Genetic structuring across marine biogeographic boundaries in rocky shore invertebrates

Habitat suitability modelling to predict the distribution of deep coral ecosystems: The case of Linosa Island (southern Mediterranean Sea, Italy)

In areas with limited field data, predictive habitat mapping is a valuable method for elucidating species-environment relationships and enhancing our knowledge of the spatial distribution and complexity of benthic habitats. Species distribution models (SDMs) can be an important tool to support in science-based ecosystem management. The availability of direct observations of mesophotic species, including gorgonians and black corals, during costly surveys is generally limited. Therefore, predicting the distribution of mesophotic species in relation to key physical parameters of the seafloor would help improving conservation strategies in existing and new Marine Protected Areas (MPAs). This study aims to assess the distribution of gorgonians and black corals off Linosa Island, in the Strait of Sicily, a biogeographic boundary area between the western and eastern Mediterranean. The volcanic island of Linosa represents a small, naturally preserved area, with very limited human pressure, hosting rich marine benthic biodiversity on its wide submarine portions. Distribution of the most common coral species off Linosa Island was modelled under an SDM framework, relying on direct observations collected during two research cruises in 2016 and 2017 and a series of terrain parameters acquired through geophysical techniques. We used the so-called "ensemble of small models" approach to calibrate SDMs, which achieved fair-to-excellent results (AUC >0.7). In addition to identifying depth as the primary factor influencing coral distribution, our study also highlighted ruggedness as a significant terrain variable. Specifically, the depth range of 110-230 m emerged as the critical parameter determining habitat suitability for all modelled species, also highlighting peculiar and specie-specific habitat requirements.

Genomic analyses indicate resilience of a commercially and culturally important marine gastropod snail to climate change

Genomic vulnerability analyses are being increasingly used to assess the adaptability of species to climate change and provide an opportunity for proactive management of harvested marine species in changing oceans. Southeastern Australia is a climate change hotspot where many marine species are shifting poleward. The turban snail, Turbo militaris is a commercially and culturally harvested marine gastropod snail from eastern Australia. The species has exhibited a climate-driven poleward range shift over the last two decades presenting an ongoing challenge for sustainable fisheries management. We investigate the impact of future climate change on T. militaris using genotype-by-sequencing to project patterns of gene flow and local adaptation across its range under climate change scenarios. A single admixed, and potentially panmictic, demographic unit was revealed with no evidence of genetic subdivision across the species range. Significant genotype associations with heterogeneous habitat features were observed, including associations with sea surface temperature, ocean currents, and nutrients, indicating possible adaptive genetic differentiation. These findings suggest that standing genetic variation may be available for selection to counter future environmental change, assisted by widespread gene flow, high fecundity and short generation time in this species. We discuss the findings of this study in the content of future fisheries management and conservation.

Spineless and overlooked: DNA metabarcoding of autonomous reef monitoring structures reveals intra- and interspecific genetic diversity in Mediterranean invertebrates

The ability to gather genetic information using DNA metabarcoding of bulk samples obtained directly from the environment is crucial to determine biodiversity baselines and understand population dynamics in the marine realm. While DNA metabarcoding is effective in evaluating biodiversity at community level, genetic patterns within species are often concealed in metabarcoding studies and overlooked for marine invertebrates. In the present study, we implement recently developed bioinformatics tools to investigate intraspecific genetic variability for invertebrate taxa in the Mediterranean Sea. Using metabarcoding samples from Autonomous Reef Monitoring Structures (ARMS) deployed in three locations, we present haplotypes and diversity estimates for 145 unique species. While overall genetic diversity was low, we identified several species with high diversity records and potential cryptic lineages. Further, we emphasize the spatial scale of genetic variability, which was observed from locations to individual sampling units (ARMS). We carried out a population genetic analysis of several important yet understudied species, which highlights the current knowledge gap concerning intraspecific genetic patterns for the target taxa in the Mediterranean basin. Our approach considerably enhances biodiversity monitoring of charismatic and understudied Mediterranean species, which can be incorporated into ARMS surveys.

