Postglacial floodings of the Marmara Sea: molluscs and sediments tell the story

The early Holocene marine flooding of the Black Sea has been the subject of intense scientific debate since the “Noah’s Flood” hypothesis was proposed in the late 1990s. The chronology of the flooding is not straightforward because the connection between the Black Sea and the Mediterranean Sea involves the intermediate Marmara Sea Basin via two sills (Dardanelles and Bosphorus). This study explores the chronology of late Pleistocene–Holocene flooding by examining sedimentary facies and molluscs from 24 gravity cores spanning shelf to slope settings in the southern Marmara Sea Basin. A late Pleistocene Ponto-Caspian (Neoeuxinian) mollusc association is found in 12 of the cores, comprising 14 mollusc species and dominated by brackish (oligohaline–lower mesohaline) endemic taxa (dreissenids, hydrobiids). The Neoeuxinian association is replaced by a Turritella–Corbula association at the onset of the Holocene. The latter is dominated by marine species, several of which are known to thrive under dysoxic conditions in muddy bottoms. This association is common in early Holocene intervals as well as sapropel intervals in younger Holocene strata. It is an indicator of low-salinity outflows from the Black Sea into the Marmara Sea that drive stratification. A marine Mediterranean association (87 species) represents both soft bottom and hard substrate faunas that lived in well-ventilated conditions and upper mesohaline–polyhaline salinities (ca. 25 psu). Shallower areas were occupied by hard substrate taxa and phytopdetritic communities, whereas deeper areas had soft bottom faunas. The middle shelf part of the northern Gemlik Gulf has intervals with irregular and discontinuous sedimentary structures admixed with worn Neoeuxinian and euryhaline Mediterranean faunas. These intervals represent reworking events (slumping) likely related to seismic activity rooted in the North Anatolian Fault system. The core data and faunas indicate an oscillating postglacial sea-level rise and phases of increased/decreased ventilation in the Marmara Sea during the Holocene, as well as palaeobiogeographic reorganisations of Ponto-Caspian and Mediterranean water bodies since the latest Pleistocene (<30 ka). The findings contribute to arguments against a single catastrophic flooding of the Black Sea at about 7.5 ka (Noah’s Flood).     

West versus East Mediterranean Sea: origin and genetic differentiation of the sea cucumber Holothuria polii

We studied the genetic structure of the sea cucumber Holothuria (Roweothuria) polii (Delle Chiaje 1823) by analysing the mitochondrial DNA variation in two fragments of cytochrome oxidase I (COI) and 16S genes. Individuals were collected in seven locations along the Mediterranean Sea, which cover a wide range of the species distribution. We found high haplotype diversity for COI and moderate diversity for 16S, and low nucleotide diversity for both genes. Our results for the COI gene showed many recent and exclusive haplotypes with few mutational changes, suggesting recent or ongoing population expansion. The Western and Eastern Mediterranean populations exhibited slight but significant genetic differentiation (COI gene) with higher genetic diversity in the East. The most ancient haplotype was not present in the westernmost sampling location (SE Spain). The oldest expansion time was observed in Turkey, corresponding to mid‐Pleistocene. Turkey had also the highest genetic diversity (number of total and exclusive haplotypes, polymorphisms, haplotype and nucleotide diversity). This suggests that this region could be the origin of the subsequent colonizations through the Mediterranean Sea, a hypothesis that should be assessed with nuclear markers in future research.     

