The Vertical Migration of Planktonic Crustacea

Abstract

Summary There are four methods of analysing the vertical migration of plankton in the field: (a) One day and one night observation at the surface. (b) One day and one night observation at depths between surface and the bottom. (c) Observations at long time intervals at all depths during day and night. (d) Observations at short time intervals at all depths during day and night. The last method, using horizontal closing tow‐nets with flow meters at measured depths, shows that migration consists of four parts: (a) ascent from the day depth; (b) midnight sinking; (c) dawn rise; (d) descent to the day depth. This pattern has been shown to be modified by wind (or state of sea), rain, sun on a calm sea, extremes of temperature, age of the individual animal and possibly by phytoplankton concentrations. These different parts of migration have been examined in detail and linked together in a single and continuous process. Ascent in the evening and descent in the morning become the continuous change of day depth with the changing penetration of light; the midnight sinking is assumed to be due to a passive state in full darkness; the dawn rise is a return by the animals to the mean optimum light intensity for the population. This is supported by the fact that the order in time of arrival at the surface for some fresh‐water species is the same as the order in depth of these species in full daylight. Theoretical interpretations of migration are reviewed. It is argued that the most likely theory has as its basic assumption the idea of an optimum light intensity. Experiments on migration are divided into three parts: (a) those showing that randomly oriented movement can take place; (b) those showing that the speeds of individual animals can vary with varying light intensities; (c) those showing that animals in full darkness will move at minimal speeds or not at all. It is concluded that the vertical migration of planktonic Crustacea is mediated by the change in light penetration throughout the day. Animals aggregate in an optimum band of light intensity. They have the capacity of moving phototactically, i.e. moving at constant speed towards or away from light; they also have the capacity of moving photokinetically, i.e. moving at speeds that vary with varying light intensity. In full darkness they move probably at minimal speeds. Migration between periods of full darkness may be operated by phototaxis, photokinesis or by a combination of these mechanisms.

Influence of lunar cycle and hydrological parameters on the depth-wise distribution of zooplankton in the inshore waters off Tuticorin, Gulf of Mannar

“…The full moon and new moon variation in the density was statistically significant only for bivalve larvae and Lucifer (p<0.05). It is likely that the zooplankton activity is oriented to a band of optimum moon light intensity and they adjust their upward and downward movement accordingly (Cushing, 1951;Hardy and Bainbridge, 1954).…”

The Coevolution of Blue-Light Photoreception and Circadian Rhythms

“…Since UV radiation can penetrate up to 25 m depth in clear marine waters (Fleischmann 1989), and increased mortality rates were documented in both marine and freshwater organisms after exposure (Huntsman 1924;Klugh 1930), UV radiation represents a major selective force. Both field studies and laboratory experiments have led to the general conclusion that the zooplankton migrates to a depth of optimal light intensity (Cushing 1951;Leech and Williamson 2001). C.S.…”

Composition, species richness and patterns of nycthemeral vertical distribution of planktonic cladocereans in a black water Amazonian lake

“…In tropical lakes, this heterogeneity generally occurs seasonally in a spatial-temporal scale and daily in a vertical-last two centuries (reviews e.g. Cushing, 1951;Hutchinson, 1967;Lampert, 1989;Lampert and Sommer, 1997) the real adaptive significance of the phenomenon is still not completely understood. Zaret and Suffern (1976) explained vertical migration as a mechanism of zooplankton to avoid predation, which is related to luminosity, body size and visibility of the prey.…”