ABSTRACT: The association between the symbiont Symbiodinium microadriaticum (zooxanthellae) and its host jellyfish, Cassiopea xamachana, was investigated as a function of jellyfish size and season. Symbiont cell diameter and volume were higher during January than September. Although zooxanthella-specific chlorophyll was independent of jellyfish size, both chlorophyll a and c were higher during January. Regardless of season, algal density and jellyfish size were inversely related. The diel mitotic index (MI) of zooxanthellae was phased, with a peak of 0.25% occurring between 09:00 and 12:00 h. September photosynthetic rates were always higher than January rates and reflected the seasonal light and temperature regimes at the latitude of the Florida Keys (USA). Photosynthesis, when normalized to either zooxanthella density or protein, displayed an inverse relationship with jellyfish size. Medusan respiration rates also showed an inverse relationship with jellyfish size, with September metabolism being higher than that of January. The carbon budgets calculated for these medusae indicate that the carbon photosynthetically fixed by the zooxanthellae, and subsequently translocated to the host, is capable of satisfying about 169% of the host's metabolic demand (CZAR) and is independent of both jellyfish size and season. These seasonally influenced physiological effects underscore the necessity for seasonal examinations of algal-cnidarian symbioses in order to understand the photophysiology of the association on an annual basis.

KEY WORDS: Cassiopea xamachana · Zooxanthellae · Jellyfish · Photosynthesis · Respiration · Photophysiology · Carbon budgets · CZAR

Published in MEPS Vol. 168 (1998) on July 9
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1998