BIOCHEMICAL-COMPOSITION OF AURELIA-AURITA IN RELATION TO AGE AND SEXUAL MATURITY

Dry weight (DW), ash free dry weight (AFDW), and proximate biochemical composition were examined for a full range of sizes of whole medusae of the scyphomedusa Aurelia aurita. Dry weight ranged from 3.07 to 3.91% of wet weight (WW), and was fairly uniform throughout the size groups. Ash free dry weight ranged from 25.6 to 46.0% of DW, with values significantly greater in ephyrae and medusae < 20 mm. The sum of carbohydrate, protein and lipid fractions, termed ''total organics'', is often taken to be synonymous with AFDW, but values were consistently lower than AFDW, ranging from 5.56 to 22.76% of DW. Even after AFDW had also been calculated assuming water of hydration to be 11.7%, there were still differences between the two values. Whole Aurelia aurita medusae displayed the typical characteristics of gelatinous predators, with low carbohydrate (0.10-1.12% of DW), intermediate lipid (3.50-11.50% of DW), and high protein (2.07-28.56% of DW) content. The biochemical composition of isolated umbrellar and gonadal tissues of medusae > 50 mm were examined, and in every size group, ''total organics'' were greater in gonadal than umbrellar tissue. The greater organic content of gonadal tissue was the result of an increase in all three biochemical fractions, with carbohydrates and proteins displaying the greatest differences. Mean values ranged from 0.33 to 0.85% carbohydrate, 2.34-8.31% protein, and 0.87-2.91% lipid in umbrellar tissue, compared with 1.08-2.10%, 4.38-22.98%, and 2.59-6.08%, respectively, in gonadal tissue. The biochemical content of ripe oral arms, i.e. those containing dividing eggs and planula larvae, was similar to that of the maturing gonads. Protein content was greatest in gonads of medusae 60-110 mm, before decreasing significantly with increasing bell diameter. Rapid growth and maturation in the 60-110 mm size group was coincident with the spring peak of mesozooplankton abundance in Southampton Water, while the decline in protein content may be explained by loss in condition of ''spent'' medusae.