A Comparative Phylogeography of Three Marine Species with Different PLD Modes Reveals Two Genetic Breaks across the Southern Caribbean Sea

The comparative phylogeography of marine species with contrasting dispersal potential across the southern Caribbean Sea was evaluated by the presence of two putative barriers: the Magdalena River plume (MRP) and the combination of the absence of a rocky bottom and the almost permanent upwelling in the La Guajira Peninsula (ARB + PUG). Three species with varying biological and ecological characteristics (i.e., dispersal potentials) that inhabit shallow rocky bottoms were selected: Cittarium pica (PLD < 6 days), Acanthemblemaria rivasi (PLD < 22 days), and Nerita tessellata (PLD > 60 days). We generated a set of SNPs for the three species using the ddRad-seq technique. Samples of each species were collected in five locations from Capurganá to La Guajira. For the first time, evidence of a phylogeographic break caused by the MRP is provided, mainly for A. rivasi (AMOVA: ΦCT = 0.420). The ARB + PUG barrier causes another break for A. rivasi (ΦCT = 0.406) and C. pica (ΦCT = 0.224). Three populations (K = 3) were identified for A. rivasi and C. pica, while N. tessellata presented one population (K = 1). The Mantel correlogram indicated that A. rivasi and C. pica fit the hierarchical population model, and only the A. rivasi and C. pica comparisons showed phylogeographic congruence. Our results demonstrate how the biological traits of these three species and the biogeographic barriers have influenced their phylogeographic structure.

Spatial coalescent connectivity through multi-generation dispersal modelling predicts gene flow across marine phyla

Gene flow governs the contemporary spatial structure and dynamic of populations as well as their long-term evolution. For species that disperse using atmospheric or oceanic flows, biophysical models allow predicting the migratory component of gene flow, which facilitates the interpretation of broad-scale spatial structure inferred from observed allele frequencies among populations. However, frequent mismatches between dispersal estimates and observed genetic diversity prevent an operational synthesis for eco-evolutionary projections. Here we use an extensive compilation of 58 population genetic studies of 47 phylogenetically divergent marine sedentary species over the Mediterranean basin to assess how genetic differentiation is predicted by Isolation-By-Distance, single-generation dispersal and multi-generation dispersal models. Unlike previous approaches, the latter unveil explicit parents-to-offspring links (filial connectivity) and implicit links among siblings from a common ancestor (coalescent connectivity). We find that almost 70 % of observed variance in genetic differentiation is explained by coalescent connectivity over multiple generations, significantly outperforming other models. Our results offer great promises to untangle the eco-evolutionary forces that shape sedentary population structure and to anticipate climate-driven redistributions, altogether improving spatial conservation planning.

Genetic Structure of the Endangered Coral Cladocora caespitosa Matches the Main Bioregions of the Mediterranean Sea

Population connectivity studies are a useful tool for species management and conservation planning, particular of highly threatened or endangered species. Here, we evaluated the genetic structure and connectivity pattern of the endangered coral Cladocora caespitosa across its entire distribution range in the Mediterranean Sea. Additionally, we examined the relative importance of sexual and asexual reproduction in the studied populations and their genetic diversity. A total of 541 individuals from 20 localities were sampled and analysed with 19 polymorphic microsatellite markers. Of the genotyped individuals, 482 (89%) had unique multilocus genotypes. Clonality percentages of the populations varied from 0% (in eight populations) to nearly 69% (in one population from Crete). A heterozygosity deficit and a high degree of inbreeding was the general trend in our data set. Population differentiation in C. caespitosa was characterised by significant pairwise FST values with lower ones observed at an intraregional scale and higher ones, between populations from different biogeographic regions. Genetic structure analyses showed that the populations are divided according to the three main sub-basins of the Mediterranean Sea: the Western (Balearic, Ligurian and Tyrrhenian seas), the Central (Adriatic and Ionian seas) and the Eastern (Levantine and Aegean seas), coinciding with previously described gene flow barriers. However, the three easternmost populations were also clearly separated from one another, and a substructure was observed for the other studied areas. An isolation-by-distance pattern was found among, but not within, the three main population groups. This substructure is mediated mainly by dispersal along the coastline and some resistance to larval movement through the open sea. Despite the low dispersal ability and high self-recruitment rate of C. caespitosa, casual dispersive events between regions seem to be enough to maintain the species’ considerable genetic diversity. Understanding the population connectivity and structure of this endangered scleractinian coral allows for more informed conservation decision making.

