COS 88-5
Exploring changes to the northern San Francisco Estuary phytoplankton community by probing a 40-year monthly monitoring record
The northern San Francisco Estuary (SFE) has experienced major ecological disturbances due to a combination of landscape alterations, species invasions, water withdrawals, and contaminants introduction. In order to detect and understand historical changes and long-term trends in phytoplankton community composition, we probed a 40-year monthly record of water quality and ecological indicators in the northern SFE. What kind of information is contained in multidecadal records of community change, and what analyses are available to extract that information?
Results/Conclusions
An ordination method called Principal Coordinate Analysis (PCoA) based on Bray-Curtis dissimilarity first allowed us to quantify the compositional dissimilarity in the phytoplankton community, identify the community’s states, and detect shifts in states over time. Then a constrained ordination method called Canonical Analysis of Principal Coordinates (CAP) revealed substantial and abrupt shift in the phytoplankton composition beginning in the mid-1980s, from assemblages (1970s to mid-1980s) that moved between only a few stable and similar states to one that shifted more frequently among a larger number and more heterogeneous set of compositions (post-1980s). This presentation also explores the importance of the effort at cell enumeration to make reliable estimates of the phytoplankton density and composition.