Red Gorgonian Research Articles

Variation in the Health Status of the Mediterranean Gorgonian Forests: The Synergistic Effect of Marine Heat Waves and Fishing Activity.

Over the past thirty years, the red gorgonian Paramuricea clavata in the Mediterranean Sea has faced increasing threats, including heat waves and human activities such as artisanal and recreational fishing. Epibiosis on damaged gorgonian colonies is generally used as an indirect indication of stressed conditions. The density and height of P. clavata and the percentage of colonies affected by epibiosis and entangled in lost fishing gear were monitored to investigate the phenomenon and its trend over time in the Ligurian Sea. Analyses were based on transects collected during ROV campaigns between 2015 and 2022 at depths of 33-90 m. A strong correlation was observed between fishing efforts in the study area and the level of epibiosis. Maximal percentages of colonies affected by epibiosis and entanglement were recorded at depths of 50-70 m. Temporally, marine heat waves before 2019 were identified as the primary cause of damage to P. clavata. The decrease in epibiosis percentages after 2019, despite the 2022 heat wave, may be due to a quick recovery ability of the populations and a reduction in fishing activities during the COVID-19 lockdown in 2020. Long-term monitoring programmes are essential to understand the changes in marine benthic communities exposed to different stressors.

The deep vault: a temporary refuge for temperate gorgonian forests facing marine heat waves

Climate change poses a significant threat to coastal areas, marked by the increasing intensity and frequency of marine heat waves observed in various ecosystems around the world. Over the last 25 years, a vast number of Mediterranean populations of the red gorgonian Paramuricea clavata have been impacted by marine heatwaves. The last mass mortality occurred during the summer of 2022 in the Western Mediterranean Sea, affecting mostly shallow populations (down to 30 m depth). Here we provide an assessment of the health status of mesophotic P. clavata populations down to 90 m depth to investigate a depth refuge hypothesis. Results show that the impact of marine heat waves decreases with depth, with a significant drop in mortality below 40 m depth. These observations support the hypothesis of a depth refuge from marine heat waves that may allow, at least temporarily, the maintenance of P. clavata in the Western Mediterranean Sea. The present study strongly advocates for further investigations and monitoring of the mesophotic zone to chart potential areas that could serve as deep refuge for gorgonians.

Marine protected areas in a changing ocean: Adaptive management can mitigate the synergistic effects of local and climate change impacts

During the last two decades, several Marine Heatwaves (MHWs) have affected coralligenous assemblages in the Mediterranean Sea, causing catastrophic mass mortalities of several habitat-forming species such as gorgonians, corals, and sponges. Even though Marine Protected Areas (MPAs) are contributing to effectively protect marine ecosystems, the impacts associated to extreme climatic events within MPAs are jeopardizing their protective role. Therefore, minimizing local stressors within MPAs is crucial to minimize interactive effects with global, more difficult to manage, stressors. To address this, we assessed to what extent the regulation of diving frequentation can support more effective protection to climate change, focusing on the case study of the Medes Islands, which has recently suffered the impacts of different global stressors and is one of the most visited MPAs in the Mediterranean Sea. We combined 6 years of demographic data of the red gorgonian Paramuricea clavata with population modelling tools, to explore the long-term viability of this species to different managing schemes and mass mortality events scenarios. Overall, our results show that climate-adaptive management of the recreational diving activity under climate change can enhance the long-term viability of this key Mediterranean habitat-forming octocoral, which is otherwise predicted to go locally extinct at shallow depths (<25 m) within the next 20 years. This study provides one of the few attempts to quantify to what extent an adaptive management scheme may help delay climate change impacts in a Marine Protected Area.

Marine strategy framework for detecting mass mortality: From local surveys to monitoring improvements in the coralligenous habitat

Mediterranean coralligenous assemblages are threatened by the effects of climate change and human activities that have led to mass mortality events (MMEs) in recent decades. The ecological roles of this habitat and the possible consequences of its loss have necessitated the scientific analysis of MMEs on a Mediterranean regional scale, highlighting the need of new standardized monitoring and data collection tools across the basin. In September 2021, during the monitoring activities of the Marine Strategy Framework Directive (MSFD) for the coralligenous habitat of the Egadi Islands Marine Protected Area (MPA), an MME of the red gorgonian Paramuricea clavata was recorded. Five of the six surveyed sites revealed a high degree of impact, with mortality values ranging from 46.9% in the least affected site to 100% in the most affected. The observed MME occurred during a prolonged period of anomalous warmer sea temperatures down to 60 m in depth. By enhancing the MSFD protocols for coralligenous habitat with the addition of a series of biotic/abiotic variables (e.g., temperature, pH and mucilaginous bloom) and methodologies (e.g., scuba survey and citizen science activities) to evaluate and monitor Good Environment Status (GES), we propose to implement a monitoring and data collection system which is able to provide essential information about MMEs. This multiple shared surveillance tool would allow the tracking of MME events in the Mediterranean region, as well as the planning of mitigation and/or restoration strategies for these vulnerable habitats on an inter-regional scale.

