Limnetica 35

Diel horizontal migration (DHM) and diel vertical migration (DVM) of planktonic microcrustaceans and invertebrate predators were studied simultaneously in a tropical shallow lake. DHM was not performed, and DVM was irregularly performed by the species. DHM of microcrustaceans does not seem to replace DVM as a strategy for decreasing predation risk in this shallow lake. The invertebrate predators, the IV instar of Chaoborus brasiliensis and the water mite Krendowskia sp., were mostly limnetic, the latter undergoing a nocturnal DVM that was not evident for the chaoborid larvae because a portion of the individuals remained in the water column in the daytime. DVM of some microcrustaceans, such as Ceriodaphnia richardi, Daphnia ambigua, Daphnia gessneri, and Thermocyclops decipiens, decreased the overlap with predators. Other behaviours, such as onshore location and occupation of the uppermost layers, seem to be more effective for coping with predation by limnetic invertebrate predators. Dissolved oxygen is a counteracting factor for only the vertical distribution because its concentration is low near the bottom in summer but not in the littoral zone. The lack of DHM in this study agrees with the results of most warm shallow lakes.