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Abstract
Ultraviolet light can be a major source of stress to phytoplankton, especially in the optically clear waters of the oligotrophic gyres. Diatoms are important primary producers in these gyres, yet the responses of diatoms that occur here to UV-radiation have not been characterized. In this study, Pseudo-nitzschia delicatissima was isolated from the Sargasso Sea and its response to UV-A and full spectrum UV was monitored over the course of a two week experiment. The diatom showed significant growth rate inhibition and decreased chlorophyll fluorescence in response to UV-A, indicating a loss in photosynthetic reaction center efficiency. The UV-A cultures also showed an increase in optical density indicative of UV-screening pigments. The full spectrum treatment evoked significantly less response than the UV-A treatment. This indicates that UV-A is more damaging than UV-B for this diatom. Overall, the observed responses are consistent with UV-resistance in Pseudo-nitzschia delicatissima.