Exploring the response of a key Mediterranean gorgonian to heat stress across biological and spatial scales

Understanding the factors and processes that shape intra-specific sensitivity to heat stress is fundamental to better predicting the vulnerability of benthic species to climate change. Here, we investigate the response of a habitat-forming Mediterranean octocoral, the red gorgonian Paramuricea clavata (Risso, 1826) to thermal stress at multiple biological and geographical scales. Samples from eleven P. clavata populations inhabiting four localities separated by hundreds to more than 1500 km of coast and with contrasting thermal histories were exposed to a critical temperature threshold (25 °C) in a common garden experiment in aquaria. Ten of the 11 populations lacked thermotolerance to the experimental conditions provided (25 days at 25 °C), with 100% or almost 100% colony mortality by the end of the experiment. Furthermore, we found no significant association between local average thermal regimes nor recent thermal history (i.e., local water temperatures in the 3 months prior to the experiment) and population thermotolerance. Overall, our results suggest that local adaptation and/or acclimation to warmer conditions have a limited role in the response of P. clavata to thermal stress. The study also confirms the sensitivity of this species to warm temperatures across its distributional range and questions its adaptive capacity under ocean warming conditions. However, important inter-individual variation in thermotolerance was found within populations, particularly those exposed to the most severe prior marine heatwaves. These observations suggest that P. clavata could harbor adaptive potential to future warming acting on standing genetic variation (i.e., divergent selection) and/or environmentally-induced phenotypic variation (i.e., intra- and/or intergenerational plasticity).

Mucilage-induced necrosis reveals cellular oxidative stress in the Mediterranean gorgonian Paramuricea clavata

The red gorgonian Paramuricea clavata is a fundamental ecosystem engineer of coralligenous biocenosis in the Mediterranean Sea, where it plays crucial ecological functions and enhances the habitat biodiversity. However, this species is strongly endangered due to climate change-related stressors such as mucilage events, which have increased in recent decades causing extensive damage and mortality, but whose impacts at the molecular and cellular levels are still unexplored. In this study, different cellular stress biomarkers were analyzed in mucilage-colonized P. clavata specimens living in the Portofino Marine Protected Area (Ligurian Sea, Italy), in order to elucidate the cellular pathways affected by mucilage and the cellular defense mechanisms adopted. Within these colonies, portions of healthy tissue located at different distances from mucilage-induced necrosis were considered. Our results showed that mucilage affected the cellular oxidative status and impaired lipid cell membranes of the whole P. clavata colony. Indeed, an increase in the superoxide dismutase (SOD) and glutathione reductase (GR) enzymatic activity and in the level of lipid peroxidation (LPO) was detected in colonies showing mucilage-induced necrotic tissues compared to healthy ones. In particular, fragments sampled just next to the necrotic tissue displayed the highest levels of SOD and LPO, indicating that harmful oxidative damage was in progress, especially in portions neighboring the mucilage colonization. In this context, the up-regulation of the antioxidant mechanisms might represent a defense and a barrier from hypoxic or anoxic conditions created by mucilage overgrowth or by the invasion of toxic organisms embedded in the mucilaginous aggregates. On the contrary, the cellular protein homeostasis, analyzed by the expression of the 60-kDa Heat shock protein (Hsp60), was not altered by the mucilage. This analysis contributes to provide new insights into the cellular and molecular response of gorgonians to a stress source whose effects are likely to worsen in a climate change scenario.

