Species Gymnodinium Research Articles

Planktonic Protozoa in Lakes Huron and Michigan: Seasonal Abundance and Composition of Ciliates and Dinoflagellates

The abundance and biomass of surface (5 m) and deep (30–45 m) ciliate and dinoflagellate protozoa in the offshore waters of Lakes Huron and Michigan were determined from December 1986 to November 1987. Protozoan (ciliates and dinoflagellates) abundance (4 to 15 cells·mL −1) and biomass (13–140 μg·L −1, wet wt.) were comparable between lakes and similar to those reported from other oligotrophic environments. On average, ciliates comprised the majority of protozoan abundance (80%) and biomass (73%). The mean size (ESD) of these communities was small (20.6 μm) due to the numerical dominance of small choreotrichs, oligotrichs, and species of Gymnodinium. Total biomass in both lakes peaked during late June-July and again during the October-November period. These seasonal changes in biomass were accompanied by species replacements: tintinnids, strobilids, oligotrichs, and Gymnodinium species were abundant in the spring isothermal period, shifting to oligotrich dominance during summer stratification (May–July); a more diverse assemblage followed during late stratification (October–November) in which haptorids, prorodontids, and Peridinium species became more important. Deep and surface communities were comparable in terms of abundance and biomass, although deep community biomass decreased as stratification intensified. Because the biomass of ciliates alone represents approximately 30% of crustacean zooplankton biomass, protozoa may be more important grazers than once thought.

Eutrophication and red tide in aegean coastal waters

The abundance, species composition and taxonomic diversity of phytoplankton has been studied in relation to sewage pollution north of the Pagassitikos Gulf, Greece. Surface water samples were collected from a series of stations in the Pagassitikos Gulf, during July 1987. Samples were preserved, concentrated by settling, and the concentration of each species of phytoplankton enumerated in an inverted microscope. Water samples from the vicinity of the major sewer outfalls showed very high concentrations of nutrients, greater total concentration of phytoplankton, and a lower taxonomic diversity than samples remote from outfalls. Phytoplankton abundance and taxonomic diversity depend upon the supply of nutrients in natural waters, where abundance increases and diversity decreases with increasing nutrient concentrations in the Pagassitikos Gulf. A considerable variation in the occurrence of species and dominance occurred along the nutrients pollution gradient. Dinoflagellates were dominant in polluted waters, while diatoms dominated in cleaner water away from major sewage outflow. From the dominance and relative distribution of the taxa along the pollution gradient certain species of Gymnodinium emerge as indicator species of red tide pollution. These changes correspond to a typical degradation of a complex community to a less mature state by the inflow of nutrient‐rich sewage (eutrophication) in the north Pagassitikos Gulf.

Does The Fish-Killing Dinoflagellate Gymnodinium CF. Nagasakiense Produce Cytotoxins?

The naked dinoflagellate Gymnodinium cf. nagasakiense is responsible for red tides frequently associated with mortality of marine organisms in North European waters during summer (see reviews by Tangen, 1977 and Partensky & Sournia, 1986). This species is currently referred to as Gyrodinium aureolum Hulburt in the literature, since its first occurrence in Norwegian waters in 1966 (Braarud & Heimdal, 1970). However, it was recently found to be morphologically closer to the Japanese bloom-forming species Gymnodinium nagasakiense Takayama & Adachi than to the original Gyrodinium aureolum (Partensky et al., 1988).

MORPHOLOGICAL AND NUCLEAR ANALYSIS OF THE BLOOM‐FORMING DINOFLAGELLATES GYRODINIUM CF. AUREOLUM AND GYMNODINIUM NAGASAKIENSE1

ABSTRACTTwo red‐tide forming naked dinoflagellates, the Japanese species Gymnodinium nagasakiense Takayama et Adachi and the north European species Gyrodinium cf. aureolum Hulburt, were compared with regard to their external morphology, chromosome number and DNA content. Morphological studies were performed using both light and scanning electron microscopy; analytical flow cytometry was used to compare DNA contents. Our strains of G. cf. aureolum and G. nagasakiense were morphologically indistinguishable, and both closely fit the original description of the latter species. In contrast, several details, including the shape and position of the nucleus, differed between our strains and the original description of Gyrodinium aureolum. However, despite an equal number of chromosomes, the Japanese taxon possessed about 40% more DNA than the European one. Moreover, the latter taxon was able to form two subpopulations of vegetative cells, which we called “small” and “large,” whereas the former one only formed “large” cells. These discrepancies cast doubt upon the conspecificity of G. cf. aureolum and G. nagasakiense. The appellation Gymnodinium cf. nagasakiense is therefore proposed for the species encountered in the northern European seas, waiting for a future reconsideration of both the genera and the species.

Nutrient uptake kinetics of freshly isolated zooxanthellae

Zooxanthellae of the species Gymnodinium (=Symbiodinium) microadriaticum freshly isolated from a variety of hosts (Zoanthus spp., Tridacna crocea, Seriatopora hystrix, Montastrea annularis, Porites furcata, and Stylophora pistillata) in the tropical Pacific Ocean and the Caribbean Sea exhibited saturation uptake kinetics when incubated in seawater enriched with nitrate, nitrite or ammonium. Half-saturation constants (Ks) for nitrate ranged from 0.23 to 3.14 μM, for nitrite from 0.23 to 7.15 μM, and for ammonium from 5.03 to 21.99 μM. Maximum specific uptake rates (Vmax) for ammonium (1.05 to 2.79 d-1) exceeded those for both nitrate (not detectable to 0.54 d-1) and nitrite (not detectable to 0.67 d-1). Light did not affect the uptake rate of any substrate tested, nor did the addition of ammonium in concentrations up to 20 μM reduce the rate of nitrate uptake at Vmax, but nitrite uptake was inhibited by the addition of nitrate to the medium. The inhibition of nitrite uptake by nitrate could not be described either as competitive or non-competitive. Although maximum specific uptake rates obtained for ammonium appear to exceed maximum potential specific growth rate in terms of nitrogen of the algae, the actual growth potential of the algae must be limited not only by nutrient concentrations to which they are exposed, but also by the percentage of assimilated nitrogen that they translocate to their host. Uptake rates obtained for isolated zooxanthellae in this study are similar to those obtained previously for intact coral-zooxanthellae symbioses. This evidence is consistent with the hypothesis that nutrient uptake by intact zooxanthellae-host symbioses occurs by diffusion down a concentration gradient created by localized substrate depletion by the zooxanthellae in host tissue.

On the morphology, Reproduction and cytology of two new freshwater dinoflagellates from India

The morphology, reproduction and cytology of two new species of Gymnodinium (G. dodgei and G. lalitae) are described, as also are morphological variations encountered in natural populations and cultures. Chromosome numbers determined for these two new taxa are: G. dodgei, 195 ± 5; G. lalitae, 90 ± 4. Some systematic aspects of the genus Gymnodinium and the process of encystment in G. dodgei are discussed.

Additional Microplankton from Australian Late Mesozoic and Tertiary Sediments.

New Australian Late Mesozoic species of Gymnodinium and Deflandrea (Dinoflagellata) and Odontochitina and Palaeotetradinium (Incertae Sedis) have been described. A new species of Wetzeliella from a South Australian Eocene deposit has thrown light on the taxonomic position of the genus. Hystrichokolporna cinctum Klumpp (Hystrichosphaeridae) has been recorded from Victorian Tertiary deposits.