Holst S.,German Museum
Marine Biology | Year: 2012
Jellyfish blooms or invasions could be detected in an early phase of development if the youngest medusa stages (ephyrae) and their early growth stages (post-ephyrae) were identifiable in plankton samples but a useful identification key for ephyrae in early growth stages is lacking for most species. In the present study, the identification characteristics of adult North Sea scyphomedusae (Aurelia aurita, Cyanea capillata, Cyanea lamarckii, Chrysaora hysoscella, Rhizostoma octopus) collected around the island of Helgoland (German Bight) in July-August 2003 and 2004 are described. Planula larvae were measured and reared to polyps in the laboratory. The process of ephyrae development asexually produced by the polyps (strobilation) was photo-documented. Photographs of the ephyrae growth stages were combined with drawings of features useful for the species identification. The provided identification key allows discrimination among post-ephyrae from plankton samples, probably leading to conclusions on the development of jellyfish blooms and their causes. © 2012 Springer-Verlag.
Cortese G.,Institute of Geological & Nuclear Sciences |
Gersonde R.,Alfred Wegener Institute for Polar and Marine Research |
Maschner K.,German Museum |
Medley P.,University of Colorado at Boulder
Paleoceanography | Year: 2012
The valve area of Fragilariopsis kerguelensis, the most abundant diatom species in the Southern Ocean, strongly changes in size in response to varying conditions in the surface ocean. We examined the link, both in two iron fertilization experiments and in sediment samples covering several glacial Terminations, between size variability in this species and environmental conditions across the Antarctic Polar Front, including sea ice extent, sea surface temperature, and the input of eolian dust. The iron fertilization experiments show valve area to be positively correlated with iron concentrations in ambient waters, which suggests the possibility of a causal relation between valve size of Fragilariopsis kerguelensis and ambient surface water iron concentration. Larger valves are usually found during glacial times and thus seem to be related to lower sea surface temperature and wider sea ice coverage. Moreover, our results indicate that there usually is a strong correlation between larger valve size and increased input of eolian dust to the Southern Ocean. However, this correlation, obvious for the fertilization experiments and for glacial Terminations I, II, III, and V, does not seem to be valid for Termination VI, where size appears to be inversely correlated to dust input. Copyright 2012 by the American Geophysical Union.
Holst S.,German Museum |
Laakmann S.,Senckenberg Institute
Journal of Plankton Research | Year: 2014
Detecting fluctuations in the species composition of bloom-forming jellyfish requires the ability to correctly identify each species in each developmental stage. We verified diagnostic morphological and molecular genetic characters to discriminate Cyanea lamarckii and Cyanea capillata from northern European waters. Intrusions in the subumbrellar muscle folds were present in all C. capillata >80 mm r-diameter (between opposite rhopalia tips), but absent in C. lamarckii. Clearly visible wart-like papillae on the central exumbrella were present in all C. lamarckii >10-80 mm r-diameter, but absent in C. capillata. Both morphological features were retained in formaldehyde-seawater (4%) preserved medusae which had shrunk by 12.8% (±2.7%) after 1 year of preservation. Our molecular genetic analyses demonstrated that fragments of mitochondrial cytochrome c oxidase subunit I (COI) and nuclear 18S rDNA clearly distinguished C. lamarckii from C. capillata, with intra- and inter-specific pairwise genetic distances of 0.0-1.5% and 15.5-17.0% (COI) and 0.0 and 0.2% (18S rDNA), respectively. The study revealed various bell colours in both species underlining that the identification based on the bell colours can result in misidentification. Our integrated taxonomic approach can help to correctly identify jellyfish species, which is fundamentally important for understanding the causes of jellyfish fluctuations and the development of jellyfish blooms. © The Author 2013.
Ausich W.I.,Ohio State University |
Bartels C.,German Museum |
Kammer T.W.,West Virginia University
Lethaia | Year: 2013
Fossilized tube feet are described on Codiacrinus schultzei Follmann from the Lower Devonian Hunsrück Slate of Germany. This is the first definitive proof of tube feet on any fossil crinoid. Three lightly pyritized, flattened tube feet are preserved in a single interray of this cladid crinoid. The tube feet were at least 7 mm long. Their preservation is very similar to the tube feet reported previously from a Hunsrück ophiuroid, except that the Codiacrinus tube feet have small papillae, similar to living crinoids. © 2013 The Lethaia Foundation.
Ruedrich J.,University of Gottingen |
Kirchner D.,German Museum |
Siegesmund S.,University of Gottingen
Environmental Earth Sciences | Year: 2011
Damages to natural building stones induced by the action of frost are considered to be of great importance. Commonly, the frost resistance of building stones is checked by standardised freeze-thaw tests before using. Corresponding tests normally involve 30-50 freeze-thaw action cycles. In order to verify the significance of such measurements, we performed long-term tests on four selected rocks over 1,400 freeze-thaw action cycles. Additionally, numerous petrophysical parameters were analysed to compare the behaviour of rocks in the weathering tests according to the current explanatory models of stress formation by growing ice crystals in the pore space. The long-term tests yield more information about the real frost sensibility of the rocks. A clear deterioration cannot be determined in most cases until 50 weathering cycles have been completed. In the freeze-thaw tests, the samples are also stressed by changing temperature and moisture, indicating that different decay mechanisms can interfere with each other. Thus, thermohygric and moisture expansion are important damage processes. © 2010 The Author(s).