Abstract
SUMMARY: The feeding behaviour of the size fractionated copepod assemblage was studied over a diel cycle in Coliumo Bay. In this shallow environment the photic layer reached the bottom and salinity, temperature, and food availability were fairly homogeneous throughout the water column. All four size-fractions (250-500 ∝m, 500-1000 ∝m, 1000-2000 ∝m, >2000 ∝m) showed a period of high feeding activity during the night and low feeding activity during the day. The persistence of nocturnal feeding in the presence of high food concentration over the 24-h cycle is interpreted as a predator avoidance strategy: empty guts by day make copepods less conspicuous to their visual daytime predators.
Highlights
IntroductionThe vertical migration of zooplankton between deeper layers during the day and shallow layers at night is generally thought to occur when the water column is stratified into a shallow, lighted, food-rich layer and a deep, dark, oligotrophic layer
The persistence of nocturnal feeding in the presence of high food concentration over the 24-h cycle is interpreted as a predator avoidance strategy: empty guts by day make copepods less conspicuous to their visual daytime predators
The vertical migration of zooplankton between deeper layers during the day and shallow layers at night is generally thought to occur when the water column is stratified into a shallow, lighted, food-rich layer and a deep, dark, oligotrophic layer
Summary
The vertical migration of zooplankton between deeper layers during the day and shallow layers at night is generally thought to occur when the water column is stratified into a shallow, lighted, food-rich layer and a deep, dark, oligotrophic layer. Under such conditions, the coupling of nocturnal feeding (NF) and diel vertical migration (DVM) would permit surface feeding at night when exposure to visual predators there is minimized (Gauld, 1953; Zaret and Suffern, 1976; Ohman et al, 1983; Verity and Smetaceck, 1996). The results of studies addressed to answer these questions would give an indication of the importance of the pressures exerted on zooplankton, be they either food limitations or predation
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