Interspecific differences in the efficiency and photosynthetic characteristics of the symbiosis of "solarpowered" Nudibranchia (Mollusca: Gastropoda) with zooxanthellae

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ABSTRACT – In this study the photosynthetic performance and efficiency of the symbiosis of different species of the Cladobranchia (Nudibranchia) with zooxanthellae (Dinophyceae) of the genus Symbiodinium Freudenthal, 1962 is investigated. The species studied include members of the Aeolidoidea (Aeolidiella alba Risbec, 1928, Limenandra nodosa Haefelfinger and Stamm, 1958, Phestilla lugubris (Bergh, 1870) Phyllodesmium briareum (Bergh 1896), Spurilla australis Rudman, 1982), one member of the former Arminoidea (Dermatobranchus sp.) and one of the Dendronotoidea (Melibe cf. bucephala Bergh, 1902). Long term cultivation under starving conditions indicates a symbiotic relationship with zooxanthellae in all investigated species by means of Pulse Amplitude Modulated Fluorescence. The data taken by a Diving-PAM (submersible Pulse Amplitude Modulated Fluorometer) indicate interspecific differences in the ability to retain photosynthetic active zooxanthellae and suggest different stages in the evolution of this symbiosis represented by different species of Nudibranchia. The efficiency of the symbiotic relationship can be correlated with morphological adaptations, especially the branching system of the digestive gland. Interspecific differences in the photosynthetic characteristics suggest different involved types or strains of Symbiodinium, depending on the specific food source and its distribution in geographic range and depth.