Pruning dead branches in gorgonian forests as an effective restoration tool against mortality events induced by global change

Abstract

Marine animal forests are increasingly experiencing mass mortality events worldwide linked to anthropogenic impacts. The unprecedented impacts of climate change on marine habitats demand active restoration actions to enhance the resilience of key habitat-forming species. To this end, we tested the benefits of a novel restoration technique for habitat-forming gorgonians consisting of pruning dead apical branches and removing epibionts from dead basal branches, as a tool to implement nature-based management. By using the Mediterranean gorgonian Paramuricea clavata as a model, the effectiveness of pruning was assessed by comparing the demographic parameters of individually tracked pruned and control colonies (>1000 gorgonians) over a 3-yr study period. Here, we show that pruning contributed to a time-sustained improvement of health status of colonies (i.e., reducing colony partial mortality by ∼70 % and doubling the proportion of healthy colonies with 0–10 % partial mortality). Given the negative relationship between the extent of colony partial mortality and gorgonian performance, reducing partial mortality with pruning doubled colony survival and led to positive cascade effects that enhanced wound healing of denuded basal branches, growth on the apical tips of the colonies and branching, resulting in 2.5-fold higher live biomass growth rate compared to control colonies and contributing to revert the declining trend observed in natural populations. This study supports pruning gorgonians as a cost-effective, low-tech restoration technique that enhances natural resilience to improve the conservation status of worldwide gorgonian forests threatened by global change.