Strong population genetic structure and contrasting demographic histories for the small-spotted catshark (Scyliorhinus canicula) in the Mediterranean Sea

Coastal and demersal chondrichthyans, such as the small-spotted catshark, are expected to exhibit genetic differentiation in areas of complex geomorphology like the Mediterranean Basin because of their limited dispersal ability. To test this hypothesis, we used a fragment of the mitochondrial cytochrome c oxidase subunit I gene and 12 nuclear microsatellite loci in order to investigate the genetic structure and historical demography of this species, and to identify potential barriers to gene flow. Samples were collected from the Balearic Islands, the Algerian Basin, the Ionian Sea, the Corinthian Gulf and various locations across the Aegean Sea. Additional sequences from the Atlantic and the Levantine Basin retrieved from GenBank were included in the mitochondrial DNA analysis. Both mitochondrial and nuclear microsatellite DNA data revealed a strong genetic subdivision, mainly between the western and eastern Mediterranean, whereas the Levantine Basin shared haplotypes with both areas. The geographic isolation of the Mediterranean basins seems to enforce the population genetic differentiation of the species, with the deep sea acting as a strong barrier to its dispersal. Contrasting historical demographic patterns were also observed in different parts of the species'' distribution, most notably a population growth trend in the western Mediterranean/Atlantic area and a slight decreasing one in the Aegean Sea. The different effects of the Pleistocene glacial periods on the habitat availability may explain the contrasting demographic patterns observed. The current findings suggest that the small-spotted catshark exhibits several genetic stocks in the Mediterranean, although further study is needed.     

High Mortality of Red Sea Zooplankton under Ambient Solar Radiation

High solar radiation along with extreme transparency leads to high penetration of solar radiation in the Red Sea, potentially harmful to biota inhabiting the upper water column, including zooplankton. Here we show, based on experimental assessments of solar radiation dose-mortality curves on eight common taxa, the mortality of zooplankton in the oligotrophic waters of the Red Sea to increase steeply with ambient levels of solar radiation in the Red Sea. Responses curves linking solar radiation doses with zooplankton mortality were evaluated by exposing organisms, enclosed in quartz bottles, allowing all the wavelengths of solar radiation to penetrate, to five different levels of ambient solar radiation (100%, 21.6%, 7.2%, 3.2% and 0% of solar radiation). The maximum mortality rates under ambient solar radiation levels averaged (±standard error of the mean, SEM) 18.4±5.8% h⁻¹, five-fold greater than the average mortality in the dark for the eight taxa tested. The UV-B radiation required for mortality rates to reach ½of maximum values averaged (±SEM) 12±5.6 h⁻¹% of incident UVB radiation, equivalent to the UV-B dose at 19.2±2.7 m depth in open coastal Red Sea waters. These results confirm that Red Sea zooplankton are highly vulnerable to ambient solar radiation, as a consequence of the combination of high incident radiation and high water transparency allowing deep penetration of damaging UV-B radiation. These results provide evidence of the significance of ambient solar radiation levels as a stressor of marine zooplankton communities in tropical, oligotrophic waters. Because the oligotrophic ocean extends across 70% of the ocean surface, solar radiation can be a globally-significant stressor for the ocean ecosystem, by constraining zooplankton use of the upper levels of the water column and, therefore, the efficiency of food transfer up the food web in the oligotrophic ocean.     

The microcopepod fauna in the Eastern Mediterranean and Arabian Seas: a comparison with the Red Sea fauna

Multiple opening-closing nets of 0.05 mm mesh size were employed to study the community structure and vertical distribution of microcopepods at selected stations in the Red Sea, Arabian Sea and Eastern Mediterranean Sea down to a maximum depth of 1850 m. Calanoids, cyclopoids (Oithona and Paroithona) and poecilostomatoids (mainly Oncaea) were the 3 most abundant orders. In the epipelagic zone (0–100 m), these orders occurred at similar abundance levels, whereas in the meso- and bathypelagic zones the poecilostomatoid genus Oncaea dominated numerically by about 60–80% of all copepodids.The species diversity of Oncaea in the Red Sea is compared with preliminary results from the two adjacent regions. In the deep Eastern Mediterranean Sea, the number of species appears to be similar to that in the deep Red Sea and low as compared to the deep Arabian Sea. In this latter area an extremely speciose Oncaea fauna was found at depth below the oxygen-minimum-zone (900–1850 m). The results are related to the differences in the hydrographic conditions of these 3 areas.     

