Global change enhances complexity of UVR effects on coastal and estuarine plankton.

HELBLING, E.W.; R.J. GONÇALVES; V.E. VILLAFAÑE

Bahía Blanca, Argentina

Simposio; Estuarine and Coastal Sciences Association (ECSA) 44 Symposium: Science and management of estuaries and coasts: A tale of two hemispheres; 2008

Global change involves many variables and one of the feedbacks of this process is the relationship between the increase of “greenhouse gases” (GHGs) and ultraviolet radiation (UVR). Increased atmospheric GHGs result in an increase of global temperature in the troposphere with their concomitant decrease in the stratosphere. The stratospheric cooling result in a slower recovery of the ozone layer (than previously expected) and thus it might expose living organisms and ecosystems to a larger exposure to relatively high UVR levels. Other potential outcomes of global change include an increase of stratification in the water column and changes in both ocean circulation patterns and mixing rates. These changes, in turn, would induce a higher stress in phytoplankton cells by exposing them to higher UVR levels due to their circulation within a shallower upper mixed layer (UML). On the other hand, an increase of CO2 concentration favors some phytoplankton species enhancing their growth rates, while changing the pH of the water harms others. Moreover, metabolic processes, including repair of UVR-induced damage to the DNA or photosystem are temperature-dependent; thus increased temperature might benefit some phytoplankton species. Hence it is evident that the effects of global change on the aquatic biota are very complex. The picture is more complicated in estuarine environments, where organisms are exposed to large gradients in their physical, chemical, optical and biological properties. Overall, these kind of interactions suggests that the outcome and the future behavior of the system lies in a narrow line of balance between damage and repair.