<p>The brackish Baltic Sea is a marginal environment for both marine and freshwater species. The rate of ecological differentiation is presumably high due to strong selection pressure from a gradient of decreasing salinity that has been present in its current state for only about 3 000 years. Even more recently, increased nutrient loading due to human activities has affected the growth rate of species, with potential effects on their competitive interactions and responses to other regulating factors. I have investigated the potential effects of low salinity and nutrient enrichment on the distributional ranges of two marine macroalgae with a wide distribution in the Baltic Sea, the red alga <i>Ceramium tenuicorne</i> (Kütz.) Wærn and the brown alga <i>Fucus vesiculosus</i> L. </p><p>A field study in the northern Baltic Sea indicated a strong relationship between the community structure of macroalgae and abiotic factors even on a small, local scale. The abiotic factors are potentially modulated by eutrophication, which may have a strong effect on the depth distribution and abundance of macroalgae. On a regional scale, laboratory experiments suggested that nutrient enrichment is unlikely to affect the distribution of <i>Ceramium</i> and <i>Fucus</i> along the salinity gradient. Growth in <i>Ceramium</i> from the Baltic Proper was enhanced by nitrate and phosphate, but the response did not override growth constraints due to low salinity. <i>Ceramium</i> from the Gulf of Bothnia had an inherently lower growth rate that was not positively affected by nitrate and phosphate increase. In <i>Fucus vesiculosus</i>, reproductive performance was impaired by nitrate and phosphate levels corresponding to ambient levels in eutrophicated areas of the Baltic Sea, when measured by their effect on zygote attachment, germination, and rhizoid development.</p><p>The wide distribution of <i>Ceramium</i> in the inner Baltic Sea is probably related to local adaptation, rather than a generalized tolerance of different salinity levels. Ecotypic differences were observed when comparing strains from the Baltic Proper (salinity 7 psu) and the Gulf of Bothnia (4 psu). A high rate of vegetative reproduction was evident, although sexual reproduction was occasionally observed in salinity 4. In <i>Fucus vesiculosus</i>, genetic and morphological analyses of sympatric and allopatric populations of the common, vesicular, morphotype and a dwarf morphotype, characteristic for the Gulf of Bothnia, showed that the dwarf morphotype represents a separate evolutionary lineage. Also, vegetative reproduction was observed in <i>Fucus</i> for the first time, as supported by genetic and experimental data. </p><p>The results show that the biota of the inner Baltic Sea may have unique adaptive and genetic properties, and that it is highly relevant to consider subspecies diversity in Baltic Sea management.</p>

<p>I combined comparative and experimental studies in the field and in the greenhouse to examine factors influencing reproductive success in two insect-pollinated herbs, the tristylous, selfincompatible perennial <i>Lythrum salicaria</i> and the self-compatible, biennial <i>Pedicularis palustris</i>. More specifically, I explored (i) the effects of plant population characteristics on the intensity and outcome of interactions with pollinators and seed predators, (ii) whether flower morphology affects duration of stigma receptivity, and (iii) whether damage-induced reduction in floral display reduces pollinator visitation and increases pollen limitation.</p><p>As predicted, the rate of pollinator visitation tended to increase and the number of flowers probed per plant tended to decrease with increasing population size in <i>L. salicaria</i>, but these relationships only approached statistical significance. By taking advantage of the pollen size polymorphism that is typical of many heterostylous plants, I could show that the number of compatible pollen grains received increased with population size, and that this was associated with a reduction in pollen limitation and increased seed output per flower. The deposition of high numbers of incompatible conspecific and heterospecific pollen grains did not appear to reduce seed set.</p><p>In <i>P. palustris</i>, fruit set and seed predation varied markedly among populations and years, but this variation could only partly be explained by variation in population size. Fruit set was positively related to population size, and seed predation was negatively related to population size, in one of three years. Similarly, the level of pollen limitation, which was quantified in two years, varied among populations, but was not related to population size, density or isolation.</p><p>In <i>L. salicaria</i>, both the duration of stigma receptivity and the effect of prior self-pollination on seed output varied among style morphs. These differences may contribute to morph-specific differences in pollen limitation and seed production documented in the field.</p><p>The results of a field experiment demonstrated that damage to the shoot apex may markedly reduce fruit production in <i>L. salicaria</i>, and suggested that this is mainly because damage reduces flower number. I found no evidence that a reduced floral display increased the severity of pollen limitation.</p><p>Taken together, the results show that interactions with both pollinators and herbivores may markedly affect reproductive output in the two plant species, and that the intensity of both mutualistic and antagonistic interactions vary considerably in space and time. Moreover, they are consistent with the hypothesis that pollination success should depend less on population size in selfcompatible than in self-incompatible plants.</p>

