Gert Hansen

Gert Hansen
DHI Group · Ballastwater & Laboratories

Ph.D.

About

61
Publications
23,279
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
2,825
Citations
Citations since 2017
6 Research Items
962 Citations
2017201820192020202120222023050100150
2017201820192020202120222023050100150
2017201820192020202120222023050100150
2017201820192020202120222023050100150
Introduction
Gert Hansen currently works as taxonomist at Ballast-water & Laboratories, DHI, but is also associated researcher at Biological Institute, University of Copenhagen. Main research interest are algal taxonomy, in particular dinoflagellates, but recently also desmids.

Publications

Publications (61)
Article
A dinoflagellate isolated from a small rainwater rockpool in Finland was found to be a new species of Baldinia, here described as B. droopii sp. nov. This is only the third formally described Baldinia species and the second described by modern methods. The new species had a complement of generic characters that clearly affiliated it to Baldinia: pr...
Article
Full-text available
Specimens of a new species of blue diatoms from the genus Haslea Simonsen were discovered in geographically distant sampling sites, first in the Canary Archipelago, then North Carolina, Gulf of Naples, the Croatian South Adriatic Sea, and Turkish coast of the Eastern Mediterranean Sea. An exhaustive characterization of these specimens, using a comb...
Article
Phytoplankton are present in a large variety of aquatic environments, ranging from small freshwater ponds to the oceans. Typically, freshwater and marine species are not closely related, indicating an ancient divergence and that salinity poses a strong dispersal barrier. Here we reveal a common recent origin of two dinoflagellates that are well ada...
Article
Desmids are unicellular green algae dominating habitats that are vulnerable and highly threatened, like raised bogs, mires and fens. Desmid diversity was studied in four different localities on the Danish island Bornholm. A total of 186 species, 58 of which not recorded from Denmark before, were observed. Species composition from the locality ‘Kohu...
Article
The rarely recorded dinoflagellate Hemidinium ochraceum Levander was isolated from a rainwater rock-pool in Finland and the motile stage studied by light- and electron microscopy and molecular sequencing. The ultrastructure of the motile stage revealed several features not previously observed in other dinoflagellates, e.g. thecal plates with inward...
Article
Full-text available
Here we report the lipid profiles of ten dinoflagellate species originating from different freshwater habitats and grown at 4, 13, or 20°C akin to their natural occurrence. Lipids were determined by High Performance Liquid Chromatography-ElectroSpray Ionization-Mass Spectrometry in positive and negative ion modes. Besides the well-studied monogalac...
Article
Haslea provincialis Gastineau, Hansen & Mouget, sp. nov., is a new, morphologically semicryptic blue diatom discovered on the French shores of the Mediterranean Sea. Like H. ostrearia and H. karadagensis, H. provincialis shares the capacity to synthesize a marennine-like blue pigment. Sexual reproduction between clones of H. provincialis has been r...
Article
Full-text available
Processes of rapid radiation among unicellular eukaryotes are much less studied than among multicellular organisms. We have investigated a lineage of cold-water microeukaryotes (protists) that appear to have diverged recently. This lineage stands in stark contrast to known examples of phylogenetically closely related protists, in which genetic diff...
Chapter
Diatoms are usually referred to as golden-brown microalgae, due to the colour of their plastids and to their pigment composition, mainly carotenoids (fucoxanthin, diadinoxanthin, diatoxanthin), which mask chlorophylls a and c. The species Haslea ostrearia Gaillon/Bory (Simonsen) appears unique because of its extraplastidial bluish colour, a consequ...
Article
Full-text available
Freshwater woloszynskioid dinoflagellates were collected independently in Scotland and Portugal and found to belong to a previously unknown species of the genus Borghiella, here described as B. andersenii. The new species differs in morphology and nuclear-encoded LSU rDNA and ITS sequences from B. dodgei and B. tenuissima, the two species presently...
Article
Full-text available
In diatoms, the main photosynthetic pigments are chlorophylls a and c, fucoxanthin, diadinoxanthin and diatoxanthin. The marine pennate diatom Haslea ostrearia has long been known for producing, in addition to these generic pigments, a water-soluble blue pigment, marennine. This pigment, responsible for the greening of oysters in western France, pr...
Article
Full-text available
In diatoms, the main photosynthetic pigments are chlorophylls a and c, fucoxanthin, diadinoxanthin and diatoxanthin. The marine pennate diatom Haslea ostrearia has long been known for producing, in addition to these generic pigments, a water-soluble blue pigment, marennine. This pigment, responsible for the greening of oysters in western France, pr...
