Cross-shelf distribution of decapod larvae in a coastal upwelling zone of northern Chile: some oceanographic implications

Abstract

The northern of Chile is one of the most productive and permanent upwelling systems of the large Humboldt Current System. However, do not investigations have been developed about the decapod larvae dynamics in this region, characterized by its narrow continental shelf and an oxygen minimal zone (OMZ) very shallow (<50 m). Four oceanographic campaigns carried out in a coastal upwelling zone off northern Chile in 2003 were used to analyze the dispersal patterns of 15 taxa from decapods larvae selected. The coastal upwelling conditions showed a maximum Ekman transport value (Mx) in January and a minimum in May, while the temperature and salinity characteristics defined four types of waters named a) cold upwelling waters (UW), b) warm trapped waters (WTW), c) upwelling front waters (UFW) and d) oceanic front waters (OFW), which showed different concentrations of dissolved oxygen, OMZ depth (<1 mL L−1) and chlorophyll-a concentrations, respectively. Decapod larvae with the highest abundance and frequency were Cancer spp., Emerita analoga, Pinnaxodes chilensis, Callianassidae sp., Pagurus sp. and Allopetrolisthes sp., from adults of diverse habitats, characterized by different development stages and periods. The offshore weighted distance (Ğ) estimated for the decapod larvae allowed the differentiation of three main groups. a) group formed by high dispersion larvae (>11 km), with five zoea stages and associated to the UFW waters, b) group formed by mean dispersion larvae (between 5 and 8 km) and distributed in upwelling waters (UW), and c) group showing lower horizontal dispersions (<4 km), which significantly and negatively correlated to the OMZ in UW and WTW-type waters. The different cross-shelf distribution patterns relative to the oceanographic conditions were compared with other upwelling system, and larval behavior, morphology, environmental requirements and development period of different decapods were discussed.