A mesocosm experiment with four triplicated treatments (control, clear carbon, pigment and dissolved organic matter) was carried out to investigate the effects of light (by pigment addition) and carbon (C) on phytoplankton communities and on the grazing pressure of microzooplankton on phytoplankton in the Baltic Sea. Phytoplankton concentration and species composition were determined by using an inverted microscope following the Utermöhl method. In order to measure differences in phyto-zooplankton trophic interactions between treatments, a dilution experiment was performed at the end of the mesocosm experiment. Surprisingly, the results show that light attenuation was beneficial to phytoplankton production while carbon enrichment had negative effects on phytoplankton production, the highest phytoplankton production was in the low light treatment and lowest phytoplankton production was in the clear C treatment. Cyanobacteria were the most dominant group, representing over 95% of the phytoplankton community. Diatoms were the least dominant group, representing less than 5% of the phytoplankton community. Microzooplankton grazing pressure was affected by light attenuation and C enrichment. Grazing pressure was highest on cyanobacteria in the clear C treatment, but chrysophytes experienced low grazing pressure and had high growth rates in the Control treatment where microzooplankton fed selectively on chrysophytes. The least abundant group, diatoms, decreased although they experienced no grazing pressure in the Control and clear C treatments. This experiment resulted in two surprising findings. First, increased light intensity reduced phytoplankton biomass, especially in the clear C treatment, and second, cyanobacteria constituted an important food source for microzooplankton grazers. This study adds to the increasing evidence that light effects can be counterintuitive and that cyanobacteria are not necessarily grazing resistant and can meditate nutrient transport to higher trophic levels.

Our understanding of turbot and flounder ecology in the Baltic Sea is insufficient for sound management decisions. This thesis aims to fill some gaps in current knowledge by providing information of the ecology of turbot and flounder within their juvenile habitat, and to relate these findings to issues assumed relevant for recruitment variation. Main focus is on turbot due to its relatively low abundance and high variability in recruitment. The distribution of both species was studied on different scales, as was environmental effects on food consumption in 0-group turbot. The 0-group turbot display a relatively restricted spatial distribution compared to flounder. This is possibly due to a more specialized diet, which may make them more vulnerable to habitat degradation, especially eutrophication as a strong negative correlation was found with the organic content in the sediment. The species show high temporal and spatial overlap when settling in July-September, with peak abundances in August, and at depths <1 m. Both species display sedentary behavior within the nursery ground. Compared to flounder, turbot was more mobile potentially due to its restricted diet calling for extended searches. For turbot, feeding conditions appear to vary between size groups, which potentially could cause variations in survival between years through size-selective mortality. But, the predation may be low in central Baltic Sea as the abundance of the main predator, brown shrimp are comparatively low during flatfish occupancy. A significant positive relationship was found between the recruitment of turbot and flounder, which suggests that no inter-specific interactions during the juvenile stage affect recruitment. This co-variation also suggests that the recruitment of the species is determined by the same phenomena, potentially by large scale abiotic factors during the egg- and larval stage. For turbot, additional variability is potentially generated during the juvenile stage due to its relatively restricted food and habitat requirements. The specific habitat demands of turbot revealed in this thesis may be used to protect and restore essentially nursery grounds. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Submitted. Paper 3: Submitted. Paper 4: Submitted.

Observations of feeding behaviour of common guillemots, Uria aalge, in June 2002 at the island Stora Karlsö in the Baltic Sea proper, and measurements of morphology and energy density in the prey fish sprat, Sprattus sprattus, showed that fish delivered to chicks at present are shorter and weigh less than in the 1970s. Long lasting attending periods and a feeding rate of 4.6 feeds per day indicate that parents are feeding their chicks at a maximum rate. Because of a decline in the energy density in sprat (22.4 kJg-1 dry weight) the daily energy intake of common guillemot chicks have declined noticeably. This could probably explain the observed decrease in fledging body weight of chicks through the 1990s. Baltic common guillemots do not seem to be able to select more energy-dense prey sizes or to switch to other prey species.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2008. / Härtill 6 uppsatser.

Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniversitet, 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Akademisk avhandling--Lund. / Extra t.p. with thesis note, inserted. "Källor och litteratur": p. [451]-466.

