Micronecton et macroplancton en Mer Ligue (Méditerranée) : migrations nycthémérales et distributions verticales

• Main Authors: Sardou, J, Andersen, V
• Format: Article in Journal/Newspaper
• Language: French
• Published: Gauthier-Villars 1993
• Subjects: DIEL VERTICAL MIGRATION; MICRONEKTON; MACROPLANKTON; Meganyctiphanes norvegica
• Online Access: https://archimer.ifremer.fr/doc/00099/21063/18689.pdf; https://archimer.ifremer.fr/doc/00099/21063/

Vertical distributions and diel migration of some species of micronekton and macroplankton are given in the 0-965 m water column on a fixed station in the Ligurian Sea (Northwestern Mediterranean Sea). The hauls performed with a multiple opening/closing net system permit detailed description of the vertical distributions of eighteen species: five euphausiids, one mysid, one decapod, three fishes, three siphonophores, one hydromedusa, one pyrosomid and three pteropods. Only the euphausiid Stylocheiron longicorne and the fishes Cyclothone braueri and C. pygmaea show no migratory behavior. The other species perform migrations of more or less large amplitude: 155 m as a mean for the mysid Eucopia unguiculata until 630 m for the decapod Gennadas elegans. All the individuals of the population undergo a diel migration in the cases, for example, of the euphausiid Thysanopoda aequalis, the siphonophore Abylopsis tetragona and the pteropod Cymbulia peroni; or only part of the population migrates, as observed for Eucopia unguiculata and the euphausiid Nematoscelis megalops. The most abundant euphausiid species, N. megalops and Meganyctiphanes norvegica, present bimodal vertical distributions during the day, with the shallower peak composed of small individuals exclusively. Results of horizontal hauls at a given depth of about 250 m around sunrise and sunset show that: 1) the individuals begin their descent before sunrise and their upward migration before sunset; 2) the migratory cycles show a diurnal symmetry relative to noon; 3) the timing of the migrations is related to the daytime depths of the species.