Contributed Paper Assessing the Effectiveness of Marine Reserves on Unsustainably Harvested Long-Lived Sessile Invertebrates CRISTINA LINARES, ∗ †,‡‡ JOAQUIM GARRABOU,† BERNAT HEREU, ∗ DAVID DIAZ,‡ CHRISTIAN MARSCHAL,§ ENRIC SALA, ∗∗ †† AND MIKEL ZABALA ∗ ∗ Departament d’Ecologia, Universitat de Barcelona, Avda Diagonal 645, 08028 Barcelona, Spain †Institut de Ci` encies del Mar, CSIC, Passeig Mar´ ıtim de la Barceloneta 37-49, 08003 Barcelona, Spain ‡Instituto Espa˜ nol de Oceanograf´ ıa, C/ Moll de Ponent s/n, 07015 Palma de Mallorca, Spain §Aix-MarseilleUniversit´ e, UMR 6540-DIMAR CNRS, Centre d’Oc´ eanologie de Marseille, Station Marine d’Endoume, rue Batterie des Lions, 13007 Marseille, France ∗∗ Centre d’Estudis Avanc ¸ats de Blanes (CSIC), Acc´ es Cala St. Francesc 14, 17300 Blanes, Girona, Spain ††National Geographic Society, 1145 17th Street NW, Washington, D.C. 20036, U.S.A. Abstract: Although the rapid recovery of fishes after establishment of a marine reserve is well known, much less is known about the response of long-lived, sessile, benthic organisms to establishment of such reserves. Since antiquity, Mediterranean red coral (Corallium rubrum) has been harvested intensively for use in jewelry, and its distribution is currently smaller than its historical size throughout the Mediterranean Sea. To assess whether establishment of marine reserves is associated with a change in the size and number of red coral colonies that historically were not harvested sustainably, we analyzed temporal changes in mean colony diameter and density from 1992 to 2005 within red coral populations at different study sites in the Medes Islands Marine Reserve (established in 1992) and in adjacent unprotected areas. Moreover, we compared colony size in the Medes Islands Marine Reserve, where recreational diving is allowed and poaching has been observed after reserve establishment, with colony size in three other marine protected areas (Banyuls, Carry- le-Rouet, and Scandola) with the enforced prohibition of fishing and diving. At the end of the study, the size of red coral colonies at all sampling sites in the Medes Islands was significantly smaller than predicted by growth models and smaller than those in marine protected areas without fishing and diving. The annual number of recreational dives and the percent change in the basal diameter of red coral colonies were negatively correlated, which suggests that abrasion by divers may increase the mortality rates of the largest red coral colonies within this reserve. Our study is the first quantitative assessment of a poaching event, which was detected during our monitoring in 2002, inside the marine reserve. Poaching was associated with a loss of approximately 60% of the biomass of red coral colonies. Keywords: Corallium rubrum, marine protected areas, Mediterranean Sea, overfishing, poaching, scuba-diving effects Evaluaci´ on de la Efectividad de las Reservas Marinas sobre Invertebrados S´ esiles Longevos Recolectados de Manera No Sostenible Resumen: Aunque la r´ apida recuperaci´ on de peces despu´es del establecimiento de una reserva marina es bien conocida, se sabe mucho menos sobre la respuesta de organismos b´ enticos, s´ esiles y longevos al establecimiento de tales reservas. Desde la antig¨ uedad, el coral rojo del Mediterr´ aneo (Corallium rubrum) ha ‡‡email cristinalinares@ub.edu Paper submitted January 26, 2011; revised manuscript accepted June 28, 2011. 88 Conservation Biology, Volume 26, No. 1, 88–96 C 2011 Society for Conservation Biology DOI: 10.1111/j.1523-1739.2011.01795.x