The effect of UV-B on the photosynthetic efficiency of Zostera marina when exposed to the antifouling herbicide Irgarol 1501

Decreases in stratospheric ozone is leading to increases in biologically damaging ultraviolet B radiation reaching the earth's surface, yet little is known about the impact this will have on ecologically important species with respect to other environmental stresses such as pollution. The herbicide Irgarol 1051 (2- methylthiol-4-terf-butylamino-6-cyclopropylamino-s-triazine) and UV-B have been identified individually as being a threat to seagrass. These stressors can co-occur and potentially interact resulting in increased toxicity and potential threat to seagrass meadows. Chlorophyll fluorescence (Fv:Fm) was used as a measure of photosynthetic efficiency. Preliminary exposure trials were run to define the exposure of UV-B and concentration of Irgarol which results in a 25 % decrease in photoinhibition when applied singly. These were interpolated to be 48 hours continuous exposure to UV-B and 24 hours exposure to 5^g Irgarol 1051. The interaction between UV-B was carried out by first applying the UV-B to the seagrass and then exposing the plants to Irgarol 1051 in combination with UV-B with a four day recovery period. It was shown that the pre-exposure to UV-B significantly increased the sensitivity of Z. marina to Irgarol 1051 producing a significant decline in photosynthetic efficiency afer simultaneous exposure which was not achieved when the stressors were applied in isolation. This experiment is an important step to assessing the impact of UV-B on seagrass in combination with pollutants which occur in the present environment but with as yet uncharacterised effects.Faculty of Scienc