Late glacial to recent deep-sea benthic foraminifera from the northeastern Atlantic (Cadiz Gulf) and western Mediterranean (Alboran Sea): Paleooceanographic results

Deep-sea benthic foraminifera of the region of water exchange between the Mediterranean and the Atlantic Ocean, at the Gibraltar Strait, show significant water-mass relationships for the past 18,000 years.Cores used in this benthic foraminifera analysis were selected, according to the context of the distribution of various deep bottom water masses, on each side of the Gibraltar Strait:

• 1.(1) on the Atlantic side of the Strait, two cores (KS 8228, KS 8229) are located in the present day NADW, and one (KC 8221) in the upper part of the present Mediterranean outflow water,
• 2.(2) on the Mediterranean side of Gibraltar, two cores (KC 8241, SU 8107) are located in the deep water mass, and one (KS 8230) in the intermediate water mass.

In the two deep basins (1500–2800 m depth in the Gulf of Cadiz, 1200–1300 m depth in the Alboran Sea), the paleooceanographic changes appear to be in an opposite way for the past 18,000 years. The Alboran basin shows a paleooceanographic evolution from a well-oxygenated, nutrient-rich environment at about 18,000 yr B.P. to a nutrient-poor, oxygen-depleted environment from 13,000 to the present time; moreover, for the time-span synchronous with the well-known development of sapropels in the eastern Mediterranean basins between 10,000 and 7000 yr B.P., the faunal assemblage shows most unusual characteristics implying drastic environmental conditions. Conversely, in the Gulf of Cadiz, the environment pass as from a biotope occupied by an oxygen-depleted, nutrient-poor water mass at about 18,000 years B.P. to a biotope occupied by NADW since the Younger Dryas; this agrees with previous data obtained in the northeastern Atlantic Ocean (Caralp, 1987).In the epibathyal zones (550–800 m depth), on both sides of the Gibraltar Strait, paleohydrographic changes do not seem so important. According to the present and very late Holocene assemblages, which are similar on both sides of the Strait with a strong east-west flow, two other stratigraphic episodes have shown the same conditions of water exchanges: the end of the isotopic stage 2 and the Younger Dryas. Conversely, during the last glacial maximum, the Bølling-Allerød and the lower Holocene, westward water fluxes were probably lower. At no time, the hypothesis of a reversal or a stop in the east-west exchanges between Mediterranean and Atlantic Ocean may be justified.     

Ecological distribution of four co-occurring Mediterranean heath species

Erica australis, E. scoparia, E. arborea and Calluna vulgaris are the most abundant heath species on acid, sandstone-derived soils of the Strait of Gibraltar region (southern Spain and northern Morocco). Despite their apparently similar ecological requirements, these four species are somewhat ecologically segregated. Erica australis is abundant only on poor, shallow soils, with a high content in soluble aluminium, generally on mountain ridges and summits. Erica scoparia becomes dominant on deeper sandstone soils with lower aluminium. Calluna vulgaris coexists with these Erica species in communities under low or no tree cover. In the Spanish side of the Strait (Algeciras), Erica arborea tends to be relegated to communities under moderate to dense tree cover, whereas this species is more abundant and widespread in the Moroccan side (Tangier). Tolerance to extreme physical conditions - high aluminium and dense tree cover - and interspecific competition seem to explain the ecological distribution of these four heath species in the Strait of Gibraltar region. The more fragmented pattern of sandstone patches and higher disturbance levels in Tangier might account for the differences in the patterns of ecological distribution of these four heath species between both sides of the Strait of Gibraltar.     

Migration and winter distribution of Iberian and central European black storks Ciconia nigra moving to Africa across the Strait of Gibraltar: a comparative study

This paper compares the migratory movements of Iberian and central European satellite‐tagged black storks Ciconia nigra moving to Africa across the Strait of Gibraltar. Results show that the populations differ in departure dates from breeding areas (central European birds start to move 15 d before Iberian birds), cross the Strait of Gibraltar together and reach the Sahel on similar dates. This synchronic arrival to the Sahel may be related with the onset of suitable conditions for the species after summer rains, when many pools are available for fishing. In this area, Iberian birds occupied westernmost localities compared to central European birds crossing the Strait of Gibraltar, which were distributed closer to those storks arriving in Africa across the Bosporus. This suggests that the parallel distribution of breeding and wintering areas results from posterior rearrangements of the two populations crossing Gibraltar. These patterns appear to be linked to the increasing population of central European black storks located on the western side of the migratory divide that moves throughout the western flyway to sectors of the Sahel close to their ancestral wintering grounds.     

