Effects of slight salinity increases on Moina micrura (Cladocera) populations: field and laboratory observations

Abstract

Salinity is a well-recognised factor that shapes population dynamics and community structure through direct and indirect effects. The responses of Moina micrura (Cladocera) to slight salinity increases (up to 6.0) were evaluated through laboratory manipulative experiments and field observations at Cabiúnas lagoon (Rio de Janeiro, Brazil). From the field data, a positive relationship between M. micrura density and salinity was observed, whereas the opposite was found for other co-occurring microcrustaceans. Life-table observations from laboratory experiments showed better performance of individuals exposed to control conditions (no salt addition) and 1.0 and 2.0 of salinity. The difference between field and laboratory results may be explained considering possible direct and indirect effects of salinity on M. micrura populations. Salinity may have direct negative physiological effects in individuals. However, under natural conditions, M. micrura might benefit from reduced invertebrate predation and interspecific competition. This balance between negative and positive effects of salinity is probably more positive under natural conditions, explaining the success of M. micrura in Cabiúnas lagoon under mild salinity conditions. Although salinity negatively affects many species living in freshwater systems, slight increases may be beneficial for some species under natural conditions.

Acute and chronic effects of sodium and potassium on the tropical freshwater cladoceran Pseudosida ramosa

“…For example, although the vast majority of cladocerans appear to be restricted to freshwater environments with salinity \1,000 mg l -1 (Hart et al 1991), there are a few species that are euryhaline, such as Daphnia salina (Ghazy et al 2009) and Moina mongolica (He et al 2001). However, there is yet little information on how the increase of salinity affects freshwater organisms (Nielsen et al 2003), principally in relation to cladocerans from tropical regions (Santangelo et al 2008). …”

Genetic variability in the tolerance of natural populations ofSimocephalus vetulus(Müller, 1776) to lethal levels of sodium chloride

“…Ceriodaphnia lacustris, D. thomsoni, D. pulex and D. pulicaria have also been found in habitats with moderate (5-13) salinities (Weider and Hebert, 1987;Barry et al, 2005;Northcote and Hall, 2010). However, most cladocerans are restricted to freshwater (Alonso, 1996) and are only able to cope with low salinities (usually < 2; see Sarma et al, 2006) (for field data, see Jeppesen et al, 1994;Schallenberg et al, 2003;Marques et al, 2006;Santangelo et al, 2008). In fact, Schallenberg et al (2003) predicts that severe alterations of zooplankton community structure and abundance may occur at salinities > 1.2.…”

“…Although sensitive to minor salinity increases (Schallenberg et al, 2003;Sarma et al, 2006;Gonc¸alves et al, 2007), freshwater cladoceran populations also occur in coastal systems with distinct degrees of connectedness to the sea (e.g., Jeppesen et al, 1994;Schallenberg et al, 2003;Marques et al, 2006;Santangelo et al, 2008). Such physiological plasticity is likely due to genetic factors associated with osmoregulation shifts (Arne´r and Koivisto, 1993;Aladin and Potts, 1995;Martı´nez-Jero´nimo and Martı´nez-Jero´nimo, 2007).…”

Zooplankton characterisation of Pampean saline shallow lakes, habitat of the Andean flamingoes

“…Derry et al (2003) found that in Canadian shallow lakes with chloride waters, B. plicatilis and the hapacticoid copepod Cletocampus sp., were the dominant species. However, it cannot be claimed that some abundant species such as Moina micrura and Metacyclops mendocinus should be considered indicators of a narrow range of salinity or a limited ionic concentration because they generally show a relatively wide range of tolerance (Rzóska, 1961;Alonso, 1996;Sterza and Fernández, 2006;Santangelo et al, 2008;Brucet et al, 2009).…”