Seasonal and ontogenetic variation in diel vertical migration of Chaoborus flavicans and its effect on depth‐selection behavior of other zooplankton

Abstract

We analyzed diel vertical migration (DVM) of zooplankton in June, July, and September in Lake Kä rnsjön, Sweden. In this lake, the density of the invertebrate predator Chaoborus flavicans was high, and they performed normal DVM. However, the migration pattern of Chaoborus differed between its four larval instars. Larger instars were found at greater mean depths during the day than were the smaller instars. In both June and July, very few observations of the fourth instar were made at a depth of 1 m during the night. Hence, in June, when only the fourth instar was present, the upper 1-m layer was a Chaoborus-free refuge for other zooplankton during the night. This was not the case in July, when the smaller instars (1-3) hunt at that depth, or in September, when instar four was present there. Crustacean zooplankton showed great flexibility in their DVM behavior. In September, both Bosmina and small Daphnia tended to perform reverse DVM (i.e., they resided closer to the surface during the day). However, no migration was observed in July. In June, most species performed normal DVM by crowding in the Chaoborus-free stratum close to the surface during the night. Both this pattern of normal DVM of zooplankton in June and the reverse DVM in September indicate that invertebrate predation has a strong effect on the zooplankton community in this fish-rich lake, showing that ontogenetic changes in migration pattern of an invertebrate predator may influence the seasonal variation in the depth-selection behavior of other zooplankton.

Predators modify the evolutionary response of prey to temperature change

“…All populations reared at 258C went extinct by week 10 of the experiment. The predator-mediated reduction in prey population size was likely due to direct predation and predator avoidance behaviour [23].…”

Toward a more comprehensive theory of zooplankton diel vertical migration: Integrating ultraviolet radiation and water transparency into the biotic paradigm

“…Another example of important interactive effects of predation and UV is reverse migrations by smaller zooplankton into the surface waters during the day to avoid tactile predators (Neill 1990;Frost and Bollens 1992;Lagergren et al 2008). These migrations would tend to expose smaller zooplankton to higher levels of damaging UV in more transparent lakes.…”

Seasonal and diel abundance and feeding patterns ofChaoborus flavicansin Sang-Chun reservoir

“…However, the migration pattern was not detected during summer seasons (June 2009). A possible explanation for this would be much less fish predation on C. flavicans (Lagergren et al 2008), which, unfortunately, could not be examined in this study due to lack of fish abundance data.…”

“…In an environment where fish, Daphnia, and Chaoborus coexist, Chaoborus is generally known to stay in the hypolimnion to avoid the preying pressure of fish and Daphnia stay in the epilimnion to escape from their predator, Chaoborus, during the daytime in summer (Hanazato 1997;Neill 1992;Lagergren et al 2008). However, during the night, Chaoborus migrate to the epilimnion to prey upon Daphnia (Hanazato 1997;Bezerra-Neto and Pinto-Coelho 2007).…”