Atlantic-Mediterranean Region Research Articles

Exceptional population genomic homogeneity in the black brittle star Ophiocomina nigra (Ophiuroidea, Echinodermata) along the Atlantic-Mediterranean coast

The Atlantic-Mediterranean marine transition is characterised by strong oceanographic barriers and steep environmental gradients that generally result in connectivity breaks between populations from both basins and may lead to local adaptation. Here, we performed a population genomic study of the black brittle star, Ophiocomina nigra, covering most of its distribution range along the Atlantic-Mediterranean region. Interestingly, O. nigra is extremely variable in its coloration, with individuals ranging from black to yellow-orange, and different colour morphs inhabiting different depths and habitats. In this work, we used a fragment of the mitochondrial COI gene and 2,374 genome-wide ddRADseq-derived SNPs to explore: (a) whether the different colour morphs of O. nigra represent different evolutionary units; (b) the disruptive effects of major oceanographic fronts on its population structure; and (c) genomic signals of local adaptation to divergent environments. Our results revealed exceptional population homogeneity, barely affected by oceanographic fronts, with no signals of local adaptation nor genetic differentiation between colour morphs. This remarkable panmixia likely results from a long pelagic larval duration, a large effective population size and recent demographic expansions. Our study unveils an extraordinary phenotypic plasticity in O. nigra, opening further research questions on the ecological and molecular mechanisms underpinning coloration in Ophiuroidea.

On some “Hemicyclopora” Norman, 1894 and “Escharella” Gray, 1848 species (Bryozoa, Cheilostomatida) from the Atlantic-Mediterranean region. Re-examination of their generic status and description of new species and a new genus

Sur quelques espèces d'“Hemicyclopora” et d'“Escharella” (Bryozoa, Cheilostomatida) de la région atlanticoméditerranéenne. Réexamen de leur statut générique et description de nouvelles espèces et d'un nouveau genre. Il est admis depuis longtemps que les genres de bryozoaires chéilostomes Hemicyclopora Norman, 1894 et Escharella Gray, 1848 se différencient par la présence d'une lyrule dans l'orifice des autozooides d'Escharella. L'examen d'un abondant matériel de Méditerranée et de l'Atlantique NE en utilisant des critères spécifiques réévalués a révélé une diversité insoupçonnée impliquant plusieurs espèces non-décrites, typiques du genre Hemicyclopora, mais aussi des espèces présentant des caractères morphologiques intermédiaires entre les deux genres ci-dessus. Globalement, la diversité du matériel examiné comprend dix espèces, dont cinq nouvelles (Hemicyclopora neatonensis n. sp., H. hexaspinae n. sp., “Hemicyclopora” celtica n. sp., “H.” pytheasi n. sp., “Escharella” massiliana n. sp.), et deux espèces non décrites par manque de matériel suffisant. Un nouveau genre, Scutocyclopora n. gen., est érigé pour l'espèce méditerranéenne Hemicyclopora dentata López de la Cuadra & García-Gómez, 1991, dont les caractères divergent par l'absence d'épines orales et la production d'une ancestrule non tatiforme. Six espèces sont considérées dans le matériel méditerranéen (5-205 m) et sept espèces dans le matériel atlantique (128-1050 m). Toutes ces espèces vivent en eau profonde sur des petits substrats peu éclairés, principalement d'origine biogène, à l'exception de deux espèces en Méditerranée (H. hexaspinae n. sp., S. dentata (López de la Cuadra & García-Gómez, 1991) n. comb.), qui peuvent aussi vivre à faible profondeur dans des grottes sous-marines obscures.

