Patrones de migración vertical en el plancton de un lago tropical

Abstract

From 27 to 28 May 1994, plankton and water samples were collected every 3 h at multiple depths at a station placed in the middle of Laguna Escondida, a warm monomictic lake from the tropical rain forest of Veracruz, México, in order to recognize the patterns of diel vertical migration (DVM) of the main groups of the plankton community and to relate them with some hyfrological parameters. The zooplankton community in the lake appeared to be dominated by two species of copepods and one cladoceran, whereas, in the phytoplankton, volvocaceae and diatoms dominated. Size composition of both zooplankton and phytoplankton suggest that predation and grazing pressures are high in the lake. Exceptuating diatoms, all of the main plankton groups showed migratory behavior. Migration was nocturnal in Tropocyclops prasinus (with an upward maximum velocity, UV, of 0.48 m s-1 and a migration amplitude, M, of 3.45 m), in Moia micrura (UV=0.52 m s-1, M=3.2 m) and in the naupliar and copepodite stages of copepods (UV=0.62 m s-1, M=3.2 m). Twilight migration was observed in Thermocyclops inverus (UV=0.84 m s-1, M=3.1 m) and inverse migration in the volvocaceae (Eudorina sp. in =90%; UV=0.48 m s-1, M=3.7 m). No significant relationships were detected between DVM patterns and the physical and chemical parameters of the water column. Nevertheless, given that food for zooplankton is probably concentrated at 5 m deep and not near surface, we suggest that our results supports the hypothesis that nocturnal upward migration of zooplankton involves a thermal, rather than a trophic, benefit.