ESTES, A.M.; KEMPF, S.C.; HENRY, R.P.: Carbonic anhydrase induction in the gastric pouches of Cassiopea xamachana

Endosymbiotic zooxanthellae are distributed throughout epithelial tissues of the tentacles, body column, or bell of symbiotic cnidarians. Associated with these zooxanthellae is carbonic anhydrase (CA), which catalyses the reversible dehydration of HCO₃^– to provide an unlimited supply of CO₂ for photosynthesis. The upside-down jellyfish, Cassiopea xamachana, has zooxanthellae populations and CA activity primarily associated with ectodermal tissues. However, zooxanthellae populations are also associated with the endodermal tissue of this scyphozoan’s gastrovascular system. Symbiotic animals contain zooxanthellae populations of 2.5 x 10⁶cells ^.g^-1 in gastric pouches of the manubrium, as well as bell margin tissues. Aposymbiotic animals have significantly lower zooxanthellae populations in bell margin tissue (6 x 10⁵cells ^.g^-1) and gastric pouches (1.9 x 10⁵ cells^.g^-1) than in corresponding symbiotic animals. In epithelial bell margin tissues, zooxanthellae population densities and photosynthetic rate mediate CA activity induction and degradation; however, these changes in enzyme activity occur in approximately seven days. CA activities in gastric pouches of symbiotic and aposymbiotic animals starved for eight days are approximately 160 µmoles CO^2.min^-1.g^-1 and 22.5 &micro moles CO^2.min^-1.g^-1, respectively. Unlike the extremely slow change in CA activity of bell margin tissues, preliminary experiments show gastric pouch CA activity increasing 200 % in 24 hrs and continues to increase 48 hrs following feeding Artemia (brine shrimp) to the jellyfish.