Mediterranean deep-sea amphipods: composition, structure and affinities of the fauna

The recent revision of the Mediterranean amphipod fauna includes 415 species (i.e. 8% of the worldwide fauna). The number of endemic species is estimated to be about 190 (i.e. 46% of the total fauna).The deep-sea fauna, which includes all those species inhabiting depths >150m, comprises 154 species (37.1% of the total fauna), belonging to 89 genera and 25 families. 84 of these species inhabited depths down to 400m, 47 down to 1000m, and 31 to depths >2000m. Considering the upper limits to their bathymetric ranges, 49 species are restricted to depths >150m, 15 to >400m, 9 to >1000m and just 5 to depths >2000m. 62.9% of the gammaridean fauna is restricted to the continental shelf at depths shallower than 150m. Only 11.3% of this fauna inhabits depths >1000m. and only 2.2% is restricted to these deeper depths.The composition of this deep-living fauna has complex zoogeographical relationships. There are four main categories of species: eurybathic, Atlantico-Mediterranean bathyal, endemic bathyal and endemic abyssal species.The deep-living species include 71 (46%) which are endemic. There are also 71 species which zoogeographically are Atlantico-Mediterranean, 4 which are cosmopolitan, 5 Atlantico-Pacifico-Mediterranean, one Indo-Atlantico-Mediterranean and one Pacifico-Mediterranean. The 71 endemic species belonging to 52 genera. Three of these genera are endemic and five others were previously known only as Indo-Pacific.The presence of bathyal endemic species belonging to bathyal genera, and the affinity of some other species otherwise occurring only in the Indo-Pacific, confirms that a Tethyan component persists in the amphipod fauna, and indicates that during the Messinian Crisis the Mediterranean did not completely dry up. Thus a relict amphipod fauna was able to survive in some of the residual basins.     

A Quantitative Assessment of the Reproductive System of the Mediterranean Cave-Dwelling Triplefin Blenny Tripterygion melanurus

Abstract. The breeding biology of the cave-dwelling Mediterranean triplefin blenny Tripterygion melanurus (Pisces, Blennioidei) was studied in the field. Two types of reproductive male were observed, territorial males and non-territorial males. Territorial males establish territories for mating, but not necessarily for feeding, in caves and crevices at depths between 0.5 and 33  m. Territories can be settled in clusters in a single cave. Non-territorial males occur in the vicinity of territories and attempt to parasitise matings of territorial males. Gravid females wait near territories where another female is spawning, rather than spawn with currently unmated territorial males. Waiting females intrude in matings and sometimes displace a spawning female. The frequency of mating of the territorial male, of sneaking and of female intrusions are higher in territories that border others than in isolated territories. Females may minimise predation risks both on themselves and on their eggs by spawning in clustered territories and by spawning with males that have more than one clutch of eggs. Territorial males must find a compromise between the benefits of attracting a female and the costs of parasitic spawning by sneaker males. The possibility that territorial males tolerate the proximity of other territorial males and accept a risk of cuckoldry is discussed. Parasitic spawning in T. melanurus is relatively rare and the gonadosomatic index in both non-territorial and territorial males is low, indicating that sperm competition is probably not intense.     

High occurrence of the elasipodid holothurian Penilpidia ludwigi (von Marenzeller, 1893) in bathyal sediment traps moored in a western Mediterranean submarine canyon

One hundred and fifty specimens of the elasipod holothurian Penilpidia ludwigi (von Marenzeller, 1893) were collected in sediment traps moored near the seabed in the La Fonera Canyon (Catalan Sea, north-western Mediterranean) and on the adjacent continental slope. These provide the third record of this apparently endemic Mediterranean species and the first record from the western Mediterranean. This was the only holothurian species trapped and the most abundant macroscopic organism found in the traps between 1200 and 1700 m depth over the whole sampling period (March–November 2001). It was particularly abundant in spring during the main flux of organic particles in the canyon. This coupling suggests that Penilpidia may aggregate at the seafloor during these events, making food availability a plausible explanation of the seasonal occurrence. Lateral transport of material re-suspended locally or up-canyon by near bottom currents appear to be the mechanism behind this uncommon occurrence, although in situ observations have recently been made on the swimming capability of this holothurian. The occurrence of benthic organisms in sediment traps set close to the seabed can provide information on bathyal benthic and benthopelagic populations.     

