Research Document - 2015/013

Chemical and Biological Oceanographic Conditions in the Estuary and Gulf of St. Lawrence during 2013

By L. Devine, S. Plourde, M. Starr, J.-F. St-Pierre, L. St-Amand, P. Joly and P. S. Galbraith

Abstract

An overview of chemical and biological oceanographic conditions in the Gulf of St. Lawrence in 2013 is presented as part of the Atlantic Zone Monitoring Program (AZMP). AZMP data as well as data from regional monitoring programs are analyzed and presented in relation to long-term means in the context of a strong warming event that began in 2010. Phytoplankton and zooplankton abundance indices and nutrient inventories were relatively coherent through the time series (1999-2013) between the high frequency monitoring sites and among sections and subregions. Nutrient inventories returned to near-normal levels in 2013, ending the period of strong negative anomalies that was seen in 2010-2012. The strong spring freshet of the St. Lawrence River delayed the spring bloom in the Estuary and NW Gulf and also led to lower than normal abundances of Calanus finmarchicus and C. hyperboreus Warmer temperatures overall are likely behind the shift to smaller phytoplankton (since 2004 at Rimouski station) and the lower than normal abundances of cold-water copepod species. Satellite images of ocean colour were coherent with field measurements of chlorophyll content, thus increasing our confidence in what these images revealed over larger spatial and temporal scales than were covered during sampling campaigns. Our results and independent evidence from ecosystem surveys indicate that the decreased abundance of large zooplankton might be due to a combination of detrimental environmental conditions (bottom-up processes) and an increase in predation pressure (top-down processes).

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