PHYSIOLOGICAL-RESPONSE OF THE HYDROMEDUSA CLADONEMA-CALIFORNICUM HYMAN (ANTHOMEDUSA, CLADONEMIDAE) TO STARVATION AND RENEWED FEEDING

Field studies have identified food limitation as a factor influencing medusae in their natural environment. Whereas previous laboratory stud ies have focused on food limitation of large cruising medusae, this st udy examines the effect of starvation on a small ambush predator, the hydromedusa Cladonema californicum Hyman. C. californicum survived per iods of starvation lasting up to 45 days without significant mortality ; renewed feeding resulted in resumed growth and development. Small (s imilar to 1 mm) to medium (similar to 2 mm) diameter medusae were rela tively insensitive to periods of up to one week without food. In fact, these medusae appeared to continue growing during this period. Howeve r, elemental analysis (CHN) measurements demonstrated two characterist ics of C. californicum's starvation response. First, apparent growth ( increases in diameter but not weight) resulted from organic (dry weigh t, carbon, nitrogen) dilution of body tissues. Second, true growth (in creases in both diameter and weight) occurred only when minimum carbon levels were reached in medusan tissues. The minimum carbon concentrat ions allowing true growth depended upon medusan size. (C) 1998 Elsevie r Science B.V.