Interaction of two key pelagic species in the Humboldt Current: euphausiid predation on anchoveta eggs estimated by immunoassays

摘要

The euphausiid Euphausia mucronata and anchoveta Engiaulis ringens are extremely abundant key components of the pelagic community of the Humboldt Current, and utilize a large fraction of primary production in the euphotic zone. Despite the economic importance of the Peruvian anchoveta, little information exists on the causes of mortality during their early life stages. In this study we: (1) detected and quantified E. mucronata predation on anchoveta eggs in Northern Chile during the winter peak spawning season of 2000 using enzyme-linked immunosorbent assay (ELISA); and (2) estimated the fraction of total natural mortality of anchoveta eggs produced by euphausiid predation. Immunoassay with polyclonal antibodies detected 0.1 μg of anchoveta egg proteins. Potential cross-reactions with proteins of coastal fish eggs were eliminated after the use of electrophoresis, Western blotting and ELISA. Protein detection time in euphausiid guts was 9 h (13℃) and egg protein decay rate was 0.0385 h~(-1). Geostatistical analysis identified a large area of egg abundance, and a smaller secondary egg aggregation within the area covered in the regular spawning biomass stock assessment survey in northern Chile (daily egg production method sampling grid). Eighteen percent of total captured euphausiids within the main aggregation of eggs provided positive reactions, indicating anchoveta egg proteins in their guts. Natural mortality rate calculated at the main spawning area was 0.868 d~(-1). The potential euphausiid consumption of eggs in this area varied from 3.9 x 10~(12) to 4.4 x 10~(12) eggs d~(-1). Euphausiid predation accounted for 24 to 27% of natural mortality. When added to mortality rate estimates resulting from anchoveta cannibalism in the Humboldt Current, our results suggest that half of the daily anchoveta egg production dies daily. Accordingly, these estimates challenge classical ideas of trophic webs that do not consider either young developmental stages or interspecific interaction schemes for control of dominant species in pelagic systems.