scholarly journals Species of the diatom taxa <i>Aulacodiscus</i> and <i>Trinacria</i> with biostratigraphic utility in Palaeogene and Neogene North Sea sediments

2019 ◽  
Vol 38 (1) ◽  
pp. 67-81
Author(s):  
Alexander G. Mitlehner
Keyword(s):  
North Sea ◽  
Taxonomic Status ◽  
Sem Analysis ◽  
Marine Diatom ◽  
Separate Species ◽  
The North ◽  
Northwest Europe ◽  
The North Sea ◽  
A Chain ◽  
Sem Studies

Abstract. Species of Aulacodiscus and Trinacria, two important marine diatom genera with biostratigraphic utility in offshore North Sea exploration and onshore correlation, are identified, described and emended and the North Sea microfaunal zonation scheme is revised accordingly. Occurring mainly as pyritised diatom moulds or steinkerns, detailed scanning electron microscope (SEM) analysis of several specimens, formerly in open nomenclature, has allowed the correct taxonomic identification of pyritised morphologies found to belong to the genus Aulacodiscus, including A. allorgei, A. heterostictus, A. insignis, A. singilewskyanus, A. subexcavatus and A. suspectus. The important marker species Trinacria regina is emended. SEM studies, using specimens preserved in pyrite and original silica, have shed further light on the varying forms and frustule morphology of Trinacria regina so that valves and frustules formerly thought to represent separate species are now found to be grouped within this taxon; SEM studies have shown that many of these variations represent different valves within a chain, whilst others may signify ecophenotypic variants. Emendments are therefore made to clarify the taxonomic status of different variants within T. regina, important in the Palaeocene–Eocene boundary interval onshore and offshore such as the Sele and Balder formations and the Fur Formation diatomite of Jutland, Denmark. Species of taxa formerly in open nomenclature are now assigned to Aulacodiscus insignis, which are important offshore markers in offshore late Oligocene to early Miocene sediments in northwest Europe.

scholarly journals The Size of Diatoms II. Further Observations on Rhizosolenia styliformis (Brightwell)

1946 ◽  
Vol 26 (3) ◽  
pp. 271-284 ◽  
Author(s):  
R. S. Wimpenny
Keyword(s):  
North Sea ◽  
Indicator Species ◽  
Separate Species ◽  
Southern North Sea ◽  
Auxospore Formation ◽  
The North ◽  
The North Sea ◽  
Set Up ◽  
The Antarctic

1. Diameter measurements of Rhizosolenia styliformis from the Antarctic, the subtropical Atlantic and Pacific Oceans and from the North Sea and neighbouring waters have made it appear necessary to set up two varieties, oceanica and semispina, in addition to the type of the species R. styliformis. The type as I describe it has been called var. longispina by Hustedt, but elsewhere it has often been figured as the var. oceanica of this paper. Var. semispina is synonymous with the form represented by Karsten as R. semispina Hensen. It differs from R. semispina as drawn by Hensen and its synonym R. hebetata forma semispina Gran, but is thought likely to be linked by intermediates. If this is so R. hebetata may have to be extended to include and suppress R. styliformis, as var. semispina is linked to the type by intermediates. Var. oceanica has no intermediate forms and, if R. hebetata is to be extended, this variety should be established as a separate species.2. Var. oceanica is absent from the southern North Sea and appears to be an indicator species related to oceanic inflow.3. Auxospore formation was observed for the type in the southern North Sea in 1935 and biometric observations suggest that a period of 3-4 years elapsed between the production of auxospore generations in that area. Outside the southern North Sea for the type, measurements give no indication of auxospore generations occurring at intervals exceeding a year. While auxospore formation has been seen in var. oceanica from the Shetlands area samples of June 1935 and July 1938, this phenomenon has not been observed for var. semispina.

scholarly journals Separating species using a horizontal panel in the Scottish North Sea whitefish trawl fishery

2007 ◽  
Vol 64 (8) ◽  
pp. 1543-1550 ◽  
Author(s):  
R. S. T. Ferro ◽  
E. G. Jones ◽  
R. J. Kynoch ◽  
R. J. Fryer ◽  
B-E. Buckett
Keyword(s):  
North Sea ◽  
Water Clarity ◽  
Light Level ◽  
Separation Performance ◽  
Separate Species ◽  
Trawl Fishery ◽  
The North ◽  
Acoustic Methods ◽  
Commercial Species ◽  
The North Sea

