A 20‐year study on life‐history traits of a harvested long‐lived temperate coral in the NW Mediterranean: insights into conservation and management needs

Summary 1 Long-lived species play a paramount role in the structure and functioning of terrestrial and marine ecosystems. The dramatic increase of human-induced disturbances may be irremediably affecting populations of long-lived species. Data on life-history traits on these species taking into account relevant temporal and spatial scales are very scarce for marine ecosystems, though these data are key to guarantee the conservation of these species and the communities that they shape. 2 This study examined long-term data on life-history traits of the precious red coral (Corallium rubrum L., 1758) in the NW Mediterranean. This was performed by surveying the fate of 67 red coral colonies during 21 years in a shallow-water habitat (27 m depth). 3 Photographic monitoring provided data on survivorship, whole and partial mortality, recruitment and growth of colonies allowing about 1000 observations on life-history traits. 4 Red coral showed a high survivorship, 60% of colonies reaching 22 years of age. Whole mortality was significantly higher in juvenile colonies while partial mortality displayed the inverse pattern. Recruitment showed a pulse mode with a single peak at the beginning of the study and low rates thereafter. Average growth rates over the study period were extremely low: 0·24 ± 0·05 mm year−1 for the basal diameter, 1·78 ± 0·7 mm year−1 for colony height and 3·40 ± 0·31 branches in 22 years. 5 This study also examined size-related effects of harvesting on red coral populations since shallow-water populations (between 10 and 40 m depth) have long been submitted to intensive harvesting. 6 Measurements (basal diameter and height) of 400 colonies corresponding to the largest ones dwelling in 10 currently harvested and two non-harvested populations were compared to analyse the effects on the population's recovery and potential colonies’ maximum sizes. Harvested populations showed values that were about twice as low on average and up to four times lower for maximum values in colony size than in the non-harvested populations. 7 Our study provides indisputable data on the longevity of colonies and the parsimonious population dynamics of C. rubrum. Current populations have shown a dramatic shift in their size structures characterized by the absence of large colonies. Taking into account results obtained in this study full recovery time of shallow-water harvested populations may be measured by several decades or even centuries.