Biomarkers for endocrine disruptors in three species of Mediterranean large pelagic fish

The hypothesis that Mediterranean top predator species, such as large pelagic fish, are potentially at risk due to endocrine disrupting chemicals (EDCs), is investigated. The potential estrogenic effects of PHAHs in three fish species of commercial interest, the top predators bluefin tuna (Thunnus thynnus thynnus), swordfish (Xiphias gladius), and Mediterranean spearfish (Tetrapturus belone), were investigated using vitellogenin (Vtg), zona radiata proteins (Zrp) and mixed function oxidases (EROD, BPMO) as diagnostic tools. High induction of Vtg and Zrp was detected by western blot and ELISA techniques in adult males of X. gladius and T. thynnus thynnus, suggesting that these species are at high toxicological risk in the Mediterranean sea. Comparison of BPMO and EROD activities in the three species indicated, both in male and female, much higher MFO activity in bluefin tuna. This data suggests high exposure of this species to lipophilic xenobiotic contaminants in the Mediterranean environment.     

The occurrence and significance of Pleistocene and Upper Pliocene sapropels in the Tyrrhenian Sea

Numerous sapropels and sapropelic strata from Upper Pliocene and Pleistocene hemipelagic sediments of the Tyrrhenian Sea show that intermittent anoxia, possibly related to strongly increased biological productivity, was not restricted to the eastern Mediterranean basins and may be a basin-wide result of Late Pliocene-Pleistocene climatic variability. Even though the sapropel assemblage of the Tyrrhenian Sea clearly originates from multiple processes such as deposition under anoxic conditions or during spikes in surface water productivity and lateral transport of organic-rich suspensates, many “pelagic sapropels” have been recognized. Stratigraphic ages calculated for the organic-rich strata recovered during ODP Leg 107 indicate that the frequency of sapropel formation increased from the lowermost Pleistocene to the base of the Jaramillo magnetic event, coinciding with a period when stable isotope records of planktonic foraminifera indicate the onset of climatic cooling in the Mediterranean. A second, very pronounced peak in sapropel formation occurred in the Middle to Late Pleistocene (0.73-0.26 Ma). Formainifers studied in three high-resolution sample sets suggest that changes in surface-water temperature may have been responsible for establishing anoxic conditions, while salinity differences were not noted in the faunal assemblage. However, comparison of sapropel occurrence at Site 653 with the oxygen isotopic record of planktonic foraminifers established by Thunell et al. (Proc. ODP, Sci. Results 107, 1990) indicates that sapropel occurrences coincide with negative δ¹⁸O excursions in planktonic foraminifers in thirteen of eighteen sapropels recognized in Hole 653A. A variant of the meltwater hypothesis accepted for sapropel formation in the Late Pleistocene eastern Mediterranean may thus be the cause of several “anoxic events” in the Tyrrhenian as well. Model calculations indicate that the amount of oxygen advection from Western Mediterranean Deep Water exerts the dominant control on the oxygen content in deep water of the Tyrrhenian Sea. Inhibition of deep-water formation in the northern Adriatic and the Balearic Basin by increased meltwater discharge and changing storm patterns during climatic amelioration may thus be responsible for sapropel formation in the Tyrrhenian Sea.     

Environmental features of deep-sea habitats linked to the genetic population structure of a crustacean species in the Mediterranean Sea

The deep-sea habitat, from 200 to 2000 m depth, has long been thought as an ecosystem where biotic and abiotic factors vary very little and consequently species are not disturbed by processes and phenomena which could promote fast evolutionary mechanisms. Unfortunately, biological information relating to deep water is limited, especially regarding the population genetics of species inhabiting the Mediterranean Sea, and general patterns cannot be inferred. In this study we report data on the population genetic structure of Aristeus antennatus , a deep-sea decapod crustacean species which has been widely studied due to its important economic value. We surveyed and examined the variation in a 369-bp fragment of the mtDNA control region from individuals caught by Spanish and Italian trawlers in eight localities. High levels of mitochondrial control region haplotypic diversity (ranging from 0.884 to 0.989) were observed. AMOVA showed a high level of genetic variation, more within than between populations, and a low but significant Φ_ST value was recovered. Minimum spanning network did not separate any haplotype group and haplotype distribution does not mirror the geographic origin of the samples. The absence of population substructuring was also observed with a principal coordinates analysis, which uses an individual-by-individual comparison. These results revealed extensive gene flow among populations. Information on demographic history based on mismatch analysis revealed an unstable population, showing an alternate pattern of growth and decline. Our results indicated that in the western and central Mediterranean basins A. antennatus is a large panmictic population with a fluctuating abundance. The absence of deep-sea barriers and adult migration may prevent the structuring of the species into genetically differentiated populations.     

