Latitudinal patterns in reef fish assemblages reflect the influence of long-term environmental conditions, evolutionary processes and the recent, short-term influence of fishing. Long-term processes generate the typically common latitudinal patterns in reef fish assemblages, such as decreases in diversity and herbivory towards higher latitudes. These patterns reflect the global gradient in water temperature and the isolation of temperate regions from the tropics. Fishing also influences reef fish assemblages in that it decreases the abundance of large-bodied carnivore species on reefs, often leading to over-exploitation, depletion and in some cases the extirpation of populations. Indirectly, the removal of these large-bodied carnivores can influence the abundance of their prey, leading to an increase in non-target species. This study examines the latitudinal patterns in reef fish assemblages across a unique biogeographic region, the temperate Western Australian coast, and incorporates an investigation of the influence of fishing on the structure of these assemblages. Seven regions across seven degrees of latitude and seven degrees of longitude covering approximately 1500 km of coastline were sampled. Fish assemblages were characterised at each region using diver operated stereo-video transects. At each region, four locations, and within each location, four reefs were surveyed totalling 1344 transects. A significant gradient in water temperature exists with latitude and longitude. Along the Western Australian coast, and in contrast to other regions species diversity of reef fish increased towards higher latitudes and there was no evidence for a decrease in the biomass and abundance of herbivorous reef fish. The presence of the poleward flowing warm water Leeuwin current combined with the absence of major extinction events means the temperate Western Australian coast contrasts with global latitudinal trends in reef fish assemblage structure. The unique biogeographic history of temperate Western Australia has also generated a high degree of endemism among reef fish. Nearly 30 % of the species found along the west coast in this study are endemic to Western Australia, with the narrow range of these species playing an important role in the large scale patterns and spatial vi heterogeneity in reef fish assemblage structure. Furthermore, many of these endemic species are large-bodied carnivores and targeted by fishers. The impact of fishing on the abundance of large-bodied carnivores throughout the Western Australian temperate region is clear both spatially and temporally. The distribution of fishing effort is greatest along the west coast and decreases towards the south following the gradient in SST. Along the west coast, high levels of fishing effort have reduced the biomass and abundance of target carnivores to well below the standing biomass of the south coast where a low level of fishing effort occurs. This reduction in biomass is related to the historical declines in catch per unit effort (CPUE) of many key target species. These target species include endemic species such as Choerodon rubescens, Glaucosoma herbraicum, Epinephilides armatus Nemadactylus valenciennesi and Achoerodus gouldii.

Dams play an important role in our society, but their negative impacts on aquatic ecosystems have led to a need for conservation efforts to mitigate the negative effects. In some instances, dam removal has been suggested to be the most economically and ecologically beneficial restoration method to improve longitudinal connectivity. This, however, has increased the need of more research about the effects dam removal have on aquatic ecosystems, since the outcomes of this restoration method can be unpredictable. In this study, I investigated ecological impacts of dam removals in Swedish inland waters. I collected field data from five different lakes in Värmland and Dalarna, two lakes with dam removal in 2017/2018 and three without. I studied how dam removal affected different trophic levels of the aquatic ecosystem, where I predicted that a top-down effect would increase abundances of piscivorous European perch (Perca fluviatilis) and zooplankton, but decrease phytoplankton, whereas a bottom-up effect would lead to increases in biomass at all trophic levels (with most pronounced effects on nutrient concentration). If both top-down and bottom-up effects would operate in parallel, all the above mentioned effects could occur. I also predicted that if dam removal affected the fish community, there would be a change in species diversity and fish biomass. Moreover, if perch demography was affected, there would be a change in perch length and abundance of different age classes. To investigate this, I collected data on fish, plankton, nutrients (P, N), DOC, pH and conductivity in the five lakes and compared this with already existing historical data using a BACI design. Two-way ANOVAs were used to study the effects of dam removals on these variables. There were not enough historical data on P concentration or zoo-and phytoplankton to be analyzed statistically. I did, however, conduct correlation analyses with zoo- and phytoplankton. Contradictory to my prediction, the results showed no effect of dam removal on fish biomass or diversity, water chemistry or perch demography in the studied lakes. There was, however, a statistically significant effect of time on Tot-N, with lower values after the years of 2017/2018 (regardless of dam removal). There were also some differences between the lakes in species diversity, concentration of Tot-N, potentially piscivorous perch and perch length. The outcomes of dam removal are unpredictable, as are the expected time-lapse of the effects, which means that changes may yet occur in the studied lakes. Knowledge about ecosystem responses to dam removal enables managers to better predict the effects of dam removal, and thereby facilitate decision makings related to this restoration method. / Dammar spelar en viktig roll i vårt samhälle, men deras negativa påverkan på akvatiska ekosystem har ökat behovet av bevarandeinsatser för att minska de negativa effekterna. I somliga fall har dammutrivning föreslagits vara den mest ekonomiskt och ekologiskt gynnsamma bevarandemetoden för att förbättra longitudinell konnektivitet. Detta har dock ökat behovet av mer forskning gällande dammutrivningars effekter på akvatiska ekosystem, eftersom utfallen av denna bevarandemetod kan vara oförutsägbara. I denna studie undersökte jag dammutrivningars ekologiska effekter i svenska inlandsvatten. Jag samlade data i fält från fem olika sjöar i Värmland och Dalarna, två sjöar med dammutrivningar under 2017/2018 och tre utan. Jag undersökte hur dammutrivning påverkade olika trofiska nivåer i det akvatiska ekosystemet, med förväntningarna att en top-down-effekt skulle öka abundansen av fiskätande abborre (Perca fluviatilis) samt djurplankton, men minska växtplankton, medan en bottom-up-effekt skulle leda till ökad biomassa inom samtliga trofiska nivåer (men med mest effekter på näringskoncentration). Om både top-down- och bottom-up-effekter skulle verka parallellt kunde samtliga ovanstående nämnda effekter förekomma. Jag förväntade även att om dammutrivning påverkade fisksamhället skulle det ske en förändring i artdiversitet och fiskbiomassa. Därtill bör en effekt på demografi hos abborre leda till förändringar i abborrlängd- och abundans i olika åldersklasser. För att undersöka detta samlade jag in data över fisk, plankton, näringsämnen (P, N), DOC, pH och konduktivitet i de fem sjöarna och jämförde detta med redan existerande historiska data med en BACI design. Tvåvägs-ANOVAs användes för att studera effekterna av dammutrivningar på dessa variabler. Det fanns inte tillräckligt med historiska data över P-koncentration eller djur- och växtplankton för att analyseras statistiskt. Jag utförde dock korrelationsanalyser med djur- och växtplankton. I kontrast till min förväntan visade resultaten ingen effekt av dammutrivning på fiskbiomassa- eller diversitet, vattenkemi eller demografi hos abborre i de studerade sjöarna. Det var däremot en statistiskt signifikant effekt av tid på Tot-N, med lägre värden efter 2017/2018 (oberoende av dammutrivning). Det var även en del skillnader mellan sjöarna i artdiversitet, koncentration av Tot-N, potentiellt fiskätande abborre samt abborrlängder. Utfallen av damutrivningar är oförutsägbara, och detsamma gäller tidsintervallet för effekterna, vilket innebär att det fortfarande kan ske förändringar i de studerade sjöarna. Kunskap om ekosystemrespons till dammutrivning möjliggör för förvaltare att lättare bedöma effekter av dammutrivningar, och underlättar därav beslutsfattning relaterat till denna bevarandemetod.