The ecology of Scyphozoan jellyfish in Lake Illawarra

Abstract

The scypbozoan jellyfish of Lake Illawarra are well known to most people who use Lake Illawarra for research, commercial fishing or recreation. Here we review the biology and ecology of the two most well-studied species, Catostylus mosaieus and Phyllorhiza punetata, and present preliminary results of studies that investigated their role in the trophic and nutrient dynamics of coastal lagoons. Specifically we show that C. mosaicus is a voracious predator of zooplankton and that the presence of medusae may promote production of phytoplankton either via excretion of inorganic nutrients or because grazing by C. mosaicus on zooplankton, in turn, reduces grazing by zooplankton on phytoplankton. Comparisons of rates of excretion by C. mosaicus and P. punctata show that C. mosaicus excretes substantial amounts of NH3 which, during times of their peak biomass, may account for 8% of the NH3 required by phytoplankton. In contrast P. punctata exhibits no net excretion of NH3, probably because its excretory products are predominantly translocated to symbiotic zooxanthellae within its tissues. Hence these species have contrasting roles in nutrient regeneration. Current gaps in our knowledge of the ecology of these species are identified.