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International audience; New high-resolution relative sea-level (RSL) proxy data obtained from Lithophyllum rims in the Adriatic allow usto distinguish major local, regional and global RSL driving processes during the past two millennia. RSL changeon the Elafiti islands in the Dubrovnik archipelago (Southern Adriatic) has been significantly affected by local tectonic contributions, which vary spatially and increase southeastwards from Jakljan to Grebeni. Consequently, the RSL change on northwestward islands, Jakljan and ˇSipan, is still dominantly driven by linear regional glacioisostatic adjustment (GIA) processes estimated at ~0.34 mm/yr. However, GIA effects are occasionally cancelled out by local, non-linear coseismic uplifts of small magnitude and by variations in the global mean sea level (GMSL). Thus the rapid fall in GMSL of 0.26 mm/yr offset the GIA effects between approximately ~1000–1250 cal CE, resulting in temporal hiatuses in algal rim formation. After ~1800 cal CE, GIA rates were significantly amplified by GMSL rise, which exceed 0.9 mm/yr at Jakljan and ˇSipan and goes up to 1.4 mm/yr at Koloˇcep and Grebeni, confirming the acceleration of RSL rise over the past two hundred years.The new GMSL records from the northern and southern Adriatic, allow us to reconstruct the first highresolutionGMSL curve for the Adriatic. We show that GMSL variability is in-phase with solar activity during the last two millennia, acting on cycles of ~350, 220 and 100-yrs. We also show that increased GMSL fall, which stopped the formation of algal rims around ~1000 and ~1600 cal CE, coincides with the global reduction in radiative forcing associated with the Oort and Maunder minima, with a drop in sea surface temperature (SST) and with increased salinity. Thus, our analyses revealed a consistent periodicity between the Adriatic GMSL signal, solar forcing, SST and salinity, with the most important cycle being the 350-year Great Solar Cycle.

21 pages, 4 figures, 1 table, supporting information https://doi.org/10.1002/ece3.9740.-- Data Availability Statement: Raw RNA-seq data and mt-mutS sequences have been uploaded to NCBI's SRA (BioProject ID: PRJNA847883) and GenBank databases (Accessions numbers: ON804207-ON804214), respectively. Final sequence alignments and microsatellite data are available on DRYAD (https://doi.org/10.5061/dryad.r7sqv9sfm), The accurate delimitation of species boundaries in nonbilaterian marine taxa is notoriously difficult, with consequences for many studies in ecology and evolution. Anthozoans are a diverse group of key structural organisms worldwide, but the lack of reliable morphological characters and informative genetic markers hampers our ability to understand species diversification. We investigated population differentiation and species limits in Atlantic (Iberian Peninsula) and Mediterranean lineages of the octocoral genus Paramuricea previously identified as P. clavata. We used a diverse set of molecular markers (microsatellites, RNA-seq derived single-copy orthologues [SCO] and mt-mutS [mitochondrial barcode]) at 49 locations. Clear segregation of Atlantic and Mediterranean lineages was found with all markers. Species-tree estimations based on SCO strongly supported these two clades as distinct, recently diverged sister species with incomplete lineage sorting, P. cf. grayi and P. clavata, respectively. Furthermore, a second putative (or ongoing) speciation event was detected in the Atlantic between two P. cf. grayi color morphotypes (yellow and purple) using SCO and supported by microsatellites. While segregating P. cf. grayi lineages showed considerable geographic structure, dominating circalittoral communities in southern (yellow) and western (purple) Portugal, their occurrence in sympatry at some localities suggests a degree of reproductive isolation. Overall, our results show that previous molecular and morphological studies have underestimated species diversity in Paramuricea occurring in the Iberian Peninsula, which has important implications for conservation planning. Finally, our findings validate the usefulness of phylotranscriptomics for resolving evolutionary relationships in octocorals, This work was funded by program BIOMARES, a Pew Marine Fellowship, and FCT – Foundation for Science and Technology UIDB/04326/2020, UIDP/04326/2020, LA/P/0101/2020, PTDC/BIA-CBI/6515/2020; EU-BiodivERsA BiodivRestore-253 (FCT: DivRestore/0013/2020); EU Horizon 2020 research and innovation program (MERCES: Grant no. 689518); as well as the Inaqua Conservation Fund (Oceanário de Lisboa and National Geographic Channel) and National Geographic Society/Waitt Grant no. W153-11. This article is also a product of the French network on Marine Connectivity (GDR MarCo). M.C. was supported by postdoctoral fellowships of projects HABMAR (Grant no. MAR-01.04.02-FEAMP-0018) co-financed by the European Maritime and Fisheries Fund of the Operational Program MAR 2020 for Portugal (Portugal 2020), and BiodivAMP (Grant no. FA_06_2017_045) financed by the Directorate-General for Sea Policy of the Ministry of Economy and Sea for Portugal under the Operational Program Fundo Azul. JBL was funded by assistant researcher contract framework of the RD Unit—UID/Multi/04423/2019 – Interdisciplinary Centre of Marine and Environmental Research—financed by the European Regional Development Fund (ERDF) through COMPETE2020—Operational Program for Competitiveness and Internationalization (POCI) and national funds through FCT/MCTES (PIDDAC). JB was funded by a FCT PhD scholarship SFRH/BD/72501/2010, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