<p>Heterotrophic microorganisms are important for the flow of carbon and nutrients in the sea. Bacteria, nanoflagellates and ciliates are relevant components of the pelagic food web. In order to be able to predict the outcome of e.g. eutrophication or climate change we need to know how the different components of the pelagic food web are regulated. With the focus on the northern Baltic Sea food web, this thesis deals with limitation and control of heterotrophic protists, the effect of resource heterogeneity on food web efficiency and diversity of nanoflagellates.</p><p>In-situ microcosm experiments showed that the net growth of heterotrophic flagellates were resource limited throughout the year. Field data confirmed that the abundance of flagellates was bottom-up controlled. Furthermore, field data also showed that the annual average biomass of protists, flagellates and ciliates increased with primary productivity. On a smaller seasonal scale temperature and bacterial biomass were able to explain most of the variation in flagellate biovolume. The temporal variation in ciliate biovolume could not be explained by any bottom-up factors like bacterial biomass, flagellate biomass or chlorophyll a. This and an in-situ microcosm experiment implied that the seasonal dynamics of ciliates were more regulated by predators like mesozooplankton.</p><p>The food web efficiency i.e. how much of production at the resource level is converted to production at the top trophic level, may be affected by specific size or type of resource. Indoor mesocosms revealed that the food web efficiency was 11 times lower when heterotrophic bacteria dominated basal production instead of nano- and micro-sized phytoplankton. This was due to a lengthening of the food web when pico-sized bacteria constituted the main resource.</p><p>The PCR-DGGE molecular biological method was used to study the diversity of heterotrophic or mixotrophic chrysomonads. The focus was set on chrysomonads due to their relatively large contribution to the nanoflagellate community. Group-specific PCR primers were optimized for the target group. A field survey in the northern Baltic Sea showed that a handful of chrysomonad sequences were present throughout the year. Significantly more chrysomonads were recorded in the basin with higher primary productive and salinity. In total 15-16 different chrysomonad sequences were recorded. Most of them matched uncultured chrysomonad clones.</p>

<p>Benthic diatoms are valuable tools for biological monitoring and paleo-ecological reconstruction of past environmental conditions. This thesis aims at describing size-related properties of benthic diatoms and suggests that data assessment for community analysis can be improved by considering the importance of scale. It investigates which environmental factors structure epilithic diatom communities on the coast of the Gulf of Bothnia and identifies environmental factors correlated with phytobenthic biomass. It also contributes to the floristic knowledge of the Baltic Sea. </p><p>Diatom species show large variation in size. The responses of large species (≥1000 μm3) in diatom communities to environmental factors are underestimated if solely measured as relative abundance, as is the common practice. However, relative abundance gives the best gradient resolution, as compared to surface area and biovolume, if species are counted separately in two biovolume classes. Small and large species in the same community may respond differently to the same environmental factors. </p><p>To assess the principal environmental factors structuring diatom communities in the Gulf of Bothnia, 270 quantitative samples were collected from submerged stones. Sampling was carried out in spring in four areas of the Bothnian Bay, characterized by a stable north-south salinity gradient (0.4-3.3 psu), and in three areas of the Bothnian Sea which has a rather uniform salinity of ca. 5 psu. Canonical correspondence analysis (CCA) identified salinity and exposure to wave action as the principal factors structuring the diatom communities of the Bothnian Bay, whereas exposure to wave action was the principal factor in the Bothnian Sea. Measurements of relative ignition loss suggested that the cover of macroalgae, and thereby the higher abundance of epiphytic diatoms in the epilithic samples, was positively correlated with salinity in the Bothnian Bay and with water movement in the Bothnian Sea. </p><p>Two new brackish water species are described, <i>Navicula sjoersii</i> S. Busse & Snoeijs and <i>N. bossvikensis</i> S. Busse & Snoeijs. The new species are compared with <i>N. perminuta</i> Grunow, a common brackish-water species.</p>

<p>In this thesis I examine and evaluate the effects of a documented large-scale eutrophication on macroalgal vegetation on the Swedish coast. During the past century the load of nutrients has increased manifold in the Baltic Sea area, increasing primary production and organic sedimentation significantly. By re-investigating a unique reference material of macroalgal vegetation from the 1940-60s and by conducting new diving studies at the same sites, I showed that long-term trends in macroalgal community composition and species’ distributions are consistent with changes expected from an increased nutrient availability. In the Öregrund archipelago (northern Baltic Sea), I documented a declined depth distribution of the dominant canopy forming alga, <i>Fucus vesiculosus</i>, and an increased abundance of opportunistic ephemeral algae compared to 52-53 years ago. In the Gullmar Fjord area (Skagerrak), trends included increased abundances of functional groups with opportunistic algae, decreased abundances of large perennial algae and a general decline in the depth distribution of the vegetation compared to 36-57 years ago. Sediment removal experiments in the northern Baltic Sea confirmed the hypothesis that sedimentation influences macroalgal community composition. Species depending on short periods of reproduction were clearly favoured by sediment removal, especially <i>F. vesiculosus</i> that seemed limited in depth by the local sediment load. Species with long continuous periods of dispersal by spores and/or fragments (for example the ephemerals <i>Cladophora glomerata</i>, <i>Ceramium tenuicorne</i> and <i>Enteromorpha</i> spp.) were more tolerant to the natural sediment load. In general, sediment removal favoured macroalgal establishment and development, indicating that variation in the natural sediment load is an important constraint for sublittoral rocky-shore macroalgal community development. I conclude by suggesting that the documented long-term changes in macroalgal vegetation on the Swedish coast partly are explained by an increased organic sedimentation in these areas.</p>

