Effects of UVR on phytoplankton photosynthesis

In the following paragraphs we summarize the status of our knowledge about both short-term and long-term effects upon phytoplankton photosynthesis. However, several reviews dealing with the impact of UVR on phytoplanktonic organisms have been published 45,127-130 , so we encourage the reader to refer to them for more specific details that are not addressed here. One of the best-known effects of solar radiation upon phytoplanktonic organ isms is photoinhibition, which refers to the reduction of...

A

Figure 7. (A) Skin of razorback suckers (Xyrauchen texanus) not exposed to UV. Mucous cells (open arrows) line the very outer surface of the epidermis. A major portion of the epidermis is composed of large PAS-negative cells (filled arrows). Bar equals 50 zm. (B) Skin of razorback sucker after 72 h of UV exposure. The epidermis is thickened to hyperplasia and hypertrophy of the large PAS-negative cells. There are many leucocytes infiltrating the basal portion of the epidermis (filled arrows),...

CDOM as a mediator of climateUV interactions

In addition to the effects of climate change on ozone depletion, it is now widely recognized that climate change can influence the UV transparency of inland waters by changing the concentration and characteristics of UV-absorbing compounds. This means that underwater UV environments will continue to change even if ozone depletion is arrested or reversed. Climate change effects on underwater UV are largely mediated by CDOM, the light-absorbing component of the yellow-brown gelbstoff that results...

The interaction between UVR and parasites

This type of interaction is obviously restricted to ectoparasites or to the free stadium of endoparasites. Although UVR is generally associated with negative effects, it may also play a positive role on species interactions. Thus, for example, the ectoparasite copepod Lepeophtheirus salmonis (salmon lice) uses photoreceptors to avoid UVR and eventually to optimise host finding (e.g., by utilizing UV contrast vision 74 ). Most of our knowledge on the interaction between UVR and parasites,...

Introduction

One of the most challenging questions in environmental biology today is how human-accelerated changes in multiple environmental variables are influencing natural communities and ecosystems. One of the more pervasive of these changes is the increase in UVR related to stratospheric ozone depletion. In recent years it has become increasingly clear that climate change may have at least as great an effect as ozone depletion on future changes in underwater UV environments in mid to high latitude...

Injuries can become sites of infection

Fish exposed to UV-B may experience a depressed immune system and subsequent vulnerability to infection by pathogens 29,30 . Epidermal lesions from sunburn allow invasion by pathogens, especially fungi 2,31 . During laboratory studies, fungal hyphae were frequently observed at the margins of the sunburned fish skin within one or two days of the initial sunburn 2 . These fungal infections progressed over the dorsal surface of the fish and the fish died soon after. Extensive fungal infection was...

Trends in solar UVR

The impact of the observed ozone decline on UV-B radiation at the Earth's surface is one of the key factors which motivated long-term measurements of UVR worldwide, in order to investigate if there is an associated increase in solar UV-B. However, cloudiness has a stronger modulating impact on UVR reaching the Earth's surface than ozone. Therefore statistical analyses have shown that several decades of continuous measurements with broadband detectors under all conditions of cloudiness are...

Repair mechanisms

Not all exposure to UVR can be avoided and therefore all organisms require some capacity to repair damage caused by these wavelengths. Little is known about the mechanisms that recognize and repair damage induced by UVR in marine and freshwater systems and most of what is known about repair of UVR-induced DNA damage comes from research on bacteria, which has been applied to aquatic organisms. Repair of DNA and of proteins may be induced during exposure to UVR and may continue well after the...

Summary

This chapter has covered some aspects of the physics of the upper mixed layer that modulate how molecules and organisms in aquatic ecosystems are exposed to UVR. The basic implications of a vertically mixed environment have been realized by aquatic UVR researchers for some time. The contents of the near-surface photoactive zone are in continual motion and, over some time scale, exposed constituents at the surface will exchange with relatively unexposed constituents at depth. The modulation of...

Mixing processes

The sun is the primary source of both the stirring energy that drives vertical mixing and heating that dampens vertical mixing. Variations in solar energy over the Earth (see Chapter 2) ultimately result in variations in mixing between different parts of the ocean and lakes in different latitudes. Heating of surface waters is a direct effect of the sun, which stratifies waters and dampens mixing. Surface forcing by winds is an indirect effect, caused by the gradients in solar heating of the...