<p>During the 1960´s and 1970´s the number of grey seals in the Baltic Sea was decreasing rapidly, mostly due to hunting and toxic substances like DDT and PCB. When hunting became less intense and toxic substances decreased in the environment the grey seal population started to increase. Today grey seals are found common in the Baltic Sea and have started to become a big treat and a problem to the fishing industry. The grey seal destroys and enters fishing traps and consumes large quantities of the fish that have been caught.</p><p>The knowledge of the grey seal, like abundance and food preferences, is today limited. It is also important to define the position of the grey seal in the ecosystem in the Baltic Sea and to be able to predict changes that could occur if the population would rapidly decrease or increase. This project was therefore started in an attempt to increase the knowledge about the grey seals food preferences. The study was made in tree separate parts. Part one contained analyses of prey remains from stomachs and digestive tract from fourteen individuals put down in two geographically separate areas. The collected material from the seal digestive tract was cleaned and otoliths (hearing stones from fish), scales and back vertebra from fish eaten by the grey seal were sorted out. With the help of hard parts collected from the intestines the food preferences of the seals could be estimated. Eight different species of prey was found. The species were herring (Clupea harengus membras), sprat (Sprattus sprattus), common whitefish (Coregonus spp), perch (Perca fluviatilis), salmon (Salmo salar), trout (Salmo trutta) and roach (Rutilus rutilus). In two of the digestive tracts several individuals of the isopod Saduria entomon were found. No earlier studies describe the isopod as a food source for the grey seals in the Baltic Sea. The findings are therefore unique information. The results showed that during summer the main part of the grey seal diet in the gulf of Sundsvall and in the surrounding coastal area of Hårte was herring and sprat. No significant difference in food preferences was shown between the investigated seals from the gulf of Sundsvall and seals from the surrounding coastal area of Hårte.</p><p>The second part was made to investigate if it was possible to build a floating platform that would work as a resting place for the grey seal. The surface of the platform was covered by a layer that keeps the seal scats on the platform so that it could be collected. Otoliths from herring and common whitefish were found on the floating platform. Because the platform could not be under surveillance during the whole study some uncertainties about whether the otoliths found came from grey seal or from resting cormorants or other fish eating birds. However, the otolit size is linearly related to the fish size and this relationship can be used to track the predator. Otoliths from herring taken by grey seals and otoliths found on the platform were significantly bigger than the otoliths originating from the prey of cormorants. The results indicated that the common whitefish size was too big for a full grown cormorant bird to consume. The common whitefish size showed that it probably not had been cormorants that had deposited the otoliths on the platform. The platform method was concluded promising but it needs to be modified in order to work more effective in the future.</p><p>In the third part scats were collected from the area of Österåsen to increase the amount of information about the grey seals food preferences.</p><p>The knowledge of the grey seals diet in the Baltic Sea is today limited and few similar study’s have earlier been made. The collected scats and otoliths in this project are therefore unique.</p><p>2008:Bi 2</p>

The Baltic Sea is the one of the most studied seas area in the world and it is severely affected by human activities where eutrophication is the overall environmental problem. Although there is an international agreement that nutrient input to the Baltic should be reduced, the measures taken so far have not resulted in major reductions in nutrient inputs nor in environmental improvements. Sewage reduction is the most important factor for transparency improvement of the Baltic Proper and wetland restoration and change of N spreading time have no effective role in this aspect. Within the Baltic area, establishment of sewage treatment technology in Russia and Poland is more cost-effective than it would be in Sweden. Without this measure transparency improvement would be expensive. In Sweden NOx reduction is most cost-effective measure for transparency improvement in the Baltic Proper and without this measure the total cost would be ~ 58.5 million euro.

Övergödning utgör ett av de allvarligaste hoten mot Östersjöns miljö. Storleken av näringsbelastningen till havet behöver därför bestämmas med hjälp av tillgängliga matematiska modeller. Modellen ”Generalised Watershed Loading Functions” (GWLF), en ickedistribuerad parametermodell som uppskattar hydrologi och månatlig näringsbelastning, tillämpades på avrinningsområdet till Daugava som mynnar i Östersjön. Syftet med studien var att genom modellering av historisk transport av näringsämnen till Östersjön ta fram parametrar och indata som sedan kan användas vid applicering av GWLF på omkringliggande avrinningsområden. Data från 1990-talet användes för kalibrering av modellen och data från 1980-talet för validering. Årlig kvävebelastning modellerades med R2värdet 0,78 för kalibreringsperioden. Modellerad årlig kvävebelastning för valideringsperioden underskattades med ungefär 30 % vilket troligen beror på att kvävekoncentrationer i grundvatten och ytavrinning minskade mellan 1980- och 1990-talen. Fosforbelastningen underskattades jämfört med rapporterade värden vilket troligen beror på att enskilda avlopp inte inkluderades och att rapporterade punktutsläpp är för låga. Modifikationer av modellen föreslås för prediktion av näringsbelastningar under lång tid och behovet av harmoniserad, uppdaterad och lättillgänglig data för näringstransportsmodellering diskuteras. / Eutrophication is one of the most serious threats to the Baltic Sea environment. Nutrient loading into the sea therefore needs to be quantified by available mathematical models. The Generalised Watershed Loading Functions (GWLF), a lumpedparameter model that predicts hydrology and monthly nutrient loads, was applied to the Daugava River Basin, discharging into the Baltic Sea. The aim of the study was to model historic transport of nutrients into the Baltic Sea and thereby produce estimates of parameters and input data needed for a spatial extension of the GWLF to surrounding river basins. Calibration data were taken from the 1990’s and validation data from the 1980’s. Yearly nitrogen loads were modelled with an R2 value of 0.78 for the calibration period. Predicted yearly nitrogen loads for the validation period were about 30 % lower than reported values, probably depending on decreasing groundwater and runoff concentrations between the 1980’s and 1990’s. Phosphorus loads were underestimated compared to reported values, the main reason probably being the exclusion of septic systems and too low reported point sources. Modifications of the model are suggested for longterm predictions of nutrient loads and the need for harmonised, uptodate and generally accessible data for nutrient transport modelling discussed.