Ultra Violet light 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 is examining 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 micro-organisms, such bacteria, ciliates, 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.
The basis for all UV effects is the absorption of UV energy by molecules, which can induce a chemical reaction.
Watch a video about an experiment that examines what would happen to the ocean's phytoplankton if most of the ozone layer was destroyed by cosmic radiation. Video credits: Anne Goetz, Editor; Lia Kvatum, Producer/Writer/Camera; Tony Franken, Music.
See our bibliography for books, chapters and research reports on the subject.
Ecosystems currently under study include:
Chesapeake Bay and associated subestuaries (red tides)
Antarctica: Ross Sea Temperate Lakes
Other systems that have been studied (see bibliography for more information):
Antarctica: Coastal environments (McMurdo, Palmer Station):
Open Southern Ocean (Weddell Scotia Seas)
Arctic: Kelp communities along the Canadian and Scandinavian coasts
Gulf of Mexico
Field studies in remote locations are supported by on-site operation of SR-18 radiometers, which provide high time resolution data to support evaluation of dose response relationships. The deployments also complement data sets of other monitoring instruments making higher spectral resolution, but less frequent measurements. In Antarctica, the SR-18 has been collocated with the NSF UV Network SUV-100 at Palmer Station. In the Arctic, our study area (location of the SR-18) was near the Brewer operated at Resolute by Environment Canada.