Introduction and background

The penetration of UVR into natural waters leads to exposure of organisms and nonliving matter to energetic photons. The response of organisms and nonliving matter to UVR exposure may change the UV transparency of the aquatic environment. When the intensity (irradiance) of UVR underwater is sufficient to cause biotic damage then a stressful range of depths exists in the water column. Ecological consequences of this stress will depend on the depth of penetration and spectral shifts in the...

UV radiation and infection diseases

Parasitism is an important ecological interaction that may cause dramatic changes in the host population size. As discussed above, solar UVR has the potential to act directly or indirectly in this process, for example by damaging the parasite or by causing damage to the host and increasing its susceptibility to infections. About the latter type of interaction, our knowledge is restricted mainly to studies on fish and amphibians. Solar UV-B radiation is known to cause injury to the skin...

Abstract

Pelagic metazoans cover organisms from rotifers to whales that inhabit a variety of localities from alpine pond to oceans. Knowledge on specific responses on UVR is restricted to very few taxa or species, yet the fact that all organisms share a basic set of biochemical and cellular properties and have a limited range of protective mechanisms and responses, allows for some generalizations across taxa. The main discussion in this chapter is devoted to the best examined groups zooplankton and...

References

Randerson, P. Falkowski (1998). Primary production of the biosphere Integrating terrestrial and oceanic components. Science, 281, 237-240. 2. M.J. Behrenfeld, P.G. Falkowski (1997). Photosynthetic rates derived from satellite-based chlorophyll concentration. Limnol. Oceanogr., 42,1-20. 3. P.G. Falkowski (1994). The role of phytoplankton photosynthesis in global bio-geochemical cycles. Photosynth. Res., 39, 235-258. 4. K. Mann, A.R.O. Chapman (1975). Primary...

Carbon and nitrogen allocation

There is evidence that UVR, especially UV-B, affects carbon allocation in aquatic autotrophic organisms. This has important consequences for food web dynamics, as these changes will affect growth and, consequently, the availability of food for other trophic levels, such as bacteria and heterotrophic microorganisms (see Chapters 5 and 15). Changes in lipid, protein, polysaccharide, and fatty acid levels due to UVR have been determined in some phytoplanktonic and MPB organisms 47,161-167 . These...

Conclusion

This review has highlighted some of the recent results of investigations into the ecological photochemistry of CDOM. While much information continues to accumulate on this subject, several issues remain. One issue is the relative contribution of CDOM photomineralization to atmospheric C02 flux out of natural waters. Another issue is the role of CDOM photodegradation in the transport of terrestrial C to the coastal ocean and its effectiveness relative to microbial degradation. Furthermore, it is...

Factors controlling UV injury

Injuries induced by exposure to UVR are dose-dependent. A number of factors can influence dose including intensity of exposure, spectral composition of the irradiance, and duration of exposure. Each of these may be influenced by climate and habitat. Stratospheric ozone depletion has been the focus of many investigations concerning UV impacts. Depletion of ozone concentration in the stratosphere reduces the filtering capacity of the ozone layer resulting in increased UV irradiance reaching the...

Acknowledgements

We thank Ann Gargett and Gustavo Buscaglia for their comments on the manuscript and Eric D'Asaro for comments on mixing processes. This work was supported in part by International Foundation for Science (grant H 2325-2), Inter American Institute for Global Change Research (CRN-016), U.S. National Science Foundation (OPP-9615342, OCE-9812036, DEB-9973938), Consejo Nacional de Investigaciones Cientificas y T cnicas (CONICET PIP 0457 98), Fundaci n Antorchas (No. 13887 83 and No. 13955-3), and...

Ruben Sommaruga

15.1 Introduction 15.2 UVR, competition, and changes in species 15.3 Herbivory and pr dation the complex response of trophic interactions to 15.4 Mutualism and UVR symbiosis of algae-invertebrates and 15.5 The interaction between UVR and 15.6 UV radiation and infection 15.7 Summary and concluding

Quenching mechanisms

Exposure to UVR is known to result in a variety of negative effects however, the interaction of UVR with photosensitizing molecules, some organic molecules and oxygen results in the production of toxic photoproducts including reactive oxygen species (ROS) both intracellular and in the external environment. Toxic photoproducts have the ability to cause more damage than the UVR exposure itself. Toxic photoproducts are neutralized by various agents including antioxidants such as ascorbate,...

