FIG. 2. Continued.
Flows towards macrobenthos and hake also increased with higher abundance of these groups, following improved oxygen conditions on the Peruvian shelf. Due to the overall shortage of small pelagics in the system, the trophic level of piscivores changed. On the one hand, the trophic levels of horse mackerel and mackerel decreased because they ingested a larger fraction of zooplankton, while on the other hand those of hake, the mammals, and birds increased, as they partly switched to sardine and predatory fish. Feeding of marine mammals "outside" the system (i.e., on oceanic squid and mesopelagics) was important during both periods.
The general structure of the pathways, as illustrated in trophic flow diagrams, was very similar in all four systems and all regimes, in spite of considerable differences in the magnitude of the flows. A full set of trophic flow diagrams (for all models constructed) is given in Jarre-Teichmann and Christensen (in press a), but will not be repeated here for brevity's sake.
Systems characteristics
The four upwelling systems ranked rather distinctly after the parameters primary production, total biomass sustained in the system, total catches, and total system throughput (Fig. 3), all of which are characteristics of the size of an ecosystem. Although the systems were originally ranked after decreasing primary production, a consistent pattern was observed for all four size parameters, and it is worth noting that the systems were set apart in geographic rather than in regime-specific order. The Peruvian upwelling ecosystem was the largest of these four systems. It was also the system in which the most pronounced changes of system size occurred during the periods analyzed. After the collapse of the anchovy stock (i.e., in the later period), it became more similar to the northern Benguela system. The latter decreased in size from the mid-1970s to the early 1980s, due to the marked decrease of small pelagics (notably sardine) that was not compensated by increased abundance of horse mackerel. The upwelling
