Research Document - 2009/063

Long-term variability in phytoplankton and zooplankton abundance in the Northwest Atlantic in Continuous Plankton Recorder (CPR) samples

By Erica Head and Pierre Pepin

Abstract

A new way to present Continuous Plankton Recorder (CPR) data collected in the Northwest (NW) Atlantic for reporting to the Atlantic Zone Monitoring Programme (AZMP) has been developed. Data for 12 standard CPR taxa from 8 standard regions, 4 on the Canadian continental shelf (the CPR E line) and 4 extending eastward beyond it to Iceland (the CPR Z line) are included. The reporting consists of time series of standardised annual abundance anomalies and seasonal cycles for 5 sequential multi-year periods between the 1960s and 2006. For the years prior to the 1990s, only decadal annual averages are reported for the 1960s to the 1980s, because there were numerous, sometimes prolonged, interruptions in CPR sampling during those decades. Results for the 4 regions covering the Scotian and Newfoundland shelves show that phytoplankton levels were higher in the 1990s and 2000s than in previous decades, Calanus finmarchicus levels decreased in the 1990s, but made a come-back on the Scotian Shelf in the 2000s (although not on the Newfoundland Shelf), 2 arctic Calanus species increased in abundance in the 1990s and stayed high in the 2000s, while euphausiid levels decreased and remained low over the same time periods. On the Scotian Shelf, the phytoplankton bloom started earlier and young stage Calanus appeared earlier in the year after 1992. In the deep ocean, changes in abundance were not as dramatic as on the shelf, although phytoplankton, small copepods and forams increased in abundance in the mid-2000s, possibly as a result of increased temperatures. Also, seasonal cycles beyond the shelf did not change over the decades.

In 2007, the latest year for which data were available, sampling was only possible from January to May so that annual average abundance values could not be calculated. Instead, values are reported for each month that was sampled and these are compared with multi-year monthly averages representative of earlier sampling periods, i.e. with the multi-year seasonal cycles. There were no dramatic changes in shelf or open ocean regions in 2007.

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