Nature of environmental variability experienced by benthic and pelagic animals in the St. Lawrence Estuary, Canada

Abstract

We compared the short-term variability in salinity, temperature and concentration of suspended particulate matter experienced by benthic and pelagic animals in the middle St. Lawrence Estuary on both horizontal and vertical axes. In addition, we examined the effect of 3 patterns of vertical distribution (no vertical migrations, die1 and tidal vertical migrations) on the environmental variability experienced by pelagic animals. Results demonstrated that the nature of environmental variability is different for the 2 types of animal. For benthic animals, environmental variability is experienced on the horizontal axis, whereas the vertical axis is more important for pelagic animals. The magnitude and frequency of abiotic fluctuations experienced by benthic animals depend on the environmental factors that control the longitudinal position of the estuarine gradient, whereas for pelagic animals they mostly depend on the animals' behaviour on the vertical axis. Consequently. favourable habitats for benthic and pelagic animals in the estuary are different. The most upstream section of the estuary is the most variable for benthic animals because the tides of greatest range generate the highest abiotic fluctuations on the horizontal axis. In contrast, the same section is the most abiotically stable for pelagic animals because tides of highest energy generate the strongest vertical mixing. The highest abiotic fluctuations experienced by these animals are in the most vertically stratified waters downstream in the estuary. As a result, minimum numbers of species of benthic and pelagic animals are reached at different locations in the estuary corresponding to the areas which are the most abiotically variable for each type of animal. We propose that well-mixed parts of estuaries should be considered as abiotically stable habitats for the pelagic fauna, whereas vertically stratified areas should be considered as abiotically variable except in the case where vertical rnigratlons are not necessary for the retention of animals.

Factors influencing the spatio-temporal occurrence of fish eggs and larvae in a northern, physically dynamic coastal environment

“…Second, egg distribution is influenced by circulation and most likely has a response to external forcing factors similar to that exhibited by surface temperature. Planktonic animals are transported along with water masses which allow them to remain in relatively stable habitats (Laprise & Dodson 1993. The relationship observed between wind patterns, temperature and egg distribution in Conception Bay supports this suggestion.…”

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

“…Samples were taken at each station by vertical tows of a 0.5-m diameter, 53-lm net equipped with a flowmeter, and surface salinity and temperature were determined using a SeaBird SBE-19 CTD or a YSI Model 30. Although sampling plankton according to salinity is generally preferable to geographic-based sampling in an estuary (Laprise & Dodson, 1993;Kimmerer et al, 2014b), in this study, we sampled geographically (because much of our sampling was in fresh water) and later stratified the data by salinity.…”

“…At the landscape scale, the geomorphic, hydrologic, and biological complexity of most estuaries adds variability that may interfere with detection of mechanisms of change that are related to flow. For pelagic organisms which live in a moving frame of reference (Laprise & Dodson, 1993), flow effects are probably best analyzed in a Lagrangian or moving frame of reference, which can be difficult in stratified estuaries and where mechanisms for flow effects have a geomorphic component.…”

Occurrence characteristics of two sibling species, Pseudodiaptomus inopinus and Pseudodiaptomus poplesia (Copepoda, Calanoida, Pseudodiaptomidae), in the Mankyung River estuary, South Korea

“…Most studies on the coexistence of zooplankton species in estuarine and coastal environments addressed the mechanisms responsible for interspecific competition, spatial segregation, and reproductive isolation (Greenwood 1981;Ueda 1987;Laprise and Dodson 1993). Strategies by which congeneric species may avoid or reduce direct competition include maintaining different temporal and spatial distributions and partitioning available food resources by selective feeding (Greenwood 1981;Ueda 1987;Laprise and Dodson 1993).…”