A mesocosm experiment was performed over 16 days during austral summer in 2010, in Northern Patagonia, Chile. Nutrients were added in 8 different concentrations along a gradient, simulating different levels of nutrients released by salmon farms. Nitrogen loading rate ranged from LN = 0 μg l-1 d-1 to LN = 42 μg l-1 d-1, and Silicate and Phosphorus were added in Redfield ratios. The goal of the study was to look at the effect of nutrient addition on the lower trophic levels of the marine pelagic food web represented by three groups of organisms: Phytoplankton, Ciliates and Copepods. Nutrient addition was found to have a very clear effect on chlorophyll a, POC and ciliate biomass, which showed a very clear linear increase with increasing loading rate. POC and chl a values showed that phytoplankton growth started immediately after nutrient addition. At the maximum level POC values had become 13 times larger than at the original level. Phytoplankton community composition, in the mesocosms with the highest loading rates, was found to shift from larger cells in the beginning of the experiment to smaller cells towards the end. Ciliate biomass was found to increase linearly with food concentration, indicating that ciliate population growth was closely tied to food availability. Ciliate biomass peaked on day 8 with 117 μg C l-1 found in the treatments with highest nutrient additions. A maximum of 91 ciliates ml-1 was found on day 16 during the experiment. Both these values are much higher than what has previously been reported in the area, indicating that ciliates might play a more important role in the Patagonian marine food web than previously thought. Copepod concentration and biomass were found to be uncorrelated to both nutrient addition and food concentration. This study found that nutrients released from fish farms have the potential to cause drastic increases in chl a and phytoplankton and ciliate biomass, as well as affect the community structure of phytoplankton.

The aim of this study was to enhance the knowledge on ecological and life-history parameters of Sclerocrangon boreas and Sclerocrangon ferox in Svalbard waters, including sex ratio, population structure, parasitism and prey preference. Little research has been done on S. ferox before. It has been subject to unprecedented research in the present study, considering size distribution, prey preference and DNA barcoding. The barcoding result gave a genetic distance of 13.7 % between S. boreas and S. ferox. This study shows a clear difference in size distribution between males and females. Females are considerably larger than the males. This is an indication of the two species being protandric hermaphrodite. These findings support earlier research, showing the same pattern, suggesting S. boreas being a protandric hermaphrodite. It has not been found studies looking on S. ferox considering this, but the present study shows also this species follow this pattern and are most likely protandric hermaphrodite. The largest groups of prey found in the stomach content were Crustacea, Echinoidea and Ophiuroidea. Individual specimens had mostly one type of prey in their stomach, but several types of prey were identified for both species. These findings suggest that S. boreas and S. ferox are specialists as individual specimens and generalists as species. The genetic results indicate that the specimens of S. boreas from Smeerenburg are distinguished from Grønfjorden and Rijpfjorden, and there were also variation within the specimens sampled in Smeerenburg. However, the results do not give a basis to conclude whether the populations have different genetic signatures between the fjords where S. boreas is found. It can be concluded that DNA barcoding and the CO1 gene do not together give ample information of genetic differences within populations, but it will still be able to give a genetic signal on differences between populations. Parasites were found on both S. boreas and on S. ferox. Genetic analyses, using CO1 and 18S, of the parasites conclude that they are cocoons from a piscicolid (fish) leech. The identity of this species has not been found.  

The stellate sturgeons as well as the other sturgeon populations inhabiting the Lower Danube River system (LDR) and the NW part of the Black Sea have experienced a severe decline due to heavy fishery, river regulation and water pollution. Traditionally, sturgeons have represented a great economic value for the countries along the Danube, being fished mainly for their eggs, the “black caviar”. The human population along the Danube River took advantage of the anadromous behaviour of these fishes and over decades of overfishing they depleted the stocks. In 2006 the Romanian government banned the commercial fishing of sturgeons for a period of 10 years and started a Supportive Stocking Programme of Danube with farmed juveniles originating from wild parents. The present study focuses on whether there are genetically isolated subpopulations among the adult cohorts of stellate sturgeons migrating into the LDR in the year 2010, and whether the genetic characteristics of YOY samples in the same year supports the existence of such subpopulations. Samples from fall and spring migrants and from YOY stellate sturgeons naturally born in the river in 2010 were genetically analyzed for mtDNA cyt b and D-loop regions as well as a panel of nuclear microsatellites, and revealed considerable individual variability. Hardy-Weinberg conformity tests revealed heterozygote deficit at 3 out of 4 microsatellite loci. Based on the genic differentiation at the microsatellite loci and mtDNA and cluster analyses, a genetically distinct group were demonstrated among the 2010 YOY samples, pointing to the existence of a previously unknown population substructure within the stellate sturgeons of The Lower Danube River. This was supported by biological characteristics of the YOY samples.

