Zooplankton retention in the estuarine transition zone of the St. Lawrence Estuary

Abstract

We used a three-dimensional physical-biological model consisting of a Eulerian circulation model and a Lagrangian particle-tracking model, which included vertical sinking and swimming, to explore zooplankton retention in the estuarine transition zone of the St. Lawrence Estuary (SLETZ). To test the accuracy of the model, the results were temporally and spatially compared to a passive scalar released simultaneously in the circulation model and to field data for zebra mussel veligers. The model was then used to study the effects of baroclinic density-driven flow, vertical sinking and swimming, and tidal vertical migration on retention of simulated zooplankton. Baroclinic flow, created by longitudinal and lateral salinity gradients, was a critical part of retention in the SLETZ. In the presence of baroclinic flow, vertical sinking and swimming speeds of $0.2 mm s 21 had a large effect on the residence time of the simulated zooplankton as a result of gravitational circulation. Tidal vertical migration-a pattern of upward movement on flood and downward movement on ebb-was a viable retention mechanism for the SLETZ, and its effectiveness was amplified by baroclinic flow. As the speed of tidal vertical migration increased, the simulated zooplankton were concentrated in smaller areas of the SLETZ and moved further upstream.

Advection of freshwater phytoplankton in the St. Lawrence River estuarine turbidity maximum as revealed by sulfur-stable isotopes

“…These considerations, in addition to visual The passive accumulation of phytoplankton in the St. Lawrence River ETM requires further questioning. Simons et al (2006) calculated a residence time for free-floating particles such as algae of approximately 15 d in the ETM, which is in the same range of our observed 10-to 25-fold increase in peak chl a concentrations in the ETM compared to upstream concentrations. This indicates that the phytoplankton in the ETM achieves a relatively slow turnover rate of δ 34 S since the values for phytoplankton throughout the sampling zone are very close to those of the freshwater periphyton.…”

“…towards the ETM). Moreover, Simons et al (2006) reported a residence time of 15 d for passive particles in the ETM (such as phytoplankton cells), due to the hydrodynamic entrapment zone described above. The combination of a large advection of phytoplankton cells upstream and a relatively long particle residence time may favor the retention of phytoplankton cells in the ETM.…”

Effects of freshwater flow and phytoplankton biomass on growth, reproduction, and spatial subsidies of the estuarine copepod Pseudodiaptomus forbesi

“…The lower winter abundance and delayed spring increase are most likely due to higher advective losses during periods of high flow combined with sluggish development of the copepods at low winter temperatures. Advective losses due to high flow can overcome the ability of tidal vertical migration to hold copepods in place except in deep areas with enough of a salinity gradient to cause strong stratification (Simons et al, 2006;Kimmerer et al, 2014a).…”

An Overview of Multi-Dimensional Models of the Sacramento–San Joaquin Delta

“…Effectively, by changing vertical position at appropriate tidal phases, organisms, such as copepods or larval fish, can move large distances each tidal cycle or maintain a geographic position despite water movement. For example, using 3-D modeling, Simons et al (2006) showed how various zooplankton could maintain particular positions in the LSZ of the St. Lawrence Estuary (see also North et al 2008). Tracking individual "particles" with behavior moved by flow has also been used to assess connectivity of different regions in space, e.g., different coral reefs in the Caribbean (Cowen et al 2000) and regions of the California coast (Simons et al 2013).…”

“…However, there is the substantial challenge of knowing the behavior to be used in the model. For example, depending on which of the bioenergetically possible swimming behaviors Mysid shrimp used in the St. Lawrence Estuary, Simons et al (2006) found that there could be either upstream migration from the LSZ to Montreal, maintenance of position in the LSZ, or downstream migration into the Atlantic Ocean. Nonetheless, as suggested by Banas et al (2009) in the context of modeling nutrient-phytoplankton dynamics in the Washington Shelf-Salish Sea region, this form of coupled modeling may also offer researchers the ability to invert observed data on the distribution of organisms to infer behavior.…”