<p>This thesis deals with physical factors and biological interactions affecting the distribution of two fucoid species, <i>Fucus vesiculosus</i> and <i>F. serratus</i>, in the Baltic Sea. Studies have been carried out in two quite different environments: an archipelago, and an open rocky coast. The archipelago has an extremely long coastline with a heterogeneous submerged landscape of different substrate types, slopes, water qualities, and degrees of wave exposure. The factors influencing<i> F. vesiculosus</i> distribution, morphology and epiphyte composition were studied in the Stockholm archipelago using field surveys and spatial modelling in Geographic information systems (GIS). A GIS-method to estimate wave exposure was developed and validated by comparing the result to an index based on vertical zonation of lichens. Wave exposure was considered an important factor for predicting the distribution of <i>F. vesiculosus </i>by its ability to clean hard surfaces from silt, and a predictive model was constructed based on the information of wave exposure and slope of the shore. It is suggested that the lower distribution boundary of attached <i>F. vesiculosus</i> is set by sediment in sheltered parts of the archipelago, and by light availability in highly wave exposed parts. The morphology of <i>F. vesiculosus</i> was studied over a wave exposure gradient, and several characters responded in accordance with earlier studies. However, when separating effects of wave exposure from effects of other confounding water property parameters, only thallus width was significantly different. Several water property parameters were shown to be correlated with wave exposure in the Stockholm archipelago, and the mechanism responsible for the effects on <i>F. vesiculosus</i> morphology is discussed. The composition of epiphytes on <i>F. vesiculosus</i> varied over a wave exposure gradient with a positive correlation to <i>Elachista fucicola</i>, and a negative to <i>Chorda filum</i>. </p><p>At an open coast the physical environment is much less heterogeneous compared to an archipelago. The distributions of <i>F. vesiculosus</i>, <i>F. serratus</i>, turf-forming algae, and the seafloor substrate, were surveyed along the open coasts of Öland and Gotland. Turf-forming algae dominated all hard substrates in the area, and <i>Polysiphonia fucoides</i> was most abundant. At the Gotland coast <i>F. vesiculosus</i> was less abundant than at the Öland coast, and <i>F. serratus</i> occurred only in the southern-most part. <i>Fucus serratus </i>was increasingly more common towards south which was interpreted as an effect mainly of the Baltic salinity gradient, or the variation of salinity that has occurred in the past. The effects of turf-forming algae and sediment on <i>F. serratus</i> recruitment at 7 m depth off the Öland east coast were studied in the field, and by laboratory experiments. Almost no recruits were found in the algal turf outside the <i>F. serratus</i> patches. More fine sediment was found in the turf than in the <i>F. serratus</i> patches, suggesting that the turf accumulates sediment by decreasing resuspension. Both filamentous algae and sediment decreased the attachment ability of <i>F. serratus</i> zygotes and survival of recruits, and sediment had the strongest effect. It is therefore suggested that <i>F. serratus</i> has difficulties recruiting outside its patches, and that these difficulties are enforced by the eutrophication of the Baltic Sea, which has favoured growth of filamentous algae and increased sedimentation. An overall conclusion is that <i>Fucus</i> distribution is affected by large-scale-factors, such as the eutrophication and salinity changes of the Baltic Sea, as well as by small-scale variation in wave exposure, substrate and slope, and by surface competition with neighbouring species. </p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:su-89 |
| Date | January 2004 |
| Creators | Isaeus, Martin |
| Publisher | Stockholm University, Department of Botany, Stockholm : Botaniska institutionen |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
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