Time filter

Source Type

Donovan S.K.,Nederlands Centrum voor Biodiversiteit Naturalis | Jagt J.W.M.,Natuurhistorisch Museum Maastricht | Lewis D.N.,Natural History Museum in London
Geologie en Mijnbouw/Netherlands Journal of Geosciences

New specimens described herein add to our knowledge of uncommon parataxa (embedment structures, borings and a certain type of burrow) from the type area of the Maastrichtian Stage, the material originating from the ENCI-HeidelbergCement Group (Maastricht), Ankerpoort-'t Rooth (Bemelen) and former Blom (Berg en Terblijt) quarries in southern Limburg (the Netherlands), and from the CBR-Romontbos (Eben Emael) and CPL SA (Haccourt) chalk pits in the province of Liege (northeast Belgium). Although Centrichnus eccentricus Bromley & Martinell has previously been recorded from this area, it has not received formal description; the specimen documented herein shares a test of the echinoid Echinocorys gr. conoidea with numerous other episkeletozoans. Podichnus cf. centrifugalis Bromley & Surlyk occurs both on echinocorythid echinoid tests and guards of belemnitellid coleoids; two out of seven specimens display radial discontinuous channels, indicative of the extreme penetration of filaments from the attached brachiopod's pedicle. Renichnus arcuatus Mayoral shows a range of morphologies, from the embedment structure sensu stricto through to specimens retaining internal moulds of the producing, embedded vermetid gastropod to free shells of Vermetus binkhorsti Cossmann. Burrows packed with bioclastic debris, particularly primary spines and a few test plates of phymosomatid echinoids, present a systematic conundrum, although appearing comparable to the ichnogenera Nummipera Hölder and Baronichnus Breton in several respects. Source

Macneil C.,Food and Agriculture | Platvoet D.,Nederlands Centrum voor Biodiversiteit Naturalis
Aquatic Conservation: Marine and Freshwater Ecosystems

Linkages between habitat structure, invasibility and direct species interactions were examined in a Central European river system, the Schipbeek in the Netherlands, invaded by the 'killer shrimp' amphipod Dikerogammarus villosus. The invader's arrival in other fresh waters is linked to declines in macroinvertebrate biodiversity, with previous studies indicating that the invader's impacts may be mediated by habitat heterogeneity and substrate type. Using an extensive 50km field survey, potential habitat factors influencing distribution were identified. Of 12 sites surveyed, two contained fish 'passes' (instream sections creating faster flows via concrete structures covered in cemented rocks). It was only in these sites that D. villosus was found and then only in the fish pass areas, as opposed to the surrounding river, which, like the remaining 10 sites of the survey, was characterized by sluggish flows and a muddy/silty substrate. Gammarus roeselii was the numerically dominant amphipod in these latter areas, with no D. villosus being detected. A repeated survey more than 2years later, revealed the same distribution pattern. Within both fish pass areas, D. villosus relative abundance was highest in faster flowing, less macrophyte dense patches, with the opposite true for G. roeselii. D. villosus numerical abundance decreased with increasing macrophyte cover in both passes. A transplant experiment indicated high survivorship of D. villosus outside fish pass areas and showed that slow-flowing watercourses with mud/silt substrates, previously deemed 'unsuitable', are not effective barriers to D. villosus spreading to more 'suitable', faster, rocky substrate watercourses. We recommend that when the location and cost-benefit analysis of instream rehabilitation structures, such as fish passes, is being considered, attention must be paid to the risk of hastening the spread of this invader. We also recommend that when monitoring programmes are designed for D. villosus in newly invaded regions, instream artificial structures should be included as part of the survey. © 2013 John Wiley & Sons, Ltd. Source

