Phytoplankton dynamics in the Visvijver and the Kasteelvijver (Woumen, West-Vlaanderen) in relation to nutrients and zooplankton
De Schuijmer, C.; Geenens, V.; Declerck, S.; Sabbe, K.; Muylaert, K.; Vyverman, W. (1998). Phytoplankton dynamics in the Visvijver and the Kasteelvijver (Woumen, West-Vlaanderen) in relation to nutrients and zooplankton. Biol. Jb. Dodonaea 65: 131-132 In: Biologisch Jaarboek (Dodonaea). Koninklijk Natuurwetenschappelijk Genootschap Dodonaea: Gent. ISSN 0366-0818, more Also appears in:Beeckman, T.; Caemelbeke, K. (Ed.) (1998). Populations: Natural and manipulated, symposium organized by the Royal Society of Natural Sciences Dodonaea, University of Gent, 29 October 1997. Biologisch Jaarboek (Dodonaea), 65. Koninklijk Natuurwetenschappelijk Genootschap Dodonaea: Gent. 257 pp., more |
| Keywords | Aquatic communities > Plankton > Phytoplankton
Conferences
Belgium [Marine Regions]
Fresh water |
| Authors | | Top | - De Schuijmer, C.
- Geenens, V.
- Declerck, S., more
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| Abstract | In an attempt to restore clear water conditions in the eutrophic ponds 'Visvijver' and 'Kasteelvijver' in the nature reserve 'The Blankaart', several biomanipulation measures were taken during 1995. In spring both ponds were dredged, followed by a reduction of the fish-stock in autumn to 12 kg/ha in the 'Visvijver' and to 87.6 kg/ha in the 'Kasteelvijver'. In addition, pike fingerlings were introduced in spring 1996. In order to gain a better understanding of the trophic changes after bio- manipulation, the phytoplankton dynamics were analysed in relation to nutrients and zooplankton. The 'Visvijver' was studied from March to December 1996, while the 'Kasteelvijver' was studied only in autumn 1996. Throughout the study period, phytoplankton communities in the 'Visvijver' were dominated by flagellates, of which Cryptophyta, Chrysophyta and Chlorophyta were the most important taxonomical groups. In spring nanoflagellate taxa of the Prasinophyceae, Volvocales and Cryptophyta were dominant. Cryptophyta dominated in early summer and autumn while in late summer the phytoplankton community was characterised by a succession of several auto- and mixotrophic Chrysophyte taxa. In the 'Kastee1vijver' the phytop1ankton community in autumn was dominated by Cryptophyta and Ch1orococcales. Bacillariophyta occurred in considerably larger densities than in the 'Visvijver' but they were mainly benthic species. In 1996 a clear-water state in the 'Visvijver' was established and remained stable throughout the year. Macrophytes, mainly Chara, developed abundantly. In spring top-down control by large-bodied Daphnia probably had a considerable impact on the phytoplankton community. In spite of lower grazing pressure by zooplankton and high nutrient concentrations during summer and autumn, the phytoplankton density remained moderate. This could suggest that the macrophyte vegetation plays a central role in the control of phytoplankton population density through com- petition for nutrients and probably (and perhaps more importantly) by the release of allelopathic exudates. In the 'Kasteelvijver' the effects of the biomanipulation were less obvious. Although the visibility improved remarkably, there was no massive development of macrophytes. The still considerable fish biomass and the less efficient dredging probably had a negative influence on the development of macrophytes. Negative feed-back mechanisms induced by zooplanktivorous and benthivorous fish were presumably too strong to establish the shift from a turbid to a clear-water state. |
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