Production, respiration, and photophysiology of the mangrove jellyfish Cassiopea xamachana symbiotic with zooxanthellae:effect of jellyfish size and season

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 dunng 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 die1 mitotic index (MI) of zooxanthellae was phased, with a peak of 0.25 y: occurring between 09:OO and 12:OO 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 slie ? v ? ~i i ~l ~d l i I B ~~I I ~L I U I I 1die3 dlbu biluwed iuve~be ~eidii~llsilip w ~i i ~ jeiiyiisil size, w ~i i l Sepielll'uer metabolism being higher than that of January. The carbon budgets calculated for these rnedusae 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 syrnbioses in order to understand the photophysiology of the association on an annual basis