Other organisms

Research efforts to evaluate the impact of increases in UVB have focussed on phytoplankton under the assumption that ecosystem effects will most likely originate through reductions in primary productivity; however, phytoplankton do not represent the only significant component in ecosystem response to elevated UVB radiation (Karentz and Bosch 2001).

Aside from a few studies that included fish (mostly larval stages) (Karentz 1991; Malloy et al. 1997; McClintock and Karentz 1997), there is little information available on UV responses of larger Antarctic marine animals. Fish, birds, seals and whales are physically well protected from UV-induced damage by scales, feathers, fur and thick skin layers. The only study relating to the UV-photobiology of Antarctic organisms prior to the inception of ozone depletion examined sensitivity of UV-induced corneal damage in the eyes of Antarctic birds, as compared to birds from temperate latitudes (Hemmingsen and Douglas 1970). Polar birds have higher UV thresholds for damage, attributed to their existing adaptation to the higher albedo of snow and ice that creates a high UV environment (Karentz and Bosch 2001).

Heat shock proteins (HSPs) are synthesised under stressful conditions such as exposure to elevated temperatures, contamination, free radicals, UV light or patho-physiological states resulting from parasites and/or pathogens. HSPs function to protect cells by means of modulation of protein folding. The Antarctic Peninsula region has shown strong latitudinal changes in several factors which could influence HSP levels such as variation in temperature, UV radiation and contamination and human pressure. Barbosa et al. (2007) studied the variation in HSP levels in several populations of three penguin species along the Antarctic Peninsula to establish a baseline for future comparisons.

The pattern of latitudinal variation found in the Adélie penguin, opposite that of the gentoo, could be related to changes of UV radiation, although nothing is known about the direct effects of UV radiation on penguins (Karentz and Bosch 2001). On the other hand, temperature decreases

Chapter 2 – Antarctica

21

from north to south, and low temperatures can increase the levels of HSPs even in homeotherms (Barbosa et al. 2007).

If there is an impact of ozone depletion on larger marine organisms, it is expected to occur through potential limitation of food sources. Evaluation of the UV effects on birds and mammals is confounded by the fact that there are many environmental variables that can be implicated in regulating the size and fitness of a population. The multi-year life histories of these organisms also make it especially difficult to establish cause and effect; therefore, the impact of a single environmental variable is not readily apparent (Karentz and Bosch 2001).

Antarctic bacterioplankton are adversely affected by UVB radiation exposure (Karentz and Bosch 2001). In addition, invertebrates and fish, particularly early developmental stages that reside in the plankton, are sensitive to UVB. Understanding the balance between direct biological damage and species-specific potentials for UV tolerance (protection and recovery) relative to trophic dynamics and biogeochemical cycling is a crucial factor in evaluating the overall impact of ozone depletion (Karentz and Bosch 2001).

While there have been a number of investigations of UV effects on freshwater Antarctic cyanobacteria (e.g. Vincent and Quesada 1994; Quesada et al. 1995; Quesada and Vincent 1997; Roos and Vincent 1998), relatively little has been reported about the impact of ozone depletion on Antarctic marine heterotrophic bacteria, although Martin et al. (2008) confirmed that sea ice is a productive microbial habitat. Martin et al. (2009) observed significantly reduced metabolic activity in sea ice bacteria exposed to hyposaline seawater combined with rapid exposure to increased UVB radiation, conditions simulating those experienced during the thaw process. Early studies show that Antarctic bacterioplankton isolates do not possess UV- screening compounds that might protect cells, but they do have capability for recovery from UV- induced damage (Karentz 1994). A primary cellular target for UVB is deoxyribonucleic acid (DNA). DNA absorbs UVB, altering the molecular structure and potentially impairing DNA function. There are several metabolic pathways that repair DNA damage and an organism can have various combinations of these repair mechanisms. Some Antarctic bacteria have photoreactivation, an enzymatic repair process that requires UVA or higher wavelength radiation (Karentz 1994; Karentz and Bosch 2001). Another repair pathway in bacteria is the “SOS” response – a post-replication DNA repair system that allows DNA replication to bypass lesions or errors in the DNA. The timing of induction of genes involved in the “SOS” response is an important factor in the level of UV-tolerance within Antarctic microbial populations (Helbling et al. 1995).

Research has shown that increased UVB radiation can also cause human illnesses (Smith et al. 1992; Caldwell et al. 1998; Rousseaux et al. 2001; Searles et al. 2002), which is of particular significance to the temporary population of Antarctic researchers. The Antarctic vortex is usually more pole-centred, but by spring has slightly shifted off the pole towards the Atlantic sector. The vortex air masses reach populated areas of South America on about 10-20% of all days in

Chapter 2 – Antarctica

October, the month of most severe ozone depletion (Karpetchko et al. 2005). UV measurements at Ushuaia, Argentina (54.9° S, 68.3° W) (see Figure 2.3) have revealed that the UV dose can increase by more than 50% when the vortex passes over the station as compared to typical levels (Pazmiño et al. 2005). Punta Arenas (at latitude 53.1° S) (see Figure 2.3) is the southernmost city in Chile, with a population of approximately 154,000. Due to its location, well within the area affected by the Antarctic ozone hole, this population may well be the first group to show health problems from environmental effects of severe ozone depletion (Casiccia et al. 2003). A considerable increase in the number of sunburns was reported during periods of low ozone and high ultraviolet radiation during the mid to late austral spring of 1999 (Abarca et al. 2002).

Exposure to UV radiation is a risk factor for all three forms of skin cancer: (i) squamous cell carcinoma (SCC), (ii) basal cell carcinoma (BCC) and (iii) cutaneous malignant melanoma (CMM) (Longstreth et al. 1998). Because UVB levels rise with declining ozone (other variables being equal), skin cancer rates are expected to increase worldwide. There is also a special concern for an increase in the rate of malignant melanoma in regions close to Antarctica (Longstreth et al. 1998; Abarca and Casiccia 2002).

Snow is not uncommon in and around Punta Arenas during spring; consequently, the already high UVB levels reported could be further increased by surface reflection, by as much as 90% (Diffey 1998), therefore reaching or surpassing levels commonly experienced by people living closer to the Equator (Abarca and Casiccia 2002). The surface-based radiometers do not accurately measure reflected or scattered radiation, therefore, people living in areas subject to high levels of reflected light can receive higher levels of UVB than what is reported by these instruments (Abarca and Casiccia 2002). There is a need to educate people regarding the harmful effects of exposure to high levels of UVB such as the use of photoprotective clothing and the application of sunscreen. A more recent approach to reduce the harmful effects of solar radiation is through the use of phytochemicals that have been found to be photoprotective in nature (Adhami et al. 2008).

Chapter 2 – Antarctica

23

Figure 2.3: Map of Antarctica displaying relevant geographic features for this study. (The map was created using the m_map high resolution coastline in Matlab, which did not include the Antarctic ice shelves).