MEDUSA: Marine benthic Ecological Data from Underwater imagery Surveys of sub-Antarctic Crozet environments.

Inscribed on the UNESCO World Heritage list, the sub-Antarctic Crozet archipelago is located in a region facing significant environmental changes impacting a poorly known marine biodiversity. Underwater imagery constitutes a valuable non-invasive approach for gathering ecological data and improving our knowledge of ecosystems' vulnerability. We here compiled two datasets, encompassing 17 video-imagery surveys of Crozet nearshore environments conducted in 2021 and 2022 at two sites of Ile de la Possession: Baie du Marin and Crique du Sphinx. Faunal abundance and algal cover data related to each survey are also provided. A total of 755 images were analysed, comprising 52 faunal and 14 algal taxa identified in 2021, as well as 45 faunal and 14 algal taxa identified in 2022. Video-transects were performed in shallow waters by scuba divers using a GoPro®HERO7 multiple camera set-up, and in deeper waters using a remotely operated vehicle. These data provide a first baseline for biodiversity and ecosystem studies, and for monitoring the long-term dynamics of Crozet benthic habitats facing natural and anthropogenic disturbances.

A radiocarbon spike at 14 300 cal yr BP in subfossil trees provides the impulse response function of the global carbon cycle during the Late Glacial.

We present new 14C results measured on subfossil Scots Pines recovered in the eroded banks of the Drouzet watercourse in the Southern French Alps. About 400 new 14C ages have been analysed on 15 trees sampled at annual resolution. The resulting Δ14C record exhibits an abrupt spike occurring in a single year at 14 300-14 299 cal yr BP and a century-long event between 14 and 13.9 cal kyr BP. In order to identify the causes of these events, we compare the Drouzet Δ14C record with simulations of Δ14C based on the 10Be record in Greenland ice used as an input of a carbon cycle model. The correspondence with 10Be anomalies allows us to propose the 14.3 cal kyr BP event as a solar energetic particle event. By contrast, the 14 cal kyr BP event lasted about a century and is most probably a common Maunder-type solar minimum linked to the modulation of galactic cosmic particles by the heliomagnetic field. We also discuss and speculate about the synchroneity and the possible causes of the 14 cal kyr BP event with the brief cold phase called Older Dryas, which separates the Bølling and Allerød millennium-long warm phases of the Late Glacial period. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

Correction: A Well-Kept Treasure at Depth: Precious Red Coral Rediscovered in Atlantic Deep Coral Gardens (SW Portugal) after 300 Years.

[This corrects the article DOI: 10.1371/journal.pone.0147228.].

A Well-Kept Treasure at Depth: Precious Red Coral Rediscovered in Atlantic Deep Coral Gardens (SW Portugal) after 300 Years.

BACKGROUND: The highly valuable red coral Corallium rubrum is listed in several Mediterranean Conventions for species protection and management since the 1980s. Yet, the lack of data about its Atlantic distribution has hindered its protection there. This culminated in the recent discovery of poaching activities harvesting tens of kg of coral per day from deep rocky reefs off SW Portugal. Red coral was irregularly exploited in Portugal between the 1200s and 1700s, until the fishery collapsed. Its occurrence has not been reported for the last 300 years. RESULTS: Here we provide the first description of an Atlantic red coral assemblage, recently rediscovered dwelling at 60-100 m depth in southern Portugal. We report a very slow growth rate (0.23 mm year-1), comparable to Mediterranean specimens. In comparison with most of the Mediterranean reports, the population reaches much larger sizes, estimated to be over one century old, and has a more complex coral branch architecture that promotes a rich assemblage of associated species, with boreal and Mediterranean affinities. Atlantic red coral is genetically distinct, yet mitochondrial analyses suggest that red corals from the Atlantic may have introgressed the Mediterranean ones after migration via the Algeria current. Our underwater surveys, using advanced mixed-gas diving, retrieved lost fishing gear in all coral sites. Besides illegal harvesting, the use and loss of fishing gears, particularly nets, by local fisheries are likely sources of direct impacts on these benthic assemblages. CONCLUSIONS: We extended the knowledge on the distribution of C. rubrum in the Atlantic, discovered its genetic distinctiveness, and reveal a rich deep-dwelling fauna associated to these coral assemblages. These findings support a barrier role of the Atlantic-Mediterranean transition zone, but reveal also hints of connectivity along its southern margin. The results highlight the genetic and demographic uniqueness of red coral populations from SW Iberia. However, we also report threats to these vulnerable populations by direct and indirect fishing activities and argue that its protection from any mechanically destructive activities is urgent as a precautionary approach. This study advances our understanding of phylogeographic barriers and range edge genetic diversity, and serves as a baseline against which to monitor future human and environmental disturbances to Atlantic C. rubrum.

Potential for adaptive evolution at species range margins: contrasting interactions between red coral populations and their environment in a changing ocean.

Studying population-by-environment interactions (PEIs) at species range margins offers the opportunity to characterize the responses of populations facing an extreme regime of selection, as expected due to global change. Nevertheless, the importance of these marginal populations as putative reservoirs of adaptive genetic variation has scarcely been considered in conservation biology. This is particularly true in marine ecosystems for which the deep refugia hypothesis proposes that disturbed shallow and marginal populations of a given species can be replenished by mesophotic ones. This hypothesis therefore assumes that identical PEIs exist between populations, neglecting the potential for adaptation at species range margins. Here, we combine reciprocal transplant and common garden experiments with population genetics analyses to decipher the PEIs in the red coral, Corallium rubrum. Our analyses reveal partially contrasting PEIs between shallow and mesophotic populations separated by approximately one hundred meters, suggesting that red coral populations may potentially be locally adapted to their environment. Based on the effective population size and connectivity analyses, we posit that genetic drift may be more important than gene flow in the adaptation of the red coral. We further investigate how adaptive divergence could impact population viability in the context of warming and demonstrate differential phenotypic buffering capacities against thermal stress. Our study questions the relevance of the deep refugia hypothesis and highlights the conservation value of marginal populations as a putative reservoir of adaptive genetic polymorphism.

Assessing the effectiveness of marine reserves on unsustainably harvested long-lived sessile invertebrates.

Although the rapid recovery of fishes after establishment of a marine reserve is well known, much less is known about the response of long-lived, sessile, benthic organisms to establishment of such reserves. Since antiquity, Mediterranean red coral (Corallium rubrum) has been harvested intensively for use in jewelry, and its distribution is currently smaller than its historical size throughout the Mediterranean Sea. To assess whether establishment of marine reserves is associated with a change in the size and number of red coral colonies that historically were not harvested sustainably, we analyzed temporal changes in mean colony diameter and density from 1992 to 2005 within red coral populations at different study sites in the Medes Islands Marine Reserve (established in 1992) and in adjacent unprotected areas. Moreover, we compared colony size in the Medes Islands Marine Reserve, where recreational diving is allowed and poaching has been observed after reserve establishment, with colony size in three other marine protected areas (Banyuls, Carry-le-Rouet, and Scandola) with the enforced prohibition of fishing and diving. At the end of the study, the size of red coral colonies at all sampling sites in the Medes Islands was significantly smaller than predicted by growth models and smaller than those in marine protected areas without fishing and diving. The annual number of recreational dives and the percent change in the basal diameter of red coral colonies were negatively correlated, which suggests that abrasion by divers may increase the mortality rates of the largest red coral colonies within this reserve . Our study is the first quantitative assessment of a poaching event, which was detected during our monitoring in 2002, inside the marine reserve. Poaching was associated with a loss of approximately 60% of the biomass of red coral colonies.