Influence of conductivity on life history traits of exotic and native amphipods in the St. Lawrence River

Abstract

We compared the survival, growth and fecundity of the Ponto-Caspian amphipod Echinogammarus ischnus and the North American amphipod Gammarus fasciatus across a range of conductivities in a fl uvial lake at the confl uence of the St. Lawrence and Ottawa rivers (Quebec, Canada). Previous work has found that water chemistry (conductivity) regulates the direction and intensity of intraguild predation between these two species. Because E. ischnus evolved in ion-rich waters, we hypothesized that low conductivity has a negative effect on its life history traits, whereas G. fasciatus would be more tolerant. Consistent with this hypothesis, E. ischnus is abundant along the south shore of the lake in water of high conductivity (300 µS/cm), but rare along the north shore where conductivity is subject to strong fl uctuations (85-230 µS/cm). In laboratory experiments using water with low (108 µS/ cm), high (300 µS/cm) and intermediate (50:50 mix) conductivities, both species showed reduced growth at low conductivity, but E. ischnus also suffered higher mortality. E. ischnus collected from both shores did not differ in size-specifi c fecundity, size at reproduction, or size of adults. On the north shore, E. ischnus was present in low abundance at one site and absent from another site where it had been recorded in previous years. We conclude that low conductivity negatively affects the growth rate and mortality of E. ischnus, which is apparently eliminated from the north shore during periods of strong infl ux of ion-poor water from the Ottawa River, but re-establishes populations temporarily when higher conductivity is restored.

Possible influences of plasticity and genetic/maternal effects on species coexistence: nativeGammarus fasciatusfacing exotic amphipods

“…Head length was measured directly on field‐caught female amphipods (F 0‐field ) from both habitats in early summer and was measured throughout the summer at the ion‐rich habitat. Head length is often used to estimate body size in amphipods (Wilhelm & Lasenby ; Kestrup & Ricciardi ), and we measured it here with a Leica MZ 12.5 dissecting microscope (Leica Microsystems Inc., Concord, ON, Canada) equipped with digital software (QCapturePro). All other F 0 traits (dry weight biomass, fecundity and postmoult calcification) were measured on field‐caught individuals that were held in the laboratory under experimental conditions (F 0‐field/lab ).…”

“…) since its introduction to North American waters in 1994 (Detroit River; Witt, Hebert & Morton ). However, the amphipod species assemblage in the upper St. Lawrence River at Lac St. Louis (Montréal, QC Canada; 45°N, 73°W) continues to be dominated by the native amphipod (Palmer & Ricciardi ; Kestrup & Ricciardi ). This spatial variation in exotic–native interactions appears to be mediated by the ability of the native amphipod to persist beyond the exotic species along a particular habitat gradient.…”

“…This spatial variation in exotic–native interactions appears to be mediated by the ability of the native amphipod to persist beyond the exotic species along a particular habitat gradient. Whereas native amphipods inhabit both ion‐rich and ion‐poor habitats, the exotic amphipod is restricted to ion‐rich habitats (Palmer & Ricciardi ; Kestrup & Ricciardi ). In fact, dissolved calcium and ion gradients determine the relative abundance of the two species (Palmer & Ricciardi ; Kestrup & Ricciardi ), as well as interactions between them (Kestrup & Ricciardi ; Kestrup, Dick & Ricciardi ).…”

“…Native adults and larvae attach to floating and uprooted macrophytes (Palmer & Ricciardi ) and can be transported among habitats within Lac St. Louis on this vegetation by wind and water currents. Third, temporal variation in ion concentration is high because the relative contribution of water from the St. Lawrence or Ottawa rivers varies seasonally and with precipitation – relative contributions from the latter are higher during spring floods (Centre St‐Laurent ; Kestrup & Ricciardi ). All of the conditions expected to favour the evolution of trait plasticity were present for the native amphipod in Lac St. Louis.…”

New records of the invasive amphipod Echinogammarus ischnus (Stebbing, 1899) in Croatia

“…Ovigerous females in the native range produce more eggs (Ukraine population had an average 33 and a maximum 55 eggs) than those in the invaded range (Poland: avg-10 and max-27; Germany: <20) (Konopacka & Jesionowska, 1995). Populations from a fluvial lake at the confluence of the St. Lawrence and Ottawa rivers in Canada were found to have maximum brood size of only 19 eggs probably due to the low conductivity of these waters (Kestrup & Ricciardi, 2010). Therefore, fecundity of E. ischnus in the invading range is relatively low, which could be expected in Drava as well.…”