Unexpected diversity of the genus Collarina Jullien, 1886 (Bryozoa, Cheilostomatida) in the NE Atlantic-Mediterranean region: new species and reappraisal of C. balzaci (Audouin, 1826) and C. fayalensis Harmelin, 1978

The genus CollarinaJullien, 1886 (Cribrilinidae Hincks, 1879) has until now been known from the Atlantic-Mediterranean region as just two species, C. balzaci (Audouin, 1826), synonym of Collarina cribrosaJullien, 1886, type species of the genus, considered to be widely distributed from the northern British Isles to the SE Mediterranean, and C. fayalensis Harmelin, 1978 from the Macaronesian Isles. Abundant material collected in the Mediterranean and the NE Atlantic, coupled with examination of museum specimens, allowed better definition of the species-specific morphological features in this genus and some generic traits (ooecium formation, avicularia with nested cystids). Besides the redescription of C. balzaci and C. fayalensis, this study led to the description of four new species: C. denticulata Harmelin, n. sp., recorded only in the Mediterranean, C. gautieri Harmelin, n. sp., present in both the NE Atlantic and the Mediterranean, C. macaronensis Harmelin, n. sp., from Madeira, Azores and Galicia, and C. speluncola Harmelin, n. sp., from the Mediterranean and the Gulf of Cadiz. A seventh morphotype (Collarina sp., from the Mediterranean, seemingly close to C. speluncola Harmelin, n. sp., has been left unnamed pending the availability of more abundant material. It was proven that C. balzaci: 1) has often been confused with C. gautieri Harmelin, n. sp.; 2) is exclusively epiphytic (mainly on Posidonia oceanica (L.) Delile, 1813 and brown seaweeds), with life-cycle adapted to ephemeral hosts; 3) is widely distributed in the Mediterranean, but also present in the Canaries on seaweeds, and has probably been overlooked in similar habitats in other warm-temperate NE Atlantic localities; and 4) is able to proliferate dramatically on Posidonia leaves in association with diatoms under unusual environmental conditions (Gulf of Gabes, chemical disturbance). All Collarina species live in coastal areas, mostly at shallow depth, in shaded microhabitats: plants (C. balzaci), dark cave walls (C. speluncola Harmelin, n. sp.) and small hard substrates, e.g. shells, pebbles, and anthropogenic debris (all other species).

Improved phylogeny of brown algae Cystoseira (Fucales) from the Atlantic-Mediterranean region based on mitochondrial sequences.

Cystoseira is a common brown algal genus widely distributed throughout the Atlantic and Mediterranean regions whose taxonomical assignment of specimens is often hampered by intra- and interspecific morphological variability. In this study, three mitochondrial regions, namely cytochrome oxidase subunit 1 (COI), 23S rDNA (23S), and 23S-tRNAVal intergenic spacer (mt-spacer) were used to analyse the phylogenetic relationships of 22 Cystoseira taxa (n = 93 samples). A total of 135 sequences (48 from COI, 43 from 23S and 44 from mt-spacer) were newly generated and analysed together with Cystoseira sequences (9 COI, 31 23S and 35 mt-spacer) from other authors. Phylogenetic analysis of these three markers identified 3 well-resolved clades and also corroborated the polyphyletic nature of the genus. The resolution of Cystoseira taxa within the three clades improves significantly when the inclusion of specimens of related genera was minimized. COI and mt-spacer markers resolved the phylogeny of some of the Cystoseira taxa, such as the C. baccata, C. foeniculacea and C. usneoides. Furthermore, trends between phylogeny, embryonic development and available chemotaxonomic classifications were identified, showing that phylogenetic, chemical and morphological data should be taken into account to study the evolutionary relationships among the algae currently classified as Cystoseira. The resolution of Cystoseira macroalgae into three well supported clades achieved here is relevant for a more accurate isolation and identification of natural compounds and the implementation of conservation measures for target species.