NOTOLIMEA CLANDESTINA A NEW SPECIES OF NEOTENOUS BIVALVE (BIVALVIA: LIMIDAE) ENDEMIC TO THE STRAIT OF GIBRALTAR

Notolimea clandestina new species (Bivalvia: Limidae) is describedfrom the littoral of the Strait of Gibraltar. The small size(1 mm) and the persistence of the larval hinge suggest a neotenousspecies. Its area of distribution is likely to be restrictedto the Strait of Gibraltar. (Received 7 July 1993; accepted 2 December 1993)     

The effects of northern italian rivers and Eastern Mediterranean ingressions on the phytoplankton of the Adriatic Sea

An analysis of the distribution of the phytoplankton standing crop during a period of high stability characterized the relative influence of northern Italian rivers and Mediterranean waters on the Adriatic Sea. The region influenced by northern Italian rivers was marked by low community diversities, relatively high chlorophyll a standing crops and cell densities, high microplankton to nannoplankton community volume ratios, and the dominance of Nitzschia seriata. To the contrary, the region influenced by Mediterranean waters exhibited high community diversities with prominent oceanic and warm water elements, low chlorophyll a standing crops and microplankton cell densities, low microplankton to nannoplankton ratios, and a relatively conspicuous coccolithophore flora.Nannoplankton populations remained relatively constant throughout the Adriatic. However eutrophication resulted in a marked increase in the microplankton component of the community, with the diatom Nitzschia seriata serving as a prime indicator of the process, even in regions several hundred kilometers downstream from nutrient sources.Even under relatively low rates of river discharge, the influence of northern Italian rivers could be traced along the entire western sode of the sea to the Otranto Strait, with low north to south and high west to east gradients resulting from the effect of a cyclonic surface circulation pattern on inflowing Mediterranean waters in the south and river discharge in the north.     

Population Genetic Structure of a Sandstone Specialist and a Generalist Heath Species at Two Levels of Sandstone Patchiness across the Strait of Gibraltar

Many habitat specialist species are originally composed of small, discontinuous populations because their habitats are naturally fragmented or patchy. They may have suffered the long-term effects of natural patchiness. Mediterranean heathlands, a representative habitat in the Strait of Gibraltar region, are associated with nutrient-poor, acidic sandstone soils. Sandstone soil patches in the African side of the Strait (Tangier) are, in general, smaller and more scattered than in the European side (Algeciras). In this study, we analyze the effect of this sandstone patchiness on the population genetic diversity and structure of two Erica species from these Mediterranean heathlands that differ in their edaphic specificity, E. australis, sandstone specialist, and E. arborea, generalist. Average levels of within-population genetic diversity and gene flow between populations were significantly lower in Tangier (high sandstone patchiness) than in Algeciras (low patchiness) for the sandstone specialist, whereas no differences between both sides of the Strait were detected in the edaphic generalist. Since most endemic species in Mediterranean heathlands of the Strait of Gibraltar are sandstone specialists, these results highlight an increased vulnerability to loss of genetic diversity and local extinction of the heathland endemic flora in the Tangier side of the Strait of Gibraltar.     

Historical colonization of the Mediterranean Sea by Atlantic fishes: do biological traits matter?

