Long-term settlement plates: some clues for demography and restoration of Mediterranean red coral (Corallium rubrum) shallow water populations

International Workshop on Red Coral Science, Management, and Trade: Lessons from the Mediterranean, 23-26 September 2009, Naples, Italy.-- 6 pages, 3 figuresRecovery of coral populations is a slow process, especially in Mediterranean Sea where octocorals, characterized by slow growth rates, are dominant. Until now, restoration techniques are based on transplantation, a technique requiring high degree of manipulation leading to high colony mortality. Mediterranean red coral (Corallium rubrum, L 1758) is a long-lived, slow-growing gorgonian, endemic to Mediterranean rocky shores. Its high economic value determined over-harvesting which brought many coastal, shallow-water populations to depletion. Moreover, shallow-water populations could be extremely vulnerable to mass mortality events putatively linked to global warming. Therefore, these populations need conservation and restoration actions. Due to their fragility, transplantation of adult colonies does not give any effective result. Within this framework we set out a method suitable to foster red coral recruitment on artificial, carbonatic substrates (marble tiles), following a patented protocol. This protocol allowed red coral larvae settlement and growth on marble tiles. In the framework of a study carried out in Italy with 54 100 cm2 marble tiles, overall, 388 settlers colonized the tiles and their densities varied between 12.37 ± 6.1 and 2.75 ± 2.4 dm-2. Even if mortality affected these colonies (24.35 ± 9.12 colonies % y-1), after 4 years the tiles still harbored a persistent population (19 ± 4.97 dm-2) with positive net-recruitment rates (recruitment-mortality). As permanently colonized tiles may easily be removed and fixed again in new areas by a central screw, red coral re-colonization may be fostered by transferring and re-fixing tiles in areas depleted of red coral colonies. Moreover, none of the colonies settled on such tiles was affected by boring sponges, which are one of the main sources of red coral mortality and also reduce their economic value. These findings suggest marble tiles could be a useful tool both to study recruitment and to foster restoration of red coral shallow-water populationsPeer Reviewe