Climate change and ozone depletion A brief global synopsis

The Antarctic ozone hole was the largest ever in 2000 (> 28 million km2, Significant trends of increasing UV-B related to ozone depletion have also been observed at Arctic and north temperate latitudes 5-7 . Modeling efforts estimate that localized losses of column ozone may be as high as two-thirds of the Arctic ozone column in the years 2010-2019. Atmospheric processes related to climate change are also influencing stratospheric ozone depletion. In particular, greenhouse gases are expected...

Dag O Hessen

12.1 Introduction 12.2 Direct damage and means of protection (lines of defense) 12.2.1 Seasonal and spatial 12.2.2 Photoprotective 12.2.2.1 MA As 12.2.2.4 Other UVR screening 12.2.2.5 UV, pigments, predation and evolutionary 12.2.4 Recovery and DNA 12.3 Indirect 12.3.1 ROSin 12.3.2 Food web 12.4 Ambient parameters and their interaction with 12.4.1 Oxygen and 12.4.2 UV and water 12.5 Taxa specific responses evidence for in situ effects of UVR on pelagic 12.5.1 Case studies of UVR and 12.5.2 Case...

Mutualism and UVR symbiosis of algaeinvertebrates and algaeprotists

Most of our knowledge on the interaction between UVR and mutualistic associations is based on studies on algal-invertebrate symbiosis, particularly on scleractinian corals and their endosymbiotic dinoflagellates, the so-called zooxanthellae from the genus Symbiodinium. Recently, the scientific literature on this topic has been extensively reviewed 33,62,63 . Here, I will only briefly highlight the most important aspects regarding potential population changes in this association as affected by...

David J Kieber Barrie M Peake and Norman M Scully

8.1.1 Reaction 8.2 Formation and removal of 8.2.1 Hydroxyl 8.2.2 Singlet 8.2.3 Superoxide 8.2.4 Hydrogen 8.2.4.1 Sources of H202 8.2.4.2 H202 removal 8.2.4.3 Reactions of H202 with 8.3 Other 8.4 Impact of ROS on aquatic The absorption of solar energy by dissolved organic matter (DOM) in natural waters results in a variety of photochemical transformations involving oxygen as a major reactant. These photochemical transformations generate a suite of reactive oxygen species (ROS) including the...

Metals cycling

Complexation of metals has important interactive effects on biological availability and photochemical reactivity 117,152,165,196-225 . Iron, copper and manganese are essential micronutrients whose free metal ion concentrations in water, and hence biological availabilities, are affected by complexation or, in the case of metal oxides, by redox transformations. Complexation reduces biological availability by reducing free metal ion concentrations and dissolved iron 202 and copper 212,213 are...

UVB induced DNA photoproducts and repair pathways

All organisms, including humans, which are regularly or occasionally exposed to natural solar radiation may be subjected to DNA damage. In fact, structural changes in DNA are thought to be among the most important deleterious biochemical consequences of UVR 9,10 . UV-B can cause dimerization of DNA bases, leading to the formation of CPDs and 6-4 PPs (Figure 2). These photo-products block DNA transcription and replication such that only a single distortion of DNA may be sufficient to stop DNA...

O2

Photochemical processes involved in photoactivated toxicity. Generation of excited states and pathways for their decay are illustrated in (A). Possible mechanisms underlying toxic activity are illustrated in (B). excited-state orbitals. The excess energy is then dissipated in radiationless transitions from excited to ground rotational and vibrational electron levels, radiative transitions from excited-state orbitals to ground-state orbitals (fluorescence or phosphorescence, depending...

Characterization of CDOM

Because CDOM is an optical description of the photoreactive component of bulk DOM, several methods exist to characterize CDOM physically and chemically. These properties exhibit wide variations among CDOM source (e.g., freshwater vs. marine CDOM). At present, no universally accepted method for isolating CDOM from the bulk fraction exists, and here we briefly review several methods for its isolation. Each method has its benefits and limitations and we urge readers to carefully consider the...

Other ROS

Aquatic Organisms

OH+ HCO3- -+H20 + C03- OH+ C032- -> 0H-+C03- The carbonate radical will also form its conjugate acid, the bicarbonate radical The bicarbonate radical, HCO3', is more acidic than HC03 (pKa 10.3 vs. 106, respectively), but the pKa for equilibrium (16) is poorly constrained with reported values between 7.0-9.6 150-152 . In many fresh water systems the predominant species will be the bicarbonate radical, while both the bicarbonate and carbonate radicals will be important in seawater. As may be...