In micro tidal settings, processes of bioerosion and bioconstruction can lead to the development of distinct morphological features that define the modern shoreline. When such features are discovered above or below the present-day mean sea level, they reveal relative sea-level (RSL) change. Among the best sea-level indicators on rocky coasts are fixed biological and geomorphological markers – algal rims, Lithophaga lithophaga borehole upper limits, and tidal notches [1, 2]. For instance, the coralline alga Lithophyllum byssoides can build algal rims that are considered one of the most precise RSL markers along rocky coasts [3, 4]. Consequently, studying RSL markers on Lopud, Koločep and Grebeni two elevated palaeoshorelines have been distinguished. Their detailed survey allowed the distinction of seismotectonically uplifted sectors of the coast. The established high-resolution geochronology enables separation of coseismic uplift events from the periods of interseismic subsidence. Studying the local tectonic contribution to RSL change, we approach aspects of neotectonics and palaeoearthquakes offering new insights in a timetable (500 BC up to 1800 AD) where earthquake related data are either missing or incorporate high uncertainties, both regarding their epicentral localities and estimated magnitudes. Our reconstruction provides evidence on two successive major earthquakes which affected approximately 5 km of coasts in the Pelješac- Dubrovnik fault zone, with an uplift amplitude between 40 and 80 ± 15 cm per event (Fig. 1). The earlier, older events, caused larger displacements (60-80 cm), while the later, younger events, revealed on average lower displacements (40-55 cm) corresponding to the 1520 AD quake and the 1667 Dubrovnik earthquake [5, 6]. Here we demonstrate the importance of Lithophyllum rims in the studies of RSL change as they make creation of high-resolution geochronology possible. This new approach refers to algal rims as a possible tool for constraining palaeoseismic events, allowing to supplement the database of instrumental records and historical observations through field-based evidence. Furthermore, the study of algal rims, tidal notches and upper limits of L. lithophaga boreholes allow us to reconstruct the 2.6 ka evolution of Koločep and Grebeni islands and islets coasts, detect seismic events and demonstrate their effects, reconstruct the RSL changes at high resolution and finally distinguish the drivers of RSL change. As the southern part of the eastern Adriatic coast is the area of highest seismic risk in Croatia, the new obtained data will thus be essential for assessment of recurrence rates of the largest earthquakes that the main faults in the area can produce, as well as for understanding of the Late Holocene geodynamics.

The relative sea-level (RSL) change is a sum of effects of processes acting on local, regional and global scales. By far the most variable component of RSL change relates to local, non-linear scale processes, that is to active tectonics. The studied islands and islets, Lopud, Koločep and Grebeni are part of Dubrovnik archipelago, situated near the external front of the Dinarides where seismicity attains one of the highest levels in Croatia. The focal mechanisms in the area show that reverse and transpressive faulting prevails.Studying the RSL markers: algal rims, tidal notches and Lithophaga lithophaga borehole upper limits, we identified one elevated palaeoshoreline at Lopud island (today 25-30 cm above the mean sea-level (MSL)) and two elevated palaeoshorelines at Koločep island and Grebeni islets (60-90 cm and 25-40 cm above MSL). The high-resolution geochronology built on radiocarbon dating of algal rims (77 sea-level index points) enabled the distinction of coseismic uplift events from subsidence periods during the last 3300 years. As a result, we provide new, field-based reconstruction of palaeoearthquakes, describe spatial patterns of differential uplift and distinguish the main drivers of RSL change.Two major seismically triggered uplift events with displacements between 40 and 80 ± 15 cm per event have been differentiated along investigated sectors of the coast related to the Pelješac-Dubrovnik fault zone pointing to repeated earthquakes of magnitudes exceeding Mw = 6.5. The earlier, older events, caused larger displacements (60-80 cm) related to 4th to 6th century AD and 750-1100 AD earthquakes, while the later, younger events, revealed on average lower displacements (40-55 cm) corresponding to the 1520 AD quake and the 1667 Dubrovnik earthquake. The cumulative offsets increase from around 0.57 ± 0.15 m at Lopud to 1.00-1.25 ± 0.15 m at Koločep and Grebeni.Interseismic periods allow further insight into regional and global driving mechanisms of RSL change. The distinction of local coseismic displacements of RSL history together with the previously obtained regional glacio- and hydro-isostatic adjustment estimates (between 0.30 and 0.34 mm/yr) allow us to approach the global contribution, which seems to be minimal between ~0 and 1800 cal AD as RSL changed at rates of 0.3 to 0.4 mm/yr. The increased rates of RSL change occurred prior to 0 cal AD, with rates of around 0.7 mm/yr, and go up to 1.4 mm/yr after 1800 cal AD.Overall, here we demonstrate the importance of Lithophyllum rims in the studies of RSL change as they make creation of high-resolution geochronology possible. Moreover, this new approach refers to algal rims as a possible tool for constraining palaeoseismic events, allowing to supplement the database of instrumental records and historical observations through field-based evidence. This research was supported by Croatian Science Foundation project HRZZ-IP-2019-04-9445 – Relative sea-level change and climate change along the eastern Adriatic coast – SEALeveL.