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Fytoplanktongemeenschappen in de estuaria van de Elbe, Schelde & Gironde
Muylaert, K. (1994). Fytoplanktongemeenschappen in de estuaria van de Elbe, Schelde & Gironde. MSc Thesis. Rijksuniversiteit Gent. Faculteit Wetenschappen: Gent. Vol..1 (81 pp.); Vol. 2 (tables, plates) pp.

Thesis info:
    Universiteit Gent; Faculteit Wetenschappen; Vakgroep Biologie; Laboratorium Plantkunde, more

Available in  Author 
    VLIZ: Non-open access 140750
Document type: Dissertation

Keywords

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  • Muylaert, K., more

Abstract
    In spring 1993 samples were taken in and around the maximum turbidity zone of the estuaries of the Schelde, the Elbe and the Gironde. The sampling campaign took place in the framework of the MATURE-project (Biogeochemistry of the MAximum TURbidity zone in Estuaries). The phytoplankton was taxonomically analysed by means of light and/or scanning electron microscopy. Phytoplankton counts were performed using the Utermöhl method and biovolumes were calculated. These data were then analysed with the aid of two multivariate techniques (TWINSPAN, a classification technique and DCA, an ordination technique). The results of these analyses allowed the delimitation and description of phytoplankton communities. Indices for diversity (Hill-numbers N0, N1, N2 en N+) were calculated for each station. Correlation of the DCA--axes with some abiotic factors (salinity, temperature, particulate suspended matter and nutrients: ammonia, nitrate, phosphate and silicate) and a canonical analysis (DCCA) were used to investigate the relationship between species composition and the abiotic factors. Total cell numbers, total phytoplankton biovolumes, chlorofyl a data and Hill numbers were correlated with the same abiotic factors (Spearman and Pearson correlation). A systematic list of all identified taxa with a description, light or electron microscopic photographs and/or pictures of most taxa is given. A preliminary checklist is presented for the three estuaries. The Schelde estuary appeared to have the highest number of species while the Gironde estuary had the smallest species number. After a comparison with previous checklists, about half of the identified species appeared to be reported for the first time in the estuaries of the Schelde and the Elbe. For the Gironde 85% of the species found were new for this estuary. Some taxa could not be identified up to species level by means of the investigated literature: a Cyclotella species and a centric diatom. In the oligohalinicum of the Schelde estuary we found a phytoplankton community dominated by Cyclotella meneghiniana and several Chlorophyta species. In the polyhalinicum Skeletonema costatum was the dominant species, accompanied by taxa associated with sediment and detritus particles (mostly Thalassiosira spp. and Cymatosiraceae). In the mesohalinicum Coscinodiscus commutatus was typical together with taxa from both previous communities. In the limnetic pan of the Elbe estuary we mainly encountered allochtonous taxa (e.g. which were flushed in from the riverine pan of the Elbe); predominantly Stephanodiscus hantzschii (with a parasitic Chytridium sp.) and Chlorophyta. In the polyhalinicum the same community occured as in the corresponding zone in the Schelde. In the euhalinicum typical marine species as Ceratium fusus and Chaetoceros eibenii were present. In the meso- and oligohalinicum taxa from the poly- and oligohaline zones occurred, but in low numbers, together with one characteristic species: Cyclotella striata. In the Gironde estuary we found low numbers of the taxa of the previous estuaries and also some typical taxa. These were mainly Dinoflagellates and one Chlorophyta species. In the stations in the mouth of the estuary some typical marine taxa were present in low numbers, probably flushed in from the sea. Salinity appeared to be an important factor controlling species composition; there were no species that clearly prefered intermediate salinities. Particulate suspended matter and nutrients possibly have an important influence on the size of the plankton. The higher residence time in the Schelde estuary probably resulted in a higher diversity then in the Elbe estuary, although pollution is higher in the Schelde. The total number of taxa observed was also higher in the Schelde then in the Elbe, in spite of the broader salinity range sampled in the Elbe. In the sampling stations around the zones where the strongest change in salinity takes place. salinity stress was most probably responsible for the absence of phytoplankton communities with many characteristic taxa. This factor could also explain the low cell numbers. biovolumes and diversity in these zones. The high amounts of particulate suspended matter, an important factor for the light climate, were probably responsible for the species composition in the Gironde estuary: here, taxa belonging to the Dinophyta were dominant, a group known to contain many heterotrophic taxa. The same factor might also explain the low cell numbers and biovolumes and the low diversity in this estuary.

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