Fossil evidence of past UVR environments in lakes

Present concern about the interactive effects of ozone depletion, DOM-degrading acidic precipitation and global warming has led several investigators to conclude that extreme variations in the biogeochemistry of DOM and its impacts on UVR penetration may be the most significant challenge to aquatic ecosystem integrity and function e.g., 66,108 . Because the range of historical variance in DOM flux and UVR attenuation is often greater than that arising from modern processes 15,24 ,...

Nitrogen cycle

UVR can affect nitrogen cycling in several ways (1) through effects on nitrogen-related enzymatic activity by microorganisms such as photoinhibition of nitrogen fixation by prokaryotes, principally cyanobacteria and, indirectly, through effects on the biological availability of essential trace elements, such as iron that stimulate the growth of nitrogen fixers (2) through enhanced decomposition of persistent DON to biologically labile nitrogenous photoproducts. In addition, UV absorption by...

Peter R Leavitt Dominic A Hodgson and Reinhard Pienitz

16.1 Introduction 16.2 Impacts of UVR on lake 16.2.1 Natural controls of UVR in 16.2.2 Impacts of UVR on aquatic 16.3 Paleoecological methods for UVR 16.3.1 Microfossil indices of past UVR 16.3.2 Other microfossil metrics of past UVR 16.3.3 Biogeochemical indices of past UVR 16.3.4 Sedimentary organic matter as an index of past UVR 16.4 Fossil evidence of past UVR environments in 16.4.1 Holocene climate 16.4.2 Early lake 16.4.3 Historical changes in polar UVR 16.4.4 Rapid variation in UVR 16.5...

Anita GJ Buma Peter Boelen and Wade H Jeffrey

9.2 UV-B induced DNA photoproducts and repair 9.3 Penetration of DNA effective UVR in marine 9.4 Measurement of DNA damage in marine 9.5 Patterns of DNA damage accumulation and repair in aquatic 9.5.1 Evidence from laboratory 9.5.2 Depth related CPD patterns, diel cycles and mixing effects 303 9.5.3 Residual DNA damage and 9.5.4 Effects of varying ozone 9.6 Species specific differences and cell size 9.7 Latitudinal and seasonal 320 320

Modeling climateUV interactions in aquatic ecosystems

Interaction Among Aquatic Organisms

The complex spatial and temporal interactions between climate change and UVR make it difficult to model and predict effects of these processes on aquatic ecosystems. Ozone depletion, as modified by greenhouse gases, will alter the levels of UV incident at the water's surface. In contrast, climate change is more likely to alter the underwater UV environment by influencing watershed and in-lake processes (Figure 6). Removing riparian or littoral vegetation, clear-cutting forests, increasing water...

Changing UV warming

Altered II Changes in N, S. 1 decomposition, H & metals cycling Figure 1. Schematic illustrating factors that influence the effects of solar UVR on aquatic ecosystems. Aquatic biogeochemical cycles are affected by increased UVR caused by stratospheric ozone depletion and its interaction with other co-occurring environmental changes such as global warming and land use change. Changes in precipitation chemistry are caused by UV-induced photoreactions in cloud droplets and changing climate...

Solar radiation as an ecosystem modulator

1.2 Size matters - radiation attenuation in relation to loadings of organic matter 6 1.3 Precipitation matters - importance of frequency and intensity of 7 1.5 Allochthonous vs. autochthonous organic matter - key UV-VIS mediated processes regulate heterotrophic 9 1.5.1 Alterations of enzymatic accessibility by the macromolecules 10 1.5.3 Photolysis of dissolved organic nitrogen and phosphorus 11 1.5.4 Complete photolysis of humic substances to CO and CO2 11 1.5.5 Less direct but important...

Indirect effects

There are several ways by which aquatic organisms may be indirectly influenced by UVR. UVR plays a major role in surface water chemistry that in numerous ways may aifect the aquatic biota. Breakdown or oxidation of complex macro-molecules, notably humus molecules, may both induce availability of organic substratum for microbial heterotrophs 61, Chapter 8 . This may also liberate mineral nutrients such as N and P, and in fact the effects on biogeochemical cycling of key elements like C, N and P...

Direct damage and means of protection lines of defense

The general, direct effects of UVR at the cellular level are rather uniform within the animal kingdom. These include first of all DNA-damage, membrane damage and a range of other cellular injuries that may be caused by intracellular photoproducts. They also include immunosuppression, yet the responses here may be more different across phyla, especially between invertebrates and vertebrates. Finally skin lesion, cancers and eye-damage (cataract) may be common responses in vertebrates. These...