Since its opening 5.33 million years ago, the Gibraltar Strait has always contributed to the Mediterranean fauna and flora. Despite the increasing importance of the phenomenon, ecological determinants underlying colonization success of Atlantic fishes in the Mediterranean Sea have been poorly investigated. Here we reconstruct the recent historical colonization of the whole Mediterranean Sea by Atlantic fishes and we aim to determine where Atlantic fishes preferentially establish and whether some biological traits and ecological factors can be correlated to the colonization success (climate match, position in the water column, maximum body length, propagules, confamilial resistance, depth). A database on Atlantic fish species records from 1810 to 2006 was built and the colonization rate of each introduced species was estimated. Analysis of Variance, Chi squared test and logistic regression were used to investigate the relationships between ecological variables and colonization success. In addition, an index of asymmetry was used to analyse the relative colonization on the two sides of the Mediterranean Sea. Overall 48.33% of Atlantic species introduced in the Mediterranean Sea succeeded in colonizing eastwards. We found that habitat depth of Atlantic species is significantly related to their colonization success due to the obstacle of the shallow depth of the Gibraltar Strait (300 m). It also appears that despite the cyclonic general water circulation on the North Western basin, the northern side is more colonized than the southern one: 70.40% of the studied species colonize the northern side, while only 29.62% colonize the southern one. Two hypotheses may explain this trend: the bottom-up process that enhances the colonization success of Atlantic fishes along the Spanish coast of Alboran Sea owning to its high productivity and the intensiveness of the scientific explorations along the northern Mediterranean side. We conclude that crossing the Gibraltar Strait does not guarantee the colonization success and that species life-history and functional traits are poor predictors. Instead we suggest that environmental factors may determine favourable locations for invasive species installation. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: J. Cambray.     

Complex biogeographical distribution of genetic variation within Podarcis wall lizards across the Strait of Gibraltar

Abstract Aim To examine the effect of a known geological barrier on genetic variation within a wall lizard species complex. Location The Iberian Peninsula and North Africa. Methods Sequencing of partial 12S rRNA and cytochrome b mtDNA. Results The current distribution of genetic variability is not related to the opening of the Strait of Gibraltar. Conclusions Podarcis hispanica in North Africa is probably a species complex. The Strait of Gibraltar should not be used as a known barrier to gene flow in other land based organisms without careful sampling to test for multiple crossings since its formation.     

Polychaete assemblages and sediment pollution in a harbour with two opposing entrances

The harbour at Ceuta is one of the most important harbours in the Strait of Gibraltar. The sediments are moderately polluted with organic matter and heavy metals but the harbour has two opposing entrances and a connecting channel which increases water renewal and dissolved oxygen across the harbour. For these special conditions, the value of the soft bottom polychaete community as a bioindicator, and possible advantages of the presence of two harbour entrances on biotic assemblages, were studied. Twenty-one stations were selected, and 27 variables were measured in the sediment of each station. The polychaete species richness and Shannon diversity values were similar inside and outside the harbour. Nevertheless, the Pielou evenness index was significantly higher in the external stations due to high densities of some species of polychaetes such as Pseudomalacoceros tridentata and Capitella capitata inside the harbour. The multivariate approach based on polychaete species composition was much more sensitive than univariate analyses at discriminating between internal and external stations. The pollution gradient and granulometric parameters were the main factors affecting polychaete distribution. Polychaete species richness and diversity in sediments inside Ceuta harbour were higher than in conventional harbours due to the positive effects of increased water renewal. These results should be taken into consideration in design, construction and remodelling of future harbours.Communicated by: H.-D. Franke     

Zooplankton distribution and diversity in a frontal area of the Aegean Sea

This study was carried out in the northern Aegean Sea during late summer and spring. The aim was to examine the spatial and temporal distribution of the zooplankton community across a dynamic frontal area and to investigate how the oceanographic heterogeneity structures the composition of the zooplankton assemblages. The low-salinity and cold Black Sea water coming from the Dardanelles Strait is modified by mixing with the underlying warm and saline Aegean water. These hydrological features result in a pronounced thermohaline front in the northern Aegean Sea throughout the year. In both seasons, zooplankton was collected using both 45 and 200 µm mesh plankton nets. A high abundance of zooplankton was observed in the surface layer at the stations closest to the Dardanelles Strait on the stratified side of the front. The zooplankton distribution and community structure in the northern Aegean Sea were strongly influenced by the hydrological features. The frontal structure acts as a boundary for the zooplankton community. The surface layer at the stratified stations had the lowest copepod diversity, from where it increased with depth and horizontally as the stratification weakened outside of the front. The total abundance of zooplankton collected with the 200 µm net was between two and 20 times lower than samples taken with the 45 µm net. The most pronounced differences were observed for the adults and copepodids of the small genera Oithona, Oncaea and Microsetella. Thus, to manage and understand the transfer of primary production up the food chain in the Aegean Sea, the smaller fraction of copepods should be taken into account in future investigations.     

