title: No evidence for a critical salinity threshold for growth and reproduction in the freshwater snail Physa acuta.
abstract: The growth and reproduction of the freshwater snail Physa acuta (Gastropoda: Physidae) were measured at various salinity levels (growth: distilled water, 50, 100, 500, 1000 and 5000 microS/cm; reproduction: deionized water, 100, 500, 1000 and 3000 microS/cm) established using the artificial sea salt, Ocean Nature. This was done to examine the assumption that there is no direct effect of salinity on freshwater animals until a threshold, beyond which sub-lethal effects, such as reduction in growth and reproduction, will occur. Growth of P. acuta was maximal in terms of live and dry mass at salinity levels 500-1000 microS/cm. The number of eggs produced per snail per day was maximal between 100 and 1000 microS/cm. Results show that rather than a threshold response to salinity, small rises in salinity (from low levels) can produce increased growth and reproduction until a maximum is reached. Beyond this salinity, further increases result in a decrease in growth and reproduction. Studies on the growth of freshwater invertebrates and fish have generally shown a similar lack of a threshold response. The implications for assessing the effects of salinisation on freshwater organisms need to be further considered.
authors.affiliation: Biotechnology and Environmental Biology, School of Applied Science, RMIT University, PO Box 71, Bundoora 3083, Vic, Australia. ben.kefford@rmit.edu.au
authors.forename: Ben J
authors.initials: BJ
authors.lastname: Kefford
authors.forename: Dayanthi
authors.initials: D
authors.lastname: Nugegoda
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004784:Environmental Monitoring / Q000379:methods*; D005618:Fresh Water; D012098:Reproduction / Q000187:drug effects; D012908:Snails / Q000187:drug effects / Q000254:growth & development*; D012965:Sodium Chloride / Q000633:toxicity*; D014876:Water Pollution
chemical_list: D012965:Sodium Chloride