The Effect of Salinity on the Egg Production Rate of the Sac-Spawning Calanoid Copepod, Pseudodiaptomus hessei, in a Temporarily Open/Closed Southern African Estuary

Abstract

Global climate change is anticipated to be associated with changes in the salinity regimes of southern African estuaries as a result of the increased frequency of occurrences of extreme weather events (droughts and coastal storms) and the rise in sea level. The current investigation assessed the impact of salinity on the egg production rate (EPR) of the numerically important sac-spawning calanoid copepod, Pseudodiaptomus hessei, in a temporarily open/closed southern African estuary. The EPR of the copepod was determined using in vitro incubations during three distinct salinity regimes corresponding to the freshwater-deprived (hypersaline-salinity 38 PSU), freshwater-dominated (mesohaline-salinity 5 PSU), and polyhaline water phase (salinity 24 PSU). The egg production rate (EPR) and clutch size of P. hessei during the study ranged from 5.9 to 28.1 eggs F−1 d−1 and between 12 and 36 eggs sac−1, respectively. The EPR and clutch size of P. hessei during the polyhaline phase was significantly higher than during the freshwater-dominated and freshwater-deprived phases (p < 0.05). There were no significant differences in prosome length, egg size, or the hatching success of P. hessei during the three salinity regimes (p > 0.05 in all cases). The results of the current study suggest that the salinity changes in TOCEs in response to global climate warming are likely to be associated with a decrease in the reproductive success of P. hessei along the southeastern coastline of South Africa.