To examine this we analysed the unique data series from the California current, spanning the gradient from nutrient rich coastal upwelling waters to the nutrient starved oceanic regions. As governing traits, we chose body size, trophic strategy (auto-, mixo-, or heterotrophic) and the feeding mode (active vs. passive). We did so on the entire size range from bacteria to mesozooplankton.
The biomass varied by approximately a factor 5 between the regions. Despite this contrast, the trait distribution was surprisingly similar; the size distribution was roughly flat, the trophic strategies varied similar with size, as did the feeding mode. There were differences; these were mainly due to the high abundance of autotrophic diatoms in eutrophic waters (sizes >20 
m). The analysis challenges the classic interpretation of fundamental differences between oligotrophic and eutrophic region – we see differences, but it is the similarities in the trait distributions that are most striking.
The work was led by Kasia Kenitz, now at Scripps, and is published in Ecosystems: link to article