Abstract
Overexploitation leads to the ecological extinction of many oceanic species. The depletion of historical abundances of large animals, such as whales and sea turtles, is well known. However, the magnitude of the historical overfishing of exploited invertebrates is unclear. The lack of rigorous baseline data limits the implementation of efficient management and conservation plans in the marine realm. The precious Mediterranean red coral Corallium rubrum has been intensively exploited since antiquity for its use in jewellery. It shows dramatic signs of overexploitation, with no untouched populations known in shallow waters. Here, we report the discovery of an exceptional red coral population from a previously unexplored shallow underwater cave in Corsica (France) harbouring the largest biomass (by more than 100-fold) reported to date in the Mediterranean. Our findings challenge current assumptions on the pristine state of this emblematic species. Our results suggest that, before intense exploitation, red coral lived in relatively high-density populations with a large proportion of centuries-old colonies, even at very shallow depths. We call for the re-evaluation of the baseline for red coral and question the sustainability of the exploitation of a species that is still common but ecologically (functionally) extinct and in a trajectory of further decline.
Highlights
Overexploitation in the marine realm has been a major driver of the ecological extinction of many species
An unexploited population of the precious red coral Corallium rubrum was found within the Scandola Marine Reserve in Corsica in 2010 (Fig. 1, Extended data Fig. 1)
Previous research comparing shallow (10–50 m) and deep (50–200 m) habitats in the Western Mediterranean showed that shallow red coral populations are composed of high-density small colonies, and deep populations of large colonies in low-density patches[13]
Summary
Red coral shallow populations are commonly found along crevices, overhangs and cave entrances while in deeper water habitats colonies can be found either on horizontal surfaces and in overhangs[30,31,32] This species is a sessile, aposymbiotic, long-lived cnidarian that exhibits slow population dynamics[26,33] and late sexual maturity (at approximately 10 years of age and small size about 25 and 3.6 mm in height and diameter respectively[34]). Large colonies provide the architectural complexity necessary for natural population and community functioning It has been suggested the conservation status of C. rubrum populations can be well approximated by quantifying the proportion of colonies greater than >10 cm in height and >7 mm in diameter[43] (Supplementary Table 1). We separately analysed populations from protected and unprotected areas because the population trajectories in these contrasted management schemes are expected to differ
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