Resistance of three co-occurring resprouter Erica species to highly frequent disturbance

The resistance to experimental, highly frequent disturbance has been analysed in three congeneric, strong-resprouter species (Erica australis, E. scoparia and E. arborea) that co-occur in heath-dominated communities of the northern side of the Strait of Gibraltar, southern Spain. To do so, mature individuals of the three species from a long undisturbed location were clipped at the ground level every sixth month during two years. The relationship between the resprouted biomass dry weight (as indicative of the resprouting vigour) and the upper surface area of the lignotuber along the experiment was established separately for each species at each clipping event by means of linear regressions analysis. The resprouting vigour of the three species was compared by means of independent one-way ANOVAs within each clipping event. Resprouting vigour decreased after recurrent clippings in the three species. Nevertheless, significant differences between species in this loss of resprouting vigour were detected, being E. scoparia the most resistant to the experimental, highly frequent clipping. It is concluded that experimental levels of recurrent disturbance may help to find out differences in resilience within similar (taxonomically, morfologically and/or ecologically), strong-resprouter plant species. Considering the history of forestry management in the nothern side of the Strait of Gibraltar, differences in this regard between the three Erica species may contribute to explain their somewhat segregated ecological distribution in this region.     

Phylogeographic patterns of two tiger beetle species at both sides of the strait of Gibraltar (Coleoptera: Cicindelini)

The Strait of Gibraltar is one of the major barriers to gene flow between land masses of Europe and Africa at the western end of the Mediterranean. Since the opening of the Strait at the end of the Miocene 5.33 million years ago (Mya) it has exerted a strong influence on the dispersal and colonization of whole biotas, particularly with regard to the retreat of organisms during glaciation peaks and the northward colonization events during the warm periods of Pleistocene. The aim of this study is to elucidate the influence of the Strait of Gibraltar in the gene flow among populations of two tiger beetle species collected in Morocco, Cicindela campestris (L. 1758) and Lophyra flexuosa (Fabricius 1787), with regard to both new and published data from populations of southern Iberia. The phylogeographic analysis showed that Moroccan haplotypes of L. flexuosa belonged to a single coastal mitochondrial clade and that populations at both sides of` the Strait of Gibraltar were genetically well connected. The haplotype network of C. campestris showed that Moroccan populations made up a robust cluster clearly differentiated from those of Iberian and other European populations. These differences are thought to reflect the distinct evolutionary history (dispersal capacity, ecological strategies) of both species, as L. flexuosa shows an almost continuous distribution on the coasts located at both sides of the West Mediterranean, whereas C. campestris shows a patchy distribution and prefers montane habitats in the Western Palaearctic.     

Distribution patterns of the peracarid crustaceans associated with the alga <Emphasis Type="Italic">Corallina elongata</Emphasis> along the intertidal rocky shores of the Iberian Peninsula

Spatial patterns of intertidal peracarids, associated with the alga Corallina elongata, were studied along the whole Iberian Peninsula. A total of 28,215 specimens were collected, comprising 78 different species (57 amphipods, 16 isopods, 4 tanaids and 1 cumacean), most of them with Atlantic-Mediterranean distribution (60%) and only 9% of Mediterranean endemics. Gammarids were dominant in abundance and number of species, representing more than 70% of the total peracarids. The most common species collected during the present study were the caprellid Caprella penantis, the gammarids Hyale schmidti, Hyale stebbingi, Jassa cf. falcata and Stenothoe monoculoides, the isopod Ischyromene lacazei and the tanaid Tanais dulongii. Caprellids and tanaidaceans presented their highest populations in the stations of the Strait of Gibraltar, whereas isopods were more abundant in Atlantic stations. Univariate analyses did not reflected differences in number of species, abundance and Shannon-Weaver diversity between Mediterranean and Atlantic. However, cluster analyses and Whittaker index, as measure of ß-diversity, showed a different species composition between Mediterranean and Atlantic and a replacement of species along the coast, especially at the Strait of Gibraltar. The turnover mainly affected species of the same genera, probably related with sympatric speciation. CCA and BIO-ENV analyses showed high correlations between environmental measures (especially conductivity) and peracarid distribution. Mediterranean species tolerated higher values of conductivity and temperature, while Atlantic species were associated with stations characterized by higher oxygen concentrations.     

