Vertical distribution of chaetognaths and their role as biological indicators of water masses in the Cape Verde frontal zone (NW Africa)

Abstract

The Cape Verde Frontal Zone (CVFZ) is an area located in the southern boundary of the Canary Current. The interaction between the Cape Verde Front and the Mauritanian coastal upwelling promotes an area of highly dynamic water mass circulation, enhancing primary production and zooplankton biomass and abundance. Chaetognaths are a main component of zooplankton in oceanic areas, and they are poorly studied besides their important role as predators and their distribution matching specific water masses. Our aim was to study the effect of water mass dynamics on the distribution and abundance of the chaetognath community in an area of important water mass interaction, and to test their role as ocean bio-indicators. We studied the species composition, vertical distribution, size structure, and gonadal development of chaetognaths at six stations located at the CVFZ. Vertical stratified sampling covering epi-and mesopelagic depths were analyzed to assess the match of chaetognaths with different water masses. We found a total of 18 species of chaetognaths. The most frequent species was Flaccisagitta enflata (41.37 %), followed by Serratosagitta serratodentata (18.15 %), and Pterosagitta draco (14.92 %). The distribution patterns of six chaetognath species in the CVFZ were closely associated with oceanographic events and water masses, being Eukrohnia hamata a bio-indicator of Mauritanian upwelling. Flaccisagita enflata was associated with the mixed layer, Decipisagitta decipiens with the South Atlantic Central Water of 18 degrees C and Decipisagitta sibogae with the Northeast Atlantic Central Water of 15 degrees C, while Eukrohnia fowleri and Caecosagitta macrocephala were associated with the SubPolar Mode Water. These findings highlight the biodiversity of chaetognath community in the CVFZ and their importance to study their relationship with oceanic habitats in a scenario of climate change.