UV penetrates into aquatic environments though transparency varies. Pure water is transparent to UV so that in clear waters (e.g. mid-ocean, alpine lakes) much of the upper layer is exposed to UV.  Even in coastal waters, where terrestrial runoff blocks much of the UV, exposure is still high in shallow waters. UV responses are strongest in the suspended microorganisms abundant in surface waters – the plankton. These organisms are too small to screen out UV. One of the main biological impacts of UV exposure on aquatic ecosystems is a reduction in the rate of photosynthesis. This can have a direct effect on primary productivity and, since different species may vary in their sensitivity to UV exposure, may eventually affect biodiversity. Research in the Photobiology Lab at SERC examines effects of UV on many types of planktonic organisms, particularly the suspended microalgae (phytoplankton), as well as benthic macroalgae (e.g. kelp).

Phytoplankton photosynthesis is inhibited by UV exposure, but impacts differ with wavelength. Short wavelength UVB is more effective than longer wavelengths of UVB; UVA is even less photoinhibiting (per unit exposure). These differential effects can be documented by measuring photosynthetic rates under defined experimental irradiances containing varying proportions of UVB, UVA and visible (photosynthetically active) irradiance. Given high resolution spectral measurements, a biological weighting function (or action spectrum) can be estimated for UV inhibition of photosynthesis. We have developed experimental methods for estimating biological weighting functions using environmentally realistic irradiance  treatments (polychromatic exposures).  A tutorial on biological weighting functions can be seen at this link.

By defining the relative importance of UVB, UVA and visible irradiance in inducing photoinhibition for many types of phytoplankton, we are learning more about what factors control sensitivity to UVB damage. Within each species, UVB sensitivity is being related to factors such as growth rate, optical properties and chemical composition.

Heterotrophic microorganisms, such as bacteria, ciliates, and planktonic larvae, are also sensitive to UV exposure. Genetic material (DNA) and cellular components (proteins, membranes) are damaged, causing mortality if exposure is sufficient. The sensitivity and spectral dependence of these effects are also being studied using biological weighting functions.

For more information:

See more details on the ecological importance of UV at the Ecology of UV web site (link)

Also books, chapters and research reports on the subject (link to bibliography)

contact Dr. Patrick Neale.