Zooplankton assemblages and influence of environmental parameters on them in a Mediterranean coastal area

Temporal dynamics of zooplankton communities and assemblages,as well as the influence of environmental factors on them, werestudied in Saronikos Gulf (Aegean Sea, Greece). Different multivariatetechniques (hierarchical clustering, multidimensional scalingand correspondence analysis) were applied on a 2 year data setof zooplankton species composition, based on samples collectedat five stations of the study area. A clear discrimination oftwo communities was revealed, the first one in the semi-enclosedpolluted northern part (Elefsis Bay) andthe second in SaronikosGulf proper. Within the latter community, five assemblages weredistinguished: (i) the coastal winter assemblage characterizedby Ctenocalanus vanus, Oithona similis, Clausocalanus pergensand Fritillaria pellucida; (ii) the psychrophilic assemblageinfluenced by the open sea and characterized by Oithona plumiferaand Clausocalanus jobei; (iii) the spring assemblage characterizedby Evadne nordmanni and Centropages typicus; (iv) the coastalthermophilic assemblage characterized by Penilia avirostis,Evadne ergesrina and Temora stylifera; (v) the thermophilicassemblage influenced by the open sea and characterized by Clausocalanusfurcatus. Both zooplankton and environmental data were treatedby multiple correspondence analysis which revealed the importanceof some environmental factors on zooplankton community composition(eutrophication-pollution, temperature, water mass circulation,hydrology and topography).     

Untersuchungen zur Zoogeographie der Euphausiaceen (Crustacea) des Roten Meeres

A joint programme on “Biota of the Red Sea and the Eastern Mediterranean” has been carried out by the Hebrew University of Jerusalem and the Smithsonian Institution of Washington between 1967 and 1972 in order to study the role played by the Suez Canal as a route for faunal exchanges between the Red Sea and Eastern Mediterranean. The euphausiids of this material have been examined and additional samples of zooplankton have been taken in the Gulf of Elat (Aqaba) in 1973 in order to study the vertical distribution of the euphausiids. Four species have been found to occur in the Northern Red Sea and the Gulf of Elat:Euphausia diomedeae, E. sanzoi, Stylocheiron affine andS. abbreviatum. Seven species were found in the Eastern Mediterranean of whichEuphausia brevis is the dominant species. The present studies revealed that an exchange of Euphausiacea through the Suez Canal does not take place. The species of the Red Sea belong to the Indopacific fauna. Despite the particular historic-geographical and ecological situation of the Red Sea, no endemisms or subspecies have evolved there within the Euphausiacea.     

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.     

Distribution patterns of micro- and meso-zooplankton communities in sea ice regions of Lützow-Holm Bay, East Antarctica

In the Southern Ocean, zooplankton research has focused on krill and macro-zooplankton despite the high densities of micro- and meso-zooplankton. We investigated their community structure in relation to different sea ice conditions around Japan’s Syowa Station in Lützow-Holm Bay, in the summers of 2011 and 2012. Zooplankton samples were collected using vertical hauls (0–150 m), with a closing net of 100-μm mesh size. The results of cluster analysis showed that the communities in this region were separated into fast ice, pack ice, and open ocean fauna. The fast ice fauna had lower zooplankton abundance (393.8–958.9 inds. m^?3) and was dominated by cyclopoid copepods of Oncaea spp. (54.9–74.8 %) and Oithona similis (6.6–19.9 %). Deep-water calanoid copepods were also found at the fast ice stations. Pack ice and open ocean fauna had higher zooplankton abundance (943.6–2,639.8 inds. m^?3) and were characterized by a high density of foraminiferans in both years (6.6–61.9 %). Their test size distribution indicated that these organisms were possibly released from melting sea ice. The pteropod Limacina spp. was a major contributor to total abundance of zooplankton in the open ocean zone in 2012 (26.4 %). The physical and/or biological changes between 2 years may affect the abundance and distribution of the dominant zooplankton taxa such as cyclopoid copepods, foraminiferans, and pteropods. Information on the relationships between the different species associated with sea ice will help to infer the possible future impacts of climate change on the sea ice regions.     

