Numerous papers have been published on the animal and algal communities of fresh-water and marine biotopes, and their relation to the physical and chemical factors of their environment. Brackish-water biotopes have been studied much less intensely, presumably due to their limited distribution and to the complexity of their bioco­ enoses, composed of fresh-water, brackish-water and marine organisms. The reduced size of the species present forms a supplementary difficulty, which is especially pronounced in the algal communities, a major part of which are composed of nanno-phytoplankters. The University of Ghent considered a detailed survey sufficiently attractive to set up because of the high species diversity, the gaps in the knowledge of brackish-water nannophytoplankton at the species and population levels, and the convenient proximity of brackish-water biotopes. Moreover, the brackish-water biotopes proved to be unique, and consist of a series of landlocked creeks, con­ nected to the sea by means of an underground salt water supply. VII Contents Chapter 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chapter 2 Study area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. 1. Topographical situation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. 2. Historical aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. 3. Edaphic factors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. 4. Hydrology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. 4. 1. Salinity fluctuations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. 4. 2. Origin of the brownish colour of certain creeks. . . . . . . . . . . . . . . . . . . . . . . . 6 2. 4. 3. Hydrography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2. 5. Biotopes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2. 6. Climatic features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Chapter 3 Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3. 1. Sampling procedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3. 2. Physical properties, water chemistry, chlorophyll a and phaeophytin a . . . . . . . . . . . . . 11 3. 3. Phytoplankton samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3. 4. Periphyton and benthos samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Inhalt

1 Introduction.- 2 Study area.- 2.1. Topographical situation.- 2.2. Historical aspects.- 2.3. Edaphic factors.- 2.4. Hydrology.- 2.4.1. Salinity fluctuations.- 2.4.2. Origin of the brownish colour of certain creeks.- 2.4.3. Hydrography.- 2.5. Biotopes.- 2.6. Climatic features.- 3 Methods.- 3.1. Sampling procedure.- 3.2. Physical properties, water chemistry, chlorophyll a and phaeophytin a.- 3.3. Phytoplankton samples.- 3.4. Periphyton and benthos samples.- 4 Data analysis.- 4.1. Classification techniques.- 4.2. Ordination techniques.- 4.2.1. Principal component analysis (P.C.A.).- 4.2.2. Detrended correspondence analysis (D.C.A.).- 4.3. Transformations.- 4.4. Selection of the number of the variables.- 5 Physical properties, water chemistry and phytoplankton production.- 5.1. Temperature.- 5.2. Conductivity.- 5.3. Chlorides.- 5.4. pH.- 5.5. Carbonate, bicarbonate and alkalinity.- 5.6. Calcium, magnesium, total hardness.- 5.7. Ammonia.- 5.8. Nitrite.- 5.9. Nitrate.- 5.10. Orthophosphate.- 5.11. Dissolved oxygen.- 5.12. Active chlorophyll a of the total phytoplankton.- 5.13. Phaeophytin a of the total phytoplankton.- 5.14. Active chlorophyll a of the net phytoplankton.- 5.15. Phaeophytin a of the net phytoplankton.- 5.16. Surface area of the total phytoplankton.- 6 Phytoplankton groups.- 6.1. Seasonal phytoplankton groups.- 6.1.1. Seasonal phytoplankton groups in the Grote Geule (1).- 6.1.2. Seasonal phytoplankton groups in the Rode Geule (2).- 6.1.3. Seasonal phytoplankton groups in the Kapellen-polderkreek (5).- 6.1.4. Seasonal phytoplankton groups in the Boerenkreek (10).- 6.1.5. Conclusions.- 6.2. Synopsis of the seasonal phytoplankton groups.- 6.2.1. Chlamydomonas umbonata-group.- 6.2.2. Monoraphidium contortum-group.- 6.2.3. Anabaena spiroides var. longicellularis-group.- 6.2.4. Hemiselmis simplex-group.- 6.2.5. Gymnodinium splendens-group.- 6.2.6. Chaetoceras orientalis- group.- 6.2.7. Prymnesium spec. 1-group.- 6.2.8. Comparison of the synoptic seasonal groups.- 6.2.9. Salinity preferences of the synoptic seasonal groups.- 6.3. Spatial phytoplankton distribution.- 6.3.1. Spatial phytoplankton groups in the sample set of January 1973.- 6.3.2. Spatial phytoplankton groups in the sample set of November 1976.- 6.4. Discussion.- 7 Typification of algae.- 7.1. Brackish-water species.- 7.1.1. Subdivisions of brackish water.- 7.1.2. The origin of brackish water.- 7.1.3. Ecological features of brackish-water species.- 7.1.4. Types of brackish-water species.- 7.1.4.1. Holeuryhaline species.- 7.1.4.2. Euryhaline limnobionts.- 7.1.4.3. Euryhaline marine species.- 7.1.4.4. Brackish-water species - Hyphalmyrobionts.- 7.2. Trophic preferences.- 7.3. Saprobity preferences.- 7.4. pH preferences.- 7.5. Littoral species.- 7.6. Plankton species.- 7.7. Benthic species.- 7.8. Periphytic species.- 7.9. Rheophiles.- 7.10. Thermal preferences.- 8 Systematic account.- Taxonomic index.- References.