Out of the Celtic cradle: The genetic signature of European hake connectivity in South-western Europe

Population genetic data of marine genetic resources add up to establish their pattern of connectivity. Such pattern determines the choice of a suitable management strategy to those resources in space and time. This study addresses the pattern of connectivity among European hake grounds upon the largest sampling effort so far developed in this species. Bayesian inference made on multilocus genotypic data provides evidence that a large genetic connectivity exists among Atlantic grounds and is mediated by significant migration rates stepping up from the Celtic Sea towards its adjacent Atlantic grounds. Therefore, the spawning biomass of the northern hake population could play a crucial role at ensuring the sustainability of southern hake fish grounds. The deepest restriction to gene flow was observed at the easternmost side of the Alboran Sea what suggests that the Almeria–Oran Oceanographic Front is an effective barrier keeping apart the two major gene pools so far shown in this species. A molecular clock calibrated for cytochrome b sequences of fishes and applied to the divergence between hake pools (0.3%) suggests that the Atlantic–Mediterranean population split might date back to the Middle Pleistocene (150,000 years BP). Complementarily, Bayesian treatments of multilocus genotypes indicate that such barrier to gene flow remains active nowadays. This study shows the upmost interest of future integrative efforts to incorporate population genetic data into current assessment practices, in order to better manage European hake populations and make its exploitation sustainable.     

Depth Distribution and Abundance of Northern Adriatic Littoral Rocky Reef Blennioid Fishes (Blenniidae and Tripterygion)

Abstract. Species' depth distributions and abundances were visually assessed along 24 transects in a northern Adriatic assemblage of blennioid fishes (14 species of Blenniidae , 1 species of Triptery-giidue). Total abundance of blennioids was highest in 0.5-1 m depth, decreasing upwards and downwards. Species diversity (S hannon -W iener ) is highest at the shallowest depth (0-0.5 in). The curybathic species Parablennius incognitus, Lipophrys dalmatinus, Tripterygion tripteronotus , and Parablennius tentacularis were most abundant at all depths (relative to the species investigated). All stenobathic species were most abundant at 0-0.5 m. Depth distribution patterns and abundance ranks of species were similar at western, eastern, southern, and northern transects.     

Algal flora associated with a Halophila stipulacea (Forsskål) Ascherson (Hydrocharitaceae,Helobiae) stand in the western Mediterranean

Halophila stipulacea, a seagrass introduced into the Mediterranean Sea as a Lessepsian immigrant, is nowadays common in the eastern Mediterranean, and it was recently recorded in the western Mediterranean; very little information is available about the algal flora associated with this species. During a survey of a Halophila stipulacea stand at Vulcano Island (Eolian Islands, western Mediterranean), samples were collected at three depths (5 m, 15 m and 25 m) for identification of algal epiphytes. Thirty-six species of macroalgae were found. The epiflora of the leaves consisted of 20 species, the others being mixed with or entangled in the rhizomes. On the leaves, Ceramium tenerrimum, Dasya corymbifera, Polysiphonia cfr. tenerrima, Spyridia filamentosa, Chondria pygmaea and Laurencia sp. were the most common species; between the rhizomes, Dictyota linearis was abundant. A differentiation of the epiphytic assemblage between 5 m and the other depths was observed; the 5 m samples were characterized by the abundance of Ceramium tenerrimum, Chondria pygmaea and Polysiphonia cfr. tenerrima, while at 15 m and 25 m Laurencia sp., Dasya corymbifera and Spyridia filamentosa were the most common species. Epiphytic cover was generally very low. No rare species were found among the epiphytes. In comparison with other Mediterranean seagrasses, Halophila stipulacea has a qualitatively and quantitatively poor epiphytic flora. In particular, the virtual absence of encrusting corallines is noteworthy. A fast turnover rate of the leaves is hypothesized to be the main reason for this scarcity. Differences between this and other studies on epiphytes of Halophila stipulacea stands are discussed.     