Article
Full-text available
Gymnodinium fissum was described by Levander (1894) from the Baltic Sea near Helsinki, and we argue, based on morphological and molecular studies of material from the type locality, and on cultures from the Åland islands, Puerto Rico, Portugal and USA identified as Gyrodinium instriatum, Gymnodinium instriatum, Gyrodinium uncatenum and Gyrodinium s...
Book
Full-text available
Diatoms are usually referred to as golden-brown microalgae, due to the colour of their plastids and to their pigment composition, mainly carotenoids (fucoxanthin, diadinoxanthin, diatoxanthin), which mask chlorophylls a and c. The species Haslea ostrearia Gaillon/Bory (Simonsen) appears unique because of its extraplastidial bluish colour, a consequ...
Conference Paper
Full-text available
The study of the blue diatoms from the genus Haslea is an arcane topic, due to investigations being restricted to the only species Haslea ostrearia (Gaillon/ Bory) Simonsen. This diatom, first observed in the early 19th century, has the peculiar ability to produce a non‐photosynthetic blue pigment, the so‐called marennine. This pigment’s name refer...
Article
Full-text available
A small-sized, peridinin-containing, athecate dinoflagellate (13-17 mm long) was isolated into clonal culture from a water sample collected at a nearshore location in Tenerife, Spain (October 2004). Based on phenotypic characters (size, shape, pyrenoid and nucleus position), the culture was identified as Gyrodinium oblongum. However, a detailed ult...
Article
Full-text available
Heterotrophic dinoflagellates bearing unicellular cyanobacterial symbionts are common within the order Dinophysiales. However, the ecological role of these symbionts is unclear. Due to the occurrence of such consortia in oceanic waters characterized by low nitrogen concentrations, we hypothesized that the symbionts fix gaseous nitrogen (N-2). Indiv...
Article
The external and internal ultrastructure of the harmful unarmored dinoflagellate Cochlodinium polykrikoides Margalef has been examined with special reference to the apical groove and three-dimensional structure of the flagellar apparatus. The apical groove is U-shaped and connected to the anterior sulcal extension on the dorsal side of the epicone....
Article
Full-text available
The spatial distribution of symbiont-bearing dinoflagellates was investigated during a cruise from Cape Town, South Africa to Broome, Australia. Endo- and ectosymbionts were only found in the order Dinophysiales. The genera Ornithocercus, Histioneis, Parahistioneis and Citharistes had cyanobacteria as ectosymbionts, while the genera Amphisolenia an...
Article
We examined a free-living Symbiodinium species by light and electron microscopy and nuclear-encoded partial LSU rDNA sequence data. The strain was isolated from a net plankton sample collected in near-shore waters at Tenerife, the Canary Islands. Comparing the thecal plate tabulation of the free-living Symbiodinium to that of S. microadriaticum Fre...
Article
The ultrastructure of Woloszynskia limnetica Bursa was examined using serial thin section electron microscopy. Sections of W. limnetica reveal numerous chloroplast profiles without any obvious pyrenoids. The extensive pusular complex consists of a “smooth” part and a part lined with electron-dense particles. The nucleus is located in the episome. A...
Article
Full-text available
The saline lakes of the Vestfold Hills in Antarctica offer a remarkable natural laboratory where the adaptation of planktonic protists to a range of evolving physiochemical conditions can be investigated. This study illustrates how an ancestral marine community has undergone radical simplification leaving a small number of well-adapted species. Our...
Article
Full-text available
Using ultrastructure and nuclear-encoded large subunit (LSU) rDNA sequences, the woloszynskioid dinoflagellates have been shown recently to form a polyphyletic assemblage. The first group comprises the family Tovelliaceae, with the genera Tovellia and Jadwigia. The present manuscript describes the second group, comprising Borghiella dodgei gen. et...
Article
Two freshwater armoured dinoflagellates, Peridiniopsis cf. kevei from Japan and Peridiniopsis penardii from Japan and Italy, were examined by means of light, scanning and transmission electron microscopy. Morphological studies indicated that the two dinoflagellates had similar type of cellular structure and possessed an endosymbiotic diatom. The di...
Conference Paper
The horizontal and vertical distribution of dinoflagellates with ectosymbionts and of physico-chemical parameters were investigated along a transect from Cape Town, South Africa to Broome, Australia, on a cruise carried out in October-November 2006. We found 4 genera of dinoflagellates, which had ectosymbionts: Ornithocercus, Histioneis, Parahistio...
Article
Full-text available
