Summary

PAR drives photosynthesis, whereas UVR is usually known to harm physiological processes in macroalgae as well as phytoplankton. UV-A, however, at reduced levels, has been shown to enhance photosynthesis and repairing processes of pho-todamaged molecules, whereas UV-B mostly results in harmful effects. During their long history of evolution, seaweeds have developed protective strategies against harmful UV irradiances, such as synthesizing and accumulating UVAC and the repair of DNA damage. Different life stages of seaweeds show different sensitivity to solar UVR, with less-differentiated forms being more sensitive to UVR. Species distributed at different depths in the intertidal zone also show different responses to solar UVR; upper species, that are usually exposed to higher levels of solar radiation and accumulate higher contents of UVAC (such as MAAs), are more tolerant of UVR. On the other hand, diurnal photosynthesis can be underestimated during twilight period or cloudy days and overestimated during noontime if the effects of UVR are ignored owing to positive and negative effects caused by UV-A, respectively, at low and high irradiance levels.

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Suh, H.J., Hyun-Woo Lee, H.W. and Jung, J. (2003) Mycosporine glycine protects biological systems against photodynamic damage by quenching singlet oxygen with a high efficiency. Photochem. Photobiol. 78: 109-113.

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Zou, D. and Gao, K. (2002) Effects of desiccation and CO2 concentrations on emersed photosynthesis in Porphyra haitanensis (Bangiales, Rhodophyta), a species farmed in China. Eur. J. Phycol. 37: 587-592.

Biodata of E. Walter Helbling, Virginia E. Villafañe, and Donat-P. Häder, authors of "Ultraviolet Radiation Effects on Macroalgae from Patagonia, Argentina"

Dr. E. Walter Helbling is currently the Director of Estación de Fotobiología Playa Unión (EFPU, Argentina) and a researcher from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina). He obtained his Ph.D. from Scripps Institution of Oceanography, University of California, San Diego (USA). His scientific interests are in ecophysiology of plankton and photobiology of aquatic systems in relation to climate change.

E-mail: [email protected]

Dr. Virginia E. Villafañe is currently a Researcher from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET, Argentina). She obtained her Ph.D. from University of Groningen (The Netherlands) and continued her research in Patagonia at Estación de Fotobiología Playa Unión (EFPU, Argentina). Dr. Villafañe's scientific interests are in the areas of ecophysiology of plankton and photobiology.

E-mail: [email protected]

E. Walter Helbling
Virginia E. Villafañe

A. Israel et al. (eds.), Seaweeds and their Role in Globally Changing Environments,

Cellular Origin, Life in Extreme Habitats and Astrobiology 15, 199-214

DOI 10.1007/978-90-481-8569-6_12, © Springer Science+Business Media B.V. 2010

Professor Donat-P. Häder holds the Chair of Plant Ecophysiology at the Department for Biology at the Friedrich-Alexander University in Erlangen-Nürnberg. He obtained his Ph.D. from the University of Marburg in 1973. After a Postdoc year in East Lansing Michigan state, he became Researcher in Marburg. Professor Häder's scientific interests are in the areas of the effects of stratospheric ozone depletion and resulting increasing solar UV-B radiation at the Earth's surface on the biota. He concentrates on these effects in combination with global climate change on aquatic ecosystems in many habitats over the globe.

E-mail: [email protected]

ULTRAVIOLET RADIATION EFFECTS ON MACROALGAE FROM PATAGONIA, ARGENTINA

E. WALTER HELBLING12, VIRGINIA E. VILLAFAÑE12, AND DONAT-P. HÄDER3

'Estación de Fotobiología Playa Unión, Casilla de Correos N° '5, (9'03), Rawson, Chubut, Argentina 2Consejo Nacional de Investigaciones Científicas y Técnicas, CONICET, Argentina

3Department of Biology, Friedrich-Alexander Universität Erlangen/ Nürnberg, Staudtstr. 5, 91058, Erlangen, Germany

