Research Document 2017/012
Optical, Chemical, and Biological Oceanographic Conditions on the Scotian Shelf and in the Eastern Gulf of Maine in 2015
By Johnson, C., Devred, E., Casault, B., Head, E., and Spry, J.
As warm and variable ocean conditions persisted in the Maritimes Region in 2015, there was increasing evidence of a shift in both phytoplankton and zooplankton communities away from the dominance of large phytoplankton and copepods toward smaller phytoplankton and copepod species. Although deep-water nitrate inventories were mainly higher than average in 2015, deep silicate and phosphate inventories were lower than average on the Scotian Shelf for the third year in a row. The spring bloom started later than normal and was weaker in magnitude and shorter in duration than usual. Phytoplankton biomass anomalies were mixed across the Shelf, but the abundance of large phytoplankton, particularly diatoms, was lower than average, continuing a pattern started in 2009. The abundance of the biomass-dominant copepod species Calanus finmarchicus and zooplankton biomass overall were lower than average overall in 2015, as was the abundance of Arctic Calanus species, continuing a pattern started during the last 4-7 years. In contrast, the abundances of offshore copepods were higher than average. Changes in phytoplankton and zooplankton communities observed in recent years indicate poor feeding conditions for planktivorous fish, birds, and mammals. Continuous Plankton Recorder sampling, the reporting of which lags Atlantic Zone Monitoring Program sampling by one year, indicated that in 2014 the spring phytoplankton bloom occurred earlier and was of shorter duration than normal over the entire Scotian Shelf and that the springtime peaks in abundance of the dominant zooplankton taxa Calanus I-IV and C. finmarchicus V-VI were also relatively early and relatively short-lived. 2014 annual abundance anomalies were unusually high for hyperiid amphipods and foraminifera over the entire Scotian Shelf in 2014, and unusually low for euphausiids. Annual abundance anomalies for most other taxa were at near normal levels on the western Scotian Shelf and below normal levels on the eastern Scotian Shelf.
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