Interspecific differences in the diel vertical migration of marine copepods: The implications of size, color, and morphology

Samples collected by continuous plankton recorders (CPRs) between 1948 and 1992 were used to describe the diel vertical migration (DVM) behavior of 4 1 copepod taxa in the northeast Atlantic between 45 and 55“N and 11 and 3 1”W. A total of 13,622 samples, each representing - 18.5 km (10 nm) of tow, were analyzed. Since CPRs are towed in near-surface waters, taxa that exhibit DVM occur predominantly in samples taken at night. Larger taxa showed significantly stronger DVM, with body size explaining 47% of the intertaxa variation in DVM. For small taxa ( 1 mm wide) the residual variation in DVM was correlated with body morphology but not with carotenoid pigment levels, with more elongate copepods not exhibiting DVM. Diel vertical migration (DVM) occurs in a wide range of both marine and freshwater copepods as well as in a variety of other zooplankton, with the “normal” pattern being movement from greater depths during the day to shallower depths at night (Lampert 1989). The ubiquity of DVM in zooplankton communities has provoked considerable and extended debate as to its functional significance (see Lampert 1989). Although it has been suggested that DVM may provide a metabolic advantage associated with the diel movement across a thermocline (McLaren 1963), this hypothesis is now generally refuted (Lampert 1989). Alternatively, Zaret and Suffem (1976) suggested that DVM may be an antipredator behavior, with populations moving to a greater depth during the day to reduce risk from visual predators. A considerable amount of both field and experimental evidence has accumulated to support this predator-evasion hypothesis. For example, Gliwicz (1986) reported that the