Northwest Fisheries Science Center

Copepod Community Structure

A more recently developed index of our forecasting suite is based on the presence/absence of two alternate copepod community types.  Data sets upon which this index is based are from our zooplankton samples off Newport, OR, taken biweekly since 1996, and from zooplankton samples taken since 1998 during June and September surveys of juvenile salmonid. 

As an ocean ecosystem indicator, copepod community structure is based on multidimensional scaling (MDS), an ordination technique that helps visually represent non-numerical data (Figure CCI-01). The full ordination is not shown, but rather the averaged X- and Y-axis scores: these two alone accounted for about 85% of the variability between copepod communities, with the X-axis accounting for 73% and the Y-axis for 11%. CCI-01 compares these summer-average scores.

Ordination plot showing average copepod community structure during May to September by year. Figure CCI-01. Ordination of copepod community structure averaged over May-September, by year. Years when summer community structure was dominated by cold, boreal species fall to the left (1970-1973, 1999-2002, 2007-2009, 2011-2013); years with warm subtropical species fall in to the center of the graph (1996, 1997,2003, 2004, 2006, 2010); years characterized by strong El Niño conditions (1983, 1998, 2016), or when the NE Pacific water anomalously warm in 2005 (due to delayed upwelling) and 2015 (because of “The Blob”), are grouped in the upper right quadrant Numbers indicate the warm (red) and cold (blue) years.

The different community types are clearly a function of the state and phase of the Pacific Decadal Oscillation (Figure CCI-02).  Negative X–axis scores are associated with negative PDO and vice versa.  This relationship seems to be related to advection.  That is, a negative–phase PDO results in more boreal water coming into the northern California Current from the north; whereas a positive–phase PDO results in more subtropical water coming in either from the south (as during the large El Niño events of 1983 and 1998) or from offshore (as during the El Niño–like event of 2005). 

Scatter plot showing relationship between the PDO and X–axis ordination scores.  A "cold water zooplankton community" is associated with the negative (cold) phase of the PDO and vice versa. average copepod community structure during May to September by year. Figure CCI-02. Relationship between the PDO and X-axis ordination scores. A "cold-water zooplankton community" is associated with the negative (cold) phase of the PDO and vice versa. Numbers indicate the warm (red) and cold (blue) years. Years in black were outliers and were excluded from the regression.

Coho survival is related to the copepod community structure in that when a cold–water community dominates, coho survival is often high, and vice versa (Figure CCI-03).  The link between copepods and salmon is almost certainly through the food web, since when a cold–water copepod community prevails, a cold–water fish community probably prevails.  Since juvenile coho and Chinook salmon feed primarily on fishes, we hypothesize that copepods index the abundance of cold–water coastal fishes such as herring, smelt, and sand lance. 

Plot showing relationship between coho survival and average copepod community structure during May to September by year. Figure CCI-03.  Plot showing the relationship between a) spring Chinook salmon adult returns at Bonneville dam (lag 2 years), b) fall Chinook salmon adult returns at Bonneville dam (lag 2 years), and c) coho salmon smolt-to-adult survival (SAR, lag 1 year) versus the copepod community structure index (X-axis ordination score). The X-axis ordination score for May-September 2016 was 0.85, which indicates poor subsequent salmon survival. Numbers indicate the warm (red) and cold (blue) years. Years in black were outliers and were excluded from the regression.