<p>The main aim of this work was to identify local adaptation processes in amphibian populations, thereby improving the general understanding of genetics and mechanisms behind the evolution and maintenance of biological diversity. Phenotypic and genetic variation in life-history traits was studied within and between populations common frog (<i>Rana temporaria</i>) populations along a 1600 km transect from southern Sweden to northern Finland.</p><p>Embryonic and larval development and growth was investigated both under field and laboratory conditions. The results suggest ample genetic diversity in larval life-history traits among Fennoscandian common frog populations. Larval developmental rate along the gradient has evolved a countergradient variation pattern of genotypes and phenotypes as indicated by the positive relationship between developmental rate and latitude under laboratory conditions and the lack of such a relationship in the field. The data suggest that this pattern has evolved because of time constraints due to decreasing length of growth season with latitude. Neither field-caught adults nor laboratory raised larvae displayed a linear latitudinal size cline as expected from the so called Bergmanns rule. Rather, size increased towards the mid-latitude populations and decreased thereafter, indicating that body size is a product of direct environmental induction or a trade-off with other life-history characters. Age and size at hatching showed no consistent latitudinal pattern, indicating that the embryonic stage is not as time constrained as the larval stage.</p><p>A large part of the variation in age and size at metamorphosis among populations was due to additive genetic effects. However, small, but significant maternal effects, mostly due to variation in egg size and non-additive genetic effects also contributed to among population variation. A comparison of divergence in presumably neutral molecular genetic markers (F_ST) and quantitative characters (Q_ST) revealed that although both estimates of divergence were relatively high, estimates of Q_ST was generally higher than those of F_ST, indicating that the genetic variation observed in larval traits is primarily a result of natural selection rather than genetic drift. Hence, our results reinforce the conclusion that intraspecific genetic heterogeneity in the young northern European ecosystems may be more widespread than previously anticipated</p>

<p>This thesis examines the relative importance of local conditions, dispersal and dynamics of the trees on epiphyte distribution patterns and colonization-extinction dynamics. Study species are the mosses <i>Orthotrichum speciosum </i>and <i>O. obtusifolium</i>, and the red-listed <i>Neckera pennata</i>. The thesis also includes an attempt to parameterize a model for a lichen metapopulation (<i>Lobaria pulmonaria</i>) in a dynamic landscape, based on only presence/absence data of the epiphyte and its host trees. </p><p>The results show that epiphyte colonization of trees is affected by both local conditions, and by connectivity to occupied trees. The positive effect of connectivity, implying a restricted dispersal range, was established by both demographic and genetic studies. The important local conditions were tree diameter and vitality, and shade. Local extinctions from trees occurred among small trees with low local epiphyte abundance, but more often, were the results of tree fall.</p><p>The observed importance of connectivity on epiphyte colonization agrees with the assumptions of the classic metapopulation model. However, the classic metapopulation model assumes that the landscape is static, and that local extinctions occur for stochastic reasons. The dynamics of epiphytes are different. A new conceptual model is therefore suggested, the patch-tracking metapopulation model. It differs from the classic metapopulation model in that it includes dynamics of the patches, and in that local extinctions only occur as patches are destroyed.</p><p>Simulations of the dynamics of <i>N. pennata </i>showed that its future metapopulation size will be overestimated unless the dynamics of the trees are accounted for. The simulation results further suggest that the dynamics of <i>N. pennata </i>can be characterised by the patch-tracking metapopulation model. </p><p>The attempt to parameterize the <i>L. pulmonaria </i>metapopulation model showed that more information are required for rigorous parameterization, preferably of the past historic fire regime.</p>