Using a phylogeographic approach to investigate the diversity and determine the distributional range of an isopod (Crustacea: Peracarida), Stenosoma nadejda (Rezig, 1989) in the Atlantic-Mediterranean region

The genus Stenosoma comprises 13 species in the NE Atlantic, Mediterranean and Black Sea. Recent studies have improved knowledge on the distributional patterns of the genus, reducing species ranges and allowing the identification of cryptic species. Lacking a free-swimming life-stage, Stenosoma typically display small- to medium-sized ranges, with the exception of S. nadejda which occurs in the Atlantic-Mediterranean region. In this study, we build upon previous work and examine phylogeographic patterns of S. nadejda throughout its entire range to assess levels of genetic differentiation and evidence of cryptic species. While Elongation Factor 1α gene sequences revealed an almost absence of genetic and geographic structure across the entire distribution of S. nadejda, the Cytochrome c oxidase subunit I gene sequences revealed a phylogenetic split defining two Mediterranean clades. Our results confirm the wide distribution of S. nadejda in the Atlantic/Mediterranean region and show that the distribution of the two Mediterranean clades does not match the east–west break in genetic continuity typically displayed by many species. This pattern is probably a consequence of sporadic long-distance dispersal by rafting. Conversely, an almost absence of shared haplotypes at the local level, conforms to the recognized poor ability of peracarids for autonomous dispersal.

New and little known species of Celleporina Gray, 1848 (Bryozoa, Cheilostomata) from the Atlantic–Mediterranean region

Celleporina parvula, a species present in shallow waters along the NW African coast, is re-described from its original material. Celleporina fragilis, only known from the Canaries, and Celleporina derungsi, from south Portugal, are newly reported from the Gorringe Bank and NW Iberian Peninsula respectively. Two new species are described: Celleporina algarvensis n. sp., from south Portugal, and Celleporina mediterranea n. sp., from NW Mediterranean. The structure of the ooecium and its tabula, and the structure of the frontal wall in the genus Celleporina are discussed in the light of new observations.

Summer distribution and abundance of the giant devil ray (<em>Mobula mobular</em>) in the Adriatic Sea: Baseline data for an iterative management framework

The giant devil ray ( Mobula mobular ) is a poorly understood protected endemic species of the eastern Atlantic-Mediterranean region. However, to date there are no range-wide management actions in place. This paper provides the first overview of the summer distribution and abundance of this species and other Myliobatiformes within the Adriatic Sea based on an aerial survey. Although the survey´s primary targets were cetaceans and sea turtles, the study showed that it was possible to use the survey to monitor other species. Abundance estimates are derived using conventional distance sampling analysis. Giant devil rays were observed mainly in the central-southern Adriatic (88% of total sightings). A total of 1595 giant devil rays were estimated in the central-southern Adriatic Sea [coefficient of variation(CV)=25%, uncorrected estimate for perception and availability bias]. When corrected for availability bias the number of specimens was estimated at 3255 (CV=56%). Population growth rate was estimated using life history traits and a sensitivity analysis was conducted to evaluate the benefit of improving biological knowledge on this data-poor species. A power analysis showed that a long-term commitment to an aerial survey would be necessary to monitor population trends. Conservation implications and future work, including how the study could be used to conduct an ecological risk assessment are discussed.

Phylogenetics and biogeography of the Balkan ‘sand gobies’ (Teleostei: Gobiidae): vulnerable species in need of taxonomic revision

Within the Atlantic–Mediterranean region, the ‘sand gobies’ are abundant and widespread, and play an important role in marine, brackish, and freshwater ecosystems. They include the smallest European freshwater fish, Economidichthys trichonis, which is threatened by habitat loss and pollution, as are several other sand gobies. Key to good conservation management is an accurate account of the number of evolutionary significant units. Nevertheless, many taxonomic and evolutionary questions remain unresolved within the clade, and molecular studies are lacking, especially in the Balkans. Using partial 12S and 16S mitochondrial ribosomal DNA sequences of 96 specimens of at least eight nominal species (both freshwater and marine populations), we assess species relationships and compare molecular and morphological data. The results obtained do not support the monophyly of Economidichthys, suggesting the perianal organ to be a shared adaptation to hole-brooding rather than a synapomorphy, and urge for a taxonomic revision of Knipowitschia. The recently described Knipowitschia montenegrina seems to belong to a separate South-East Adriatic lineage. Knipowitschia milleri, an alleged endemic of the Acheron River, and Knipowitschia cf. panizzae, are shown to be very closely related to other western Greek Knipowitschia populations, and appear conspecific. A distinct Macedonian–Thessalian lineage is formed by Knipowitschia thessala, whereas Knipowitschia caucasica appears as an eastern lineage, with populations in Thrace and the Aegean. The present study combines the phylogeny of a goby radiation with insights on the historical biogeography of the eastern Mediterranean, and identifies evolutionary units meriting conservation attention. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 73–91.

