Flora Lam Kim1,2, Valérie Stiger-Pouvreau2, Xavier A. Conlan3, Lawrence D. Webb3, Alecia Bellgrove1
1Deakin University, School of Life and Environmental Sciences, Centre for Integrative Ecology, Warrnambool Campus, Warrnambool, Victoria 3280, Australia
2Laboratoire des Sciences de l’Environnement Marin (UMR 6539), Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, rue Dumont d’Urville, 29280 Plouzané, France
3Deakin University, School of Life and Environmental Sciences, Geelong Waurn Ponds Campus, Waurn Ponds, Victoria 3216, Australia
Intertidal seaweeds must withstand numerous stresses such as desiccation, temperature, and UV radiation. In temperate Australasian waters, the brown alga, Hormosira banksii, dominates the rocky shores. In a place where UV radiation is among the highest in the world, the photo-protection of the habitat-forming fucoid, showing apparent resistance to light stress, was investigated. Photoprotective, and antioxidant, phlorotannins are known to have a significant role in brown algae. Nevertheless, their content is highly variable. To assess the variability of phlorotannins along a longitudinal gradient of temperature and UV index, low and high shore samples of H. banksii were collected from two sites within each of four regions (Southwest Victoria, Great Ocean Road, Mornington Peninsula and Port Phillip Bay) in Victoria, Australia. The total phenolic content (TPC) was assessed, and the antioxidant activity was estimated using DPPH (2,2-Diphenyl-1-picrylhydrazyl) radical-scavenging activity and compared with acidic potassium permanganate chemiluminescence measured by post HPLC (High Pressure Liquid Chromatography) separation. Significant variability was observed between sites but was not correlated to temperature and UV index. In fact, this may result in the interaction of various factors including some that were not primarily considered, such as wave-exposure. Moreover, some sites (especially sites within the Great Ocean Road region) revealed very high phenolic content and related antioxidant activities. The high phlorotannins contents discovered in this study suggest a real potential of H. banksii for commercial applications, but this also underlines the importance of understanding better what drives spatial variability, and how to sustainably source biomass.