Comparative studies on the metabolic rate of the isopod Idotea chelipes (Pallas) inhabiting different regions of the Baltic Sea
Introduction
Rate and efficiency of metabolic processes in animals are affected by various factors, including intrinsic ones like size, sex or locomotor activity as well as environmental ones like temperature, salinity or dissolved oxygen [1]. Two populations of the same species inhabiting geographically and ecologically different environments can exhibit altered metabolic responses to changing factors [2]. This might be due to the genetic differences created during species speciation [3]. The metabolic response to any of the environmental factors might also result from the characteristic specificity of the species [4].
Measurements of metabolic rates provide information on the energy status of organisms and are regarded as an important element in studies of energy flow in marine organisms and populations [5]. They are also useful tools in comparative studies of animal adaptation and performance [6]. The most accurate method of metabolic measurement is to determine how much heat is produced by an organism [7]. This is the sum of all exothermic and endothermic processes, and it allows for the determination of both aerobic and anaerobic metabolism [8], [9].
Idotea chelipes is a widely ranging benthic crustacean in European coastal waters. This species is of brackish water origin and occurs in different types of aquatic biotopes ranging from the brackish waters of estuaries (4–6 psu) to marine waters (32–39 psu) [10], [11]. I. chelipes inhabits the phytal of coastal lagoons where it is a common component of the benthic fauna. It is a herbivore and itself a food item for many fish species [12].
The aim of the current study was to determine the metabolic rate of I. chelipes and the effect of size and sex using direct calorimetry. Whether or not there are differences in metabolic rates between two populations from different regions of the Baltic Sea – the Gulf of Gdansk (Poland, 6.8 psu) and Mecklenburg Bay (Germany, 11.8 psu) – was also investigated.
Section snippets
Material and methods
I. chelipes specimens were collected in August 2003 in the coastal zones of the Gulf of Gdansk (S = 6.8 psu; T = 18 °C) and Mecklenburg Bay (S = 11.8 psu; T = 18 °C). Macroalgae of the genus Enteromorpha and Cladophora, which were used as feed for the isopods, were sampled at the same time. The amphipods were held in the laboratory for 7 days at the temperature and salinity of their natural habitat. The total metabolic rate was determined based on heat production measurements conducted in an isothermal LKB
Results
I. chelipes exhibited different levels of activity during the measurements (Fig. 1). Based on the analyses of the power–time curves, it was determined that the energetic cost of locomotor activity of this species from the Gulf of Gdansk was an average of 43% (12–77%) of the total metabolic rate. In animals from Mecklenburg Bay, this figure was 38% (17–60%). High inter-individual variability in the heat production rate was also observed. Only the resting metabolic rate (level without locomotor
Discussion
The current observations of I. chelipes under laboratory conditions showed that this species exhibits a rather low degree of locomotor activity. It spent most of its time sitting and feeding on Enteromorpha filaments. Swimming specimens were observed sporadically. During calorimetric measurements it was easy to distinguish periods of locomotor activity based on peaks. I. chelipes exhibited different levels of locomotor activity and the highest and the lowest ratio between resting and active
Acknowledgements
The linguistic assistance of Jennifer Zielińska is gratefully acknowledged. This research was supported by the European Community project BALTDER under the fifth FP, Contract Number EVK3-CT-2002-80005 and the Polish Ministry of Scientific Research and Information Technology Project Number 127/E-335/S/2002.
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