Opisthobranch molluscs of the Sudanese Red Sea

Eighteen opisthobranch species are described and illustrated from the Sudanese Red Sea, including seven new species, one new subspecies and three species for which this is the first Red Sea record. Eleven bullomorphs, four pleurobranchomorphs, four sacoglossans and four phyllidiid mudibranchs are now known from the Red Sea. There appears to be a high percentage of endemic species in the Red Sea. This is what one might expect, in view of the conditions of near isolation, low temperatures and high salinity that prevailed in this sea 13000 23000 years ago. Of the groups discussed in this paper, one Red Sea species has invaded the Mediterranean Sea, and one Mediterranean species has invaded the Red Sea, since the opening of the Suez Canal in 1867. Many Red Sea species are very colourful, in comparison to Mediterranean ones. This could perhaps be because Red Sea waters are cleaner, thereby favouring the evolution of greater precision in colour markings.     

Opisthobranch molluscs of the Sudanese Red Sea

Eighteen opisthobranch species are described and illustrated from the Sudanese Red Sea, including seven new species, one new subspecies and three species for which this is the first Red Sea record. Eleven bullomorphs, four pleurobranchomorphs, four sacoglossans and four phyllidiid mudibranchs are now known from the Red Sea.
There appears to be a high percentage of endemic species in the Red Sea. This is what one might expect, in view of the conditions of near isolation, low temperatures and high salinity that prevailed in this sea 13000 23000 years ago.
Of the groups discussed in this paper, one Red Sea species has invaded the Mediterranean Sea, and one Mediterranean species has invaded the Red Sea, since the opening of the Suez Canal in 1867.
Many Red Sea species are very colourful, in comparison to Mediterranean ones. This could perhaps be because Red Sea waters are cleaner, thereby favouring the evolution of greater precision in colour markings.     

Bathymetric distribution of medusae in the open waters of the middle and south Adriatic Sea during spring 2002

Twenty-eight species of hydromedusae and one scyphomedusa werecollected from the middle and south Adriatic in Spring 2002.Haliscera bigelowi was recorded for the first time in the AdriaticSea and Dicodonium adriaticum for the southern Adriatic. Thecosmopolitan species Rhopalonema velatum, Aglaura hemistomaand Persa incolorata averaged 88% of total medusan abundance.The Mediterranean species Rhabdoon singulare and Solmissus albescenswere numerous at the deeper stations. These species were foundeither in the southern or in middle Adriatic, and their abundanceis greater than in other regions of the Mediterranean Sea. Speciesdiversity and abundance generally were highest in the upper200 m and decreased with depth. Diel vertical migration patternsincluded some species that nocturnally sought shallower or deeperlayers, and some species migrated in both directions. A fewspecies did not show any vertical migration. Although lightlikely triggers vertical movements, data suggest that foragingstrategies also influence the vertical migration of medusae.     

Palaeoceanographic record of the last deglaciation in the Strait of Sicily

The palaeoceanographic evolution of the Levantine waters during the last deglacial time is investigated using the sedimentary record of a deep sea core, CS 70-5, from the Linosa basin (35° 44.4′N/13° 11.0′E, 1486 m water depth). Radiocarbon dating and oxygen isotope stratigraphy based on¹⁸O changes inGlobigerina bulloides allow us to recognize and to date the different steps of the deglaciation. These steps are synchronous with those reported in the North Atlantic, but correspond to a δ¹⁸O decrease of higher amplitude than in the Alboran sea or in the North Atlantic Ocean. Major faunal events permit the establishment of a local biozonation which differs from those reported either for the Alboran sea or the Eastern Mediterranean basin. Major breaks in the faunal assemblages occurred during Termination I_A, within the first step of the deglaciation around 14 kyr B.P., and near 10.6 kyr B.P. within the Younger Dryas. The onset of the last deglaciation induced important changes in the characteristics of the Levantine and Atlantic water masses which occupied the Strait of Sicily. The δ¹³C records ofGlobigerina bulloides andCibicidoides pachyderma indicate that the modifications observed in the assemblages of deep faunas are controlled by the oxygenation of the water column. δ¹³C records ofGlobigerina bulloides are similar throughout the West Mediterranean as well as in sediments located below the present Mediterranean outflow. The distributional pattern as well as its δ¹³C record suggest that this species could be a good recorder of the upper Levantine waters and, more precisely, of the mixing layer of the overlying Atlantic waters with the Levantine ones.Major influxes of Atlantic waters during Terminations I_A and I_B could have slowed down the vertical mixing of the different water layers present in the Strait of Sicily and caused a decrease in the oxygenation of the water column. During Termination I_B the effect of Atlantic influxes was reinforced by the occurrence of a low salinity layer in the eastern basin which led to the stagnation of the deep waters. The two episodes of decreased oxygenation in the Levantine waters also favored the precipitation of inorganic magnesium calcite.     