Effects of global warming on Mediterranean coral forests

The effects of global warming have been addressed on coral reefs in tropical areas, while it is still unclear how coral forests are reacting, particularly at temperate latitudes. Here we show how mesophotic coral forests are affected by global warming in the Mediterranean Sea. We highlight how the current warming trend is causing the lowering of the thermocline and it is enhancing mucilaginous blooms. These stressors are facilitating a massive macroalgal epibiosis on living corals, here reported for the first time from different areas in the Western and Central Mediterranean Sea. We provide a focus of this phenomenon at Tremiti Islands Marine Protected Area (Adriatic Sea), were the density of the endemic red gorgonian Paramuricea clavata decreased of up to 47% in 5 years, while up to the 96% of the living corals showed signs of stress and macroalgal epibiosis. Only populations deeper than 60 m depth were not touched by this emerging phenomenon. Spot observations performed at Tuscan Archipelago and Tavolara Marine Protected Area (Tyrrhenian Sea) suggest that this this combination of stressors is likely widespread at basin scale.

Genetic insights into recolonization processes of Mediterranean octocorals

Marine ecosystems are strongly impacted by the consequences of human activities, such as habitat destruction or artificialization and climate change. In the Mediterranean Sea, sessile benthic species, and particularly octocorals, have been affected by mass mortality events linked with positive thermal anomalies. The future survival of octocoral populations impacted by global change will depend on their recolonization abilities facing local extirpation or important modification of their habitat. We studied these processes in Mediterranean octocorals in two situations: the colonization of artificial substrates (wrecks) by the red gorgonian Paramuricea clavata, and the recolonization following mortality events in the yellow gorgonian Eunicella cavolini. With microsatellite markers (seven for P. clavata, five for E. cavolini), we analyzed the genetic diversity of populations on artificial substrates and their differentiation from other neighboring populations. For P. clavata the populations on artificial substrates were not or lowly differentiated from the closest populations (1.3–1.6 km) on natural substrates, and showed similar levels of genetic diversity. Artificial substrates can then be considered as an interesting substitute for natural substrates for this species. For E. cavolini we did not detect any variation in diversity or relatedness following recuperation after mortality events. In both cases, our results suggest the input from different populations in the recolonization process, which helps in maintaining the genetic diversity. These results are useful for the management of these species and of associated ecosystems.

Development of a set of SNP markers for population genetics of the red gorgonian (Paramuricea clavata), an emblematic species of the Mediterranean coralligenous

Transcriptome sequencing was used for the development of single nucleotide polymorphisms (SNP) for the red gorgonian (Paramuricea clavata). A total of 20,736 SNPs were identified, and 1718 had a coverage of over 100 reads. Of the 480 SNPs tested, 347 SNPs were successfully genotyped at 95 samples from the NW Mediterranean using a MassARRAY System. This set of markers will be of great value for population genetics and phylogeography.

Conservation status of Paramuricea clavata (Risso, 1826) (Anthozoa, Alcyonacea) in the Chafarinas Islands (Mediterranean Sea)

The red gorgonian Paramuricea clavata (Risso, 1826) is affected by the combined effects of environmental stress factors and diseases in the Mediterranean area. Samplings at different depths in two sites of Chafarinas Islands (South–Western Mediterranean Sea) were carried out to quantify the degree of injuries on red gorgonian colonies. The results showed that shallow colonies displayed a higher rate of injuries than deep colonies. Overall, the conservation status of the population was worse than previously considered in this area.

Genetic diversity increases with depth in red gorgonian populations of the Mediterranean Sea and the Atlantic Ocean.

BackgroundIn the ocean, the variability of environmental conditions found along depth gradients exposes populations to contrasting levels of perturbation, which can be reflected in the overall patterns of species genetic diversity. At shallow sites, resource availability may structure large, persistent and well-connected populations with higher levels of diversity. In contrast, the more extreme conditions, such as thermal stress during heat waves, can lead to population bottlenecks and genetic erosion, inverting the natural expectation. Here we examine how genetic diversity varies along depth for a long-lived, important ecosystem-structuring species, the red gorgonian, Paramuricea clavata.MethodsWe used five polymorphic microsatellite markers to infer differences in genetic diversity and differentiation, and to detect bottleneck signs between shallow and deeper populations across the Atlantic Ocean and the Mediterranean Sea. We further explored the potential relationship between depth and environmental gradients (temperature, ocean currents, productivity and slope) on the observed patterns of diversity by means of generalized linear mixed models.ResultsAn overall pattern of higher genetic diversity was found in the deeper sites of the Atlantic Ocean and the Mediterranean Sea. This pattern was largely explained by bottom temperatures, with a linear pattern of decreasing genetic diversity with increasing thermal stress. Genetic differentiation patterns showed higher gene flow within sites (i.e., shallow vs. deeper populations) than between sites. Recent genetic bottlenecks were found in two populations of shallow depths.DiscussionOur results highlight the role of deep refugial populations safeguarding higher and unique genetic diversity for marine structuring species. Theoretical regression modelling demonstrated how thermal stress alone may reduce population sizes and diversity levels of shallow water populations. In fact, the examination of time series on a daily basis showed the upper water masses repeatedly reaching lethal temperatures for P. clavata. Differentiation patterns showed that the deep richer populations are isolated. Gene flow was also inferred across different depths; however, not in sufficient levels to offset the detrimental effects of surface environmental conditions on genetic diversity. The identification of deep isolated areas with high conservation value for the red gorgonian represents an important step in the face of ongoing and future climate changes.