Hydrography and biochemical indicators of microplankton biomass in the Bransfield Strait (Antarctica) during January 1994

 The relationships between hydrography and spatial distribution of several biochemical indicators of microplankton biomass (chlorophyll, protein and ATP) were studied in an area covering the eastern part of the Bransfield Strait and the northern part of the Weddell Sea, during Antarctic summer (January 1994). Four hydrographic zones were identified: (a) the northern part of the Bransfield Strait, covered by waters of Bellings- hausen Sea origin; (b) a Weddell Sea water mass that affected most of the study area; (c) the Weddell-Scotia Confluence waters, observed north of Elephant Island; and (d) waters influenced by ice melting, found towards the southeastern part of the sampled area. The highest values of biomass indicators (chlorophyll a, ATP and protein) were found in the zones affected by ice-melting processes and in waters from the Bellingshausen Sea. The lowest values of all biochemical parameters were found in the Weddell Sea and in the Weddell-Scotia Confluence waters. A high variability in the hydrographic structure and the distribution of biochemical indicators was observed. The degree of stabilization of the water column, the depth of the upper mixed layer and the grazing pressure of herbivorous zooplankton played a major role in the development, accumulation and spatial variability of microplankton biomass. Received: 15 August 1995/Accepted: 18 February 1996     

Distribution and ecology of deep-water benthic foraminifera in the Gulf of Mexico

Bathyal and abyssal foraminifera in the Gulf of Mexico are distributed among thirteen generic predominance facies. Five predominance facies nearly encircle the Gulf basin along the slope and rise; a sixth predominance facies blankets the Sigsbee Plain, and a seventh is restricted to the Mississippi Fan. The remaining eight predominance facies have more restricted distributions. The areal patterns of these predominance facies can be related chiefly to water mass and substrate characteristics; modifications are brought about by calcite dissolution, upwelling, and sill depth. Analysis of ancient generic predominance facies is useful in predicting relative paleobathymetry and other paleoenvironmental properties.     

Ultra- and microplankton assemblages as indicators of trophic status in a Mediterranean lagoon

The seasonal abundance distribution of heterotrophic prokaryotes, pico- and nanophytoplankton, was investigated in connection with environmental variables and microplankton abundance at five stations in Ghar El Melh Lagoon (northeastern Tunisia). Flow cytometry analysis of ultraplankton resolved (i) five heterotrophic prokaryote groups labelled LNA1, LNA2 (low nucleic acid content), HNA1, HNA2 and HNA3 (high nucleic acid content) and (ii) at least 14 ultraphytoplankton groups assigned to picoeukaryotes, picoprokaryotes, nanoeukaryotes, cryptophyte-like cells and some unknown communities. Redundancy analysis (RDA) revealed (i) autumn-summer outbreaks of heterotrophic prokaryotes dominated by HNA groups and (ii) winter-summer proliferation of ultraphytoplankton dominated by nanophytoplankton groups. Generalized additive models (GAM) highlighted the role of (i) water temperature and orthophosphate concentrations in heterotrophic prokaryote distribution and (ii) water temperature and salinity in ultraphytoplankton abundance variation. Based on Spearman's rank correlation, significant negative correlations were established between ultra- and microplankton communities suggesting that, through grazing pressure, microplankton may be behind the drastic decrease in ultraplankton abundances in spring.     

Narrow sea crossings present major obstacles to migrating Griffon Vultures Gyps fulvus

