystems vulnerability to non-indigenous species introductions, biodiversity of native communities and competitive resource utilization depending on the size of organisms are pervasive and closely linked to environmental changes (
Among such hotspot research fields is the estimation of ecosystem impact of the opportunistic generalist predator – the Ponto-Caspian onychopod cladoceran Cercopagis pengoi (Ostroumov, 1891), one of the recent invaders to the Baltic Sea (
However, despite the fact that much is known about population dynamics, feeding behavior and the diet of C. pengoi (
To fill in this gap, the present research aimed at direct measurement of carbon mass and dry weight of the invasive water flea Cercopagis pengoi from the eastern Gulf of Finland (the Baltic Sea), for (i) evaluating its average individual carbon mass, dry weight and carbon content, and (ii) for calculating the carbon mass-to-dry weight relationship during the period of maximum population development when the impact of C. pengoi on the native pelagic community is the greatest.
Zooplankton samples were collected in July, August and September 1997 at three sampling stations in the eastern Gulf of Finland (EGF), the Baltic Sea: station P (St. P, sampling dates 22 August and 11 September) in the coastal zone near Primorsk, station F-2 (St. F-2, sampling date 22 July) in the open waters of the EGF, and station 21 (St. 21, sampling date 10 September) in the coastal waters of the EGF in the vicinity of Zelenogorsk (Fig.
Scheme of the eastern Gulf of Finland (the Baltic Sea) showing the location of sampling stations: St. P, St. F-2 and St. 21 (asterisks).
Zooplankton at each station was sampled by several vertical tows from 1.5 m above the bottom to the surface using the Juday plankton net with the opening diameter 0.2 m and mesh size 138 µm. The composite samples from each location were preserved with formaldehyde (final concentration 4%) and frozen at -18 °C. This method is known to provide superior preservation for the purpose of carbon mass determination for many zooplankton species (
On the date of the analysis, samples were defrosted, ca. 120 individuals of C. pengoi were picked from each sample, rinsed 5 times in distilled water in Petri dishes and kept on ice at about -5 °C until processing. Prior to carbon mass determination, Cercopagis were placed in pre-weighed tin capsules individually and dried at 60 °C for 36 h. Dried organisms were kept in desiccator until carbon mass determination. Individual dry weight (DW) of each cladoceran was registered using Sartorius microbalance (± 0.0001 mg) immediately before carbon measurement. Altogether, ca. 500 individuals of Cercopagis were analyzed.
Carbon mass (CM) of each individual Cercopagis with the known dry weight was measured using the high temperature (+950 °C) combustion method (
Carbon content (CC) was calculated as percent of dry weight for each individual. Mean dry weight, carbon mass, carbon content of C. pengoi and regressions for these parameters were calculated separately for each month (July, August and September) and for the entire study period using the complete dataset.
Variations in dry weight and carbon mass of C. pengoi at three stations during different months were compared statistically using the method of Multiple Comparisons (2-tailed) that allowed to assess the impacts of categorical independent variables, controlling for the effects of the continuous predictor variable, CM. The non-parametric Kruskal-Wallis ANOVA by Ranks test was also used for comparison of multiple independent samples (groups) to determine whether DW- and CM-frequency distribution varied over months. Dry weight dependency of carbon mass and carbon content was examined using the linear and polynomial (k=2) regressions based on individual measurements of body metrics and calculated CC-values. Statistical analyses were carried out using the program package Statistica 7.0.
Dry weight of C. pengoi individuals collected in the eastern Gulf of Finland in July–September 1997 ranged one order of magnitude: from 9 to 94 µg; variation in carbon mass exceeded two orders of magnitude and ranged from 0.21 µg to 46.09 µg. The exceptionally low values of CM (< 1.0 µg) and the relevant DW and CC values were excluded from the analyses as possible results of methodological bias during CM-measurements in the smallest individuals of C. pengoi. The overall number of CM/DW measurements used for the further analyses was 432.
In July, the population of C. pengoi consisted mainly of rather small individuals with DW from 13 to 35 µg, while the organisms larger than 52 µg DW were absent, except for one individual of 88 µg (Fig.
Frequency distribution (n) of Cercopagis pengoi individuals with different dry weight (µg) at three stations in the eastern Gulf of Finland in July (A), August (B) and September (C, D).
