PARENT SESSION
Oral Session # 51: Limnology II: Plankton; Carbon.
Presiding: K Forshay
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 101.

Effects of diapause on zooplankton community dynamics: temporal patterns and the role of environmental cues.

Gyllström, Mikael^*,1, Hansson, Lars-Anders¹, ¹ Lund University, Lund, Skåne, Sweden

ABSTRACT- With the aim of assessing the impact of resting stages on zooplankton community dynamics we examined production of, and emergence from, diapausing eggs, together with planktonic community dynamics of three cladoceran genera (Bosmina, Ceriodaphnia, and Daphnia) for 16 months in a shallow lake. In a complementary field experiment, we manipulated abiotic and biotic environmental variables, potentially important as triggering cues for emergence. Ceriodaphnia and Daphnia, but not Bosmina, were dependent on emergence to initiate planktonic populations in spring. During the rest of the season, emergence was unimportant for population and community dynamics. Hatching of Ceriodaphnia and Daphnia occurred when the rate of increase of photoperiod and chlorophyll-a was highest, but Daphnia hatched before the spring rise in temperature. The timing of resting-egg production differed between genera, but always coincided with peaks in abundance. No hatching was found in any of the experimental treatments, despite manipulation of several potentially important environmental variables. Differences in resting egg production were found between some treatments however. The field study and experiment together imply that the types of environmental cues involved in diapause induction are different from the ones stimulating its termination. Abiotic factors such as photoperiod may be important cues for the hatching of resting eggs. However, the induction of resting egg production seems less dependent on season and more on biotic factors such as crowding. This conclusion is supported by a literature review on the cue used for diapause induction and termination, which also indicated interesting difference in cue utilization among taxa with different generation length.

Key words: cladocera, diapause, recruitment, succession