Résumé
A mesocosm approach was adopted for the study of the impact of UV-B radiation on coastal planktonic communities. Experiments were conducted in eight land-based 1500 1 mesocosms. The 2.25 m deep mesocosms reproduced the whole euphotic zone and vertical mixing ensured a homogeneous water column. While maintaining all other physical characteristics the same, UV-B levels were manipulated in different mesocosms by either increasing UV-B with lamps or by eliminating it using Mylar registered sheet as a filter. The resulting spectral irradiance regime produced in the mesocosms was characterised by the daily irradiance averaged over the water column. Incident irradiance was measured every 10 minutes using an International Light IL-1700 radiometer and a Biospherical PUV-511 radiometer. Underwater spectral irradiance for the different treatments was determined using a Biospherical PUV-500 profiling radiometer. One of the present challenges of UV-B research is the extrapolation of results from laboratory and short-term field experiments to natural populations and ecosystems. The merits and limitations of using mesocosms are explored in this investigation with particular attention to the underwater spectral properties.