Population biology and habitat of the stauromedusa Haliclystus auricula in southern Chile

The population biology and habitat of Haliclystus auricula was studied from samples taken every two months in southern Chile between November 2001 and November 2002. A total of 3790 medusae were collected and examined. The abundance of H. auricula varied seasonally. Maximum densities occurred in summer (1405/m 2) and minimum densities during the winter, when the population gradually disappeared. Gonads were observed in medusae starting from a size of 2.0 mm. Stauromedusae were found most often on the red filamentous alga Ceramium rubrum (69%), followed by Gymnogongrus furcellatus (12%) and Ulva sp. (10%). There were highly significant differences in mean abundance of medusae on these three algae (P<0.05). The remaining 9% of medusae were found on other seaweeds. The smallest medusae (0.08-0.9 mm umbrella height) were found exclusively on C. rubrum. The highest densities were recorded in the midlittoral zone.