UV vision and photoreception

UV vision has been documented in a variety of terrestrial organisms including insects, birds, amphibians, reptiles, and mammals 53-55 . It is therefore not surprising that many aquatic organisms also perceive light in the UV spectrum. Most UV photoreceptors in aquatic organisms have been described in fish species however, UV photoreceptors have also been reported in bacteria and algae as well as some species of protozoans, annelids, cnidarians, and crustaceans (Table 1). Many UV photoreceptors...

Rsc

A catalogue record for this book is available from the British Library The Royal Society of Chemistry 2003 All rights reserved Apart from any fair dealing for the purposes of research or private study, or criticism or review as permitted under the terms of the UK Copyright, Designs and Patents Act, 1988, this publication may not be reproduced, stored or transmitted, in any form or by any means, without the prior permission in writing of The Royal Society of Chemistry, or in the case of...

Patterns of DNA damage accumulation and repair in aquatic organisms

Dna Photorepair

9.5.1 Evidence from laboratory studies Much information on DNA damage induction in aquatic organisms is based on incubation experiments under artificial UVR. Unfortunately, the ecological relevance of such studies is restricted, mainly due to the differences in spectra between artifical sources (lamps) and solar radiation. As a result, the effects of UV-B may be overestimated even when weighted UV-B irradiances are realistic. On the other hand, laboratory experiments may provide valuable...

Direct and indirect photochemical reactions

The absorption of photon energy by CDOM can lead to several types of photophysical and photochemical reactions, and we emphasize that light absorption may be the first of many steps that can ultimately lead to the chemical changes we observe in CDOM. Most CDOM photochemistry involves the excitation of humic substances, which have a large degree of double bond character (C C and C 0) that readily absorb sunlight energy. However, beyond direct chemical reaction from absorbing photon energy,...

Experimental and modeling considerations for working with CDOM photochemistry

Miller 32 has provided a concise consideration of issues when designing photochemical experiments using CDOM, and the careful measurements that must be made. Here, we will provide a general design concept for an experimental exposure of CDOM to a polychromatic light source (e.g., solar radiation) and Figure 5. Changes in bog water DOM after exposure to solar radiation. (A) Loss of CDOM absorbance at 320 nm, (B) decrease in molecular weight (indicated by increase in ratio), (C) decrease in DOC...

Herbivory and prdation the complex response of trophic interactions to UVR

In the previous section, the response to UVR of populations at one trophic level (basal species) was considered. The interaction of UVR, however, with more than one trophic level adds substantial complexity to the possible responses, with the potential occurrence of positive and negative feedbacks (Figure 1). Both prey and predator populations might be affected by UVR, and, if so, the net effect will depend on the relative tolerance threshold of the interacting species. Yet, as soon as we...

The nature of light and its absorption in natural waters

The most essential step in photochemistry is the absorption of light by chemical species. All photochemistry is driven by the molecular excitation that occurs from the absorption of light. Light exhibits both wave and particle properties that impart the energy available for chemical and physical reactions. Wave theory can be used to describe the propagation of light through various media, where, if optically different, the light might be refracted and or reflected (e.g., transmission of light...

Methodology to assess UVR effects on photosynthesis

In order to assess UVR effects on photosynthesis, three approaches for exposing algae to UVR are used. These include (1) natural solar radiation, modified by various filters that selectively screen off certain wavebands of radiation (2) natural solar radiation which is supplemented with artificial UVR from lamps, and (3) fully artificial radiation, implying laboratory experiments. UVR experiments at their best require both that the target organisms are exposed to as realistic a light field as...

Screening mechanisms

Screening can eliminate or at least reduce exposure to UVR by absorbing or reflecting damaging wavelengths prior to reaching UVR-sensitive cellular components. Screening may consist of the production of physical barriers such as morphological or structural features that prevent damaging wavelengths from passing or by the production of chemical compounds that absorb UVR. Usually, screening mechanisms, both physical and chemical, serve more than one purpose and thereby decrease the energy...

