Abstract
To improve our knowledge of nocturnal and diurnal migratory activity in copepods and in order to assess the effect of abiotic parameters on this activity, we have undertaken at the level of the Al Massira dam reservoir (dam located on the wadi Oum Erbia, in Morocco) the monitoring of the migration of the main species, during a 24-hour nycthemeral cycle. To be done; the measurement and sampling step is carried out every 4 hours; at different depths of the prospected station. The temperature, pH, dissolved oxygen and chlorophyll a measurements are taken. The systematic position of the main species of copepods and their density are determined. Most of the results obtained show that the main species of copepods inventoried within the reservoir are Neolovenula alluaudi and Acanthocyclops robustus. The nauplii of these two species present the maximum of densities at a depth of -5 m at 12 h; i.e. 70400 individual / m3 (ind / m3). The development stages of N. alluaudi are preferentially concentrated at -2 m at midnight, with 1900 ind / m3, while at 12 h and 16 h this density is less than 500 ind / m3. The maximum density for the stages of A. robustus is noted at midnight on the surface (at -5 m), i.e. 3400 ind / m3 for C1-2 and 3200 ind / m3 for stages C3-4-5 at -2 m at the same time. Therefore, the migratory behavior of these species seems to depend on the temperature, the concentration of dissolved oxygen and the variation of the food during the different phases of the cycle.
Highlights
Zooplankton migration is a phenomenon observed in many marine and freshwater species
The authors have demonstrated the presence of a relationship between temperature, dissolved oxygen, chlorophyll a content and migration [3]
Study site The Al Massira reservoir was filled in February 1979 and is considered the centerpiece of the development plan for the watershed of the Oum Er Rbia wadi
Summary
Zooplankton migration is a phenomenon observed in many marine and freshwater species. The classic pattern of these migrations consists of a rise in the upper layers at dusk, with a maximum surface density around midnight. Some authors observe a bimodal rhythm with a descent to the deep layers in the middle of the night and at dawn [1, 2]. Most of the studies carried out on these mechanisms consider that environmental factors induce these migratory movements. The authors have demonstrated the presence of a relationship between temperature, dissolved oxygen, chlorophyll a content and migration [3]. The effect of predation [4] and the influence of hydrological and hydrodynamic factors on the migratory behavior of certain zooplankton species Berge et al [5] have aroused the interest of the authors
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