Rhodolith beds in the South-East Pacific

Abstract

Rhodolith or maerl are the most common terms used for free living coralline red algae which live and produce sediments (Nelson 2009). They are common in the North Atlantic, Mediterranean, tropical West Atlantic, Gulf of California, Southern Japan, Western Australia and New Zealand (Foster 2001). Rhodolith beds reach the deepest section of the euphotic zone, their maximum is at approximately 286 m (Foster 2001). These beds provide habitat, refuge, settlement sites and nursery ground for a variety of marine life, but also information about past and present climate changes and represent an important economic resource used as fertilizer in agriculture (Foster 2001). Climate change, ocean acidification and fisheries have negative impacts on rhodolith beds, resulting in calls for conservation (Hall-Spencer et al. 2010). In the Eastern Pacific, rhodolith beds are known from the Gulf of California to Alaska and the Galapagos Islands, Costa Rica, and Panama. The knowledge on coralline algae along the Chilean coast is still scarce focusing on crustose and non free-living forms (e.g. Vidal et al. 2003). Here we give the first record of rhodolith beds in the South-East Pacific, based on scientific expeditions to Guarello Island (Madre de Dios Archipelago, c. 50°S 75°W), Melinka and Amita Island (Guaitecas, c. 43°S 73°W,), and Robinson Crusoe Island (Juan Fernandez Archipelago, c. 33°S 78°W). At three sites, Robinson Crusoe, Guarello and Amita, we found areas of average downward slope on rocky ground mixed with sediment spots. At depths from about 10–25 m many of these spots were covered with rhodolith beds showing a lumpy growth form in Robinson Crusoe (Fig. 1a) and fruticose habit in Guarello and Amita (Fig. 1b, c). Plants were approximately 5 cm in diameter and had one or two branches per cm in lumpy material and four to six branches per cm in fruticose material. In Melinka (Fig. 1d), rhodoliths with a lumpy growth form were found at intertidal pools. These records extend the distribution of rhodoliths and raises interesting questions about their distribution, taxonomy, evolution and ecology. Thus, rhodolith beds in the South-East Pacific need to be analyzed in detail in the future and their role in coastal processes evaluated.