Artemia parthenogenetica in Lake Hayward, Western Australia. I. Interrupted recruitment into adult stages in response to seasonal limnology

Abstract

Lake Hayward, Western Australia, is a pristine, monomictic coastal lake with a residual brine (depth=1.5 m) of 200 gL−1: stratification in winter (May to October) followed the input of ground water and rain. The epilimnion had temperature ranges of 10–30°C, and salinity from 65–110 g L−1. Maximum depth in winter was 2.4 m. The population structure of the brine shrimpArtemia parthenogenetica, the dominant metazoan grazer in Lake Hayward, was studied from September, 1989, to February, 1991. The L. Hayward population ofA. parthenogenetica is predominantly ovoviviparous with little recruitment into the adult population. Cyst production occurs in summer, and there was evidence for recruitment from cyst hatching in the winters of 1989 and 1990. Nauplii were continuously present throughout the study period. Nevertheless, recruitment through to adult stages as defined by the presence of gravid females occurred only twice: in October–December, 1989 and in December, 1990. Based on limited observations of long-term survival of laboratory cultures, we believe that the major mechanism controlling nauplius survival and recruitment ofArtemia in Lake Hayward is food quality and quantity.