SEXUAL REPRODUCTION OF THE SCYPHOMEDUSA-AURELIA AURITA IN RELATION TOTEMPERATURE AND VARIABLE FOOD-SUPPLY

The effects of food availability and temperature on sexual maturation and female reproductive output of the scyphomedusa Aurelia aurita was examined in two populations from the contrasting environments of South ampton Water and Horsea Lake, England. Trends in oogenesis and subsequ ent reproductive output differed markedly between the two populations. In Southampton Water, the onset of sexual maturation occurred earlies t in the larger medusae, but eventually all females became ripe, the s mallest being 45 mm bell diameter (BD). The decrease in minimum size a t maturity was correlated with increasing temperature. In A. aurita fr om Horsea Lake, size at maturity varied on a seasonal basis, with the smallest ripe female being only 19 to 20 mm ED. There were spring and autumn periods of sexual maturation in this population. During the aut umn period, it is likely that food limitation was playing a more criti cal role in determining medusa size, with decreasing temperature indir ectly affecting A. aurita by limiting primary and secondary production . In similar-sized ripe medusae, fecundity was greater in Southampton Water, but the planula larvae produced were significantly smaller than those in Horsea Lake. It is suggested that in Horsea Lake, the qualit y of the larvae are greater in terms of biochemical content to ensure survival of the few gametes produced (i.e. K-strategy). Comparison of the reproductive effort of the two A. aurita populations revealed that medusae from Southampton Water, which experience greater food availab ility, are able to direct more energy to reproduction than Horsea Lake medusae. Tn the latter, A. aurita medusae appear to partition the ava ilable food resources into either somatic growth (and therefore increa sed future fecundity) when food is abundant, or reproductive growth wh en food is scarce.