Biofouling has become a serious problem for farmers in the Norwegian finfish aquaculture industry in recent years; with the hydroid Ectopleura larynx dominating the fouling community in southwestern and mid-Norwegian waters. Most farmers in Norway use a combination of strategies to deal with fouling: the use of copper coated nets combined with washing, the use of copper coated nets combined with drying, and the use of uncoated nets combined with frequent washing. Concerns have been raised about the use of copper coatings on nets due to possible environmental threats. A better understanding of fouling patterns with depth and time; as well as the effectiveness of environmentally friendly treatments is needed. The aims of the study were to identify the temporal and depth variability of biofouling on salmon cage nets from a farm in mid-Norway. Additionally, the effect of drying on hydroid survival and the effects of environmentally friendly anti-fouling treatments on the survival of E. larynx were investigated. The first experiment was to look at the development of biofouling on salmon cage nets at 3 different depths (1, 5 and 10 m) over a six month period (June-November). The second experiment involved the drying of hydroid colonies at 6 different drying times to determine the shortest time needed to ensure complete mortality of hydroids. The third experiment was to determine the effects of washing and drying on the recovery of hydroid colonies, using 5 different treatments; after which hydroids were allowed to recover for a two week period and analysed. The results showed that the major fouling groups were algae, molluscs, hydroids, crustaceans and bryozoans, with hydroids becoming abundant from August onwards. Hydroids began to completely colonise the nets from 10 m in September and then completely colonized the nets at all three depths in October and November. 48 hours of air drying caused a complete mortality of hydroids. Dead hydroids shed their hydranths and cut or damaged hydroids were capable of regeneration. Nets which had hydroids removed, damaged or cut by the washing process had the highest percentage growth increase after a two week recovery period. This study demonstrated that fouling communities differ with depth and time but are driven by some ecological interactions, and that, a combination of washing and then killing of hydroids with hot water; or washing and then drying can help farmers deal effectively with fouling. Further research into the feasibility of these on an industrial scale is recommended.

I investigated hoe different spacing of breeding sited affects different aspects of mating behaviour in the two-spotted goby. I found that clumped nest spacing affects nest occupations and reproductive success negatively. Clumped nest spacing incresed male agonistic behaviour and led to a higher variance in reproductive success.

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The aim of this thesis is to give insight into how a short term exposure to higher water temperatures affect photosynthesis in two of the most important species of the Norwegian kelp forest; Laminaria digitata and Saccharina latissima. In addition the effect of increased water temperature on kelp growing in the temperate regions, Trondheimsfjorden, will be compared the effect on kelp growing in the arctic region, Svalbard.

The snail fauna (class Gastropoda) associated with the two kelp species Laminaria hyperborea and Saccorhiza polyschides was sampled during September and December 2009, and March 2011. Over 1000 gastropod individuals comprising 35 identied taxa were found in the 29 kelp individuals sampled in total. The attractiveness for settlement for gastropods of L. hyperborea was clearly higher than S. polyschides, which also had very little epigrowth compared to L. hyperborea. Highest number of gastropod individuals were found on lamina and the highest number of species were found on haptera for both kelp species. High variation in gastropod numbers was found both between kelp individuals and between seasons. Detailed still images were taken of the kelp before sampling, for comparison to the sampled material. 81 % of the gastropod fauna visible in images was identied to either species or family, but only 17 % of the actual number of gastropods (sampled) were visible in images. Visibility of gastropods in images decreases with increasing complexity of the habitat (i.e. kelp part), both structural complexity in the kelp or added complexity by epigrowth. The ratio of gastropods identied from images to gastropods identied from sampled material (image detection success), showed high variation between gastropod taxa, mainly dependent on gastropod size, degree of camouflage or conspicuousness, and what habitat (i.e. kelp part) they live in.

Marine migration and habitat use of sea trout Salmo trutta from the watercourse Søa and the river Snilldalselva in Sør-Trøndelag in Central Norway was studied during summer in 2012 and 2013. Fishes were tagged with acoustic transmitters and their movements and behaviour recorded by automatic listening stations. Significant individual variation in the time spent in the marine environment was found, ranging from 7 days to 183 days during the months from April to September. The spatial distribution in the fjord system varied greatly between the tagged fishes. The innermost parts of the fjords near the tagging watercourses were particularly important areas for the tagged fishes. Both fish from Søa and Snilldalselva had significantly longer residence time in the inner areas compared other parts of the fjord system. Average swimming depth in the period from April to September (1.87 m) turned out to vary significantly between habitats. In littoral (2.11 m) and cliff habitats (2.53 m) the average swimming depth was significantly deeper than in pelagic areas (1.26 m), suggesting differences in prey selection or anti-predator behaviour between the various habitats. The average swimming depth was furthermore significantly deeper during day (1.98 m) than night (1.28 m). The sea trout had a progressively deeper swimming pattern from April towards late summer, positively correlating with water temperature, suggesting that the sea trout actively regulated its internal body temperature. While some individuals remained close to tagging watercourse (< 4 km) throughout the summer, other individuals migrated far out (> 16 km) in the fjord system. Large individuals (> 450 mm) seemed to be more likely to conduct long distance migrations than remaining in inner areas. Long distance migrants furthermore had poorer body condition in spring prior to migration, were found to have greater length at smoltification, and tended to be older and more experienced migrants. Long distance migrants seemed to use pelagic areas more than short distance migrants and tended to maintain pelagic swimming behaviour even when recorded in littoral habitat, suggesting that the migration distance might be linked to feeding behaviour. Furthermore, the observed differences in morphological characteristics and life history indicate, as suggested by previous studies, that the marine behaviour might be a continuum of a conditional strategy in partial migrating sea trout populations, affecting whether the sea trout remain in the innermost parts of the fjord, or migrate far out in the marine system. This implies that the marine behaviour of sea trout might be altered if the conditions in the marine environment change. Furthermore, variation in the marine environment might thus have great impact on an individual’s growth and survival, and potentially alter the recruitment and population structure of sea trout stocks. In terms of conservation, the present study illustrates the importance of mapping the marine behaviour of sea trout, as the threats depends heavily on the marine areas it utilises. Gathering of long term data sets on marine environmental conditions, as well as more research on the underlying causes determining the wide range of the sea trout’s marine behaviour is advocated, as it might prove to be essential for evaluating and modelling sea trout distribution, behaviour and main threats, and for identifying necessary conservation measures for Norwegian sea trout stocks.