Regional and local environmental conditions do not shape the response to warming of a marine habitat-forming species

13 páginas, 7 figuras, 1 tabla.

The differential response of marine populations to climate change remains poorly understood. Here, we combine common garden thermotolerance experiments in aquaria and population genetics to disentangle the factors driving the population response to thermal stress in a temperate habitatforming species: the octocoral Paramuricea clavata. Using eight populations separated from tens of meters to hundreds of kilometers, which were differentially impacted by recent mortality events, we identify 25°C as a critical thermal threshold. After one week of exposure at this temperature, seven of the eight populations were affected by tissue necrosis and after 30 days of exposure at this temperature, the mean % of affected colonies increased gradually from 3 to 97%. We then demonstrate the weak relation between the observed differential phenotypic responses and the local temperature regimes experienced by each population. A significant correlation was observed between these responses and the extent of genetic drift impacting each population. Local adaptation may thus be hindered by genetic drift, which seems to be the main driver of the differential response. Accordingly, conservation measures should promote connectivity and control density erosion in order to limit the impact of genetic drift on marine populations facing climate change.

The authors gratefully acknowledge the funding support given by the Alan Program (CC Doctoral Fellowship), by CSIC-Uruguay (Call Programa de pasantías en el exterior 2015) and by the Portuguese Foundation for Science and Technology (Fundação para a Ciència e a Tecnologia; FCT) which funded JBL Postdoctoral grant (SFRH/ BPD/74400/2010). Authors are also grateful to the MEDCHANGE project funded by the Agence Nationale pour la Recherche (ANR) and to the Spanish Ministry of Economy and Competitivity (http://www.mineco.gob.es) through the Biorock (CTM2009-08045), Smart (CGL2012-32194) and CSI-Coral (CGL2013-43106-R). Temperature data series data is part of the regional temperature observation network T-MEDNet (www.t-mednet.org); we thank J.M. Dominici for providing the data for the Réserve Naturelle de Scandola. The authors also thank the staff of Experimental Aquarium Facilities at the Institute of Marine Sciences E. Martinez and M. Delgado for the technical support provided. EC, JG, CL, PL and NT are part of the Marine Conservation research group MEDRECOVER www.medrecover.org (2009 SGR 1174) while RC and MR are part of the Marine Biogeochemistry and Global Change Research group (2014SGR1029) from the Generalitat de Catalunya.

Peer reviewed