Abstract
ABSTRACT Based on the hypothesis that diel vertical migration (DVM) is a mechanism of predator avoidance, the objective of the present study was to test for the occurrence of DVM in planktivorous fish larvae of Hypophthalmus edentatus (Spix, 1829) (Siluriformes, Pimelodidae) and Plagioscion squamosissimus (Heckel, 1840) (Perciformes, Sciaenidae), and zooplankton (rotifers, cladocerans and copepods) in an isolated tropical lagoon in the floodplain of the Upper Paraná River, Brazil (region of Parque Nacional de Ilha Grande). We investigated spatial overlap between predators (planktivorous fish larvae) and prey (zooplankton), and tested which physical and chemical variables of the water are related to the DVM of the studied communities. We performed nocturnal (8:00 pm and 4:00 am) and diurnal sampling (8:00 am and 4:00 pm) in the limnetic region of the lagoon for six consecutive months, from October 2010 to March 2011, which comprises the reproductive period of the fish species analyzed. During the day the larvae tried to remain aggregated in the bottom of the lagoon, whereas at night they tried to disperse in the water column. Especially for cladocerans, the diel vertical migration is an important behavior to avoid predation larvae of H. edentatus and P. squamosissimus once decreased spatial overlap between secured and its potential predators, which corroborates the hypothesis that DVM is a mechanism of predator avoidance. Although significant correlations were observed between the abiotic factors and WMD of microcrustaceans at certain times of day, the effect of predation of fish larvae on zooplankton showed more important in this environment, because the small depth and isolation not allow great variation of abiotic factors seasonally and between strata the lagoon.
Highlights
We found a significant difference in weighted mean depth (WMD) (p < 0.05, t test) between night and day for the larvae of H. edentatus, which shows that these larvae developed normal diel migration, remaining in the bottom during the day and ascending at night to superficial layers; the amplitude of vertical migration was 1.82 m
Based on the differences found in the vertical distribution between day and night, we observed that the larvae of H. edentatus have the typical behavior of normal diel vertical migration (DVM), remaining in deeper layers during the day and ascending to superficial layers at night
One possible explanation is that the larvae of P. squamosissimus explore a larger area of water than the larvae of H. edentatus
Summary
Migração vertical diária de predadores (larvas de peixes planctívoras) e presas (zooplâncton) em uma lagoa tropical. Com base na hipótese de que a migração vertical diária (MVD) é um mecanismo que visa evitar predadores, o objetivo do presente estudo foi verificar a ocorrência de MVD em larvas de peixes planctívoras de Hypophthalmus edentatus (Spix, 1829) (Siluriformes, Pimelodidae) e Plagioscion squamosissimus (Heckel, 1840) (Perciformes, Sciaenidae), e nos grupos zooplanctônicos (rotíferos, cladóceros e copépodes) em uma lagoa tropical isolada da planície de inundação do alto rio Paraná, Brasil (região do Parque Nacional de Ilha Grande). This behavior can vary between and within species, as well as seasonally It has been interpreted by several authors as a defense against predation, in which the prey avoids parts of the water column where predation pressure is high (Zaret & Suffern, 1976; Ohman, 1990; Bezerra-Neto & Pinto-Coelho, 2007). Prey-predator interactions are, strongly dependent on the spatial distribution of predator and prey, and DVM may represent an effective mechanism to minimize the risk of predation by tactile and visual predators (Sih, 1987; Williamson, 1993)
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