First insight of genetic diversity, phylogeographic relationships, and population structure of marine sponge Chondrosia reniformis from the eastern and western Mediterranean coasts of Tunisia

Despite the strategic localization of Tunisia in the Mediterranean Sea, no phylogeographic study on sponges has been investigated along its shores. The demosponge Chondrosia reniformis, descript only morphologically along Tunisian coasts, was chosen to estimate the influence of natural oceanographic and biogeographic barriers on its genetic differentiation and its Phylogeography. The cytochrome oxidase subunit I (COI) gene was amplified and analyzed for 70 Mediterranean Chondrosia reniformis, collected from eight localities in Tunisia. Polymorphism results revealed high values of haplotype diversity (H d) and very low nucleotide diversity (π). Thus, these results suggest that our sponge populations of C. reniformis may have undergone a bottleneck followed by rapid demographic expansion. This suggestion is strongly confirmed by the results of neutrality tests and "mismatch distribution." The important number of haplotypes between localities and the high genetic differentiation (F st ranged from 0.590 to 0.788) of the current C. reniformis populations could be maintained by the limited gene flow Nm (0.10-0.18). Both haplotype Network and the biogeographic analysis showed a structured distribution according to the geographic origin. C. reniformis populations are subdivided into two major clades: Western and Eastern Mediterranean. This pattern seems to be associated with the well-known discontinuous biogeographic area: the Siculo-Tunisian Strait, which separates two water bodies circulating with different hydrological, physical, and chemical characteristics. The short dispersal of pelagic larvae of C. reniformis and the marine bio-geographic barrier created high differentiation among populations. Additionally, it is noteworthy to mention that the "Mahres/Kerkennah" group diverged from Eastern groups in a single sub-clade. This result was expected, the region Mahres/Kerkennah, presented a particular marine environment.

A star is torn-molecular analysis divides the Mediterranean population of Poli's stellate barnacle, Chthamalus stellatus (Cirripedia, Chtamalidae)

Poli's stellate barnacle, Chthamalus stellatus Poli, populates the Mediterranean Sea, the North-Eastern Atlantic coasts, and the offshore Eastern Atlantic islands. Previous studies have found apparent genetic differences between the Atlantic and the Mediterranean populations of C. stellatus, suggesting possible geological and oceanographic explanations for these differences. We have studied the genetic diversity of 14 populations spanning from the Eastern Atlantic to the Eastern Mediterranean, using two nuclear genes sequences revealing a total of 63 polymorphic sites. Both genotype-based, haplotype-based and the novel SNP distribution population-based methods have found that these populations represent a geographic cline along the west to east localities. The differences in SNP distribution among populations further separates a major western cluster into two smaller clusters, the Eastern Atlantic and the Western Mediterranean. It also separates the major eastern cluster into two smaller clusters, the Mid-Mediterranean and Eastern Mediterranean. We suggested here environmental conditions like surface currents, water salinity and temperature as probable factors that have formed the population structure. We demonstrate that C. stellatus is a suitable model organism for studying how geological events and hydrographic conditions shape the fauna in the Mediterranean Sea.

Population Genetic Structure and Connectivity of the European Lobster Homarus gammarus in the Adriatic and Mediterranean Seas

Highly selective fishing has the potential to permanently change the characteristics within a population and could drive the decline of genetic diversity. European lobster is an intensively fished crustacean species in the Adriatic Sea which reaches high market value. Since knowledge of population structure and dynamics is important for effective fisheries management, in this study, we used 14 neutral microsatellites loci and partial mitochondrial COI region sequencing to explore population connectivity and genetic structure by comparing samples from the Adriatic Sea and the adjacent basins of the Mediterranean Sea. The obtained results suggest that neutral genetic diversity has not been significantly affected by decrease in population size due to overfishing, habitat degradation and other anthropogenic activities. Global genetic differentiation across all populations was low (F ST = 0.0062). Populations from the Adriatic Sea were panmictic, while genetic differentiation was found among populations from different Mediterranean basins. Observed gene flow for European lobster suggest that populations in the north eastern Adriatic act as a source for surrounding areas, emphasizing the need to protect these populations by establishing interconnected MPAs that will be beneficial for both fisheries and conservation management.