1. General Considerations

Aquatic ecosystems account for almost half of the primary production on our planet, matching the combined productivity of all terrestrial ecosystems (Siegenthaler and Sarmiento, 1993). Though most of the aquatic productivity is due to phytoplankton, macroalgae contribute to a significant share, especially in coastal areas. In their natural environment, macroalgae are generally exposed to excessive solar PAR (photosynthetic active radiation, 400-700 nm) as well as to ultraviolet radiation (UV-B, 280-315 nm, and UV-A, 315-400 nm), especially in the upper eulittoral and the supralittoral (Hanelt, 1998). The coincidence of low tides and high solar angles results in the highest radiation stress, generally reflected as photoinhibition, i.e., the reduction in photosynthetic rates. Photoinhibition (Dring et al., 1996; Franklin and Forster, 1997; Häder et al., 2001b), is determined not only in macroalgae from the tropics and temperate zones but also in Arctic and Antarctic environments (Hanelt et al., 1997; Hanelt, 1998). Most of the observed photoinhibition is due to PAR, as this waveband has a high proportion of solar radiation energy reaching the Earth's surface. However, in the top meters of the water column, a significant percentage of photoinhibition is caused by UV-B, and to a lesser extent by UV-A (Dring et al., 1996; Häder, 1997).

In this chapter, we will review our knowledge about the effects of solar radiation on macroalgae from Patagonia, Argentina. This area is especially important from a photobiological point of view, as it presents high heliophany and episodic ozone depletion events (Helbling et al., 2005). Although relatively few studies were conducted in this area, most of them were performed under in situ conditions, and thus the information is highly valuable as it reflects the natural situation of the area.

2. Macroalgae Diversity in Patagonia

Extensive literature on the different macroalgae groups present in the Patagonia area is available (see Boraso and Zaixso, 2008 and references therein). Particularly, there are many studies regarding macroalgal communities of the Chubut Province. In Golfo San José, which represents the limit between the oceanic biogeographic provinces of Patagonia and Argentina, ca. 30% of the surface at depths <10 m is covered by Dictyota dichotoma. In the intertidal zone of Golfo Nuevo, Blidingia minima and Enteromorpha spp. are characteristic. In tidal pools, Cladophora falklandica, Ulva rigida, and Polysiphonia brodiaei are commonly found; the Rhodophyta Corallina officinalis has been found very important to fix and protect the shore from the incoming waves. In the past 10 years, rocky seabeds have been dominated by the invasive Phaeophyta Undariapinnatifida (Casas and Piriz, 1996; Martin and Cuevas, 2006; Casas et al., 2008) in several areas of the Patagonia coast. Moreover, in sandy beaches of Golfo Nuevo, beach-cast seaweeds were dominated by green algae from the genera Ulva and Codium but lately U. pinnatifida displaced Codium spp. (Piriz et al., 2003). Farther south, and in the intertidal zone of Golfo San Jorge, Enteromorpha spp. and Porphyra columbina are characteristic. In the lower intertidal, C. officinallis dominates, but other species from the genera Cladophora, Ulva, Adenocystis, Bryopsis, Codium, Chondria, Leathesia, Colpomenia, Spongomorpa, and Urospora are also found.

Macroalgae of commercial interest have also been the focus of several investigations (Boraso de Zaixso et al., 1998 and references therein). The most important commercial species found in Patagonian waters are Gracilaria gracilis and Macrocystis pyrifera, which are usually found in the center and south of the Chubut Province.

In Santa Cruz Province, and particularly in the Ría de Puerto Deseado, many studies have focused on the taxonomy of macroalgal species: So far, more than 200 species have been identified (Boraso de Zaixso, 1995). In Tierra del Fuego, and in the intertidal zone near Ushuaia, the genera Rama, Rhizoclonium, Cladophoropsis, Porphyra, Bostrychia, Iridaea, Hildenbrandtia, and Caepidium are common, as also Ulvales and Cladophorales are diverse; in the subtidal zone, diverse corallinaceae are representative.

3. Solar Radiation and Ozone Conditions Over the Area of Patagonia

Solar radiation is an environmental factor that strongly affects organisms living in aquatic ecosystems. The radiation levels at which aquatic organisms are exposed depend on several factors, such as the solar irradiance reaching the Earth's surface, type and concentration of atmospheric gases (i.e., mainly ozone), altitude, and partic-ulate and dissolved material in the water column (Blumthaler and Webb, 2003; Hargreaves, 2003). In Patagonia, there is a clear trend of high radiation values during summer and low during winter (Orce and Helbling, 1997; Villafañe et al., 2004).

However, there is high variability in irradiance and daily doses values over Patagonia owing to the large latitudinal coverage with concomitant changes in solar zenith angle, day length, and atmospheric aerosols content, among other factors (HolmHansen et al., 1993) (more detailed information about latitudinal differences in radiation levels in temperate and sub-Antarctic sites of Patagonia as well as along Argentina is presented in Orce and Helbling (1997)). Representative patterns of solar radiation over Patagonia are presented in Fig. 1: daily doses of PAR (Fig. 1 a) vary from ~14 MJ m-2 in summer to <1 MJ m-2 in winter; UVR daily doses follow a similar pattern, with UV-A (Fig. 1b) ranging from ~2 to 0.15 MJ m-2, whereas UV-B (Fig. 1c) ranges from ~45 to <5 KJ m-2.

