Abstract
The body size of aquatic invertebrates is, to a great extent, dependent on ambient temperature, but size distributions are also determined by other factors like food supply and predation. The effect of temperature on organisms is formulated in the temperature–size hypothesis, which predicts a smaller body size with increasing temperature. In this study, the effect of temperature on the subfossil remains of three littoral Cladocera (Alona affnis, A. quadrangularis, and Chydorus cf. sphaericus) was investigated. Exoskeletal remains of these species can be found in large numbers in lacustrine sediments and over a wide north–south range in Europe. The total length of both headshield and postabdomen for A. affinis and A. quadrangularis and carapace length for C. cf. sphaericus were measured to observe their response to changes in latitude and temperature. A different response to ambient temperature in the growth of body parts was observed. The size of the headshields of both Alona species and of the carapace of Chydorus was significantly larger in colder regions as opposed to warm ones. It turned out that the postabdomen was not a good predictor of ambient temperature. While the sizes of all remains increased with latitude, the sizes of the Alona remains was smaller in the mountain lakes of the Southern Carpathians than in other cold lakes, in this case in Finland, a fact indicative of the importance of other factors on size distribution. This study demonstrates that a morphological response to climate is present in littoral cladocerans, and, therefore, changes in the length of headshield and carapace may be used as a proxy for climate changes in paleolimnological records.
Highlights
Crustacean cladocerans (Branchiopoda) are functionally adapted to diverse microhabitats in lakes.Some species live in open water, whereas others are attached to macrophytes or abiotic surfaces, such as lake beds covered with silt, pebbles or sand
A. quadrangularis: W = 314.5, p = 0.66; postabdomens of A. quadrangularis: W = 379, p-value = 0.87; carapaces of C. cf. sphaericus: W = 44686, p = 0.56). This is the first study in which the morphological response of littoral cladocerans has been examined in relation to the ambient temperature of the location of their sedimentary remains
Paleolimnological inferences are based on assemblages of cladoceran species, but cladoceran size structure is sensitive to changes in limnological conditions [53]
Summary
Crustacean cladocerans (Branchiopoda) are functionally adapted to diverse microhabitats in lakes.Some species live in open water (pelagic species, according to the strict definition of zooplankton), whereas others are attached to macrophytes (epiphytic) or abiotic surfaces, such as lake beds covered with silt, pebbles or sand. Crustacean cladocerans (Branchiopoda) are functionally adapted to diverse microhabitats in lakes. Cladocerans occupy a central position in the food web; their abundance and assemblage depend on bottom-up (food supply) and top-down (predation pressure) forcing to the same degree as on habitat availability. Any changes in cladoceran community composition and functional traits may well indicate changes in the prevailing environmental conditions [1]. The body size of cladocerans is a functional trait of great importance, because it has an influence on resource use, and may indicate predation patterns. This is because large-bodied zooplankton have greater grazing rates, they filter a wide range of food particles, and exert a stronger top-down effect on resources than small-bodied zooplankton do. It should be noted that a larger body size tends to make them vulnerable to vertebrate predators, while a smaller size is preferred by invertebrate predators [2]
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