Circadian rhythmicity in the location of zooxanthellae of the scyphomedusa Linuche unguiculata

Abstract

The scyphon~edusa Linuche unguiculata possesses patches of zooxanthellae whlch expand and contract u l t h circadian regularity. Zooxanthellae are enclosed by vacuole-like membranes and appear to be located within mesogleal cells. Constant Light conditions cause damping of the expansion-contraction rhythm within 24 to 48 h , while rhythms persist in constant dark conditions for at least 72 to 96 h. The timing of maximum zooxanthellae patch expansion coincides with peak zooxan-thellae photosynthetic capacity, suggesting that the expansion-contraction rhythm may aid in the mutual nutrition of both host and symbiont