Christophe Vieira

Cold war in the tropics Christophe Vieira

This doctoral study sheds new taxonomic and ecological insights on a prominent brown marine algal group in tropical reefs. Using a DNA-based taxonomic approach Christophe Vieira reassessed the species diversity of the genus Lobophora in New Caledonia and globally. He disclosed a striking, hitherto unknown, global diversity; provided the first comprehensive tree of life for this group, and exposed the global geographical patterns of species diversity. Evolutionary analyses revealed that this group originated within the Central Indo-Pacific during the Upper Cretaceous, and diversified within the tropics. The ecological study showed that although potentially chemically armed and capable of bleaching corals, Lobophora species did not or rarely bleached adjacent corals in natural conditions. Results from allelopathic bioassays and grazing experiments led the author to conclude that (1) corals and Lobophora maintain a chemical-mediated status quo on healthy reefs; (2) chemical defense apparently does not deter grazing of Lobophora by prominent herbivores; (3) it is more likely that Lobophora avoids being grazed by escape strategies such as growing under the coral canopy.