The Benguela Current's krill are not a single link in the food web; they are an entire network of dietary strategies, and treating them as one homogeneous group has been obscuring the system's true architecture. This new analysis of 15 euphausiid species off Namibia and South Africa delivers a clear, empirical correction: these organisms occupy trophic positions ranging from 2 to 3.7, with carnivory indices that vary by an order of magnitude. That is not a footnote. That is a structural finding that demands we rebuild our food-web models from the ground up.
The practical consequence is immediate for anyone modeling the BUS or similar upwelling systems. If you input krill as a single functional group, you are averaging away the very plasticity that makes the system resilient. The data show *Euphausia lucens* dominating both subsystems as a herbivore-to-omnivore generalist, while *Stylocheiron* species are exclusive carnivores with a mean carnivory index of 15.6. Meanwhile, *Hansarsia megalops* and *Euphausia similis* sit in a flexible middle, shifting their feeding behavior based on availability. This is not a simple transfer of energy from phytoplankton to fish. It is a multi-lane highway with species-specific exits, and the traffic patterns matter. As we refine ocean intelligence for climate indicators, the same logic applies to validated nitrogen pathways in the Qiongdong Upwelling: the resolution of your functional groups determines the accuracy of your predictions.
What makes this study particularly valuable is the biomarker evidence. Stable isotope and fatty acid analysis did not just infer diet from morphology; they measured it. The diatom marker 18:1(n-7) in *E. recurva* and *E. lucens* confirms a herbivorous baseline, while the elevated 18:1(n-9) in *E. hanseni* points to a carnivorous tendency. The larvae and small juveniles below 10 millimeters are predominantly herbivorous, which means the system's youngest consumers are doing very different work than the adults. Age structure is not a detail; it is a variable. This mirrors the kind of precision we have seen in prey fish nutrition shaping health risks for Indo-Pacific humpback dolphins, where the nutritional quality of specific prey species, not just their abundance, drives outcomes at higher trophic levels.
The takeaway is direct: biodiversity in the BUS increases from coastal to oceanic waters, and so does the complexity of feeding behavior. A model that ignores this will overestimate the efficiency of energy transfer and underestimate the system's capacity to buffer change. The one detail to watch is the wax ester production found only in *H. megalops*. That storage lipid strategy suggests a species built for variable food availability, a physiological buffer that may prove critical as upwelling regimes shift. We should be tracking that species specifically, not just total krill biomass, in the next generation of climate-linked ecosystem models.