A neritic species in a hypersaline lagoon; population structure of Acartia fancetti in relation to hyperhaline and thermal stresses

Phenotypic plasticity and adaptation are common traits of organisms living in highly dynamic and changing environments. Several copepod species, especially estuarine dwelling species, have demonstrated high phenotypic plasticity and adaptability to variations in environmental conditions. Copepods play a critical role in aquatic foodwebs and their population structure is closely linked to water quality fluctuations, especially salinity and temperature. However, few studies have examined the response of population structure to environmental stress. Here, we examine the population structure, egg production and hatching success of Acartia fancetti in relation to hypersalinity (30, 40, 50 and 60) and temperature (15 °C and 20 °C). A. fancetti is a neritic species occupying a key niche in the hypersaline areas of the Coorong, South Australia. Our results show a significant influence of salinity and temperature on the population size, nauplii production, copepodites production and adults of A. fancetti. The maximum numbers of nauplii, copepodites and adults were at salinity 30 and 40, at both 15 °C and 20 °C. However, substantial population sizes were also observed at salinity 50 and 60 in 15 °C treatments. At 20 °C, no individual was observed at salinity 60. This study indicates that the population of A. fancetti in the Coorong is tolerant to hypersalinity at lower temperatures, but the combined effects of haline and thermal stress significantly reduces the ability of this species to survive at higher temperatures. The distribution of A. fancetti in the Coorong is also affected by the environmental change related to anthropogenic activities.