<p>Heterotrophic bacteria utilize dissolved organic matter, and the carbon flow through an ecosystem depends on the fractions of the utilized carbon that is either respired or transferred to higher trophic levels. The major aim this thesis is to investigate 1) the relationship between composition and functioning in heterotrophic bacterioplankton communities and 2) the influence of environmental conditions on both parameters. I set up several batch culture experiments, where lake water filtrates containing bacteria but no grazers were inoculated into sterile freshwater medium to investigate the importance of the origin of the source community (the inoculum) versus the environmental conditions (the medium) for the composition and functional performance of bacterial communities. In some experiments the medium was manipulated to simulate changes in salinity, pH and dissolved organic matter quantity and quality. Functional parameters (biomass yield, respiration, growth efficiency and enzyme activities) and the genetic composition of the emerging bacterial communities were determined.</p><p>When bacterial inocula obtained from different habitats were re-grown under identical conditions, differently composed communities emerged. This indicates that the history and distribution of taxa within the inoculum was an important regulating factor of community composition. The coupling between community composition and functioning was not very tight, and there was functional equivalency with respect to aggregated functions important at the ecosystem scale (e.g., biomass production and respiration). The functional performance of bacterial communities could to a large extent be predicted from the medium alone, except when it deviated strongly from the ambient settings. When bacterial communities were exposed to dilution, a strong change in pH or an increase in salinity, growth of structurally and functionally distinct communities occurred. I therefore suggest that it depends on the disturbance regime how bacterial community structure and function are related to each other. </p>

<p>Bacteria and fungi dominate the decomposition of aquatic plants, a major process in the carbon and nutrient cycling in many aquatic systems. Although phylogenetically distant, bacteria and fungi often live in close proximity with each other. Since these microorganisms also have similar ecological functions, interactions have developed between them. This thesis explores the nature of such interactions, and the potential effects on key components of the decomposition process. The thesis includes a critical assessment of the ergosterol method for determination of fungal biomass, a survey of the environmental factors determining the distribution and taxa numbers of litter-decomposing bacteria and fungi in lakes, and a number of experiments on the interactions between bacteria and fungi. In all the experiments performed, fungi responded to bacterial presence through antagonism, although different fungal strains, bacterial communities and substrates were used. The antagonism seemed to be caused by interference competition for substrate. The fungal effect on bacteria was less consistent. Bacterial growth was suppressed, unaffected, or even enhanced by the presence of fungi. Fungi contributed more to extracellular enzyme production than bacteria, and bacteria were probably able to assimilate intermediate decomposition products formed through the activity of extracellular enzymes of fungal origin. Thus, the effect on bacteria from interacting with fungi was determined by the balance between competition and benefit from excreted enzymes. Bacteria and fungi also used different size fractions of the organic matter, according to their different enzymatic capacities. Hence, bacteria appeared to assimilate low-molecular-weight compounds, while high-molecular-weight compounds were utilized primarily by fungi. </p><p>In brief, the ecological interactions influenced the growth and hence also the biomass development of bacteria and fungi, which affected enzyme activity as well as utilization of dissolved organic matter. Therefore, I suggest that interactions between bacteria and fungi influence degradation of plant litter in aquatic systems.</p>

The effects of harvesting Pacific hake (Merluccius productus) were examined with a multi-species numerical model composed of seven logistic growth equations coupled by a food web. The food web was composed of: California sea lions (Zalophus californianus), hake, sablefish (Anaplopoma fimbria), spiny dogfish (Squalus acanthias), a generic rockfish species (Sebastes spp.), Northern anchovy (Engraulis mordax), and a generic euphausiid species (as an example, Pacific krill, Euphausia pacifica). The model was tuned to mimic stock assessment biomass estimates for the years 1980 to 1991, after which a short term experiment and a sensitivity analysis were conducted. The short term experiment used a factorial design, with hake fishing and fishing for rockfish, sablefish, and anchovy as treatments. It was analyzed with scale analysis techniques. The results indicate that hake (from a management viewpoint) is potentially most important in the offshore community as a prey item for sea lions and as a predator on anchovies, but hake fishing mortality had a small effect on either population during the time span of the experiment. Results also suggest that hake has little or no competitive interaction with other species that are trophically similar. Increased harvesting of hake would probably do little to increase the biomass of rockfish or sablefish. The general conclusion of both the sensitivity analysis and the experiment is that species below their carrying capacity are mostly affected by changes in growth and removal processes while species close to their carrying capacity are mostly affected by processes controlling prey availability. A forty year projection from 1991 to 2031 was conducted to examine the effects of hake fishing on sea lion and anchovy biomass. Results indicate that sea lion biomass will vary inversely with hake fishing effort, while anchovy biomass is directly proportional to hake fishing effort. Results also indicate that hake experience environmental conditions not favorable to recruitment. During favorable conditions the hake population builds up a "surplus" that carries it through periods of unfavorable conditions. Increased hake fishing effort reduces the response of the population to favorable conditions. The results of this research constitute a step from the theory toward the practice of proactive multi-species and ecosystem management. / Graduation date: 1995