Abstract Ferro, R. S. T., Jones, E. G., Kynoch, R. J., Fryer, R. J., and Buckett, B-E. 2007. Separating species using a horizontal panel in the Scottish North Sea whitefish trawl fishery. – ICES Journal of Marine Science, 64: 1543–1550. In the North Sea, Scottish vessels target haddock, cod, whiting, monkfish, saithe, and flatfish in a mixed whitefish trawl fishery. These species mature at different sizes and hence have a range of minimum landing sizes. Their different shapes and swimming capabilities imply different selection characteristics when escaping from trawl gear. However, they are often caught at the same time on the same grounds. Optimal exploitation can only be achieved by ensuring that the selection of each species varies appropriately with length during the fishing process. This paper describes one part of a large European project to develop species-selective trawl gear to improve the exploitation pattern of North Sea cod, while maintaining the catch of other important commercial species. A gear suitable to the Scottish mixed whitefish fishery was fitted with a horizontal panel in the tapered part of the net to separate species into an upper and lower compartment. Trials were conducted on research vessels to measure separation performance for nine species in different light conditions, at different towing speeds, and with different lengths of panel. Most haddock, whiting, and saithe pass above the panel, whereas most cod, flatfish, and monkfish pass below it. Towing speed and panel length had no significant effect on separation. At lower light levels during the night (April at latitude 58° to 61°N), fewer dab, sole, plaice, and cod pass below the panel. Observations and measurements of fish behaviour using acoustic methods are described. They suggest that the height at which fish enter the net mouth may be influenced by light level and water clarity.

scholarly journals The molecular phylogenetic status of <i>Elphidium williamsoni</i> (Haynes, 1973) as inferred from partial 18S-rDNA sequences

2001 ◽  
Vol 20 (2) ◽  
pp. 183-183 ◽  
Author(s):  
Martin R. Langer
Keyword(s):  
North Sea ◽  
Sequence Data ◽  
Taxonomic Status ◽  
Molecular Data ◽  
Small Subunit ◽  
The North ◽  
Rdna Sequences ◽  
Molecular Phylogenetic ◽  
The North Sea ◽  
Muddy Sediments

Abstract. Comparative studies on DNA nucleotide sequences have revolutionized our understanding of the phylogenetic relationships of many organisms and have become an important tool in evolutionary, ecological and palaeobiological inquiry. We have analysed partial small-subunit 18S sequences (srDNA) of Elphidium williamsoni (Haynes, 1973), a common intertidal benthic foraminiferid from the North Sea. The molecular phylogenetic analysis of the ribosomal rDNA sequence data indicate that E. williamsoni constitutes a well-defined genetic entity that is closely related to Elphidium aculeatum.Elphidium williamsoni is a prominent and frequently encountered foraminiferid in the North Sea and other tidal flats. It was originally described by Williamson (1858) as Polystomella umbilicata and subsequently renamed by Haynes (1973). Because of its phenotypic similarities with other elphidiids, this species has been frequently confused with, for example E. excavatum or Cribrononion alvarezianum (see Haynes for discussion). The molecular data provided here, and their direct comparison to other benthic foraminifera including one elphidiid, may therefore provide additional insight into the taxonomic status and the validity of this species.Individuals of the foraminiferid Elphidium williamsoni were collected in October 1997 from the intertidal mud flats of the Crildumersiel at the outer Jade Bay near Wilhelmshaven, North Sea (see Langer et al., 1989 for details). The mud flats are characterized by fine-grained, muddy sediments containing high contents of organic material. In the laboratory, specimens were transferred into petri dishes, examined and cleaned under a stereo microscope. Living specimens of E. williamsoni were picked out separately and placed into clean glass dishes containing filtered. . .

Facing the Chop: Redefining British Antler Mattocks to Consider Larger-Scale Maritime Networks in the Early Fifth Millennium Cal BC

2015 ◽  
Vol 18 (2) ◽  
pp. 222-244 ◽  
Author(s):  
Benjamin Elliott
Keyword(s):  
North Sea ◽  
Critical Review ◽  
The North ◽  
Northwest Europe ◽  
Maritime Networks ◽  
The North Sea ◽  
Technological Analysis

This paper provides a critical review of Smith's (1989) typological discussion of the antler ‘mattocks’ of the British Mesolithic. The evidence for use of the term ‘mattock’ is assessed in relation to a new technological analysis of antler tools from Britain. In the light of the data presented here and developments in the study of Mesolithic osseous technologies from elsewhere in northwest Europe, a redefinition of the terminology and typology used to study these artefacts is presented. The potential for this redefinition to shape research across Mesolithic Europe is demonstrated through a discussion of the earliest occurrence of antler T-axes around the North Sea basin.

scholarly journals THE NATURAL DEVELOPMENT OF THE WADDEN SEA AFTER THE ENCLOSURE OF THE ZUIDER SEA

2011 ◽  
Vol 1 (8) ◽  
pp. 42
Author(s):  
C.F.W. Rietveld
Keyword(s):  
Storm Surge ◽  
North Sea ◽  
Wadden Sea ◽  
The North ◽  
Natural Development ◽  
The North Sea ◽  
Tidal Movement ◽  
A Chain

The Wadden Sea and Zuider Sea used to form an internal sea which was separated from the North Sea by a chain of islands. In 1932 the Zuider Sea was enclosed by a dam 32 km in length. Owing to this, the Wadden Sea experienced changes in the normal tidal movement, the storm-surge levels and the configuration of the bed. This article discusses the movement of water and sand the Wadden Sea and its natural development since the enclosure of the Zuider.

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