Omics approaches for conservation biology research on the bivalve Chamelea gallina

The striped venus (Chamelea gallina) is an important economic resource in the Mediterranean Basin; this species has exhibited a strong quantitative decline in the Adriatic Sea. The aim of this work was to provide a comprehensive view of the biological status of C. gallina to elucidate the bioecological characteristics and genetic diversity of wild populations. To the best of our knowledge, this investigation is the first to perform a multidisciplinary study on C. gallina based on two omics approaches integrated with histological, ecotoxicological, and chemical analyses and with the assessment of environmental parameters. The results obtained through RNA sequencing indicated that the striped venus has a notable ability to adapt to different environmental conditions. Moreover, the stock reduction exhibited by this species in the last 2 decades seems not to have negatively affected its genetic diversity. Indeed, the high level of genetic diversity that emerged from our ddRAD dataset analyses is ascribable to the high larval dispersal rate, which might have played a “compensatory role” on local fluctuations, conferring to this species a good adaptive potential to face the environmental perturbations. These findings may facilitate the efforts of conservation biologists to adopt ad hoc management plans for this fishery resource.

Phylogeography of the mediterranean green seaweed Halimeda tuna (Ulvophyceae, Chlorophyta)

Populations of many Mediterranean marine species show a strong phylogeographic structure, but the knowledge available for native seaweeds is limited. We investigated the genetic diversity of the green alga Halimeda tuna based on two plastid markers (tufA gene and a newly developed amplicon spanning five ribosomal protein genes and intergenic spacers, the rpl2-rpl14 region). The tufA sequences showed that Mediterranean H. tuna represents a single, well-defined species. The rpl2-rpl14 results highlighted a genetic separation between western and eastern Mediterranean populations; specimens collected from widely scattered locations in the Adriatic/Ionian region shared a haplotype unique to this region, and formed a group separated from all western Mediterranean regions. Specimens from Sardinia also formed a unique haplotype. Within the western Mediterranean basin, a gradual shift in the frequency of haplotypes was apparent along a West-East gradient. Our results represent the first clear evidence of an East-West genetic cleavage in a native Mediterranean macroalga and offer an interesting perspective for further research into fine-scale seaweed population structure in the NW Mediterranean Sea.

Genetic and morphological divergence at a biogeographic break in the beach-dwelling brooder Excirolana hirsuticauda Menzies (Crustacea, Peracarida)

BACKGROUND

There is a biogeographic break located at 30°S in the southeast Pacific, in a coastal area of strong environmental discontinuities. Several marine benthic taxa with restricted dispersal have a coincident phylogeographic break at 30°S, indicating that genetic structure is moulded by life history traits that limit gene flow and thereby promote divergence and speciation. In order to evaluate intraspecific divergence at this biogeographic break, we investigated the genetic and morphological variation of the directly developing beach isopod Excirolana hirsuticauda along 1900 km of the southeast Pacific coast, across 30°S.

RESULTS

The COI sequences and microsatellite data both identified a strong discontinuity between populations of E. hirsuticauda to the north and south of 30°S, and a second weaker phylogeographic break at approximately 35°S. The three genetic groups were evidenced by different past demographic and genetic diversity signatures, and were also clearly distinguished with microsatellite data clustering. The COI sequences established that the genetic divergence of E. hirsuticauda at 30°S started earlier than divergence at 35°. Additionally, the three groups have different past demographic signatures, with probable demographic expansion occurring earlier in the southern group (south of 35°S), associated with Pleistocene interglacial periods. Interestingly, body length, multivariate morphometric analyses, and the morphology of a fertilization-related morphological character in males, the appendix masculina, reinforced the three genetic groups detected with genetic data.

CONCLUSIONS

The degree of divergence of COI sequences, microsatellite data, and morphology was concordant and showed two geographic areas in which divergence was promoted at differing historical periods. Variation in the appendix masculina of males has probably promoted reproductive isolation. This variation together with gene flow restrictions promoted by life history traits, small body size, oceanographic discontinuities and sandy-beach habitat continuity, likely influenced species divergence at 30°S in the southeast Pacific coast. The degree of genetic and morphological differentiation of populations to the north and south of 30°S suggests that E. hirsuticauda harbours intraspecific divergence consistent with reproductive isolation and an advanced stage of speciation. The speciation process within E. hirsuticauda has been shaped by both restrictions to gene flow and a prezygotic reproductive barrier.

