Temporal variability on the Peruvian Sea pelagic food web: Comparing El Niño vs. non El Niño years

Background/Question/Methods

 The Peruvian Sea, an abundant source of marine food, exhibits marked variability in primary productivity and temperature when data are compared from El Niño versus non El Niño years. This variation markedly effects the food web, with consequences for the commercial exploitation of the Peruvian anchovy for human consumption. We constructed two food webs, El Niño versus off years, using data from IMPARPE's trophic ecology lab, in order to understand better the effect of physical changes on the pelagic environment. The years covered by our study range from 1973 to 2000. Data were processed using Network3D (PEACE lab), which enabled each of the properties of the food web to be isolated and compared.

 Results/Conclusions

 A great bunch of the properties used to describe the food web display minor differences when the El Niño years are compared with the non El Niño years. We looked at connectance, links per species, mean shortest chain TL, mean cluster coefficients, characteristic path length and diet discontinuity. While all of these increased in the El Niño years,there were only minor changes . Other properties decreased: the variation in the number of links, maximum short-weighted TL and consumers per species; but, again were minor, Exceptions to this were the Fractions of basal and cannibal species and the mean similarity . We interpret this food web stability in two ways. First, there could be an inherent mechanism that maintains constancy of the web structure, despite the wide variation in physical environment. Second, there may be a sampling bias in our experimental design because of our focus on commercially exploited species, disguising the role of non-commercial species in providing plasticity to the food web. Even though we recommend a better sampling in the zone, we favor the first explanation.