The SST Multidecadal Variability in the Atlantic–Mediterranean Region and Its Relation to AMO

Abstract Two sea surface temperature (SST) time series, the Extended Reconstructed SST version 3 (ERSST.v3) and the Hadley Centre Sea Ice and Sea Surface Temperature dataset (HadISST), are used to investigate SST multidecadal variability in the Mediterranean Sea and to explore possible connections with other regions of the global ocean. The consistency between these two time series and the original International Comprehensive Ocean–Atmosphere Dataset version 2.5 (ICOADS 2.5) over the Mediterranean Sea is investigated, evaluating differences from monthly to multidecadal scales. From annual to longer time scales, the two time series consistently describe the same trends and multidecadal oscillations and agree with Mediterranean ICOADS SSTs. At monthly time scales the two time series are less consistent with each other because of the evident annual cycle that characterizes their difference. The subsequent analysis of the Mediterranean annual SST time series, based on lagged-correlation analysis, multitaper method (MTM), and singular spectral analysis (SSA), revealed the presence of a significant oscillation with a period of about 70 yr, very close to that of the Atlantic multidecadal oscillation (AMO). An extension of the analysis to other World Ocean regions confirmed that the predominance of this multidecadal signal with respect to longer period trends is a unique feature of the Mediterranean and North Atlantic Ocean, where it reaches its maximum at subpolar latitudes. Signatures of multidecadal oscillations are also found in the global SST time series after removing centennial and longer-term components. The analysis also reveals that Mediterranean SST and North Atlantic indices are significantly correlated and coherent for periods longer than about 40 yr. For time scales in the range 40–55 yr the coherence between the Mediterranean and subpolar gyre temperatures is higher than the coherence between the Mediterranean SST and North Atlantic Oscillation (NAO) or AMO. Finally, the results of the analysis are discussed in the light of possible climate mechanisms that can couple the Mediterranean Sea with the North Atlantic and the Global Ocean.

Holocene interdependences of changes in sea surface temperature, productivity, and fluvial inputs in the Iberian continental shelf (Tagus mud patch)

Sea surface temperature (SST), marine productivity, and fluvial input have been reconstructed for the last 11.5 calendar (cal) ka B.P. using a high‐resolution study of C37 alkenones, coccolithophores, iron content, and higher plant n‐alkanes and n‐alkan‐1‐ols in sedimentary sequences from the inner shelf off the Tagus River Estuary in the Portuguese Margin. The SST record is marked by a continuous decrease from 19°C, at 10.5 and 7 ka, to 15°C at present. This trend is interrupted by a fall from 18°C during the Roman and Medieval Warm Periods to 16°C in the Little Ice Age. River input was very low in the early Holocene but increased in the last 3 cal ka B.P. in association with an intensification of agriculture and deforestation and possibly the onset of the North Atlantic Oscillation/Atlantic Multidecadal Oscillation modes of variability. River influence must have reinforced the marine cooling trend relative to the lower amplitude in similar latitude sites of the eastern Atlantic. The total concentration of alkenones reflects river‐induced productivity, being low in the early Holocene but increasing as river input became more important. Rapid cooling, of 1–2°C occurring in 250 years, is observed at 11.1, 10.6, 8.2, 6.9, and 5.4 cal ka B.P. The estimated age of these events matches the ages of equivalent episodes common in the NE Atlantic–Mediterranean region. This synchronicity reveals a common widespread climate feature, which considering the twentieth century analog between colder SSTs and negative North Atlantic Oscillation (NAO), is likely to reflect periods of strong negative NAO.

