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Symbiotic dinoflagellates (zooxanthellae) associated with the medusa of Linuche unguicuhta constituted 22-26% of the total C and N biomass. The maximal net production for intact medusae (Pm) averaged 4.5 mg 0, (mg Chl a)-' h-l, equivalent to an assimilation number of 2.0 mg C (mg Chl a)-' h-l. At the midday maximum, gross oxygen production averaged four times the respiration rate. The saturating light intensity was 200-300 pEinst m-2 s-' (Einstein = mol quanta) and the compensation light intensity (do, = 0) was -20 PEinst m-* s-l. On a die1 basis P,,.. : R averaged 1.7 for intact medusae at ambient near-surface light. Die1 periodicity with a midday maximum was measured for the production potential under artificial, saturating light. Both intact medusae and freshly isolated zooxanthellae demonstrated similar die1 production patterns. Respiration did not show the same strong die1 pattern as net production, but respiration declined steadily when medusae were held unfed in the dark. Respiration was independent of the ambient oxygen concentration over a range from 4 to 16 mg 0, liter-l. Die1 periodicity was measured in egg release and division rates of zooxanthellae. Estimates of both algal and host growth ranged from 0.01 to 0.04 d-l. Calculations indicated that only 21% of the C fixed in photosynthesis was used in algal respiration and growth. If the remaining photosynthate were translocated, it could provide all the C required for host respiration and somatic growth. Egg production represented another large C flux in adult females, with a daily release equivalent to 4-8% of host body C for medusae of 0.Z 1.2 ml in displacement volume.Understanding of carbon flux in cnidarian-zooxanthellae associations is strongly influenced by the results of studies of relatively slow-growing, sessile corals. Species that display large annual amplitudes in their population biomass have been underrepresented in research efforts and therefore in C budgets for symbiotic cnidarians. Scyphozoans have both a scyphistoma (polyp) and medusa form and therefore are likely to demonstrate dynamic population fluctuations. Most studies of symbiotic scypho-I Present address:

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