Behavioral responses to UVR

Behavioral responses to radiation often vary with wavelength. Some Figure 3. Simultaneous images taken at (a) green (490-560 nm) and (b) ultraviolet (350-380 nm) wavelengths. Note the bright background in the UV image that silhouettes fish strongly, even against the reef. Taken from Losey et al. 27. Figure 3. Simultaneous images taken at (a) green (490-560 nm) and (b) ultraviolet (350-380 nm) wavelengths. Note the bright background in the UV image that silhouettes fish strongly, even against...

Interactions between vertical mixing and UVR effects

The previous section showed how mixing processes determine the way UML constituents (molecules or organisms) enter the photoactive zone where they may participate in a UVR-mediated process. Under strong stratification, such transport is very limited, so UVR effects will only involve those constituents already present in the active zone. Such extreme stratification can be episodically important in systems where diurnal thermoclines form, but more typically the UML extends below the photoactive...

Wavelength nm

Spectral diffuse attenuation coefficients (Kd J calculated at 10 nm intervals for Crater Lake Oregon, from downwelling irradiance scans at fixed depths, 12 00-13 00 local time, 20 August 2001 (SZA 31 , clear sky) using a LI-COR LI-1800UW spectral radiometer (8 nm bandwidth single monochromator). Kw X for freshwater estimated by Smith and Baker 18 is also compared to two new estimates computed by subtracting particulate absorption (measured similarly to spectra in Figure 10) from...

Measurements

Measurements of solar UVR started in the first decades of the 20th century with chemical detectors 8 , where the changing of the color of a solution was an indicator of UV-B irradiance. Physical measurements of UVR use photoelectric methods to give quantitative information about the intensity and spectral distribution of UVR. The first extensive data sets originate from the 1960's, from Davos (Switzerland) 9 , but it was not until the 1990's that more of such high quality spectral measurements...

Carbon cycle

Although particulates that are predominantly clay mineral in content are important attenuators of UVR in turbulent streams and rivers, dissolved and particulate organic substances largely control the penetration of UV into most lakes and the sea. Hence, this discussion of the carbon cycle begins with a discussion of the interactions of UV with CDOM, with emphasis on the optical properties of aquatic ecosystems and penetration of solar UVR into the water (see also Chapters 3 and 6). 5.2.1...

Photoprotective mechanisms

Protection of freshwater aquatic organisms from UV-induced injury is dependent on a variety of factors that can function as photoprotective mechanisms. When UVR breaches photoprotective mechanisms in sufficient amount, UV-induced injury will occur. Aquatic organisms vary in their tolerance to UV exposure. There is a likely interplay between the ecological niche occupied by an organism and its UV sensitivity. Throughout an organism's life stages, its habitats and habits will likely complement...

Photodynamic

Examples of phototoxic compounds. Solar radiation can also be harmful to biota via less direct mechanisms specifically by dramatically increasing the toxicity of many natural and anthropogenic organic compounds 16-18 (see Figure 1). In fact, many species of plants and animals have evolved mechanisms that take advantage of photoac-tivated toxicity to defend against predators, foragers, and infectious agents 19 . These defense mechanisms involve production of compounds that, once...

Sulfur cycle

Atmospheric sulfur plays an important role in the radiative balance of the atmosphere 169-174 . Anthropogenic sources are dominant in highly-industrialized regions, such as those in the mid-latitudes of the Northern Hemisphere, and are well defined. Natural sources and sinks of sulfur gases are much less well defined, but have received greater scrutiny in recent years due to their potential involvement in the regulation of climate in remote parts of the ocean. The major source of natural sulfur...

Tevini Salmo

The pathological effects of ultraviolet radiation on the epidermis of teleost fish with reference to the solar radiation effects in higher animals. Proc. R. Soc. Edinb., 81B, 199-210. 2. E.E. Little, D. L. Fabacher (1994). Comparative sensitivity of rainbow trout and two threatened salmonids, Apache trout and Lahontan cutthroat trout, to ultraviolet-B radiation. Archiv. Hydrobiol, 43,217-226. 3. R. Hofer (2000). Vulnerability of fish and amphibians to ultraviolet radiation....

Concluding remarks

It is now evident that UV-B induced CPD accumulation is a general phenomenon in aquatic organisms. Viruses and bacteria are especially vulnerable to UV-B induced DNA damage. The small size of viruses and heterotrophic bacteria obviously favors CPD accumulation. The penetration of UV-B inside these cells is high, due to the lack of pigments, nuclear membranes or efficient UV screening by compounds such as MAAs, or, for viruses, the lack of photoreac-tivation potential. CPD accumulation in...