Demosponge distribution in the eastern Mediterranean: a NW–SE gradient

The purpose of this paper was to investigate patterns of demosponge distribution along gradients of environmental conditions in the biogeographical subzones of the eastern Mediterranean (Aegean and Levantine Sea). The Aegean Sea was divided into six major areas on the basis of its geomorphology and bathymetry. Two areas of the Levantine Sea were additionally considered. All available data on demosponge species numbers and abundance in each area, as well as their vertical and general geographical distribution were taken from the literature. Multivariate analysis revealed a NW–SE faunal gradient, showing an apparent dissimilarity among the North Aegean, the South Aegean and the Levantine Sea, which agrees with the differences in the geographical, physicochemical and biological characteristics of the three areas. The majority of demosponge species has been recorded in the North Aegean, while the South Aegean is closer, in terms of demosponge diversity, to the oligotrophic Levantine Sea. The number of studies in the Aegean and Levantine subareas was positively correlated with the number of species recorded within each Aegean subarea. Demosponge species with an Altanto-Mediterranean distribution prevailed in the Aegean and the Levantine. The reduced contribution of the endemic component, as compared to the western Mediterranean, is consistent with the general NW–SE decrease in the number of endemic species in the Mediterranean. Demosponge distribution at the order level showed also a NW–SE gradient, similar to that observed in the entire Atlantic–Mediterranean region, suggesting a warm water affinity. Sublittoral, circalittoral and bathyal zones were clearly distinguishable in the Aegean Sea on the basis of their sponge fauna. The total number of species was an exponential negative function of depth.

Comparative phylogeography of Atlantic bluefin tuna and swordfish: the combined effects of vicariance, secondary contact, introgression, and population expansion on the regional phylogenies of two highly migratory pelagic fishes

Comparative phylogeography has revealed remarkable patterns of concordance in the maternal phylogenies of many species. The phylogeography and historical demography of the mitochondrial control region I for 607 Atlantic bluefin tuna ( Thunnus thynnus) and 275 swordfish ( Xiphias gladius) were analyzed to clarify the complex phylogenetic signals in the North Atlantic–Mediterranean region where they are sympatric. Atlantic bluefin tuna mtDNA is polyphyletic, and includes rare sequences sister to Pacific bluefin tuna ( Thunnus orientalis) and introgressed albacore ( Thunnus alalunga) sequences. There is no geographic partitioning between Atlantic and Mediterranean samples of Atlantic bluefin tuna ( Φ ST = 0.002). In contrast, Atlantic and Mediterranean swordfish are differentiated ( Φ ST = 0.091) due to the combined effects of vicariance, secondary contact, and dissimilar regional demographic histories. Mediterranean swordfish has substantially less variation, and a more recent history ( τ = 2.42) than that of Atlantic swordfish ( τ = 7.02). In spite of the discordant phylogenetic and phylogeographic signals, the demographic history of Atlantic swordfish and Atlantic bluefin tuna ( τ = 7.51) suggests concordance in the timeline of population expansion. Possible scenarios of cladogenesis, expansion, and contraction, influenced by glacial cycles during the Pleistocene, are formulated.

