Trophic structure in the northern Humboldt Current system: new perspectives from stable isotope analysis.
Résumé
The northern Humboldt Current system
(NHCS) is the most productive eastern boundary upwelling
system (EBUS) in terms of fish productivity despite having
a moderate primary production compared with other
EBUS. To understand this apparent paradox, an updated
vision of the trophic relationships in the NHCS is required.
Using δ13C and δ15N as a proxy of foraging habitat and
trophic position, respectively, we focused on thirteen relevant
taxonomic groups from zooplankton to air-breathing
top predators collected off Peru from 2008 to 2011. Estimates of trophic position (TP) for the anchoveta
Engraulis ringens were high (3.4–3.7), in accordance with
previous studies showing zooplankton as a major contributor
to anchoveta diet and challenging the often-cited short
food chain hypothesis for this ecosystem. The squat lobster,
Pleuroncodes monodon, a little studied consumer had similar
δ15N values that of anchoveta, and thus similar trophic
position. However, their differing δ13C values indicate that
their foraging habitat do not fully overlap, which could alleviate
potential competition between these species. Given
the current high biomass of squat lobsters in the ecosystem,
we encourage that future research focus on this species
and its role in the diet of top predators. The present
study provides first estimates of the relative TP of important
taxonomic groups in the NHCS, which are needed to
revisit anchoveta-centred ecosystem models for this region.
Further work using amino acid compound specific stable
isotope analyses is now required to confirm these TP
estimates.