Climate driven long-term evolution of oxygen concentration in the Baltic Sea: potential consequences for the Baltic cod (Gadus morhua L) stock

No abstracts are to be cited without prior reference to the author.

Variations in oxygen conditions in the Baltic Sea ecosystem might have been influenced through several mechanisms. Generally, the frequency and magnitude of Major Baltic inflows has been identified as the major process facilitating the renewal of oxygen depleted water masses in the Baltic. Secondly, enhanced degradation of suspended organic matter by bacteria over the past decades might have increased oxygen consumption. Finally, effects of global warming are causing long-term variations in oxygen content and saturation, because the observed increase in temperature has led to a general decrease in oxygen solubility of water masses. The present study provides a detailed analysis of observed negative long-term trends in oxygen content and saturation within the Bornholm Basin, Baltic Sea. Based on field data and laboratory experiments, oxygen-dependent relationships were used to analyse the impact of the observed decrease of oxygen content in the Baltic Sea ecosystem on cod (Gadus morhua) stock-specific processes (e.g. survival rates of eggs, settlement probability of juveniles, habitat utilisation of adult spawning fish, age-structure of successful spawners, consumption rates of adult fish). Thereby, the study attempts to give answers to the major question how the Baltic Sea ecosystem and especially the Baltic cod stock may respond to future changes of the oxygen environment