DAILY PHOTOSYNTHESIS, RESPIRATION, AND CARBON BUDGETS IN A TROPICAL MARINE JELLYFISH (MASTIGIAS SP)

From measured diel photosynthesis and respiration rates, using oxygen electrodes, estimates of carbon flux between symbiotic algae (zooxanth ellae) and host animal are presented for the marine scyphomedusan Mast igias sp. from a marine lake in Palau, Western Caroline Islands, durin g February and March 1982. The carbon budgets calculated for these lak e medusae indicate that carbon fixed photosynthetically by zooxanthell ae and made available to the host may satisfy up to 100% of the host's daily metabolic carbon demand (CZAR). The stable carbon isotope (delt a(13)C) signature of the mesogleal carbon of lake Mastigias sp. was cl ose to that of the zooxanthellae, supporting the interpretation that w hile these medusae may feed holozoically, some of their carbon comes f rom their symbionts. The diel photosynthesis, respiration, and prelimi nary estimates of carbon budgets of three individuals of another ecoty pe of Mastigias sp. collected from nearby oceanic lagoons are also giv en. Photosynthesis of lagoon medusae was generally greater than that f or lake medusae of similar size, and lagoon medusae were phototrophic with respect to carbon, with commensurately greater CZAR values. Carbo n translocated from the symbiotic algae also may contribute to the gro wth requirements of both lake and lagoon medusae. From carbon flux dat a, the lake jellyfish were estimated to contribute about 16% to the to tal primary productivity of their marine lake habitat.