Harvesting Effects, Recovery Mechanisms, and Management Strategies for a Long-Lived and Structural Precious Coral

Abstract

Overexploitation is a major threat for the integrity of marine ecosystems. Understanding the ecological consequences of different extractive practices and the mechanisms underlying the recovery of populations is essential to ensure sustainable management plans. Precious corals are long-lived structural invertebrates, historically overfished, and their conservation is currently a worldwide concern. However, the processes underlying their recovery are poorly known. Here, we examined harvesting effects and recovery mechanisms of red coral Corallium rubrum by analyzing long-term photographic series taken on two populations that were harvested. We compared the relative importance of reproduction and re-growth as drivers of resilience. Harvesting heavily impacted coral populations causing large decreases in biomass and strong size-class distribution shifts towards populations dominated by small colonies. At the end of the study (after 4 and 7 years) only partial recovery was observed. The observed general pattern of low recruitment and high mortality of new recruits demonstrated limited effects of reproduction on population recovery. Adversely, low mortality of partially harvested adults and a large proportion of colonies showing new branches highlighted the importance of re-growth in the recovery process. The demographic projections obtained through stochastic models confirmed that the recovery rates of C. rubrum can be strongly modulated depending on harvesting procedures. Thus, leaving the basal section of the colonies when harvesting to avoid total mortality largely enhances the resilience of C. rubrum populations and quickens their recovery. On the other hand, the high survival of harvested colonies and the significant biomass reduction indicated that abundance may not be an adequate metric to assess the conservation status of clonal organisms because it can underestimate harvesting effects. This study highlights the unsustainability of current harvesting practices of C. rubrum and provides urgently needed data to improve management practices that are still largely based on untested assumptions.

Structure and biodiversity of coralligenous assemblages dominated by the precious red coral Corallium rubrum over broad spatial scales

“…However, to date the effects of these disturbances have been mainly assessed at population level192037 and barely at community level. The present study provides the first community level, a base-line data on diversity, structure and composition patterns of coralligenous outcrops dominated by red coral.…”

“…This species is typically associated with animal dominated communities growing in dim light habitats, such as caves, vertical cliffs and overhangs, between 10 and 200 m in depth. The main threat to the red coral is intensive historical harvesting, which causes an overall shift in the population structure, resulting in a decrease in both biomass and colony size171819. Climate warming and the potential effects of ocean acidification are also major threats affecting populations12202122.…”

Strong linkages between depth, longevity and demographic stability across marine sessile species

“…While conferring stability under natural conditions, this extreme life history will also hinder the ability of longlived species to overcome increased mortality rates, but whether these species will be able to cope with rapidly changing perturbation regimes driven by the ongoing global change is still unclear. For instance, while the red coral has persisted after millennia of historical overharvesting owing to the combination of consistent survival of partially harvested colonies [25] and small size at maturity [29], new human-related stressors such as global warming have increased mortality rates and put some shallow populations at risk [20,21,57]. Worryingly, although declines may already be driving populations of some long-lived species towards collapse, in some cases, these trajectories may be too subtle to be noticed by ecologists and managers [58].…”

Response diversity in Mediterranean coralligenous assemblages facing climate change: Insights from a multispecific thermotolerance experiment

“…Coralligenous assemblages are biogenic formations built by the growth of crustose coralline algae and diverse calcareous macroinvertebrates at low irradiance levels and are characterized by their great structural complexity and species richness (harbouring ~10% of marine Mediterranean species) (Ballesteros, 2006). Most of the structural species of these habitats exhibit slow population dynamics and long life spans (+100 years; Garrabou & Harmelin, 2002;Linares, Doak, Coma, Diaz, & Zabala, 2007;Teixidó, Garrabou, & Harmelin, 2011); therefore, they are very sensitive to disturbances, including climate change (Balata, Piazzi, & Benedetti-Cecchi, 2007;Ferrigno, Appolloni, Russo, & Sandulli, 2018;Garrabou et al, 2009;Montero-Serra et al, 2015). In fact, more than 30 coralligenous species from different phyla and different structural roles have been affected in various mass mortality events (hereafter MMEs) associated with Mediterranean heat waves, suffering extensive tissue necrosis (partial and total mortality) and long-term population declines (Cerrano et al, 2000;Crisci, Bensoussan, Romano, & Garrabou, 2011;Garrabou et al, 2009;Garrabou, Perez, Sartoretto, & Harmelin, 2001;Linares et al, 2005).…”