Connectivity Among Populations of the Top Shell Gibbula divaricata in the Adriatic Sea

Genetic connectivity studies are essential to understand species diversity and genetic structure and to assess the role of potential factors affecting connectivity, thus enabling sound management and conservation strategies. Here, we analyzed the patterns of genetic variability in the marine snail Gibbula divaricata from five coastal locations in the central-south Adriatic Sea (central Mediterranean) and one in the adjacent northern Ionian Sea, using 21 described polymorphic microsatellite loci. Observed and expected heterozygosity varied from 0.582 to 0.635 and 0.684 to 0.780, respectively. AMOVA analyses showed that 97% of genetic variation was observed within populations. Nevertheless, significant, although small, genetic differentiation was found among nearly all of the pairwise F ST comparisons. Over a general pattern of panmixia, three groups of populations were identified: eastern Adriatic populations, western Adriatic populations, and a third group represented by the single northern Ionian Sea population. Nonetheless, migration and gene flow were significant between these groups. Gibbula divaricata is thought to have a limited dispersal capacity related to its lecithotrophic trochophore larval stage. Our results indicated high levels of self-recruitment and gene flow that is mainly driven through coastline dispersion, with populations separated by the lack of suitable habitats or deep waters. This stepping-stone mode of dispersion together with the high levels of self-recruitment could lead to higher levels of population structuring and differentiation along the Adriatic Sea. Large effective population sizes and episodic events of long-distance dispersal might be responsible for the weak differentiation observed in the analyzed populations. In summary, the circulation system operating in this region creates natural barriers for dispersion that, together with life-history traits and habitat requirements, certainly affect connectivity in G. divaricata. However, this scenario of potential differentiation seems to be overridden by sporadic events of long-distance dispersal across barriers and large effective population sizes.

Genetic diversity, connectivity and gene flow along the distribution of the emblematic Atlanto-Mediterranean sponge Petrosia ficiformis (Haplosclerida, Demospongiae)

BACKGROUND

Knowledge about the distribution of the genetic variation of marine species is fundamental to address species conservation and management strategies, especially in scenarios with mass mortalities. In the Mediterranean Sea, Petrosia ficiformis is one of the species most affected by temperature-related diseases. Our study aimed to assess its genetic structure, connectivity, and bottleneck signatures to understand its evolutionary history and to provide information to help design conservation strategies of sessile marine invertebrates.

RESULTS

We genotyped 280 individuals from 19 locations across the entire distribution range of P. ficiformis in the Atlanto-Mediterranean region at 10 microsatellite loci. High levels of inbreeding were detected in most locations (especially in the Macaronesia and the Western Mediterranean) and bottleneck signatures were only detected in Mediterranean populations, although not coinciding entirely with those with reported die-offs. We detected strong significant population differentiation, with the Atlantic populations being the most genetically isolated, and show that six clusters explained the genetic structure along the distribution range of this sponge. Although we detected a pattern of isolation by distance in P. ficiformis when all locations were analyzed together, stratified Mantel tests revealed that other factors could be playing a more prominent role than isolation by distance. Indeed, we detected a strong effect of oceanographic barriers impeding the gene flow among certain areas, the strongest one being the Almeria-Oran front, hampering gene flow between the Atlantic Ocean and the Mediterranean Sea. Finally, migration and genetic diversity distribution analyses suggest a Mediterranean origin for the species.

CONCLUSIONS

In our study Petrosia ficiformis showed extreme levels of inbreeding and population differentiation, which could all be linked to the poor swimming abilities of the larva. However, the observed moderate migration patterns are highly difficult to reconcile with such poor larval dispersal, and suggest that, although unlikely, dispersal may also be achieved in the gamete phase. Overall, because of the high genetic diversity in the Eastern Mediterranean and frequent mass mortalities in the Western Mediterranean, we suggest that conservation efforts should be carried out specifically in those areas of the Mediterranean to safeguard the genetic diversity of the species.