The Trentino Province (Italy) has more than 320 lakes diverse in size, geological substrate, altitude and trophic status, and representing most physico-chemical types of temperate lakes. A recent research project (SALTO) offered the opportunity to study the dinoflagellate flora of 27 of these water bodies representing all lake types. In this paper...
Article
The ultrastructure of the green dinoflagellate Lepididodinium viride M. M. Watanabe, S. Suda, I. Inouye Sawaguchi et Chihara was studied in detail. The nuclear envelope possessed numerous chambers each furnished with a nuclear pore, a similar arrangement to that found in other gymnodinioids. The flagellar apparatus was essentially identical to Gymn...
Article
Full-text available
The green form of 'Glenodinium sanguineum Marchesoni' sensu Baldi was investigated in detail by light microscopy, scanning electron microscopy, transmission electron microscopy and by analysis of the SSU- and LSU rDNA genes. These data demonstrated it to be different from the red form of 'G. sanguineum' (now Tovellia sanguinea) and to represent a n...
Article
ABSTRACTI examined the heterotrophic non-armored dinoflaget-late Actiniscus pentasterias (Ehrenberg) Ehrenberg by light and electron microscopy. Actiniscus pentasterias contains an internal skeleton consisting of two star-like siliceous elements. Special emphasis is given to the flagellar apparatus, the nucleus, and a new type of extrusome, named a...
Article
The green dinoflagellate Gymnodinium chlorophorum (BAH ME 100, the type culture) was reexamined with emphasis on the structure of the flagellar apparatus and nuclear envelope. Like other Gymnodinium species, G. chlorophorum possessed a nuclear fibrous connective linking the flagellar apparatus and the nucleus, albeit in a very reduced and unique fo...
Article
Full-text available
The organism responsible for the former annual reddening of Lake Tovel in the Italian Alps (up to 1964) has been identified and studied in detail. Considerable confusion exists regarding the identity of this organism, and the detailed description by Baldi in 19413. Baldi , E . 1941. Ricerche idrobiologiche sul lago di Tovel. Memorie del Museo di S...
Article
Full-text available
The increasing incidence of harmful algal blooms around the world and their associated health and economic effects require the development of methods to rapidly and accurately detect and enumerate the target species. Here we describe use of a solid-phase cytometer to detect and enumerate the toxic alga Prymnesium parvum in natural samples, using a...
Article
Lake Tovel in the Italian Alps is famous for its blood-red water during summer, caused by a dinoflagellate named Glenodinium sanguineum. The red colour has been largely absent since 1964 and a project aimed at understanding the underlying cause of the colour change was begun in 2000. It appears that there are three dinoflagellates in the lake that...
Article
A detailed ultrastructural analysis of the type species of Gyrodinium, G. spirale, was made based on cells collected from Skagerrak and southern Kattegat (Denmark). This material is considered very similar to the type material studied by Bergh from southern Kattegat. The analysis revealed many characters typical for dinoflagellates as well as a num...
Article
Full-text available
The body scales of 12 Heterocapsa species including a new species, H. pseudotriquetra lwataki, Gert Hansen & Fukuyo, sp. nov. were investigated by transmission electron microscopy to clarify ultrastructural differences. All species had scales with a body-scale structure consisting of a triradiate basal plate and a three-dimensional construction com...
Article
The morphology of Alexandrium minutum Halim from Denmark was studied and compared to the morphology of material from Portugal, Spain, France and Ireland. Strains from Denmark and the French coast of the English Channel differed from the typical minutum morphotype by the absence of a ventral pore. Cells without a pore also dominated field material f...
Article
The morphology of Alexandrium minutum Halim from Denmark was studied and compared to the morphology of material from Portugal, Spain, France and Ireland. Strains from Denmark and the French coast of the English Channel differed from the typical minutum morphotype by the absence of a ventral pore. Cells without a pore also dominated field material f...
Article
Combined use of molecular, ultrastructural and micromorphological data has been applied to taxonomic studies of unarmoured dinoflagellates particularly the Gymnodinium species-complex. Characters considered important at the genus level are: apical groove structure, presence/absence of nuclear chambers and the presence/absence of a nuclear fibrous c...
Article
Examination of the ultrastucture of the unarmored dinoflagellate Gymnodinium aureolum (Hulburt) G. Hansen (syn: Gyrodinium aureolum Hulburt) revealed the presence of nuclear chambers, which are specialized differentiations of the nuclear envelope, similar to those described in the type species of Gymnodinium, G. fuscum (Ehrenberg) Stein and certain...
Chapter
