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1. Gorgonians are long-lived engineering species and their conservation is crucial to maintaining the biodiversity of marine communities. The slow dynamics displayed by these species make them especially vulnerable when faced with increasing disturbances. 2. The sessile nature and structural role of gorgonians provide several ecological similarities with trees, allowing the application of different approaches developed by forest ecology studies to overcome the constraint of long time-scales to collect valuable dynamic data. Using these approaches, we examined the distribution and demography of two representative Mediterranean gorgonian species, Paramuricea clavata and Eunicella singularis, along a regional spatial scale as well as their response to disturbances. 3. The regular spatial distribution and the upper distribution limit of E. singularis suggest that this species is more tolerant to a wide range of environmental conditions than P. clavata, which exhibited a more asymmetrical spatial distribution and variation in the upper distribution limit on the latitudinal scale. 4. Size distributions of both species showed contrasting population dynamics. The size distribution of E. singularis was characterized by initial stages of populations (0–10 cm) in contrast to the scarcity of this stage displayed by P. clavata. This suggests differences in recruitment between species. Furthermore, only P. clavata populations displayed a strong negative correlation between density and biomass with a slope close to –3/2, indicating a self-thinning mechanism and therefore the existence of a carrying capacity. This result and the trajectories of disturbed populations below the self-thinning line revealed this approach as a useful method to identify the effects of biological or physical disturbance. 5. Synthesis and applications. The approaches used in this study provide insights into management needs in face of the difficulty of having to deal with the population dynamics of very slow-growing threatened species. In particular, gorgonian populations can be used as an indicator of the effects of climatic anomalies on the coralligenous community. [ABSTRACT FROM AUTHOR]

Abstract Gorgonians play an important structural and functional role promoting high diversity and biomass of associated fauna. Up to now, studies on gorgonian ecology in the Mediterranean Sea have been focused mainly on the SCUBA diving depth range. Although increased availability of remotely operated vehicles allowed access to the deeper areas, gorgonian assemblages located on continental shelf and slopes are still barely known. Gorgonian assemblages on continental shelves are extremely vulnerable to anthropogenic impacts, especially bottom trawling and longline fishing. To implement effective management and conservation policies it is crucial to understand patterns of genetic structure among populations since connectivity enhances the resilience of populations. Paramuricea macrospina is a key structuring gorgonian in the Menorca Channel's (Balearic Archipelago) outer continental shelf where it covers vast extensions, reaching very high densities. Combining two mitochondrial makers and 10 microsatellites, this study gives the first insight into the genetic diversity and population structure of P. macrospina between 60 and 100 m depth in the Menorca Channel and at a horizontal spatial scale of about 60 Km. Overall, we demonstrate a low genetic diversity and a lack of genetic structure among populations, which may be explained by the geomorphology and hydrodynamic features of the Menorca Channel (e.g. internal waves, high currents). Our study suggests some connectivity among P. macrospina populations in accordance with the high recruitment rates observed. This connectivity may increase the resilience and foster the recovery of impacted populations since the study area will become a Marine Protected Area of the Natura 2000 network in the near future. Nevertheless, complementary studies based on a larger sample size should be conducted to complement our results. In addition, temporal genetic monitoring of these populations should be envisaged to monitor the potential reduction of genetic diversity of this mesophotic species. Graphical abstract Image 1 Highlights • Paramuricea macrospina lives in the Menorca Channel between 60 and 100 m depth. • Genetic diversity and structure of P. macrospina have been explored. • Connectivity among Menorca Channel' populations of P. macrospina were observed. • No genetic differentiation was observed among morphotypes. • This is in accordance with the high recruitment rates observed in the area. [ABSTRACT FROM AUTHOR]