Nassarius corniculus (Olivi, 1792) (Caenogastropoda: Nassariidae): a model of environmental complexity of Italian brackish and marine habitats

Strong environmental selection may give rise to complex species and/or camouflage the presence of sibling species in brackish waters. The prosobranch gastropod Nassarius corniculus (Olivi, 1792) is a common scavenger widely distributed in Mediterranean brackish and marine areas. We examined the morphological and molecular features of N. corniculus populations and related these features to the environmental complexity of brackish habitats. Morphological data revealed differences in radular features between specimens collected from two Mediterranean lagoons (Lake Faro, Messina, Sicily and Lake Fusaro, Gulf of Gaeta). Analysis of with the mitochondrial marker mt 16S rRNA revealed genetic variability within the Lake Faro population but did not show the different geographic structure between the two lagoons indicated by morphological data. We also predicted the gene flow of N. corniculus by comparing populations of two marine areas (Faro Sea and Ischia).     

A cryptic species of Mytilus (Mollusca: Bivalvia) on the west coast of South Africa

A biochemical genetic study of the mussels Perna perna and Choromytilus meridionalis on the west coast of South Africa revealed the presence of an unreported mytilid mussel that had previously been mistaken, because of its shell colour polymorphism, for either P. perna or a hybrid between P. perna and C. meridionalis. The gene products of 19 protein-coding loci in P. perna. C. meridionalis and in the newly recognized mussel were examined by means of horizontal starch-gel electrophoresis. The results showed that there was no allele-frequency overlap between any of these mussel taxa, thus implying little or no genetic relatedness between them. A morphological examination showed that the previously unreported mytilid has a pitted resilial ridge (similar to that of Perna), an anterior adductor muscle (unlike either Perna or Choromytilus), and an undivided posterior foot retractor-muscle scar (unlike Perna). Such features are diagnostic of the genus Mytilus. The South African Mytilus has morphological traits that are more characteristic of M. galloprovincialis of the Mediterranean Sea than of the more cosmopolitan M. edulis. which occurs in the northern and southern Pacific and Atlantic oceans. A large heterozygosity in Mytilus sp. argues against a recent dispersal from the Mediterranean Sea via a small founder population. Rather, the presence of Mytilus sp. in South Africa may represent a relict population of a wider geographic distribution of M. galloprovincialis resulting from Pleistocene cooling. However, the warmer water at lower latitudes could have still prevented dispersal of M. edulis, a species adapted to colder waters.     

Carbon and oxygen isotope composition of foraminifera in two cores from the Bannock Basin area, eastern Mediterranean

Two cores from the Bannock Basin in the eastern Mediterranean have been analysed for δ¹⁸0 and the δ¹³C in planktonic foraminifera. One core (02-PC) was extracted from the anoxic brine, the other (08-GC) from a plateau east of the brine.

The absence of sapropelic muds in Core 08-GC from the two Holsteinian euxinic cycles, together with the presence of isotopic spikes, suggests that the plateau has risen during the last ca. 200,000 years by ca. 2.5 mm/yr.

The δ¹⁸0 amplitude of Globigerinoides ruber in eastern Mediterranean cores is only ca. 0.5%. larger than for this species in North Atlantic cores. This suggests that the surface oxygen isotopic composition of both bodies of water followed each other fairly closely during the Late Pleistocene, except during the stagnant phases.     