SfM-Based Method to Assess Gorgonian Forests (Paramuricea clavata (Cnidaria, Octocorallia))

Animal forests promote marine habitats morphological complexity and functioning. The red gorgonian, Paramuricea clavata, is a key structuring species of the Mediterranean coralligenous habitat and an indicator species of climate effects on habitat functioning. P. clavata metrics such as population structure, morphology and biomass inform on the overall health of coralligenous habitats, but the estimation of these metrics is time and cost consuming, and often requires destructive sampling. As a consequence, the implementation of long-term and wide-area monitoring programmes is limited. This study proposes a novel and transferable Structure from Motion (SfM) based method for the estimation of gorgonian population structure (i.e., maximal height, density, abundance), morphometries (i.e., maximal width, fan surface) and biomass (i.e., coenenchymal Dry Weight, Ash Free Dried Weight). The method includes the estimation of a novel metric (3D canopy surface) describing the gorgonian forest as a mosaic of planes generated by fitting multiple 5 cm × 5 cm facets to a SfM generated point cloud. The performance of the method is assessed for two different cameras (GoPro Hero4 and Sony NEX7). Results showed that for highly dense populations (17 colonies/m2), the SfM-method had lower accuracies in estimating the gorgonians density for both cameras (60% to 89%) than for medium to low density populations (14 and 7 colonies/m2) (71% to 100%). Results for the validation of the method showed that the correlation between ground truth and SfM estimates for maximal height, maximal width and fan surface were between R2 = 0.63 and R2 = 0.9, and R2 = 0.99 for coenenchymal surface estimation. The methodological approach was used to estimate the biomass of the gorgonian population within the study area and across the coralligenous habitat between −25 to −40 m depth in the Portofino Marine Protected Area. For that purpose, the coenenchymal surface of sampled colonies was obtained and used for the calculations. Results showed biomass values of dry weight and ash free dry weight of 220 g and 32 g for the studied area and to 365 kg and 55 Kg for the coralligenous habitat in the Marine Protected Area. This study highlighted the feasibility of the methodology for the quantification of P. clavata metrics as well as the potential of the SfM-method to improve current predictions of the status of the coralligenous habitat in the Mediterranean sea and overall management of threatened ecosystems.

High genetic differentiation of red gorgonian populations from the Atlantic Ocean and the Mediterranean Sea

ABSTRACTPatterns of genetic variation within a species may be used to infer past events in the evolutionary history of marine species. In the present study we aimed to compare the genetic diversity of the red gorgonian Paramuricea clavata in the Atlantic Ocean and the Mediterranean Sea. For genetic markers we used microsatellites and a mitochondrial gene fragment. Our results revealed a distinct genetic composition and diversity between the Mediterranean and the Atlantic. The Mediterranean samples had higher microsatellite heterozygosity, allelic richness and private allelic richness. The hypotheses that can explain these patterns are the isolation of Atlantic populations and/or a founder effect. Additionally, a clear difference was obtained from the mitochondrial locus, since sequences from Atlantic and Mediterranean samples diverged by 1%, which is high for soft corals.

Low clonal propagation in Atlantic and Mediterranean populations of the red gorgonian &lt;em&gt;Paramuricea clavata&lt;/em&gt; (Octocorallia)

Clonal propagation is a common feature of benthic marine organisms. In the present study, we investigated the contribution of clonal reproduction in the red gorgonian Paramuricea clavata. Mediterranean populations of P. clavata were severely affected by mass mortality events caused by increased water temperature in 1999 and 2003. The populations are characterized by slow growth and episodic recruitment, but after the observed mortalities, an unexpectedly high recovery rate was observed in the severely affected populations from the Ligurian Sea, NW Mediterranean. Ten years after the last mortality event, we investigated the contribution of clonal propagation in populations from the Ligurian Sea, where some populations were highly affected by mass mortality events, and from the Atlantic, where mortality was never observed. All individuals were genotyped for nine microsatellite loci. The contribution of clonal reproduction varied from 0% to 13% and did not differ significantly between affected and unaffected populations. We confirm by using genetic markers that clonal propagation in P. clavata is not common, and that the contribution of clones is too low to play an important role in red gorgonian reproduction and cannot contribute to population recovery at sites that have been affected by mass mortality events.