Zooplankton annual cycle in a Mediterranean coastal area

The annual cycle of the zooplankton community in the SaronikosGulf (Aegean Sea, Greece) was studied over a period of 2 years.The sampling scheme included monthly hauls at three stationsdifferentiated according to depth and neritic character. Maximumvalues of total zooplankton abundance were found in summer monthsup to early autumn and partially in spring. Copepods dominatedduring most of the year (Clausocalanus furcatus, Paracalanusparvus, Temora stylifera, Ctenocalanus vanus, Oithona similis,Oithona plumifera), while cladocerans (Penilia avirostris) wereabundant in summer months and in September. No important fluctuationswere detected between the 2 years of study, while monthly oneswere more significant in the more neritic station during thewinter–spring period. Correspondence analysis showed thatthe seasonal evolution of zooplankton is related to environmentalparameters: temperature, hydrography expressed in open sea influenceand topography.     

The microcopepod fauna in the Gulf of Aqaba, northern Red Sea: species diversity and distribution of Oncaeidae (Poecilostomatoida)

A total of 23 species and three groups of form variants of oncaeidcopepods have been identified, which were collected in smallmesh net samples taken along a transect from the northernmostRed Sea (>27°N) to the Gulf of Aqaba down to a maximumdepth of 800 m. Two of the species were present only in theRed Sea main basin, but were not recorded in the Gulf. By comparingthe present results with previously published data from thecentral and southern Red Sea a first assessment of the zoogeographicaldistribution of Oncaeidae in the entire Red Sea has been achieved.The species diversity of Oncaeidae in the Gulf of Aqaba appearsto be considerably lower compared to the southern Red Sea, where31 oncaeid species and four groups of form variants have beenfound. The observed latitudinal gradient in species numbersof Oncaeidae generally corresponds to the gradients observedfor various other zooplankton taxa in the Red Sea. First dataon the vertical distribution of oncaeid species in the Gulfare provided.     

The Temporal Dynamics of Coastal Phytoplankton and Bacterioplankton in the Eastern Mediterranean Sea

This study considers variability in phytoplankton and heterotrophic bacterial abundances and production rates, in one of the most oligotrophic marine regions in the world–the Levantine Basin. The temporal dynamics of these planktonic groups were studied in the coastal waters of the southeastern Mediterranean Sea approximately every two weeks for a total of two years. Heterotrophic bacteria were abundant mostly during late summer and midwinter, and were positively correlated with bacterial production and with N₂ fixation. Based on size fractionating, picophytoplankton was abundant during the summer, whereas nano-microphytoplankton predominated during the winter and early spring, which were also evident in the size-fractionated primary production rates. Autotrophic abundance and production correlated negatively with temperature, but did not correlate with inorganic nutrients. Furthermore, a comparison of our results with results from the open Levantine Basin demonstrates that autotrophic and heterotrophic production, as well as N₂ fixation rates, are considerably higher in the coastal habitat than in the open sea, while nutrient levels or cell abundance are not different. These findings have important ecological implications for food web dynamics and for biological carbon sequestration in this understudied region.     

