Somatic and molt production in Euphausia mucronata off central-southern Chile: the influence of coastal upwelling variability

Seasonal and inter-annual variability in population abundance, biomass, and somatic and molt production of the Humboldt Current krill Euphausia mucronata were studied during a monthly time series (August 2002 to June 2007) at Stn 18 (36 degrees 30' S, 73 degrees 07' W) off central-southern Chile. Experimental measurements in krill were performed at Stn 18 (in 2007 and 2008) and northern Chile (2010) in order to estimate vital rates for use in E. mucronata secondary production calculation at Stn 18. Coastal upwelling intensity was the main oceanographic process found to control E. mucronata population abundance and biomass production on seasonal and inter-annual time scales. Spawning peaks and population structure indicate that E. mucronata produces at least 2 generations per year. The main spawning period occurs during the austral spring when phytoplankton concentration is high. A second, less intense spawning period occurs at the end of the austral summer and early autumn. E. mucronata had a mean biomass of 100 mg C m(-3) and an integrated annual secondary production of 2432 mg C m(-3) yr(-1), with an overall production/biomass ratio (P/B) ratio of 24. In May 2007, a maximum daily integrated biomass of 5 g C m(-3) and total daily secondary production of 63 mg C m(-3) d(-1) were observed. These estimates are considerably higher than those reported for other krill species in coastal upwelling regions. Multivariate analyses indicate that upwelling-favorable winds promote high E. mucronata biomass and secondary production, but higher abundance and biomass were found during the transition periods from upwelling to downwelling conditions. Results suggest that E. mucronata has a highly efficient behavioral strategy to attain high production rates and recover rapidly from potential offshore losses due to advective processes in a highly productive coastal upwelling ecosystem.