Historical biogeography and mitogenomics of two endemic Mediterranean gorgonians (Holaxonia, Plexauridae)

Among the Mediterranean plexaurids, four species are endemic and despite their ecological importance, comprehensive studies on the evolution and biogeography of these organisms are lacking. Here, we explore the mitogenomic variability of two endemic, ecologically important Mediterranean Paramuricea species. We assess their phylogenetic relationships and provide first insights into their evolution and biogeography. Complete mitogenome sequences of Paramuricea clavata and Paramuricea macrospina were obtained using long-range PCR, primer-walking and Sanger sequencing. For an enlarged sample of Paramuricea species, maximum likelihood and Bayesian phylogenetic trees of the mitochondrial gene mtMutS were obtained and used to study the biogeographic history of Paramuricea through a statistical Dispersal-Vicariance (S-DIVA) method and a Dispersal Extinction Cladogenesis (DEC) model. Divergence time was estimated under strict and relaxed molecular clock models in BEAST using published octocoral mutation rates. Our results revealed high nucleotide diversity (2.6%) among the two Mediterranean endemics; the highest mutation rates were found in the mtMutS, Nad4 and Nad5. In addition, we found length polymorphisms in several intergenic regions and differences in mitochondrial genome size. The red gorgonian P. clavata was closely related to the Eastern Atlantic Paramuricea grayi rather than its Mediterranean congener, P. macrospina. Our biogeographic results provide evidence for the independent speciation of the Mediterranean species and point to a Miocene origin of the two endemics, highlighting the role played by the Messinian Salinity Crisis in the evolutionary history of Mediterranean organisms.

Localization of endobacteria in the gastrodermis of a Mediterranean gorgonian coral, Paramuricea clavata, using fluorescence in situ hybridization

Gorgonian corals are among the most representative species of hard-bottom sublittoral ecosystems in the Mediterranean Sea. The red gorgonian, Paramuricea clavata, harbors a specific, spatially and temporally stable bacterial community that may have an important biological role in the function of the holobiont. However, little is known about the microbial–gorgonian relationship, specifically the nature of the interaction established by the bacteria with their host. Documenting the distribution of microorganisms within coral tissue compartments is critical for providing an overall framework for understanding their functional roles. Here, we used histology and fluorescence in situ hybridization (FISH) to detect and localize bacteria in the tissues of P. clavata. Aggregates of tightly packed bacteria were found in the endoderm of the polyps, which is consistent with previous observations of endobacteria in the tissues of scleractinian coral species. This finding suggests the existence of an intimate biological integration between specific members of the microbiota and gorgonian corals that likely results from a complex interplay mediating recognition and maintenance of the bacterial associates. In addition to providing the basis for the development of FISH studies in gorgonians, this work includes the first histological description of the inner structure of P. clavata polyps, illustrating the typical features of general gorgonian anatomy.

Genetic Diversity and Local Connectivity in the Mediterranean Red Gorgonian Coral after Mass Mortality Events.

Estimating the patterns of connectivity in marine taxa with planktonic dispersive stages is a challenging but crucial task because of its conservation implications. The red gorgonian Paramuricea clavata is a habitat forming species, characterized by short larval dispersal and high reproductive output, but low recruitment. In the recent past, the species was impacted by mass mortality events caused by increased water temperatures in summer. In the present study, we used 9 microsatellites to investigate the genetic structure and connectivity in the highly threatened populations from the Ligurian Sea (NW Mediterranean). No evidence for a recent bottleneck neither decreased genetic diversity in sites impacted by mass mortality events were found. Significant IBD pattern and high global FST confirmed low larval dispersal capability in the red gorgonian. The maximum dispersal distance was estimated at 20–60 km. Larval exchange between sites separated by hundreds of meters and between different depths was detected at each site, supporting the hypothesis that deeper subpopulations unaffected by surface warming peaks may provide larvae for shallower ones, enabling recovery after climatically induced mortality events.

