Abstract
The vertical distribution of copepod assemblages, ascertained from the surface down to 1,200 m, was investigated during two sampling periods (rainy and dry seasons), at four depths, in the oligotrophic waters of the southwestern Atlantic Ocean. Total density, diversity, and richness differed among sampling depths. Copepod density decreased with depth in the two sampling periods, with a maximum at 1 m and a slight decrease at 800 m. Higher diversities were observed at 250 m and 1,200 m during the rainy season and at 1 m and 1,200 m during the dry season. The maximum number of species was found at 1,200 m during the rainy season and at 1 m during the dry season. Various copepod assemblages were delimited in the water column in the two sampling periods. The deeper copepod assemblages occupied a wider range of depths. Salinity and temperature influenced the structure of copepod assemblages and reflected the hydrographic characteristics of the water masses in the region. Candaciapachydactyla (Dana, 1849), Scolecithrixdanae (Lubbock, 1856), and Agetuslimbatus (Brady, 1883) were the indicator species found at 1 m. The effects of different environmental factors on the copepod assemblages suggest that these consortia occupy distinct niches in the ocean.
Highlights
Oligotrophic regions are more productive and dynamic than previously thought, and have a high degree of biological variability (Dias et al 2015)
The lowest temperature and salinity values were obtained during the dry season
The environmental parameters described along the water column reflect the hydrological characteristics of the water masses in this region (Niencheski et al 1999, Rezende et al 2007)
Summary
Oligotrophic regions are more productive and dynamic than previously thought, and have a high degree of biological variability (Dias et al 2015). Oligotrophic areas constitute more than 75% of oceanic surfaces. They may play a significant role in oceanic biogeochemical budgets and global elemental cycling (Dufour et al 1999, Corno 2006 and references therein). The southwest Atlantic Ocean is one of the most oligotrophic areas of all oceans worldwide (Andrade et al 2007). Copepods are known for their diversity and importance in the food web. They are the most abundant primary consumers in the ocean and the main food source for several planktophagous fishes (such as herring, anchovy, sardine, and corvine), fish larvae, and planktonic- and benthic invertebrates (Björnberg 1981)
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