Restoration of the animal forests: Harnessing silviculture biodiversity concepts for coral transplantation

Coral reefs and rain forests are among the most diverse and productive ecosystems on earth, sharing numerous ecological and functional properties. Decades of anthropogenic activities and the overexploitation of reef/forest resources have led to a worldwide rapid degradation of both ecosystems, threatening the continued function of these habitats and their ability to provide numerous goods and services. Inspired by silviculture, an emerging approach to reef restoration is the gardening coral reefs tenet, in which numerous new coral colonies are farmed in situ in mid-water coral nurseries and are subsequently available for transplantation on degraded reefs. As in forestation, transplantation of corals can be used as a sustainable tool that carries ecological engineering benefits, such as the reconstruction of rehabilitated coral reefs with a particular coral coverage and associated species' compositions, increased rugosity (3-d structural complexity), and enhanced biodiversity. Forest restoration initiatives have been underway for over a century, leading to the development of consolidated silviculture rationales. In contrast, many theoretical aspects have yet to be elucidated in the newly emergent discipline of active reef restoration. Due to the numerous similarities between coral reef and forest ecosystems, as well as between their restoration approaches, insights regarding the use of tree plantations for forest restoration could substantially advance the restoration of coral reefs. Here, we synthesize recent advances in farmed coral transplantation and discuss the influence of active reef restoration on biodiversity outcomes. We particularly focus on diversity estimates at the population genetics, species, and ecosystem levels, consulting forest restoration literature for rationales, tools, and recommendations that can be harnessed in the gardening approach for active reef restoration.