Influence of increased cod abundance and temperature on recruitment of northern shrimp (Pandalus borealis)

Despite an increase in northern shrimp (Pandalus borealis) female biomass in the past years, the recruitment of the offshore population north and northeast of Iceland has remained very low. In this study, the influence of abiotic and biotic factors was studied in relation to shrimp recruitment. Two factors, cod (Gadus morhua) abundance and summer sea surface temperature (SST), were found to have a negative effect on offshore shrimp recruitment, explaining 71 % of the observed variation. Both cod abundance and temperature on the offshore shrimp grounds have increased in the past years, while recruitment has decreased and been at historically low levels since 2005. No significant relationship was found between recruitment and spawning biomass, indicating that recruitment variability is mainly driven by other factors. Cod abundance and summer SST are likely to affect different life stages of shrimp, as SST influences shrimp during its planktonic phase while cod abundance influences the demersal stage.     

Relation of growth and condition with the <Emphasis Type="Italic">Pan</Emphasis> I locus in Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis> L.) around Iceland

Growth and condition (both somatic and hepatosomatic index) of Atlantic cod spawning at different locations around Iceland was studied in relation to the Pan I locus. South of Iceland cod carrying the Pan I^AB and Pan I^BB genotypes were more frequent while cod carrying the Pan I^AA genotype was more frequent north of Iceland. Differences in growth were detected between cod spawning at different areas around Iceland. Cod spawning south of Iceland grew faster than cod spawning north of Iceland. Differences in growth rate were also observed among cod carrying different Pan I genotypes within a spawning area. The least frequent Pan I genotype expressed the highest growth in both south and north of Iceland. Cod carrying the Pan I^AA grew fastest at spawning locations south of Iceland, while cod carrying the Pan I^BB genotype grew fastest in north of Iceland. A consistent relationship between condition and the different Pan I genotypes was also observed in all the areas. Cod carrying the Pan I^AA expressed the highest somatic condition and the lowest hepatosomatic index. Together, these results indicate that the relation of growth and condition with the Pan I locus is more complicated than earlier thought and is likely to be influenced by other factors, like size-selective fishing and food supply.     

Responses to projected changes in climate and UV-B at the species level

Environmental manipulation experiments showed that species respond individualistically to each environmental-change variable. The greatest responses of plants were generally to nutrient, particularly nitrogen, addition. Summer warming experiments showed that woody plant responses were dominant and that mosses and lichens became less abundant. Responses to warming were controlled by moisture availability and snow cover. Many invertebrates increased population growth in response to summer warming, as long as desiccation was not induced. CO2 and UV-B enrichment experiments showed that plant and animal responses were small. However, some microorganisms and species of fungi were sensitive to increased UV-B and some intensive mutagenic actions could, perhaps, lead to unexpected epidemic outbreaks. Tundra soil heating, CO2 enrichment and amendment with mineral nutrients generally accelerated microbial activity. Algae are likely to dominate cyanobacteria in milder climates. Expected increases in winter freeze-thaw cycles leading to ice-crust formation are likely to severely reduce winter survival rate and disrupt the population dynamics of many terrestrial animals. A deeper snow cover is likely to restrict access to winter pastures by reindeer/caribou and their ability to flee from predators while any earlier onset of the snow-free period is likely to stimulate increased plant growth. Initial species responses to climate change might occur at the sub-species level: an Arctic plant or animal species with high genetic/racial diversity has proved an ability to adapt to different environmental conditions in the past and is likely to do so also in the future. Indigenous knowledge, air photographs, satellite images and monitoring show that changes in the distributions of some species are already occurring: Arctic vegetation is becoming more shrubby and more productive, there have been recent changes in the ranges of caribou, and "new" species of insects and birds previously associated with areas south of the treeline have been recorded. In contrast, almost all Arctic breeding bird species are declining and models predict further quite dramatic reductions of the populations of tundra birds due to warming. Species-climate response surface models predict potential future ranges of current Arctic species that are often markedly reduced and displaced northwards in response to warming. In contrast, invertebrates and microorganisms are very likely to quickly expand their ranges northwards into the Arctic.