Impact of air exposure on the photobiology and biochemical profile of an aggressive intertidal competitor, the zoanthid Palythoa caribaeorum

The colonization of intertidal habitats is a challenging process. During low tide, many photosynthetic organisms, including symbiotic zoanthids, can be partially exposed to air eliciting significant physiological impairments, which may ultimately dictate the rate of colonization in such environments. Within this context, the present study aims to investigate, for the first time, the effects of air exposure on the fatty acid (FA) content and photobiological parameters of Palythoa caribaeorum, by comparing emerged and immersed polyps, within the same colony, during low tide. Tidal environment did not significantly affect FA percentages, but polyps that were emerged showed lower FA content than the immersed ones. Saturated FA fraction contributed the most to those dissimilarities, followed by the highly unsaturated and polyunsaturated FA fractions. Concomitantly, polyps that were permanently immersed displayed significantly higher values of the maximum quantum yield of photosystem II (F-v/F-m) when compared with emerged polyps. An opposite pattern was observed regarding the indices derived from the rapid light-response curves of relative electron transport rate (a, ETRmax and E-k). We argue that FA differences within each colony seem to be a consequence of impairments in carbon production with photoautotrophic origin. Our findings also suggest that emerged polyps display higher efficiency in responding to rapid light fluctuation, which seems to be a peculiar adaptation to these challenging environments. Thus, in addition to its morphological plasticity, P. caribaeorum seems to display a large trophic plasticity that may be linked with the aggressive competitive nature for vital resources in such tidal habitats and widespread distribution.