An ecological and behavioural approach was used to investigate links among populations of the edible jellyfish, Catostylus mosaicus, in estuaries in New South Wales, Australia. Specific aims were to: (1) describe the life history to identify stages when dispersal may occur (2) examine patterns of recruitment and abundance at multiple spatial and temporal scales to investigate the degree of synchrony among estuaries separated by a range of distances (10s to 100s of kilometres); (3) investigate the role of physical forcing in determining patterns of abundance and recruitment; (4) investigate the swimming ability of medusae across a range of size classes and determine growth rates of medusae;

The life history consisted of an alternation between a sexual, medusoid stage and an asexual, polypoid stage, and was similar to that described for other members of the order Rhizostomeae. In the laboratory, larvae settled on glass, shell, sandstone and wood approximately four days after collection from the adults and metamorphosed into four-tentacled polyps. Polyps strobilated when they had between 12 and 20 tentacles, approximately 15 days after settlement. Ephyrae were raised for one month and were observed developing oral arms. Jellyfish may disperse during any of the pelagic stages of the life history. However, larvae were brooded, were negatively buoyant and had a relatively rapid rate of settlement, indicating that dispersal was most likely to occur during the ephyral or medusoid stages.

Variation in abundance and recruitment were studied in six estuaries separated by distances ranging from 70 to 800km. Patterns of abundance differed greatly among estuaries and the rank abundance among estuaries changed on five out of six times sampling was done. Great variation in the timing of recruitment was also observed among estuaries. Variation in abundance and recruitment were as extreme among nearby estuaries as distant ones. This suggested that factors operating at the scale of individual estuaries were responsible for determining patterns of abundance and timing of recruitment. Temperature and salinity within individual estuaries appeared to fluctuate within ranges commonly considered to be non-lethal for medusae and the occurrence of medusae at a location did not appear to be determined by temperature or salinity. There was a trend for medusae to be found in highest abundances at sites in the inner areas of estuaries, usually close to riverine influence. Maintenance in the inner-estuary may minimise the likelihood of advection from an estuary. Detailed sampling over 2.7 years at two locations showed contrasting patterns of abundance. At Botany Bay, patterns of abundance among seasons varied between years, however, at Lake Illawarra, there appeared to be a consistent seasonal trend for medusae to be most abundant between March and July. Recruitment was monitored over a period of nine years in Botany Bay and recruitment most frequently occurred between December and July. Although there was some concordance between peaks in recruitment and rainfall there was no significant correlation between these variables.

Medusae were capable swimmers and large medusae could swim at rates exceeding 8m min-1. Swimming may aid medusae in maintaining themselves in the upper-reaches of estuaries. Small medusae could grow at rates of up to 5mm day-1 but the rate of growth decreased as medusae grew larger. A rapid growth rate would enable small medusae to quickly attain a size and swimming ability that would reduce the risk of them being advected to coastal waters.

Variation in patterns of abundance and recruitment suggested regulation by processes occurring at the scale of individual estuaries and, combined with a relatively strong swimming ability and rapid growth rate, supported a model of population retention within estuaries. Populations within individual estuaries, therefore, correspond to fishery stock units.