Approximately 25 million years ago, the onset of the Antarctic circumpolar current closed off Antarctica and drastically limited exchange of species with the South American continent (Clarke et al. Trends Ecol Evol 20,1-3, 2005). To date, the Antarctic marine fauna is highly endemic and physiologically optimized to function at constant and very low temperatures. In most invertebrates and fish, the thermal slow down of function is associated with an elevated susceptibility to any kind of physiological disturbance from warming to salinity stress, elevated radiation to physical impact of sediment cover and iceberg scouring (Peck et al. Funct Ecol 18, 625-630, 2004). This goes along with loss of function, apparent in the absence of haemoglobin and failure of the heat shock response in ice fish (Hofmann et al. J Exp Biol 203, 2331-2339). Due to the exceptional local climate warming at the Western Antarctic Peninsula (2.5 C within 50 yrs), the ecological background is changing for the coastal marine species with presently unpredictable consequences for them and for the ecosystem as a whole.Almost any form of physiological stress causes formation of reactive oxygen species (ROS), and oxidative stress parameters can be used in combination with other physiological and molecular markers, to study stress response and tolerance limits with respect to changing environmental conditions. In my talk, I will summarize a new concept for the characterization of the stress response in ectotherms and also present the IPY programme 34, ClicOPEN, which investigates the effects of the rapid climate change on coastal communities of the Western Antarctic Peninsula.