Factors influencing latitudinal pattern of biodiversity: an example using Sabellidae (Annelida, Polychaeta)

The ‘latitudinal gradient of biodiversity’ hypothesis was tested utilising the geographical distribution of species taxa belonging to the family Sabellidae (Annelida: Polychaeta), one of the polychaete families studied by only a few specialists around the world. An increase in species richness towards the Tropical region was revealed, with an asymmetric distribution between the two hemispheres. Data show that most of the species were found in Northern latitudes, producing a Northern area much richer than the Southern one. The Atlantic-Mediterranean Region was particularly rich, with the number of species close to those from the Indo-Pacific Region. Mediterranean species richness is discussed in the light of the particular history of the basin, also emphasising the importance of naturalistic studies that have made the Mediterranean marine flora and fauna one of the best known in the world. The existence of ‘extrinsic factors’ that obscure the real pattern of distributions is hypothesised. Differences found between the two hemispheres could be attributed primarily to the higher number of specialists working in the Boreal Domains, including the Mediterranean area. Global trends produced by some representative genera are also discussed with respect to the distribution of the taxonomic specialists.

Paleoclimatic history and vicariant speciation in the “sand goby” group (Gobiidae, Teleostei)

Vicariant and climatic cycling speciation hypotheses of the ‘sand gobies’ belonging to the genera Pomatoschistus, Gobiusculus, Knipowitschia, and Economidichthys are tested using molecular phylogenies constructed of nuclear DNA (ITS1 locus) and mitochondrial DNA (12S and 16S fragments). These gobies are among the most abundant in the Eastern Atlantic-Mediterranean region, and play an important role in the ecosystem. Considerable ITS1 length differences, primarily due to the presence of several tandem repeats, were found between species and even within individuals. Therefore, phylogenetic analyses focused on fragments of the 12S and 16S mtDNA region that have been sequenced for 16 goby taxa. The ‘sand gobies’ clustered as a monophyletic group as proposed on morphological grounds. However, G. flavescens, E. pygmaeus, and K. punctatissima clustered within the Pomatoschistus species, pointing to a paraphyletic origin of these genera. Furthermore, the genetic divergence between P. minutus from the Adriatic Sea versus the Atlantic-Mediterranean region was as high as the divergence within the P. minutus complex, suggesting that P. minutus from the Adriatic Sea should be considered as a distinct species. The “star” phylogeny might suggest that these gobies evolved in a very short time period, possibly linked to the drastic alterations in the Mediterranean Sea during and immediately after the Messinian salinity crisis at the end of the Miocene. The freshwater life-style appeared monophyletic; equating its origin with the salinity crisis resulted in a molecular clock estimate of 1.4% divergence per million years. The last common ancestor probably occupied sandy bottoms and a coastal niche while several species subsequently adapted to new habitats (pelagic, freshwater or stenohaline). The origin of the shallowest clades dated back to the glacial cycling during the Pleistocene epoch.

Model of Cretaceous Paleogeography and its Consequences: ABSTRACT

Growing acceptance of continental drift as expressed in the plate tectonics model leads to consideration of its use as a basis for investigating certain aspects of paleogeography and paleobiogeography. As a first step the geophysical, stratigraphic, and paleontologic data for the Cretaceous, with particular reference to mid-Cretaceous events were examined. The final separation of South America and South Africa dates from about Aptian/Albian time, which implies that the Mid-Atlantic Ridge as a relief feature dates from about that time. Unless there was compensating downwarping a change in the volume of the oceanic basins would occur. The stratigraphic records of Africa, North America, and Western Europe show that the major transgressive and regressive movements are synchronous and that a major transgression began about that time, perhaps reflecting the ridge activity. Major changes can be seen in the biogeography of mollusks, forams, and other groups between the Early and Late Cretaceous. Pre-Albian marine faunas in the Pacific regions are linked by a large number of taxa with faunas in the Atlantic-Mediterranean region. After the mid-Cretaceous there is a reduction in the cosmopolitan End_Page 614------------------------------ aspect and more intense provincialism. The biogeographic changes appear related to changing ocean basin configuration and initiation of the breakup of the circum-equatorial Tethys. In the present preliminary phase of investigation firm conclusions cannot be drawn, but the convergence of such diverse approaches encourages the interpretation that ridge activity caused mid-Cretaceous biogeographic changes. End_of_Article - Last_Page 615------------