Influence of day–night and tidal cycles on phenol content and antioxidant capacity in three temperate intertidal brown seaweeds Solène Connan ⁎ , Eric Deslandes, Erwan Ar Gall LEBHAM, EA 3877, European Institute for Marine Studies, Technopole Brest-Iroise, Place Nicolas Copernic, F-29280Plouzane, Brittany, France Received 19 October 2005; received in revised form 24 May 2007; accepted 28 May 2007 Abstract The daily variations of phenol contents and antioxidant capacities were surveyed in a 32-h field experiment in three temperate brown seaweeds belonging to Fucales – Pelvetia canaliculata, Ascophyllum nodosum and Bifurcaria bifurcata – living at different intertidal levels — high-, mid- and low-tide level, respectively. Phenolic compounds of brown seaweeds are secondary metabolites involved in many different protection mechanisms, as for example against grazer and pathogen attack as well as UV damage. This study was thus aimed at understanding the influence of both day/night and tidal cycles on the brown seaweed phenol pool with respect to their bathymetric level on the shore. These cycles affect the quantity and quality of light received by intertidal seaweeds (protection via the water layer during immersion), and the photoprotective role of phlorotannins was thus evaluated. Phenol levels and antioxidant capacities were monitored every hour during a tidal cycle and a half at the equinox spring tide, in March 2003. The three species contained rather high phenol levels, i.e. about 3, 6 and 4% DW in P. canaliculata, A. nodosum and B. bifurcata, respectively. Antioxidant capacities globally paralleled phenol contents in the three species under study. Moreover, the measured antioxidant capacities and the phenol contents of the extracts were significantly and positively correlated in the three species. Significant effect of neither cycles nor their interaction was observed in any species despite a trend to follow day/night alternation for P. canaliculata, and emersion/immersion cycle for A. nodosum. No trend was observed for the third species. However, significant correlations between phenol levels of P. canaliculata and A. nodosum and measured air-temperature were found. Our results suggested an effect of aerial, aquatic and both conditions on the phenolic pool of P. canaliculata, B. bifurcata and A. nodosum, respectively, and a fast evolution of the phenolic pool on a day time scale. © 2007 Elsevier B.V. All rights reserved. Keywords: Antioxidant capacity; Day–night cycle; Fucales; Phlorotannin; Seaweed zonation; Tidal cycle 1. Introduction The intertidal zone is characterised by large variations of its environmental traits essentially due to the alter- nation of emersion and immersion phases. The seaweed species living on the rocky intertidal habitats are thus under the alternate influence of aquatic and aerial cli- matic regimes and must be adapted to short-term en- vironmental variations over 12-h tide cycles (Lüning, Journal of Experimental Marine Biology and Ecology 349 (2007) 359 – 369 www.elsevier.com/locate/jembe ⁎ Corresponding author. Present address: Department of Botany, Martin Ryan Institute and Environmental Change Institute, National University of Ireland, Galway, Ireland. Tel.: +353 91493197; fax: +353 91525005. E-mail address: solene.connan@nuigalway.ie (S. Connan). 0022-0981/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2007.05.028