ORIGINAL ARTICLE Factors influencing the distribution of coastal lichens Hydropunctaria maura and Wahlenbergiella mucosa Niall F. Higgins 1 , Sol ene Connan 1,2,3 & Dagmar B. Stengel 1 1 Botany and Plant Science, School of Natural Sciences, Ryan Institute, National University of Ireland Galway, Galway, Ireland 2 Photobiotechnology, INTECHMER, Conservatoire National des Arts et M etiers, Cherbourg Cedex, France 3 CNRS, GEPEA UMR 6144, bd de l’Universit e, CRTT, Saint-Nazaire Cedex, France Keywords Desiccation; distribution; maritime lichen; photosynthesis; pigments; polyphenols. Correspondence Niall F. Higgins, Botany and Plant Science, School of Natural Sciences, Ryan Institute, National University of Ireland Galway, Galway, Ireland. E-mail: niall.f.higgins@gmail.com Accepted: 24 September 2014 doi: 10.1111/maec.12239 Abstract Responses to abiotic and biotic stresses that potentially drive the vertical zona- tion of the intertidal lichens Hydropunctaria maura, an upper littoral lichen, and Wahlenbergiella mucosa, a lower littoral lichen, were investigated in field and laboratory experiments. When transplanted, both lichens exhibited an inability to survive outside their normal vertical distribution range. W. mucosa appeared to be unable to tolerate prolonged periods of desiccation following translocation from lower to upper littoral regions, whereas H. maura was unable to survive in lower littoral zones possibly owing to increased grazing pressure. The effect of desiccation in both lichens was compared using pulse amplitude modulated chlorophyll fluorescence and infra-red gas analysis; results indicated a more hydration-dependent nature of W. mucosa. Photosyn- thetic (algal) pigments and phenolic compounds were determined in both lichen thalli, and a range of additional coastal lichens occupying a natural gra- dient from upper to lower shore levels. Pigment composition and concentra- tion in both lichen thalli were similar whereas levels of phenolic compounds were up to three times higher in W. mucosa than H. maura. Pigment and phe- nolic concentration and composition exhibited some seasonality across 13 dif- ferent lichens originating from different shore levels. Phenolic concentration increased towards the lower shore, suggesting a potential anti-herbivory func- tion. This marks the first study of pigments and phenolics in coastal lichen communities, and prompts further investigations on the particular physiologi- cal features of marine and maritime lichens that enable them to thrive in this extreme environment. Introduction Rocky intertidal shores are among the most physiologi- cally stressful environments for an organism to occupy as they provide an unstable, rapidly changing habitat (Lewis 1964; Lobban & Harrison 1994; Davison & Pearson 1996; Raffaelli & Hawkins 1996). During low tide, emersed organisms are subjected to prolonged periods of desicca- tion, hyper- and hypo-saline conditions, osmotic and thermal stresses and exposure to UV-radiation (Schon- beck & Norton 1979; Sousa 1984; Harley & Helmuth 2003; Scrosati & Heaven 2007). However, maritime lichens exemplify the ‘plastic physiology’ required to inhabit this extreme environment; they adapt both physi- ologically and metabolically to rapid shifts in environ- mental conditions to achieve optimum assimilation rates necessary for survival. Nevertheless, with little or no quantitative data available comparable to that for inter- tidal macroalgae (e.g. Harley & Helmuth 2003; Dethier & Williams 2009), the mechanisms that enable their local dominance are poorly understood (e.g. Fletcher 1973, 1975, 1980). Marine Ecology (2014) 1–15 ª 2014 Blackwell Verlag GmbH 1 Marine Ecology. ISSN 0173-9565