UBC Theses and Dissertations
Copepod dynamics of the Fraser River estuary Breckenridge, Joanne Kathryn
How the zooplankton in estuaries of nival basins will respond to a warming water column and earlier peak flows is unknown. The goal of this dissertation is to increase our knowledge of zooplankton dynamics in snowmelt-dominated estuarine systems by studying the Fraser River Estuary (FRE). To describe the copepod community of the FRE and identify drivers of species composition and abundance, an intensive zooplankton sampling program was carried out over a period of 33 months, from August 2013 – May 2016. I coupled the sampling program with investigations of the depth distribution and egg production of the most abundant pelagic copepod in the estuary, Eurytemora affinis. Using the information gained in these studies and data from the literature, I built a stage-structured, concentration-based population model to explore the response of E. affinis abundance to projected changes in temperature and Fraser River discharge. The results outlined in this dissertation demonstrate that mesozooplankton abundance, biomass, and production in the FRE were low in comparison to other studied estuaries and limited by water residence times in the estuary. Targeted study of E. affinis provided evidence of tidal vertical migration behaviour and a first record of the production of resting eggs to bridge periods of rapid flushing and low salinity. The presence of these retention mechanisms highlights the role advection risk has played in shaping both the behaviour and life history of the E. affinis population in the FRE. Results of model simulations suggest that the response of E. affinis abundance to predicted changes in water temperature and river discharge is dependent on how those changes influence spring contributions to the egg bank. My simulations suggest that warming of 1.5 ℃, in combination with predicted changes to the Fraser River’s hydrograph, has the potential to lead to a near doubling (+ 92%) of abundance of E. affinis and significant changes in their phenology (from 50 days earlier to 25 days later, depending on the timeframe of the river discharge scenario). I suggest that zooplankton production in snowmelt-dominated estuarine systems may be sensitive to changes in hydrology, particularly where channelization has occurred.
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