Mean DW of C. pengoi in the study area in July–September was 34.0 ± 14.2 µg, CM averaged 15.8 ± 8.8 µg; these parameters, however, varied between months; the highest average DW (39.6 µg) and CM (18.5 µg) values were registered in August (Table
Carbon mass, dry weight and carbon content (mean ± SD) of Cercopagis pengoi in the eastern Gulf of Finland (the Baltic Sea).
|Parameter||July||August||September*||Average for July–September|
|Carbon mass (CM, µg)||10.8 ± 7.7||18.5 ± 8.4||17.1 ± 8.5||15.8 ± 8.8|
|Dry weight (DW, µg)||26.3 ± 11.4||39.6 ± 14.9||35.2 ± 13.4||34.0 ± 14.2|
|Carbon content (CC, %)||37.0 ± 12.3||44.9 ± 7.1||45.9 ± 10.7||43.4 ± 11.0|
|Number of individuals analyzed (n)||112||111||209||432|
Variation in the data on C. pengoi DW- and CM-frequency distribution during three months was statistically significant (Kruskal-Wallis ANOVA by Ranks test for DW: H (3, N=432) =59.908; p<0.001; test for CM: H (3, N=432) =50.830; p<0.001). However, the Multiple Comparison (2-tailed) p values witnessed for the fact that only data for July were statistically different from the rest of the dataset (p<0.001), while the differences in data for August and September were statistically insignificant. Univariate test of significance for CM allowed concluding that DW was the major contributor to standard deviation of CM-values while the input of the factor “Month” was negligible (p<0.001).
The CM-to-DW relationships for different months can be sufficiently well described by the linear regressions (r2 = 0.951–0.969, p<0.001). However, the best approximation was achieved by applying the polynomial (quadratic) regression model (r2 = 0.975–0.984, p<0.001); moreover, slopes and intercepts for these regressions for different months did not differ statistically (p<0.001). Therefore, the general polynomial regression (k=2), describing CM-to-DW relationship during July through September, was calculated for the entire dataset of individual measurements of C. pengoi body metrics (Fig.
CM = – 0.0028 DW2 + 0.8296 DW – 8.6507 (1)
where CM is carbon mass (in µg), and DW is dry weight (in µg); r2=0.96, p<0.001.
Relationship between carbon mass (µg) and dry weight (µg) of Cercopagis pengoi for July–September.
Average carbon content of C. pengoi in July-September was estimated as 43.4%. The highest mean CC (45.9%) was recorded in September; this value, however, was close to the one for August (44.9%); in July, CC of crustaceans was the lowest and averaged 37.0% (Table
CC = – 0.0177 DW2 + 1.9507 DW + 0.8942 (2)
where CC is carbon content (in percent of dry weight), and DW is dry weight (in µg); r2=0.66, p<0.001.
The fishhook water flea Cercopagis pengoi (Ostroumov, 1891) has recently become an important component of the pelagic food web in the eastern Gulf of Finland. On the one hand, planktivorous pelagic fishes such as herring and sprat can feed on Cercopagis (
In general, the predator capture rates are known to scale positively with consumer mass (
Results of the current study for the first time allowed calculating the carbon mass-to-dry weight relationship based on the precise, direct carbon mass measurement by the high temperature combustion method (
The discovered differences in averaged values of DW and CM of C. pengoi between July and August-September (Table
Other reasons can involve shifts in the diet of C. pengoi at different developmental stages (
Meanwhile, the obtained values of carbon content, calculated as percent of dry weight, averaged 43.4% for July-September which is in good correspondence with the 44% value obtained earlier for other cladocerans (
Interestingly, the mean CC values for C. pengoi in July were significantly lower than in August-September (Table
Besides, the brood pouch of the instar III parthenogenetic females of C. pengoi is known to be 236% larger than that of instar I individuals of the smaller size (
According to our results, the assumed individual dry weight of 20 µg (
These data along with equations (1) and (2) for calculation of carbon mass-to-dry weight and carbon content-to-dry weight regressions reported in this study will allow avoiding miscalculations of C. pengoi biomass and favor adequate assessment of the food web structure and energy fluxes. These results may be applied also to C. pengoi from the Laurentian Great Lakes, albeit regional variations in the diet of these cladocerans likely exist (
The research presents new data on the average individual carbon mass (15.8 µg), dry weight (34.0 µg) and carbon content (43.4%) of the invasive cladoceran Cercopagis pengoi from the eastern Gulf of Finland (the Baltic Sea), and suggests the polynomial (k=2) regressions for describing carbon mass-to-dry weight and carbon content-to-dry weight relationships during the period of maximum population development of C. pengoi when the invader’s impact on the native community and food web is the greatest. This impact jointly with ecosystem vulnerability to invasions, food web structure and biodiversity are closely interrelated and tightly linked with the on-going environmental alterations (
The author is grateful to the Associate editor Emili García-Berthou, the reviewer Francesc Rubio and the anonymous reviewer for their valuable comments that allowed improving the manuscript significantly. H. Ryan-Timothy is acknowledged for checking the English language in the text of the manuscript. The author acknowledges M. Viljanen for providing the facilities for carbon mass determination in Cercopagis pengoi at the Department of Biology, Faculty of Science and Forestry, University of Eastern Finland (Joensuu, Finland) in 1997. V.E. Panov is acknowledged for collecting zooplankton samples for carbon mass determination in C. pengoi in the EGF in July-September 1997. The author thanks T. Kazantseva for the comments and advices on the statistical methods used in the article. The data analysis for this publication, performed in 2015-2016, was funded by the Russian Foundation for Basic Research (project 15-29-02706 at the Zoological Institute RAS).