Genetic and morphological divergence in the purple sea urchin Paracentrotus lividus (Echinodermata, Echinoidea) across the African Mediterranean coast

The present investigation focuses on population structure analysis of the purple sea urchin Paracentrotus lividus across the African Mediterranean coast, with the main aim of assessing the influence of the Siculo-Tunisian Strait on gene flow disruption in this highly dispersive echinoid species. For this purpose, patterns of morphological and genetic variation were assessed among its populations from the western and eastern Mediterranean coasts. A total of 302 specimens from seven Tunisian sites were collected and examined for morphometric variability at twelve morphometric traits. Concordant results, inferred from CDA (canonical discriminant analyses), pairwise NPMANOVA (non parametric multivariate analysis of variance) comparisons and MDS (multidimensional scaling) plot, unveiled significant inter-population differences in the measured traits among the studied populations. Furthermore, the combined use of the one way ANOSIM (analysis of similarities) and the Discriminant/Hotelling analysis allowed unravelling two morphologically differentiated groups assigned to both western and eastern Mediterranean basins. The SIMPER (similarity percentages) routine analysis showed that total dry weight, test diameter and spine length were major contributors to the morphometric separation between locations and between groups. Pattern of phenotypic divergence discerned in P. lividus across the Siculo-Tunisian Strait is interestingly in congruence with that inferred from the genetic investigation of the purple sea urchin populations from the same region based on the analysis of the mtDNA COI (cytochrome oxidase I) gene in 314 specimens from nineteen locations covering a wider geographic transect, streching westward to the Algerian coast and eastward to the Libyan littoral. The specific haplotypic composition characterizing each Mediterranean basin, as inferred from the minimum spanning network, confirmed the geographic partioning of genetic variation, as revealed by F-statistics and AMOVA (analysis of molecular variance) analyses, yielding significant genetic differentiation between eastern and western Mediterranean populations. The newly detected phylogeographic patterns, observed for the first time in P. lividus throughout the explored distribution range, suggest the involvement of different biotic and abiotic processes in shaping such variation, and provide evidence that a large and geographically exhaustive dataset is necessary to unveil phylogeographic structure within widespread marine species, previously cathegorized as panmictic in part of their distribution range.     

Significant genetic differentiation among meroplanktonic barrel jellyfish Rhizostoma pulmo (Cnidaria: Scyphozoa) in the Mediterranean Sea

Molecular data have shown that jellyfishes are more geographically restricted and evolutionarily divergent than previously thought. We examined genetic variation and divergence within the meroplanktonic barrel jellyfish Rhizostoma pulmo in the Mediterranean Sea; specific sampling areas were the northern Adriatic, western Mediterranean and Tunisian coast. A total of 19 sampling sites and 68 sequences of the mtDNA cytochrome c oxidase subunit I (COI) gene were used. Of the 68 COI sequences, 45 were newly collected specimens which originated from nine sampling sites along the Tunisian coast. A total of 24 haplotypes were obtained and the specimens sampled were characterised by relatively high levels of haplotype diversity (h = 0.866) and low levels of nucleotide diversity (π = 0.004). Haplotype network analysis showed the presence of three distinct phylogenetic lineages (populations), with separate geographic ranges in the northern Adriatic, western Mediterranean and Tunisian coast. The observed genetic differentiation between these three lineages was supported by the presence of significant genetic differentiation between the 19 populations (F_ST = 0.757, p < 0.001). The high level of genetic differentiation detected in the barrel jellyfish investigated could be attributed to either intrinsic and/or extrinsic barriers to genetic exchange between different populations that may have adapted to different environmental conditions.     

