title: Interactive effect of salinity decrease, salinity adaptation, and chlorpyrifos exposure on an estuarine harpacticoid copepod, Mesochra parva, in South Africa.
abstract: This study tested the hypothesis: "does adaptation to fluctuating salinities lead to enhanced survival of the harpacticoid copepod M. parva when exposed to a combination of particle associated chlorpyrifos (CPF) exposure and hypoosmotic stress during a 96h sediment toxicity test?" The CPF exposure concentrations of 5.89-5.38mug/kg and the salinity decrease from 15 to 3ppt were based on conditions observed in the temporarily open Lourens River estuary, South Africa, in order to simulate changes during a runoff event. Results of the three-factorial ANOVA showed that pre-adaptation to varying salinities (p=0.02; p=0.001), salinity decrease (p=0.035; p<0.001), and CPF exposure (p<0.001; p<0.001), all had a significant negative impact on the survival rate of female and male M. parva, with a higher sensitivity of males specimens. The significant two-way interaction of salinityxadaptation for females and males (p=0.021; p<0.001), indicate that adaptation to fluctuating salinities was beneficial for male and female copepods, but the hypothesis of a three-way interaction was not supported. However, a trend indicated a lower survival rate of non-adapted females and males exposed to CPF and hypoosomotic stress (38+/-17%; 0+/-0%), compared to pre-adapted organisms (59+/-6.6%; 8.9+/-10%), which requires further elucidation. This study has important implications for the management of temporarily open estuaries in South Africa regarding regulation of freshwater abstraction from rivers.
authors.affiliation: Freshwater Research Unit, University of Cape Town, Private Bag, Rondebosch 7701, South Africa.
authors.forename: S
authors.initials: S
authors.lastname: Bollmohr
authors.forename: R
authors.initials: R
authors.lastname: Schulz
authors.forename: T
authors.initials: T
authors.lastname: Hahn
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D000818:Animals; D004390:Chlorpyrifos / Q000032:analysis / Q000633:toxicity*; D033342:Copepoda / Q000502:physiology*; D017753:Ecosystem; D005260:Female; D019015:Geologic Sediments / Q000737:chemistry; D008136:Longevity / Q000187:drug effects; D008297:Male; D009997:Osmotic Pressure; D010575:Pesticides / Q000032:analysis / Q000633:toxicity*; D045483:Rivers / Q000737:chemistry; D054712:Salinity; D012737:Sex Factors; D012965:Sodium Chloride / Q000032:analysis / Q000494:pharmacology*; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000633:toxicity*
chemical_list: D010575:Pesticides; D014874:Water Pollutants, Chemical; D012965:Sodium Chloride; D004390:Chlorpyrifos