The phosphorus cycle is one of the main substance flows in ecosystems of inland water bodies, and its rate determines their biological productivity [1]. Mineral.
ISSN 00124966, Doklady Biological Sciences, 2012, Vol. 444, pp. 192–194. © Pleiades Publishing, Ltd., 2012. Original Russian Text © S.M. Golubkov, N.A. Berezina, 2012, published in Doklady Akademii Nauk, 2012, Vol. 444, No. 5, pp. 580–582.
GENERAL BIOLOGY
Phosphorus Excretion by Bottom Invertebrates of Inland Water Bodies Corresponding Member of the RAS S. M. Golubkov and N. A. Berezina Received February 3, 2012
DOI: 10.1134/S0012496612030167
The phosphorus cycle is one of the main substance flows in ecosystems of inland water bodies, and its rate determines their biological productivity [1]. Mineral phosphorus excreted by bottom animals is important for ensuring the necessary level of primary production [2]. At the same time, there are few quantitative assess ments of the intensity of the mineral phosphorus excretion by representatives of zoobenthos: only sev eral species of bottom invertebrates have been investi gated in this respect [2–5]. The modern metabolic theory of ecology predicts that the intensity of the majority of functional charac teristics of animals on the individual and population levels of organization decrease with increasing body weight [6]. Therefore, the goal of this study was the estimation of the quantitative dependence of the intensity of the mineral phosphorus excretion on the body weight of different representatives of bottom ani mals. Investigations were carried out under laboratory conditions at temperatures of 12, 15, 20, and 21°C. The majority of measurements were carried out at 20– 21°C. Animals were collected in the oligotrophic Lake Krivoe (northern Karelia), the Neva Bay and the Gulf of Finland of the Baltic Sea (Leningrad oblast), and the eutrophic Lake Donghu (central China) [7]. Experiments were conducted in vessels from 50 to 800 ml in volume, depending on the animal sizes. The excretion of mineral phosphorus was estimated by the difference between its concentrations in the control and experimental vessels. The concentration of phos phorus was determined by the molybdate method with the use of ascorbic acid as a reducer. To determine the general parameters of the dependence of the intensity of phosphorus excretion on the animal body weight at 20°C, all experimental data were recalculated for this temperature using the coefficient Q10, which is equal to 2.25 [8]. The intensity of phosphorus excretion by mollusks was calculated for dry weight without the shell.
Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, St. Petersburg, 199034 Russia
The intensity of phosphorus excretion was mea sured in oligochaetes Limnodrilus hoffmeisteri Cla parède; bivalve mollusks Unio pictorum (L.), Unio tumidus Philipsson, Anadonta sp., and Pseudoana donta sp.; gastropod mollusks Lymnaea ovata (Draparnaud) and Alocinma longicornis (Benson); amphipods Gammarus lacustris Sars and Gammara canthus loricatus (Sabine); and larvae of insects, including mayflies Baetis sp., Caenis horaria (L.), Heptagenia fuscogrisea (Retzius), Heptagenia sulfurea (Müller), Ephemera vulgata L., Leptophlebia margin ata (L.), and Leptophlebia vespertina (L.); dragonflies Aeshna squamata (Müller); caddis flies Agrypnia obso leta Hag., Potamophylax latipennis (Curtis), Chaetop teryx sahlbergi MacLachlan, Grammotaulius sp., and Hydropsyche contubernalis MacLachlan; and dipter ans Chironomus plumosus L. and Tanypus chinensis Wang. The results of the measurement of the phosphorus excretion intensity (Ex, µg P/(mg dry weight h)) of bivalve mollusks, amphipods and, aquatic insect larvae are presented in Fig. 1. It can be seen that, in all groups of bottom animals, the intensity is reduced with increasing body weight (W, mg of dry weight), and its dependence on the body weight fits the following power equations: Unionidae Ех = 0.023W–0.31, (1) –0.47 Amphipoda Ех = 0.053W , (2) Insecta Ех = 0.028W–0.18. (3) The general equation of the dependence of the mineral phosphorus excretion on the body weight of animals at 20°C within the wide range from 0.05 to 2475 mg was calculated from all experimental data (Fig. 2): – 0.359
( Ex = 0.031W ) (4) (number of measurements—215; R 2 = 0.74). According to Eqs. (1)–(4), the intensity of phos phorus excretion is inversely proportional to the ani mal body weight. Undoubtedly, this is connected with the decrease in the metabolic rate in large animals compared to small animals. Thus, the dependence of
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PHOSPHORUS EXCRETION BY BOTTOM INVERTEBRATES
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Ex, µg P/(mg dry weight h) 0.1 (a) y = 0.0229x−0.31 0.01
0.001 10 0.1
100
10000
1000 (b) y = 0.0528x−0.47
0.01
0.001 10
1
100
1
1000
(c) y = 0.0281x−0.18
0.1
0.01
0.001 0.01
1
0.1
10
100 W, mg
Fig. 1. Dependence of the intensity of phosphorus excretion (Ex) on the dry body weight (W) in (a) bivalve mollusks of the family Unionidae, (b) amphipods, and (c) aquatic insect larvae.
Ex, µg P/(mg dry weight h) 1 y = 0.0309x−0.359 R2 = 0.74
0.1 0.01 0.001 0.0001 0.01
0.1
1
10
100
1000
10000 W, mg
Fig. 2. Dependence of the intensity of phosphorus excretion (Ex) on the dry body weight (W) in macrobenthos animals. DOKLADY BIOLOGICAL SCIENCES
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GOLUBKOV, BEREZINA
the phosphorus excretion intensity on the body weight is in full correspondence with the modern metabolic theory [6]. According to Eq. (4), the intensity of phosphorus excretion in small animals of zoobenthos, e.g., chi ronomid larvae with a body weight of 1 mg, is 0.031 µg P/(mg dry weight h), whereas in large ani mals, e.g., bivalve mollusks with a body weight of 1000 mg, it is 0.0026 µg P/(mg dry weight h), i.e., 12 times lower. Consequently, the change in the struc ture of bottom animal communities accompanied by changes in the zoobenthos size structure may consid erably alter the flow of nutrients through the bottom subsystem of a water body. ACKNOWLEDGMENTS This study was supported by the Russian Founda tion for Basic Research, project nos. 0804092217 GFEN and 110400591.
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