The flight behaviour of Griffon Vultures Gyps fulvus was studied at a major migration bottleneck, the Strait of Gibraltar in southernmost Spain, during the autumns of 2004 to 2007. The 14‐km‐wide sea channel significantly impeded the southern migration of the species into Africa, with many birds attempting repeated passage for weeks before crossing, and others not crossing at all and overwintering in Southern Spain. Water‐crossing attempts were restricted to times between 11:00 and 14:00 h on days with light or variable winds, or on days with strong winds from the north or west. No crossing attempts were made on days with strong winds from the south or east. Vultures attempted to cross the Strait in large flocks and never attempted to do so alone. Although 29% of the birds soared during crossing attempts, at least until they flew beyond visible range of approximately 4 km, most engaged in considerable flapping flight when attempting to cross. Overall, birds flying over water flapped more than 10 times as frequently as those flying over land prior to crossing attempts. Vultures did not flap continuously, but intermittently in brief bouts of flapping interspersed with periods of gliding or soaring flight. The number of flaps per bout over water was significantly greater than the number of flaps per bout over land. Vultures flying over water that flapped at rates of 20 flaps or more per minute typically aborted attempted crossings and returned to Spain in intermittent flapping and gliding flight. There are numerous reports of Vultures falling into the Strait and drowning while attempting to cross, as well as reports of returning Vultures collapsing on the beach having reached Spain in spring ( Barrios Partida 2006 ). Our observations indicate that passage of Griffon Vultures at the Strait of Gibraltar is limited by the species’ over‐water flapping‐flight abilities, including its inability to flap continuously for even short periods of time. We suggest that even relatively short sea crossings represent significant obstacles to migrating Vultures and discuss the implications of this limitation on the distribution and abundance of the species.     

Phylogeographic patterns in Hypochaeris section Hypochaeris (Asteraceae, Lactuceae) of the western Mediterranean

Aim  To analyse phylogeographic patterns in the four species of Hypochaeris sect. Hypochaeris , evaluating possible areas of origin and the microevolutionary processes that have shaped their morphology, genetics and distribution.
Location  Western Mediterranean area.
Methods  We applied amplified fragment length polymorphism (AFLP) markers to a total of 494 individuals belonging to 82 populations of Hypochaeris arachnoidea , H. glabra , H. radicata and H. salzmanniana to determine population structure.
Results  Populations with the largest proportion of private and rare AFLP fragments were found in Morocco. This region was consequently inferred to be the ancestral area for H. arachnoidea , H. glabra , H. radicata and H. salzmanniana . The Guadalquivir River (southern Spain) was inferred to be an effective dispersal barrier for H. glabra and H. radicata. The Strait of Gibraltar was inferred to be a somewhat weaker barrier than the Guadalquivir River for H. radicata and a much weaker barrier for H. glabra . The main barrier for H. salzmanniana coincides with the extension of the Rif Mountains to the Atlantic coast in Morocco, and the Strait of Gibraltar is a much weaker barrier for this species. Hypochaeris arachnoidea appears to have originated in the Atlas Mountains.
Main conclusions  The highest levels of genetic variation in La Mamora forest ( H. glabra and H. salzmanniana ) or the adjacent central Middle Atlas ( H. arachnoidea and H. radicata ) in Morocco suggest that these areas were a centre of origin of Hypochaeris sect. Hypochaeris . All three potential barriers – the Guadalquivir River, the Strait of Gibraltar, and the Rif Mountains – have been important in shaping genetic diversity in species of section Hypochaeris .     

Trends of autumn counts at Iberian migration bottlenecks as a tool for monitoring continental populations of soaring birds in Europe

Migration monitoring may allow us to detect population trends over large geographic areas because the pattern of change in migrant counts may be expected to follow the pattern of change in population size. We analysed recent regional European population trends of migratory soaring birds from rates of change in migration counts over the Strait of Gibraltar (Spain) during the years (1999–2013). An additional bottleneck (Organbidexka, France) within the same migratory route and period was also considered. We estimated count trends by fitting a log-generalized linear model to the time series of each species counts. The counts in Organbidexka were used to test the consistency in the observed trends over the Strait of Gibraltar. Migration counts of White and Black Storks, Black Kites, Short-toed and Booted Eagles as well as Egyptian Vultures showed a linear increase over the Strait of Gibraltar throughout the 15-year period. In contrast, Honey Buzzard numbers remained stable. Trends were highly consistent with those recorded in Organbidexka. We suggest that the larger slopes for the trends in Organbidexka when compared with the Strait reflect an increasing tendency in these species to overwinter in southern Europe. A combination of complementary data sets collected at different bottleneck sites within the European–African flyway system may become a fundamental tool for the investigation of migratory patterns and population trends and changes of soaring migrant birds all over Europe.