An automatically operated system for simulating global change temperature and ultraviolet B radiation increases: application to the study of aquatic ecosystem responses in mesocosm experiments

We report on a new, automatically operated system that can provide accurate simulations of the increases in ultraviolet-B radiation (UVBR: 280-320 nm) and temperature predicted by climate change scenarios. The system was employed in mesocosms using a factorial design. The originality of this system is that the increases in UVBR and water temperature are proportional to the prevailing ambient levels. In this system, a 20% increase above natural UVBR generated by UV lamps, and a 3 C increase in water temperature generated by submersible heating elements, are both regulated within very short time scales ( 0.5 s for UVBR and 30 s for water temperature). Thus, the system follows the natural fluctuations that the control mesocosms experience, and so reproduces the high degree of environmental variability that is inherent to aquatic systems. In 2006, eight mesocosms were set up and moored at the Mediterranean platform for Marine Ecosystem Experimental Research ( South of France), and 4 treatments were applied in duplicate over a period of 13 d: ( i) Control; ( ii) a 20% increase in UVBR above ambient UVBR incident at the water surface of the control mesocosms, ( iii) a 3 C increase in water temperature above that of control mesocosms, and ( iv) a combination of the increased UVBR and temperature. The system proved highly reliable, and therefore represents an adaptable, robust, and accurate tool that can realistically mimic scenarios for temperature and UVBR increases linked to global change to study the effects on aquatic organisms.