Spatio-temporal patterns of genetic variation in Arbacia lixula, a thermophilous sea urchin in expansion in the Mediterranean

The genetic structure of 13 populations of the amphiatlantic sea urchin Arbacia lixula, as well as temporal genetic changes in three of these localities, were assessed using ten hypervariable microsatellite loci. This thermophilous sea urchin is an important engineer species triggering the formation of barren grounds through its grazing activity. Its abundance seems to be increasing in most parts of the Mediterranean, probably favoured by warming conditions. Significant genetic differentiation was found both spatially and temporally. The main break corresponded to the separation of western Atlantic populations from those in eastern Atlantic and the Mediterranean Sea. A less marked, but significant differentiation was also found between Macaronesia (eastern Atlantic) and the Mediterranean. In the latter area, a signal of differentiation between the transitional area (Alboran Sea) and the rest of the Mediterranean was detected. However, no genetic structure is found within the Mediterranean (excluding Alboran) across the Siculo-Tunisian Strait, resulting from either enough gene flow to homogenize distance areas or/and a recent evolutionary history marked by demographic expansion in this basin. Genetic temporal variation at the Alboran Sea is as important as spatial variation, suggesting that temporal changes in hydrological features can affect the genetic composition of the populations. A picture of genetic homogeneity in the Mediterranean emerges, implying that the potential expansion of this keystone species will not be limited by intraspecific genetic features and/or potential impact of postulated barriers to gene flow in the region.

Chasing genetic structure in coralligenous reef invertebrates: patterns, criticalities and conservation issues

Conservation of coastal habitats is a global issue, yet biogenic reefs in temperate regions have received very little attention. They have a broad geographic distribution and are a key habitat in marine ecosystems impacted by human activities. In the Mediterranean Sea coralligenous reefs are biodiversity hot spots and are classified as sensitive habitats deserving conservation. Genetic diversity and structure influence demographic, ecological and evolutionary processes in populations and play a crucial role in conservation strategies. Nevertheless, a comprehensive view of population genetic structure of coralligenous species is lacking. Here, we reviewed the literature on the genetic structure of sessile and sedentary invertebrates of the Mediterranean coralligenous reefs. Linear regression models and meta-analytic approaches are used to assess the contributions of genetic markers, phylum, pelagic larval duration (PLD) and geographical distance to the population genetic structure. Our quantitative approach highlight that 1) most species show a significant genetic structure, 2) structuring differs between phyla, and 3) PLD does not appear to be a major driver of the structuring. We discuss the implication of these finding for the management and conservation, suggesting research areas that deserve attention, and providing recommendations for broad assessment and monitoring of genetic diversity in biogenic reefs species.

A multispecies approach reveals hot spots and cold spots of diversity and connectivity in invertebrate species with contrasting dispersal modes

Genetic diversity is crucial for species' maintenance and persistence, yet is often overlooked in conservation studies. Species diversity is more often reported due to practical constraints, but it is unknown if these measures of diversity are correlated. In marine invertebrates, adults are often sessile or sedentary and populations exchange genes via dispersal of gametes and larvae. Species with a larval period are expected to have more connected populations than those without larval dispersal. We assessed the relationship between measures of species and genetic diversity, and between dispersal ability and connectivity. We compiled data on genetic patterns and life history traits in nine species across five phyla. Sampling sites spanned 600 km in the northwest Mediterranean Sea and focused on a 50-km area near Marseilles, France. Comparative population genetic approaches yielded three main results. (i) Species without larvae showed higher levels of genetic structure than species with free-living larvae, but the role of larval type (lecithotrophic or planktotrophic) was negligible. (ii) A narrow area around Marseilles, subject to offshore advection, limited genetic connectivity in most species. (iii) We identified sites with significant positive contributions to overall genetic diversity across all species, corresponding with areas near low human population densities. In contrast, high levels of human activity corresponded with a negative contribution to overall genetic diversity. Genetic diversity within species was positively and significantly linearly related to local species diversity. Our study suggests that local contribution to overall genetic diversity should be taken into account for future conservation strategies.

