Coping with environmental stress : from the individual and population perspective

Abstract: Natural stress and disturbances are important factors affecting the structure and function of ecosystems. However the magnitude of stress has escalated due to anthropogenic activities. Environmental monitoring and toxicity assessments try to protect ecosystems from unwanted human alterations. The aim of this Doctoral thesis was to increase the understanding of the complex effects that environmental stress has on individuals and invertebrate populations. The low saline environment in the Baltic Sea is perceived as stressful for most organisms living there. In Paper I, it was found that Baltic blue mussels living in the less saline northern Baltic Proper (~5 psu) had lower basal metabolism and were more susceptible to toxic exposure than the mussels in the south (~7 psu). There was no genetic differentiation between the mussels from the northern and southern areas while there were genetic differences between mussels from sites within the respective areas (Paper III), indicating that there is not a simple relationship between the health of the mussels and genetic diversity in the microsatellite loci studied. In Paper IV it was found that the heat tolerance of the intertidal dogwhelk Nucella lapillus is oxygen dependent. Increased oxygen levels resulted in higher survival rate. Protein expression profiles also became more similar to those of the controls, compared to the whelks exposed to high temperature and normal oxygen levels. In Paper V and VI it was found that exposure to a single toxicant for more than one generation decreased the genetic diversity in exposed copepod populations even though abundances remained unaltered. In Paper VI, exposure to naturally contaminated sediments, which contained of a mixture of toxicants, did not decrease genetic diversity. However the genetic divergence (FST) within the treatments was very high, probably due to small effective population sizes in the replicates. Likewise in Paper III, the very low blue mussel abundance in the north together with the stressful environment suggests a small effective population in the northern Baltic Proper. In conclusion, my studies show that, measuring effects on several levels, including both functional and structural endpoints will both increase the sensitivity of the tests and increase their ecological relevance.