The influence of year‐to‐year variations in winter weather on the dynamics of Daphnia and Eudiaptomus in Esthwaite Water, Cumbria

Abstract

IntroductionIn a recent report, the Inter-governmental Panel on Climate Change (IPCC 1996) suggested that average winter temperatures in the UK could be 2-3°C higher than they are today by the year 2040. The planktonic micro-crustacea found in lakes can tolerate quite high summer temperatures, but small increases in the winter temperature can have a significant effect on their seasonal dynamics. One of the most important factors influencing the winter survival of these short-lived animals is the rate at which they acquire and store energy. In winter, their food requirement is controlled by the temperature of the water but the growth rate of their phytoplankton food is limited by light (Talling 1971). Mild winters could therefore favour the survival of species that require less food or those that are less susceptible to periods of starvation. The overwintering performance of the micro-crustacea can also be influenced by qualitative as well as quantitative changes in the phytoplankton community. Such qualitative changes can be influenced by a number of factors (Reynolds 1984) but one of the most important is the frequency and intensity of wind-induced mixing. For example, the large diatoms that dominate the winter phytoplankton grow best in a well-mixed water column but the flagellates that serve as an important source of food for many filter feeders require more stable mixing conditions.In this paper, we analyse some of the physical and biological factors that influence the winter abundance of the cladoceran Daphnia hyalina var lacustris Sars and the copepod Eudiaptomus gracilis Sars. These two species are functionally very different and have evolved different physiological strategies for coping with life in a rapidly changing environment. Daphnia hyalina is particularly common in large lakes and feeds by filtering small species of phytoplankton from the water with an array of rapidly beating limbs. Eudiaptomus gracilis is found in a wider range of habitats and feeds by actively grasping large particles and passively filtering small particles by low frequency movements of its feeding appendages. In this paper, we analyse some of the physical and biological factors influencing the winter abundance of the two species in a small lake (Esthwaite Water in Cumbria).2. The results demonstrate that much of the year-to-year variation in their relative abundance can be related to long-term changes in the weather. The highest numbers of Daphnia were typically found in cold, calm winters when small flagellates were relatively abundant. In contrast, the highest numbers of Eudiaptomus were found in mild, windy winters when the phytoplankton community was dominated by colonial diatoms.3. Year-to-year variations in the winter abundance of Eudiaptomus had no effect on their subsequent development but the numbers of overwintering Daphnia had a significant effect on the size of their first spring 'cohort'. The most important factor influencing the overwintering performance of the two species was the water temperature. 4. Winter ai...

The response of freshwater ecosystems to climate variability associated with the North Atlantic Oscillation

“…This suggests that changes in temperature are more likely to have a large impact on copepod populations when they result in changes in food availability and/or predation pressure that alter the copepods' survival chances. Supporting this hypothesis, changes in copepod abundance were indeed found to be associated not only with changes in water temperature but also with changes in food availability in both Esthwaite Water and Heiligensee [Adrian, 1997;George and Hewitt, 1999].…”

“…This mechanism has been suggested for the negative relationship between the NAO and Daphnia abundance in winter in Esthwaite water [George, 2000b]. Additionally, competition between Daphnia and a calanoid copepod, Eudiaptomus gracilis, whose abundance was positively related to the NAO during this period, might have contributed to the decline of Daphnia in mild winters [George and Hewitt, 1999].…”

“…Up to now the only freshwater copepod species whose abundance is known to be related to the NAO is the calanoid copepod Eudiaptomus in Esthwaite water [George and Hewitt, 1999]. In addition, Adrian [1997] showed that the abundance of copepod species in Heiligensee (Berlin, Germany) is associated with winter temperatures.…”

Response of freshwater microcosm communities to nutrients, fish, and elevated temperature during winter and summer

“…Similarly, models looking at the predatory behavior of young of year perch indicate that feeding rates on Daphnia are substantially increased during simulated warmer springs (Mehner 2000). In European lakes, links between temperature, the North Atlantic Oscillation, and plankton dynamics have been made (George and Hewitt 1999;Weyhenmeyer et al 1999;Straile 2000). Here, an underlying pattern seems to be the promotion of earlier seasonal successional events by milder climatic conditions.…”

Coexisting overwintering strategies in Daphnia pulex: A test of genetic differences and growth responses

“…Their offspring are born into the algal spring bloom (Sommer et al 1986). In contrast, hatching of neonates from diapause eggs in response to an environmental cue needs time, and the hatchlings must first grow and mature, before they can contribute offspring to the Daphnia population, which gives the offspring of overwintering females a clear advantage (Hanazato 1989;George and Hewitt 1999). Also, only a small proportion of ephippia hatch in a deep lake (Caceres and Tessier 2003;Jankowski and Straile 2004).…”