Evidence for rangewide panmixia despite multiple barriers to dispersal in a marine mussel

Oceanographic features shape the distributional and genetic patterns of marine species by interrupting or promoting connections among populations. Although general patterns commonly arise, distributional ranges and genetic structure are species-specific and do not always comply with the expected trends. By applying a multimarker genetic approach combined with Lagrangian particle simulations (LPS) we tested the hypothesis that oceanographic features along northeastern Atlantic and Mediterranean shores influence dispersal potential and genetic structure of the intertidal mussel Perna perna. Additionally, by performing environmental niche modelling we assessed the potential and realized niche of P. perna along its entire native distributional range and the environmental factors that best explain its realized distribution. Perna perna showed evidence of panmixia across >4,000 km despite several oceanographic breaking points detected by LPS. This is probably the result of a combination of life history traits, continuous habitat availability and stepping-stone dynamics. Moreover, the niche modelling framework depicted minimum sea surface temperatures (SST) as the major factor shaping P. perna distributional range limits along its native areas. Forthcoming warming SST is expected to further change these limits and allow the species to expand its range polewards though this may be accompanied by retreat from warmer areas.

Assessing larval connectivity for marine spatial planning in the Adriatic

There are plans to start building offshore marine renewable energy devices throughout the Mediterranean and the Adriatic has been identified as a key location for wind farm developments. The development of offshore wind farms in the area would provide hard substrata for the settlement of sessile benthos. Since the seafloor of the Adriatic is predominantly sedimentary this may alter the larval connectivity of benthic populations in the region. Here, we simulated the release of larvae from benthic populations along the coasts of the Adriatic Sea using coupled bio-physical models and investigated the effect of pelagic larval duration on dispersal. Our model simulations show that currents typically carry particles from east to west across the Adriatic, whereas particles released along western coasts tend to remain there with the Puglia coast of Italy acting as a sink for larvae from benthic populations. We identify areas of high connectivity, as well as areas that are much more isolated, and discuss how these results can be used to inform marine spatial planning and the licensing of offshore marine renewable energy developments.

Habitat continuity and stepping-stone oceanographic distances explain population genetic connectivity of the brown alga Cystoseira amentacea

Effective predictive and management approaches for species occurring in a metapopulation structure require good understanding of interpopulation connectivity. In this study, we ask whether population genetic structure of marine species with fragmented distributions can be predicted by stepping-stone oceanographic transport and habitat continuity, using as model an ecosystem-structuring brown alga, Cystoseira amentacea var. stricta. To answer this question, we analysed the genetic structure and estimated the connectivity of populations along discontinuous rocky habitat patches in southern Italy, using microsatellite markers at multiple scales. In addition, we modelled the effect of rocky habitat continuity and ocean circulation on gene flow by simulating Lagrangian particle dispersal based on ocean surface currents allowing multigenerational stepping-stone dynamics. Populations were highly differentiated, at scales from few metres up to thousands of kilometres. The best possible model fit to explain the genetic results combined current direction, rocky habitat extension and distance along the coast among rocky sites. We conclude that a combination of variable suitable habitat and oceanographic transport is a useful predictor of genetic structure. This relationship provides insight into the mechanisms of dispersal and the role of life-history traits. Our results highlight the importance of spatially explicit modelling of stepping-stone dynamics and oceanographic directional transport coupled with habitat suitability, to better describe and predict marine population structure and differentiation. This study also suggests the appropriate spatial scales for the conservation, restoration and management of species that are increasingly affected by habitat modifications.

Low genetic diversity and recent demographic expansion in the red starfish Echinaster sepositus (Retzius 1816)

Understanding the phylogeography and genetic structure of populations and the processes responsible of patterns therein is crucial for evaluating the vulnerability of marine species and developing management strategies. In this study, we explore how past climatic events and ongoing oceanographic and demographic processes have shaped the genetic structure and diversity of the Atlanto-Mediterranean red starfish Echinaster sepositus. The species is relatively abundant in some areas of the Mediterranean Sea, but some populations have dramatically decreased over recent years due to direct extraction for ornamental aquariums and souvenir industries. Analyses across most of the distribution range of the species based on the mitochondrial cytochrome c oxidase subunit I gene and eight microsatellite loci revealed very low intraspecific genetic diversity. The species showed a weak genetic structure within marine basins despite the a priori low dispersal potential of its lecithotrophic larva. Our results also revealed a very recent demographic expansion across the distribution range of the species. The genetic data presented here indicate that the species might be highly vulnerable, due to its low intraspecific genetic diversity.