The dinoflagellate genus Gymnodinium is a complex assemblage of species. Clearly, not all species are evolutionarily related but many representatives are providing valuable insight into fundamental phylogenetic and biochemical questions. Taxa assigned to this genus are known to be toxin producers of extreme importance to biomedicine.
Article
A new dinoflagellate species; Karenia longicanalis sp. nov. is described from a bloom, which occurred in mid-May, 1998 in Victoria Harbour, Hong Kong and the southwestern coastal waters of Hong Kong Island. Live cells have up to 30 yellow-green, round chloroplasts, each containing a pyrenoid, and a spherical centrally located nucleus surrounded by...
Article
Gymnodinium fuscum (Ehrenberg) Stein is the type species of Gymnodinium. one of the largest genera of dinoflagellates. It has the typical fine structure of dinoflagellates, but also possesses several unusual features. The nuclear envelope is specialized by having vesicular chambers in which the nuclear pores are located: the pusular complex include...
Article
Full-text available
Evidence from partial large-subunit (LSU) rDNA sequencing has been combined with ultrastructure, including details of the flagellar apparatus, in a number of phototrophic dinoflagellates. with the aim of trying to solve some of the most pressing taxonomic problems and to contribute to an improved understanding of the phylogeny within the group. Spe...
Article
Light and electron microscopy, nuclear-encoded LSU rDNA sequences, and pigment analyses were performed on five geographically separate isolates of Gymnodinium mikimotoi. The morphological variation between the isolates equals that found within the isolates. The nuclear-encoded LSU rDNA sequences were nearly identical in all isolates, and molecular...
Article
Full-text available
The ultrastructure of Peridinium cinctum, was examined by serial sectioning with particular emphasis on the detailed construction of the flagellar apparatus. The pusular system of P. cinctum included two sac pusules in open connection with the flagellar canals; disorganized material was found inside the pusules and near the flagellar pores, indicat...
Article
Full-text available
The coldwater dinoflagellate Peridiniella catenata has been examined by light and electron microscopy. The fine-structure resembles that of other dinoflagellates with regard to the dinokaryon, the chloroplast enveloped by three membranes, and the pusule. The flagellar apparatus also resembles that of most other dinoflagellates. The main difference...
Article
Full-text available
Cells of the potentially toxic dinoflagellate Alexandrium catenella have a complement of features typical of dinoflagellates, including dinokaryon, pusule and amphiesma. No endosymbiotic bacteria were found in the Californian strain examined, which is weakly toxic. The chloroplast consists of a central pyrenoid complex with radiating chloroplast lo...
Article
Light and electron microscopical observations have been made on the gonyaulacoid dinoflagellate Protoceratium reficulatum (Claparède et Lachmann) Bütschli collected close to the type locality of Protoceratium acerosBergh, the type species of Protoceratium. Analysis of plate tabulation shows agreement with Gonyaulax grindleyiREINECKE and supports co...
Article
The fine structure of Gonyaulax spinifera (Claparede et Lachmann) Diesing has been investigated by transmission electron microscopy, using serial sections. The cell has a single multilobed chloroplast and a central pyrenoid complex; a common plastidial origin for gonyaulacoid dinoflagellates is indicated. The cell contains an apical fibrous pore co...
Article
Analysis of the thecal plate pattern in Katodinium rotundatum (Lohmann) Loeblich has revealed that the tabulation is identical to that of Heterocapsa Stein. Other similarities between Katodinium rotundatum and Heterocapsa include the presence of triangular scales on the cell surface, the pyrenoid structure and the structure of the flagellar apparat...
Article
The unarmoured dinoflagellate Katodinium rotundatum possesses organic body scales almost identical to those of Heterocapsa triquetra, an armoured dinoflagellate. Scale formation takes place in the periphery of the Golgi apparatus, the Golgi cisternae forming moulds in which scale precursors are assembled. Microfilaments are associated with the base...

Network

Cited By

Projects

Projects (2)
Project
MIRRI is the pan-European research infrastructure for microbial resources. By provision of high quality microorganisms, associated data and the broad expertise of our partners, MIRRI aims to support research and development in the field of biotechnology. The MIRRI Preparatory Phase project ended in April 2016 but the consortium has continued working in the implementation of the Infrastructure with the H2020 project "IS_MIRRI21 - Implementation and Sustainability of Microbial Resource Research Infrastructure for 21st Century" (see https://bit.ly/3igdmoh here on ResearchGate). You can also find more information at mirri.org.