UV-B radiation is additionally affected by ozone concentrations (Madronich, 1993; Blumthaler and Webb, 2003). During the past 2 decades, there was an increasing interest in evaluating the effects of enhanced UV-B radiation due to the thinning of the ozone layer (i.e., ozone "hole") on aquatic biota (Häder et al., 2007). Total column ozone concentration over mid-Patagonia varies throughout the year, with low values (~220-230 Dobson Units, D.U.) in April-May, and high ones (~400 D.U.) during September (Fig. 1d), which is in agreement with the reported dynamics of photochemical production of ozone over the stratosphere (Molina and Molina, 1992). During early spring, however, there are some days (ovals in Fig. 1d) characterized by relatively low ozone concentrations (220-270 D.U.) that are associated with the Antarctic polar vortex and to the ozone "hole"; in fact, the signaling of the Antarctic ozone "hole" over Patagonia has been determined as far north as 38°S (Orce and Helbling, 1997). Several studies have shown the presence of low-ozone air masses over Patagonia, either because the Antarctic polar vortex covers the tip of South America for short periods of time (Frederick et al., 1993; Diaz et al., 1996), or because ozone-depleted air masses detach from the polar vortex (i.e., end of November to early December) and circulate northward (Atkinson et al., 1989; Kirchhoff et al., 1996). However, these studies have highlighted the temporal and spatial variability of low-ozone air masses over Patagonia. Moreover, Helbling et al. (2005) used TOMS data to determine the aerial coverage of low-ozone air masses (<275 D.U.) that were related to the Antarctic ozone "hole" over Patagonia and they found that, in general, they covered ~20% of the Patagonia area during 1979 and then increased up to ~95% during 2002. However, it should be stressed that these data represent the maximum coverage of low-ozone air masses during 1 day, and the dynamics of the polar vortex is such that it influences Patagonia only during a few days per year (Orce and Helbling, 1997).

4. Impact on Macroalgae Photosynthesis

The photosynthetic performance under solar radiation of several macroalgae has been measured on site on the coast of Patagonia. On the rocky shore, the organisms cover a wide habitat from the supralittoral to the sublittoral with substantial differences in exposure to PAR and UVR. The Chlorophyte Ulva rigida grows

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0.0x100 440 400

CD 320-c

8 280 O

240 200

1/1999 1/2000 1/2001 1/2002 1/2003 1/2004 1/2005 1/2006 1/2007

Figure 1. Daily doses of solar radiation and ozone concentration in the area of Bahía Engaño from 1999 to 2007. (a) PAR (400-700 nm); (b) UV-A (315-400 nm); (c) UV-B (280-315 nm); (d) Ozone concentrations (in D.U.). Solar radiation data were obtained with a broadband ELDONET radiometer (www.eldonet.org) permanently installed on the roof of Estación de Fotobiología Playa Unión. Ozone concentrations data were obtained from NASA (http://jwocky.gsfc.nasa.gov). Note the low ozone values during springtime (inside ovals).

throughout the upper eulittoral to the supralittoral zone in shallow rock pools. Using a pulse amplitude modulated fluorometer (PAM, 2000, Walz, Effeltrich, Germany), it was found that the nonphotochemical quenching (qN) rises with increasing irradiances of actinic light starting as low as 10 W m-2, whereas the photochemical quenching (qP) decreases antagonistically (Häder et al., 2000). This physiological response has also been found in higher plants (Niyogy et al., 1998). When exposed to solar radiation for 15 min during low tide and at solar noon on a bright day, the photosynthetic yield (Y) decreased to about 50% of its value in dark-adapted plants, but recovered rapidly within 30 min in dim light. When solar UV-B radiation was excluded using filter foils (Montagefolie, Folex, Dreieich, Germany), Y was significantly less impaired.

