Composition, distribution and abundance of zooplankton and ichthyoplankton along the Senegal-Guinea maritime zone (West Africa)

Abstract

A study of zooplankton and ichthyoplankton was carried out from samples collected along the Senegal-Guinea maritime area on board the Norwegian research vessel 'Dr Fridtjof Nansen' in November 2011. Nineteen groups of zooplankton were identified with a dominance of copepods representing 68.5%. The Copepods included 35 species, where Paracalanus parvus was dominant (21.5%). As to ichthyoplankton, 29 fish families were encountered, and Clupeidae were dominant (35.8%). They were represented by Sardinella spp (98.0%) and by Sardina pilchardus (2.0%). An area of high density of copepods (5250 individuals/m3) was located at the mouth of the Gambia River. Two areas of high densities of fish eggs were identified in the waters off Senegal and Guinea; one was characterized by high surface temperature and salinity (29 °C and 35) and moderately oxygenated (3.8 ml/l), while the other was slightly warm (25.5–27.5 °C), less salty (31.5) and highly oxygenated (4.8 ml/l). Areas of high zooplankton biomass correspond to the zones of high dissolved oxygen concentration (4–4.5 ml/l) of low salinity (31.5–34.5). This pattern is supported by the results of the PCA, through the station PL4.