- 期刊
Vertical Distribution Patterns of Pelagic Copepods as Viewed from the Predation Pressure Hypothesis
並列摘要
As habitats of pelagic copepods, epipelagic oceanic environments are characterized by greater food availability but higher risks of predation. Both food supply and predation risk rapidly drop with increasing depth. We studied day/night vertical distribution patterns of copepodid stages of 6 epipelagic (Neocalanus cristatus, N. flemingeri, N. plumchrus, Eucalanus bungii, Metridia pacifica, and M. okhotensis), 2 mesopelagic (Gaetanus simplex and Pleuromamma scutullata), and 6 bathypelagic copepods (Gaidius variabilis, Paraeuchaeta elongata, P. birostrata, P. rubra, M. asymmetrica, and M. curticauda) based on zooplankton samples collected from depths of 0~4000 m at stn. Knot (44°N, 155°E) in the western subarctic Pacific. All epipelagic species exhibited ontogenetic vertical migration (OVM) characterized by descent with progression of copepodid stages, although species-specific variations in the degree of its magnitude were seen. One of the 6 epipelagic species (M. pacifica) showed diel vertical migration (DVM) behavior by its ascent to upper layers at night. Mesopelagic species were characterized by a lack of OVM, although their older copepodid stages undertook DVM. Bathypelagic species underwent OVM in a pattern that was the opposite (ascent with progression of development) of that of epipelagic species. No DVM behavior was recognized for bathypelagic species. From the viewpoint of the predation pressure hypothesis, these differential vertical distribution modes of copepods living in dissimilar bathymetric strata can be interpreted as results of life history traits toward reducing predation mortality of early (bathypelagic copepods) or late copepodid stages (epipelagic copepods). The absence of OVM in mesopelagic copepods is a life history trait that falls somewhere between these 2 extremes (the DVM behavior of their late copepodid stages apparently imparts an advantage for better feeding). This explanation appears to be consistent with the observation that the fecundity of these copepods decrease with increasing depth.
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延伸閱讀
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