First insights into the demography of the rare gorgonian Spinimuricea klavereni in the Mediterranean Sea

We present the results of the first study to highlight the demography, morphometry and growth rates of Spinimuricea klavereni, a rare Mediterranean endemic gorgonian exceptionally common in shallow depths of the Northeast Marmara Sea. In the study area, this species forms vast populations on rocks, boulders and attached to pebbles/stones/shells on soft substrates between 20 and 45 m depth, with a total average density of 0.3 colonies·m^?2 but comprising patches up to 3 colonies·m^?2. Colonies, which are on average 42.9 (±20.1) cm in height, can reach up to 110 cm. Unlike other Mediterranean gorgonians, the colonies studied here showed fast growth rates that decreased with increasing colony height, between 1.5–11.1 and 4.96 ± 3.01 cm·year^?1 on average. The low necrosis and high growth rates displayed by this species in the Northeast Marmara Sea confirm the previously hypothesized opportunistic behaviour of the species. The unique community consisting of S. klavereni and other rare gorgonian/soft corals has limited distribution in this area and should be considered to be a vulnerable marine ecosystem. Therefore we recommend that some conservation measures are taken, including the prohibition of all fisheries and anchoring over these assemblages.     

Evaluating the genetic effects of the invasive Ocenebra inornata on the native oyster drill Ocenebra erinacea

Studies focusing on the effect of invasive species on the genetic diversity of native marine invertebrates remain scant. Here we report diversity among French populations of the intertidal gastropod Ocenebra erinacea (Linnaeus, 1758) sampled in the presence and absence of the invasive Ocenebra inornata (Recluz, 1851). Between 1999 and 2004, a total of 352 individuals of O. erinacea was collected from 15 sites (five of which had the invasive present) and was genotyped at the mitochondrial locus Cytochrome Oxidase 1 (cox1). No statistical difference was observed between polymorphism levels recorded within native populations exposed to the invasive, compared with populations sampled in the absence of O. inornata. No sign of native population decline was detected in response to the invader. While significant shifts in native O. erinacea population sizes have previously been reported in the literature, genetic effects may take longer to accumulate, or may be undetectable without a larger panel of genetic markers. By contrast, large genetic distances and significant population differentiation were recorded between Atlantic and Mediterranean O. erinacea samples, suggesting that these populations have distinct evolutionary histories. Comparison of genetic divergence within the closely related genus Nucella suggests that the Atlantic populations of O. erinacea and those from Thau Lagoon in the Mediterranean may belong to different species or subspecies.     

Cryptic diversity of marine gastropod Monodonta labio (Trochidae): did the early Pleistocene glacial isolation and sea surface temperature gradient jointly drive diversification of sister species and/or subspecies in the Northwestern Pacific?

Formation of glacial refugia during the Pleistocene climatic oscillations has been put forward to elucidate the diversification of marine organisms in the north‐western Pacific. The marine gastropod Monodonta labio is one of the most common species in the Northwestern Pacific and possibly possesses cryptic diversity. Here, we investigate the phylogeographic pattern of this species to test the potential mechanisms driving its diversification in the Northwestern Pacific. Genetic information for two mitochondrial genes (Cytochrome oxidase subunit I and 16S rDNA) and one nuclear gene (internal transcribed spacer 1) was acquired to detect genetic structuring and to reconstruct the gastropod's phylogenetic history. Our results revealed that M. labio is comprised of five main clades, and divergence time estimates place their cladogenesis as corresponding to the initiation (c. 2.5 mya) and intensification (c. 0.9 mya) of large‐scale Northern Hemisphere ice sheets. The early and middle Pleistocene divergence times are consistent with the emergence times of the Dongshan land bridge, which would seperate the ancient East China Sea and the ancient South China Sea forming two potential refugia. In addition, the deep trough in the Qiongzhou Strait would possibly act as another potential refugium with the uplift of the Qiongzhou Strait at mid‐Pleistocene. This study suggests that the current genetic architecture of M. labio is probably correlated with glacial isolation and sea surface temperature gradient. We also put forward the possibility that these factors were probably an important driver for the diversification of sister species or subspecies of other taxa in the Northwestern Pacific.