The phytoplankton production issues are subtler and require consideration in a separate paper now in preparation. Our historical reconstruction of phytoplankton productivity was surprising, in that Delta-wide production was relatively invariant from year to year, despite the wild swings at individual stations. It appears that different locations compensate for each other to a large extent. Total production therefore has not been declining and is unlikely to underlie species changes at higher levels. There have been large changes in species composition, however.
Different taxa are of different nutritional value.
A current view is that the highly unsaturated fatty acid content determines not only their food value but also the extent to which detrital organic matter can be used. We have developed a class-dependent nutritional index to characterize how the food value has changed over the past few decades. We are also working with colleagues at these institutions on other aspects of the primary food supply. First, phytoplankton often contributes to taste and odor problems in Delta water supplies, as well as filter clogging problems. These problems develop at high concentrations.