YOLDIELLA SEGUENZAE, A NEW SPECIES OF NUCULANIDAE (BIVALVIA; NUCULOIDA) FROM THE MEDITERRANEAN SEA

A new species, Yoldiella seguenzae (Bivalvia, Nucu-loida), froma deep sea community off the north east coast of Sardinia (MediterraneanSea), is described. Morphometrical and statistical comparisonwith the very similar Yoldiella philippiana (Nyst, 1845), andgeneral morphological comparison with other Mediterranean andAtlantic species support the distinc-tivness of Y. seguenzaewhich is distributed in deep waters of the Central MediterraneanSea, Alboran Sea and the Atlantic Ocean. (Received 21 October 1993; accepted 1 July 1994)     

The family Xystonellidae (Ciliophora, Tintinnina) in the Adriatic Sea

This paper reports quantitative, horizontal and vertical distributiondata of the 11 species of the family Xystonellidae found inthe Adriatic Sea and in the Strait of Otranto. The samples werecollected in coastal and open waters, with a plankton net equippedwith a closing system, in the period from 1973 to 1986. At thedeeper stations of the South Adriatic Pit, hauls were takenin eight vertical layers, while at other stations sampling dependedon the respective depth of each station. Xystonellidae are oceanictintinnines, mainly present in the South Adriatic and the Straitof Otranto throughout the year. They are characteristic of SouthAdriatic and Eastern Mediterranean water masses. Horizontaldistribution of lower mesopelagic species is limited by the200 m isobath. Only sparse individuals of the upper mesopelagicand epipelagic species were found in the Jabuka Pit, probablydue to the late autumn and winter current. These species werenot registered to the north of this region. They were registeredbelow the 200 m depth as dominant tintinnines, while in summerthey represented an average of 81% of the total tintinnine population.     

Selective predation by herring and mysids, and zooplankton community structure in a Baltic Sea coastal area

In lakes, fish and invertebrate predation are recognized asstrong structuring forces on zooplankton communities. The objectof this investigation was to study whether predation has a similarpotential in a coastal area of the brackish Baltic Sea and ifit could explain observed differences in zooplankton communitystructure between a reference area and an eutrophied area. Speciescomposition and daily vertical migration of zooplankton andzooplanktivores, and the diets of the latter, were studied inJuly and August at two 30 m deep stations differing in primaryproductivity. The biomass of zooplankton >35 µm wasdominated by copepods, but cladocerans and rotifers also occurredin significant numbers. The dominating zooplanktivores wereherring (Clupea harengus) and the mysid shrimp Mysis mixta.They fed almost exclusively on zooplankton, mainly copepods,and their estimated food consumption equalled or exceeded thesummer copepodite production. The structure of the zooplanktoncommunity cannot be explained by effects of predation or byfeeding conditions alone. Increases in rotifer and cladoceranabundances with increased primary production suggests effectsof food supply. However, a generally rapid decline in the annualsummer peak of cladocerans may be caused by predation. The totalabundance of copepods did not increase with improved feedingconditions, but there was a shift in species dominance. Thecopepod Ewytemora affinis hirundoides, which was intensivelypreyed upon, increased with increased phytoplankton production,while Acartia bifilosa and/or A.longiremis, which was less eaten,decreased. Predation may explain a pronounced daily verticalmigration of the most predated copepods. They occurred in deeperwater during the day, when the visually feeding herring wereactive, and moved closer to the surface at night when M.mixtaleft the bottom, to forage in the water column.     

东海大陆架外缘和大陆坡深海渔场浮游动物研究——Ⅰ.生物量

本文首次描述了本海区中浮游动物生物量及其分布。其平均生物量为41毫克/米~3,仅及东海西部沿海生物量的四分之一,从而表示了一般大洋性的特征。 生物量随水深增加而逐渐下降,其所下降的近似值能以对数关系值表示: logY=α-k~z Y是生物量(湿重),Z是深度, α是常数,k是递减系数。 y=α'e~(-kz) 在东海海槽深海区内,在从表层至100米以内浅水层中,平均生物量为75毫克/米~3,但自500米至2170米水层中,其生物量仅及其上层生物量的1/10或1/20。其变化也可以下列公式来表示: y=58.886e~(-2.074×10~(-3)z) r=-0.7558 r是相关系数。 本文还对浮游动物生物量和渔业水文等之间的关系作了阐述。