Population structure and connectivity in the Mediterranean sponge Ircinia fasciculata are affected by mass mortalities and hybridization

Recent episodes of mass mortalities in the Mediterranean Sea have been reported for the closely related marine sponges Ircinia fasciculata and Ircinia variabilis that live in sympatry. In this context, the assessment of the genetic diversity, bottlenecks and connectivity of these sponges has become urgent in order to evaluate the potential effects of mass mortalities on their latitudinal range. Our study aims to establish (1) the genetic structure, connectivity and signs of bottlenecks across the populations of I. fasciculata and (2) the hybridization levels between I. fasciculata and I. variabilis. To accomplish the first objective, 194 individuals of I. fasciculata from 12 locations across the Mediterranean were genotyped at 14 microsatellite loci. For the second objective, mitochondrial cytochrome c oxidase subunit I sequences of 16 individuals from both species were analyzed along with genotypes at 12 microsatellite loci of 40 individuals coexisting in 3 Mediterranean populations. We detected strong genetic structure along the Mediterranean for I. fasciculata, with high levels of inbreeding in all locations and bottleneck signs in most locations. Oceanographic barriers like the Almeria-Oran front, North-Balearic front and the Ligurian-Thyrrenian barrier seem to be impeding gene flow for I. fasciculata, adding population divergence to the pattern of isolation by distance derived from the low dispersal abilities of sponge larvae. Hybridization between both species occurred in some populations that might be increasing genetic diversity and somewhat palliating the genetic loss caused by population decimation in I. fasciculata.

Contrasted phylogeographic patterns on mitochondrial DNA of shallow and deep brittle stars across the Atlantic-Mediterranean area

Previous studies on Ophiothrix in European waters demonstrated the existence of two distinct species, Ophiothrix fragilis and Ophiothrix sp. II. Using phylogenetic and species delimitation techniques based on two mitochondrial genes (cytochrome c oxidase I and 16S rRNA) we prove the existence of a new congeneric species (Ophiothrix sp. III), occurring in the deep Atlantic coast of the Iberian Peninsula and the Alboran Sea. We compared phylogeographic patterns of these three Ophiothrix species to test whether closely related species are differentially affected by past demographic events and current oceanographic barriers. We used 432 sequences (137 of O. fragilis, 215 of Ophiothrix sp. II, and 80 of Ophiothrix sp. III) of the 16S rRNA from 23 Atlantic-Mediterranean locations for the analyses. We observed different geographic and bathymetric distributions, and contrasted phylogeography among species. Ophiothrix fragilis appeared genetically isolated between the Atlantic and Mediterranean basins, attributed to past vicariance during Pleistocene glaciations and a secondary contact associated to demographic expansion. This contrasts with the panmixia observed in Ophiothrix sp. II across the Atlantic-Mediterranean area. Results were not conclusive for Ophiothrix sp. III due to the lack of a more complete sampling within the Mediterranean Sea.

Octopus vulgaris (Cuvier, 1797) in the Mediterranean Sea: Genetic Diversity and Population Structure

The common octopus, Octopus vulgaris Cuvier 1797, is a largely exploited cephalopod species in the Mediterranean Sea and the Atlantic Ocean, as well as along the coasts of Africa, Brazil and Japan, where its taxonomic identity is still debated. The assessment of its genetic structure is a pressing need to correctly manage the resource and to avoid overfishing and collapsing of local stocks. Here we analysed genetic variation and population structure of O. vulgaris using thirteen microsatellite loci in seven sampling localities from the Mediterranean Sea and one from the Atlantic Ocean. We also used a DNA barcoding approach by COI gene fragment to understand the phylogenetic relationships among the specimens here investigated and the ones whose sequences are available in literature. Our results reveal high levels of allelic richness and moderate heterozygosity in all samples investigated, and a pronounced differentiation of the Atlantic and Sicilian specimens. This latter aspect seems to support the isolation of the biota within the Strait of Messina. A certain degree of differentiation was detected among the other geographic samples within the Mediterranean Sea, which is more compatible with an island model than isolation by distance. The occurrence of null alleles affected more genetic diversity indices than population structure estimations. This study provides new insights about the genetic diversity and structure of O. vulgaris in the area of interest, which can be used as guidelines for a fisheries management perspective.