Escaped introduced sea bass (Dicentrarchus labrax) infected by Sphaerospora testicularis (Myxozoa) reach maturity in coastal habitats off Canary Islands

Aquaculture activities have introduced European sea bass (Dicentrarchus labrax) along the coasts of some of the Canary Islands. We present the first record of simultaneous male and female gonad maturation of escaped sea bass in the wild, indicating that this species is finding its essential fish habitat (EFH). Individuals with ripe gonads were only caught during January and February 2009, although the maturation and spawning season may last from November to February in the studied area (Tenerife island). Bass infected by Sphaerospora testicularis were found and the incidence of the parasite was checked. This represents the southernmost record of the parasite, probably introduced together with sea bass stock. The results are discussed from the point of view of risk assessment and the ecology of invasions being valuable for aquaculture management in Central North Atlantic and Mediterranean areas.     

A Triggered Depth‐Dependent Sampling System to Overcome the Carry‐Over Effects of the Membrane Interface Probe

The membrane interface probe (MIP) is widely used for the in situ characterization of volatile organic compounds (VOCs) in the subsurface. A main problem using the MIP system is the carry‐over effect of VOCs during the transport from the point of measurement to the detector using a conventional transfer line. This effect results in compound specific retention times, which is shown in disproportionately high measuring signals after the actual penetration of contaminated zones. In consequence, the lower extent of contamination is not clearly identifiable and may be overestimated. The presented field study presents an evaluation of different methods to overcome the carry‐over effect, especially with regard to the required measurement times that are needed to wait for a complete disappearance of the detector signals before forwarding the probe. This was accomplished by comparing data collected with a MIP system with (1) unheated transfer line and (2) a system including a heated transfer line to data collected with a system using (3) a depth‐dependent triggered sampling behind the membrane including two transfer lines. A comparison with analytical results from soil samples gave a good correlation for all three methods. Furthermore, it could be shown that the use of a heated transfer line has a time improvement of 30% compared to an unheated transfer line while the depth dependent triggered sampling using two separate transfer lines yielded a time improvement of over 90%. These results confirm the benefit of the latter method, particularly for the use in highly contaminated sediments.     

Evidence from mantle xenoliths for relatively thin (<100 km) continental lithosphere below the Phanerozoic crust of southernmost South America

Garnet peridotite xenoliths in the Quaternary Pali-Aike alkali olivine basalts of southernmost South America are samples of the deeper portion of continental lithosphere formed by accretion along the western margin of Gondwanaland during the Phanerozoic. Core compositions of minerals in garnet peridotites indicate temperatures of 970 to 1160°C between 1.9 and 2.4 GPa, constraining a geothermal gradient which suggests a lithospheric thickness of approximately 100 km below this region. Previously, this lithosphere may have been heated and thinned to ≤80 km during the Jurassic break-up of Gondwanaland, when widespread mafic and silicic volcanism occurred in association with extension in southern South America. Subsequent cooling, by up to >175°C, and thickening, by about 20 km, of the lithosphere is reflected in low-temperature (<970°C) spinel peridotites by chemical zonation of pyroxenes involving a rimward decrease in Ca, and in moderate- and high-temperature (>970°C) peridotites by textural evidence for the transformation of spinel to garnet. A recent heating event, which probably occurred in conjunction with modal metasomatism related to the genesis of the Pali-Aike alkali olivine basalts, has again thinned the lithosphere to <100 km. Evidence for this heating is preserved in moderate- and high-temperature (>970°C) peridotites as chemical zonation of pyroxenes involving a rimward increase in Ca, and by kelyphitic rims around garnet. The majority of moderate- and high-temperature (>970°C) xenoliths are petrochemically similar to the asthenospheric source of mid-oceanic ridge basalts: fertile (>20% modal clinopyroxene and garnet), Fe-rich garnet lherzolite with major element composition similar to estimates of primitive mantle, but large-ion-lithophile and light-rare-earth element depletion relative to heavy-rare-earth elements, and with Sr, Nd, Pb, Os, and O isotopic compositions similar to MORB. In contrast, infertile, Mg-rich spinel harzburgite is predominant among low-temperature (<970°C) xenoliths. This implies a significant chemical gradient and increasing density with depth in the mantle section represented by the xenoliths, and the absence of a deep, low density, olivine-rich root below the southernmost South American crust such as has been inferred below Archean cratons. With respect to both temperature/rheology and chemistry/density, the subcontinental mantle lithosphere below southernmost South America is similar to that below oceanic crust. It is interpreted to have formed by tectonic capture, during the Paleozoic, of a segment of what had previously been oceanic lithosphere generated at a late Proterozoic mid-oceanic spreading ridge.     

Between the devil and the deep blue sea: Functional conflicts in Cape Town''s Victoria and Alfred Waterfront

The global phenomenon of waterfront revitalization is a planning strategy commonly employed by city and port authorities eager to overcome the redundancy and associated urban decay of their docklands. The spatial transformation that generally accompanies such initiatives often results in functional conflict. Focusing on the redevelopment of the traditional dockland precinct of the South African portcity of Cape Town, this paper shows how attempts to rationalize pre-existing harbour activities resulted in conflict between the developer, the Victoria and Alfred Waterfront Company, and its largest industrial tenant, the fishing industry. The utilization of existing harbour space and, more specifically, questions of tenure and affordable rentals are identified as the principal elements of the contentious negotiations between these parties.     

Geologie und geologischer Unterricht an den französischen Hochschulen

Ohne Zusammenfassung     

Twinned calcite as an indicator of high differential stresses and low shock pressure conditions during impact cratering

Shock-related calcite twins are characterized in calcite-bearing metagranite cataclasites within crystalline megablocks of the Ries impact structure, Germany, as well as in cores from the FBN1973 research drilling. The calcite likely originates from pre-impact veins within the Variscan metagranites and gneisses, while the cataclasis is due to the Miocene impact. Quartz in the metagranite components does not contain planar deformation features, indicating low shock pressures (<7 GPa). Calcite, however, shows a high density (>1/μm) of twins with widths <100 nm. Different types of twins (e-, f-, and r-twins) crosscutting each other can occur in one grain. Interaction of r- and f-twins results in a-type domains characterized by a misorientation relative to the host with a misorientation angle of 35°–40° and a misorientation axis parallel to an a-axis. Such a-type domains have not been recorded from deformed rocks in nature before. The high twin density and activation of different twin systems in one grain require high differential stresses (on the order of 1 GPa). Twinning of calcite at high differential stresses is consistent with deformation during impact cratering at relatively low shock pressure conditions. The twinned calcite microstructure can serve as a valuable low shock barometer.