Tidal Influence on the Diel Vertical Migration Pattern of Zooplankton in a Tropical Monsoonal Estuary

AbstractThis study investigates the diel vertical distribution and the diet of the most important chaetognath species found in the 0–50 m surface layer of a coastal area in the eastern Mediterranean during a 24-hour period in July 2004. Among the recorded chaetognaths, Sagitta enflata was the most abundant species (41.6%), followed by S. minima (32.5%) and S. serratodentata (20.8%). Those three species exhibited a “twilight migration” pattern, with only small differences among them. Vertical separation was found between S. enflata and S. minima. Both species preyed mainly on cladocerans, although copepods were the most abundant group in the zooplankton assemblage. The chaetognath species followed partially the diel vertical migration of their prey. S. enflata showed high feeding intensity at different times in both day and night, while S. minima fed more intensively at midday (12:00) and at dusk (20:00), and S. serratodentata in the morning (08:00). It seems that in order to coexist in an area of low productivity the chaetognath species follow the basic ecological rules of space, time and food-type separation, in order to reduce the inter- and intra-specific competition. The high preference of S. minima and especially of S. enflata for the cladocerans made them probably the most important predators of cladocerans during summer.

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Diel vertical migration: A possible host-finding mechanism in salmon louse (Lepeophtheirus salmonis) copepodids?

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f95-069 ◽

1995 ◽

Vol 52 (4) ◽

pp. 681-689 ◽

Cited By ~ 104

Author(s):

Peter Andreas Heuch ◽

Aengus Parsons ◽

Karin Boxaspen

Keyword(s):

Light Intensity ◽

Vertical Distribution ◽

Vertical Migration ◽

Diel Vertical Migration ◽

Host Finding ◽

Migration Pattern ◽

Lepeophtheirus Salmonis ◽

Salmon Louse ◽

Night And Day ◽

The Vertical Distribution

The vertical distribution of pelagic nauplii and copepodids of the salmon louse Lepeophtheirus salmonis Krøyer was studied in large enclosures in the sea. Copepodids, which infect salmonid hosts, displayed a distinct diel vertical migration pattern. They gathered near the surface during the day, and spread out into deeper layers at night. Nauplii showed only small differences in depth between night and day. Copepodid distribution seems to be controlled by light intensity; no effect of either salinity or temperature was found. This migration pattern, which is the reverse of that of wild salmonids, may increase the number of parasite–host encounters as hosts will swim through populations of sinking (nighttime) and rising (dawn) parasites every 24 h. Because caged salmon feed at the surface during the day, they are likely to be more exposed to infective copepodids than wild fish.

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Variability of Diel Vertical Migration in the Marine Planktonic Copepod Pseudocalanus newmani in Relation to Its Predators

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f92-126 ◽

1992 ◽

Vol 49 (6) ◽

pp. 1137-1141 ◽

Cited By ~ 66

Author(s):

Bruce W. Frost ◽

Stephen M. Bollens

Keyword(s):

Vertical Migration ◽

Diel Vertical Migration ◽

Behavioral Plasticity ◽

Migration Pattern ◽

Migration Behavior ◽

Central Basin ◽

Reverse Migration ◽

Ammodytes Hexapterus ◽

Invertebrate Predators ◽

Vertical Distributions

We report results of a 3-yr field study of the vertical distributions and diel vertical migration (DVM) of Pseudocalanus newmani in the central basin of Dabob Bay, Washington, USA. Our results include two novel findings. First, a statistically significant relationship exists between strength of DVM in P. newmani and the potential predation impact of its planktonic invertebrate predators. Second, a strong "normal" DVM (up at night, down during the day), unique for P. newmani in 5 yr of sampling at this locale, occurred at a time when the zooplanktivorous fish Ammodytes hexapterus was unusually abundant and preying on the copepod; this DVM may have been induced by the fish. DVM behavior of P. newmani was highly variable, with changes in behavior commonly occurring on a time scale of weeks; in one case the copepod switched from a normal migration pattern to a reverse migration pattern (down at night, up during the day) in less than 5 wk. These observations, combined with those of previous research, indicate that P. newmani has an exceptionally diverse repertoire of migration behavior, any particular expression of which is most likely manifested by individual copepods exercising phenotypic behavioral plasticity in response to potential predation.

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