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

Abstract

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.

Effects of experimental warming and increased ultraviolet B radiation on the Mediterranean plankton food web

“…An automatic system to regulate water temperature and UVBR enhancement was developed specifically for this experiment and has been described in Nouguier et al (2007). We briefly describe the functioning of this automatic system here.…”

“…Mesocosms were 3 m high, 1.2 m wide, and were made of 200-mm-thick vinylacetate mixed-polyethylene film (Insin-öö ritoimisto Haikonen Ky). The polyethylene film transmitted 53% and 77% of UVBR and photosynthetically available radiation (400-700 nm), respectively (Nouguier et al 2007). Mesocosms were held at 1 m above the water surface by floating structures.…”

“…Increased temperature and UVBR treatments-Water temperature was increased using a submersible heating element (Galvatec) immersed vertically at a depth of , 1 m (Nouguier et al 2007). Incident UVBR at the water surface was increased using custom-built frames holding two UV fluorescent lamps (Philips TL20RS/01), a double electronic ballast (Bag electronics AD18.22310) controlled by voltage input, and an ultra-pure polished aluminum reflector.…”

Novel temperature gradient incubator to study the effects of temperature on motile aquatic organisms

“…Past studies investigating temperature effects on plankton were limited to three basic approaches: experiments in natural systems, laboratory experiments in which each temperature exposure occurred in a discrete water bath, or the use of plankton towers at the Max-Planck Institute for Limnology at Plön (Lampert and Loose 1992). Experiments with temperature in natural systems often have confounding variables such as wind mixing, and they require enormous inputs of energy to establish changes from the natural setting, which are then difficult to control (Baulch et al 2003;Nouguier et al 2007). Furthermore, experiments in natural systems cannot separate the effects of changes in temperature from changes such as intensity and quality of light in stratified aquatic systems.…”

Use of open‐top chambers to study the effect of climate change in aquatic ecosystems

“…Heating is performed either by electrical elements (Liboriussen et al 2005;Burnett et al 2007;Nouguier et al 2007) or by running hot water through elements (McKee et al 2000;Baulch et al 2003). To prevent a vertical gradient, the water column can be mixed by pumping (McKee et al 2000) or by stirring with paddles (Liboriussen et al 2005).…”