Roselaar K.,Nederlands Centrum voor Biodiversiteit Naturalis

The national bird skin collection of the Netherlands, housed in the National Centre for Biodiversity ncb Naturalis in Leiden, contains 186 skins and mounts of Puffin Fratercula arctica. Of these, 94 were found washed ashore in the Netherlands during 1835-2010, and 84 were from the breeding grounds, especially from Iceland. Wing length (maximum chord), bill length (culmen without cere) and bill depth (at deepest point, without cere) of all birds were taken before an audience in the LiveScience hall of ncb. Wings of the Dutch sample ranged from 132 to 176 mm, pointing to the occurrence of several subspecies. The large variation is however also due to the presence of juveniles, which were found to have an average wing length 13 mm shorter than adults. Most birds had washed ashore in winter (table 1). None of the adults was in wing moult, but of five immature birds from June four were in simultaneous flight-feather moult. Comparison of wings from the Netherlands with those in ncb from the breeding grounds (fig. 1) shows that 14% of the birds of the Dutch coast belong to nominate arctica (table 2), 86% to gra-bae (including birds from southern Iceland - fig. 2). No bird with measurements suggesting the high-arctic subspecies naumanni was found. Because bills of adult winter birds are smaller than those of breeding birds and also juvenile and immature birds have small bills (table 3), bill measurements were not helpful to assess the origin of non-breeders. Measurements of European populations from the literature (table 4-5, summarised in fig. 3) show that size variation is not strictly clinal, but that two parallel clines occur, in each of which size increases from southern colonies to northern ones or from warmer August water temperatures to colder ones: an 'Atlantic' cline (western British Isles, Shetlands, Faeroes, Iceland, Bear Island) and a'continental'one (France, eastern Britain, coastal Norway) (fig 3)- Whether these two clines are due to genetic or to ecological differences has to be worked out. Because of the abrupt changes in wing and bill measurements over a short distance between southern and northern Iceland and (within Norway) between Rogaland and Runde Island, recognition of the smaller subspecies grabae and the larger nominate arctica is maintained, as is naumanni. Source

Janssen A.W.,Nederlands Centrum voor Biodiversiteit Naturalis
Scripta Geologica

A borehole was drilled at Rotterdam in 1955 as a demonstration during the E55 exhibition. Holoplanktonic molluscs (pteropods) were found to be present in the interval 504.5-655.0 m below rotary table (= RT). The upper sample of Middle Eocene (Lutetian) age yielded just a few unidentifiable limacinids. The section between 507.5-607.0 m, of Early Eocene (Ypresian) age, yielded poorly preserved pteropods and demonstrated that the complete interval belongs to pteropod zone 9. Apart from the most abundant species, Camptoceratops priscus, which is the index taxon of pteropod zone 9, the section yielded Heliconoides mercinensis and Limacina taylori, which are known to accompany the index species. Two further limacinid species are described as new to science, viz. Limacina erasmiana sp. nov. and L. guersi sp. nov., to date not known from elsewhere in the North Sea Basin. The occurrence of L. pygmaea in a restricted interval (569.0-574.0 m-RT) is remarkable; it is generally considered to be of Lutetian age, but also is found in the Ypresian of Gan, southwest France. Its occurrence in the E55 section is explained as a 'sealevel related molluscan plankton event', allowing species of oceanic distribution to enter the basin during sea level high stands, as was recently also demonstrated for several Oligocene pteropods. Source

Batenburg S.J.,University Utrecht | Reichart G.-J.,University Utrecht | Reichart G.-J.,Alfred Wegener Institute for Polar and Marine Research | Jilbert T.,University Utrecht | And 3 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology

High resolution stable isotope and trace elemental ratios of a recent Tridacna squamosa from Vietnam and a Middle to Late Miocene (10-13Ma) Tridacna gigas from Indonesia are presented. The seasonal pattern of modern sea surface temperature (SST) variability offshore Vietnam is faithfully recorded in the δ18O of the T. squamosa shell carbonate, confirming the potential of Tridacna shells as sub-annual resolution climate archives. Cultivation of the T. squamosa specimen in controlled conditions after recovery from the natural environment facilitated a quantitative calibration of the δ18O signal to ambient water temperatures. An age model for the Miocene T. gigas shell from Indonesia was therefore constructed on the basis of its δ18O profile, assuming a single-peak annual SST cycle. The magnitude of these oscillations was 5-7°C. Mg/Ca and the growth-banding pattern in the Miocene T. gigas correlates well with shell δ18O during the later part of the organism's lifespan. Ba/Ca is negatively correlated to Mg/Ca, with a lag of several months, suggesting a different phasing of the annual primary productivity cycle from that of SST. Furthermore, δ18O and Mg/Ca show prominent deviations to warmer conditions with a periodicity of ~3years. These shifts demonstrate the existence of substantial interannual sea surface temperature variability in the Miocene, a period with elevated global temperatures compared to the present day. © 2011 Elsevier B.V. Source

Discover hidden collaborations