Copepod Assemblage Dynamics in a Snowmelt-Dominated Estuary

Abstract

What limits secondary production in the estuaries of snowmelt-dominated basins? Due to substantial differences in their annual hydrographs, zooplankton dynamics in these estuaries are expected to differ from better-studied pluvial systems. We hypothesized that water residence time limited zooplankton production in the undammed, snowmelt-dominated estuary of the Fraser River, Canada. We sampled zooplankton and associated environmental variables bi-weekly to monthly in slough and channel areas of the estuary over a 33-month period. Annual mean copepod abundance at channel stations was low (2005 ± 238 ind. m −3 ) in comparison to other studied estuaries, with minima occurring during spring, concurrent with the freshet. Higher abundances (11,905 ± 3606 ind. m −3 ) observed at slough stations were attributed to estuarine copepods. Differences in abundance and species composition between slough and channel areas, and the coincidence of seasonal minima with the freshet, suggest that the low water residence time of this system limits zooplankton density and production. Heavy channelization of the Fraser River Estuary has further reduced water residence time in the estuary, likely affecting prey availability to fish and invertebrate predators. Given that peak river discharge in snowmelt-dominated basins occurs during the relatively short spring-summer growing season, the impacts of channelization on zooplankton production in the estuaries of snowmelt-dominated basins may be greater than in riverdominated estuaries subjected to different flow regimes.

Hydrodynamics structure plankton communities and interactions in a freshwater tidal estuary

“…Many estuaries have sustained severe losses of habitats such as tidal wetlands and terminal sloughs (Brophy et al, 2019; Whipple et al, 2012). These estuarine habitats, characterized by high light availability and longer residence times, often support higher primary and secondary productivity than deeper or more turbulent areas (Ahearn et al, 2006; Bukaveckas et al, 2011), where phytoplankton are limited by access to the photic zone and both phytoplankton and zooplankton biomass is rapidly advected or dispersed (Breckenridge et al, 2020). Shallow, productive habitats can subsidize adjacent areas with lower in situ production (Lopez et al, 2006).…”

Zooplankton Fluctuations in the Surface Waters of the Estuary of a Large Subtropical Urban River

“…This may be an indication that predominantly estuarine species cannot easily undergo long-distance dispersal across oceans. In different parts of the world such as India (Madhu et al, 2007;Rakhesh et al, 2013;Paul et al, 2019), Europe (Vieira et al, 2003), Africa (Kibirige and Perissinotto, 2003;Froneman, 2004;Carrasco and Perissinotto, 2015;Ounissi et al, 2016), America (Krumme and Liang, 2004;Araujo et al, 2008;Howson et al, 2017;Salvador and Bersano, 2017;Breckenridge et al, 2020), and Oceania (Rose et al, 2020), it has been shown repeatedly that differences in the composition of the dominant copepod fauna in estuaries increase with distance. The abundance and diversity of zooplankton communities showed spatial, seasonal, and interannual trends in Barnegat Bay (Howson et al, 2017), and also in the Paranagua estuary (Salvador and Bersano, 2017).…”