Lonely populations in the deep: genetic structure of red gorgonians at the heads of submarine canyons in the north-western Mediterranean Sea

The red gorgonian Paramuricea clavata plays a central role in coralligenous ecosystems of the Mediterranean Sea, being relatively abundant in shallow habitats (5–35 m depth). Recently, deeper populations have been discovered at the heads of submarine canyons in the north-western Mediterranean Sea, between 50 and 70 m deep. Colonies from some of these deeper populations were exceptionally large (>1 m high), contrasting with the general prevalence of smaller size classes in shallower populations. Importantly, the high pressure of trawling activities on the nearby continental shelf could threaten these populations of large and old colonies. Although the genetic diversity and structure of populations in shallow habitats is relatively well known, very little is known about deeper populations. We aimed to assess the genetic structure, connectivity and potential demographic decline of six deep populations of P. clavata located at the heads of La Fonera, Blanes and Arenys de Mar submarine canyons, as well as potential gene flow between those and the two nearest shallow populations. A total of 188 individuals were genotyped using nine microsatellite loci. Results showed strong genetic differentiation among populations in different submarine canyons, among populations within one of the canyons and between shallow and deep populations. Gene flow among populations was very limited, estimates of effective population size in some populations were small, and evidence of recent population reductions (bottlenecks) was detected in several populations. The large genetic differentiation in populations of P. clavata among canyons is related to limited effective dispersal.

Demographic responses to warming: reproductive maturity and sex influence vulnerability in an octocoral

Ocean warming, caused by climate change, is critically impacting marine coastal ecosystems. Benthic organisms, such as anthozoans, are increasingly submitted to high temperatures that cause massive mortalities in tropical and temperate seas. To broaden our understanding of their response to thermal stress, we tested the putative role of reproductive maturity and sex in the susceptibility of the Mediterranean red gorgonian, Paramuricea clavata, to high temperatures. We experimentally compared the response to thermal stress of sexually immature (i.e., juveniles) versus mature individuals (i.e., adults), and of males versus females. Colonies' response was firstly assessed by measuring the percentage of tissue area exhibiting necrosis. Then, the reproductive output (i.e., fertility, size, and number of gonads) of both sexes was characterized. When compared to juveniles, adults showed a significantly higher percentage of necrosis, suggesting that during the reproductive period they are more vulner- able to high temperatures. Males and females showed a similar percentage of tissue damage and a significant decrease in their reproductive output. However, females' reproduction was more impacted, suggesting that females are more susceptible to thermal stress than males. A dif- ferential energy investment in reproduction may be the underlying cause of the observed responses. Adults invest a large proportion of their energy budget in reproduction; hence, they have fewer resources available to cope with stress, compared to juveniles. A similar situation seems to apply to females, with respect to males. Considering the current ocean-warming trend, our results imply that the long-term viability of shallow populations of long-lived anthozoans may be jeopardized in the future. This study reveals potential demographic consequences of warming that go beyond its associated increment of mortality rates. Given the important ecological role of many anthozoan species, these results can help better predict the future effects of climate change on coastal ecosystems.

Structure and biodiversity of coralligenous assemblages over broad spatial and temporal scales

Coralligenous outcrops rank among the most important ecosystems in the Mediterranean Sea, primarily because of their biodiversity. Information on the spatial and temporal variability of the composition and structure of coralligenous assemblages is essentially lacking for most regions. We explored the variability of the biodiversity patterns of coralligenous outcrops dominated by the red gorgonian Paramuricea clavata in the NW Mediterranean region using a hierarchical sampling design. The study addressed two overlooked spatial and temporal scales: from 1 to >100 km and a 5-year period. Overall, no temporal changes were detected in either species composition or the 12 morphofunctional groups considered. Significant differences in species composition were found at the various spatial scales. However, variation in composition at the locality level (>100 km apart) showed the lowest values in comparison with the differences found at the site level (<1 km apart). Despite the differences, the sites displayed high similarity (average similarity 55.7 %) and shared approximately 50 % of the species. Similarly, the patterns of diversity at different scales, the alpha (site) and gamma (locality) were consistent with the specific composition trends, whereas the beta diversity showed the greatest differences among sites. Our results demonstrate the moderate spatial variability in biodiversity in the NW Mediterranean region and an extremely low temporal variability. This study provides baselines for detecting potential effects due to global change, and it furnishes a basis for the implementation of monitoring schemes of coralligenous assemblages. The development of similar sampling schemes in other Mediterranean regions will provide a global view of the biodiversity of coralligenous outcrops.