The Chlorophyte Enteromorpha linza occurs in the same habitat, but during low tide, it is exposed on the rocky surface as it rarely grows inside the rock pools. When exposed to solar radiation for 15 min during low tide and at solar noon, the decrease in Y is even more pronounced than in U. rigida and decreases to ~0.2 from the initial dark-adapted value of 0.7 (Häder et al., 2001a). Cutting off the UV-B wavelength band resulted in a less pronounced reduction in Y and cutting off the total UV band (using Ultraphan UV Opak filter, Digefra, Munich, Germany) caused an even less pronounced inhibition. The effects of the UV-B or total UV components of solar radiation were still visible throughout the recovery period in dim light. In the experiments described here, the thalli were confined to a flow-through holder and constantly exposed to solar radiation. However, when exposed free floating in a mesocosm, there was a decrease in Y by only ~35% during clear days and less pronounced on cloudy days; but in any case, the effects of especially the UV-B band were noticeable.

The filamentous Rhodophytes Ceramium sp. and Callithamnion gaudichaudii were found in the lower eulittoral inside rock pools. Both were strongly affected by solar radiation (Häder et al., 2004). Both UV-A and UV-B had pronounced effects compared with that of PAR (Fig. 2). Recovery was much slower than in the Chlorophytes and the Y was back to the dark-adapted value only during the night. However, it is interesting to note that the increase in qN and the decrease in qP started at much higher irradiances than in the Chlorophytes (about 50 W m-2). Similar results were found in the Rhodophyte Porphyra columbina, which grew on the shaded sides of the rock pools in the lower eulittoral.

Two growth forms of Corallina officinalis were found in the middle and low eulittoral (only accessible during very low tides), which differed in their morphology and calcification so that the skeleton of the low-eulittoral Corallina was less calcified than that in the mid-eulittoral algae (45% (w/w) and 49% of the total dry weight (DW), respectively (Richter et al., 2006)). Moreover, it was found that their photosynthetic parameters were different as well (Häder et al., 2003). The induction curves with quenching analysis showed a faster decrease in the current and maximal fluorescence (Ft and Fm) in the low eulittoral strain compared with the mid eulittoral growth form. Simultaneously, qN rose much faster and higher in the low eulittoral strain (Fig. 3).

Dark 15 min 14:45 15:45 17:45 20:45 00:45 06:45 Control exposure Local time [h]

Figure 2. Effective photosynthetic quantum yield in Ceramium sp. measured after 30 min dark adaptation, 15 min exposure, and after increasing recovery times in the shade. Gray bars, specimens exposed to unfiltered solar radiation. Black bars, specimens exposed to UV-A and PAR. Open bars, specimens exposed to PAR only. (After Hâder et al., 2004.)

Dark 15 min 14:45 15:45 17:45 20:45 00:45 06:45 Control exposure Local time [h]

Figure 2. Effective photosynthetic quantum yield in Ceramium sp. measured after 30 min dark adaptation, 15 min exposure, and after increasing recovery times in the shade. Gray bars, specimens exposed to unfiltered solar radiation. Black bars, specimens exposed to UV-A and PAR. Open bars, specimens exposed to PAR only. (After Hâder et al., 2004.)

The Phaeophyte Dictyota dichotoma was found in rock pools in the mid eulittoral. After exposure to 15 min of solar radiation in a fixed position, the effective Y decreased dramatically and did not fully recover until the next morning (Hâder et al., 2001b). Free floating thalli were not affected as much as those in a fixed position.

Overall, there is a wide range of photosynthetic responses of Patagonian macroalgae to solar radiation. All results from Patagonia and other coasts confirm that the sensitivity to solar radiation increases with their depth of growth (Hâder, 1997). It can be discussed whether this is due to the fact that more sensitive species select a habitat lower in the water column or whether resistance increased with higher exposure to solar radiation. In any case, macroalgae have developed a number of protective mechanisms against excessive solar radiation. In addition to UV-absorbing compounds (see Section 5), most macroalgae use an effective repair mechanism for damaged DNA and proteins in the photosynthetic apparatus. To prove that the D1 protein in the reaction center of photosystem II is resynthesized after photodamage and proteolysis, streptomycin or chloramphenicol were applied during recovery of several macroalgae (Ulva, Porphyra, Dictyota). Both delayed the recovery indicating that the D1 protein resynthesis was inhibited (Hâder et al., 2002). Several macroalgae groups use the xanthophyll cycle to dispose of excessive radiation by thermal dissipation (Niyogi et al., 1998). Dithiothreitol is an inhibitor of the violaxanthin de-epoxidase, so when administered to the same algae it affected both photoinhibition and recovery (Hâder et al., 2002). However, this was also found in the red algae, which are believed not

Time [s]

Figure 3. Induction curve with quenching analysis in the mid-eulittoral strain (a) and the low eulittoral strain (b) of Corallina officinalis. (After Hader et al., 2003.)

Figure 3. Induction curve with quenching analysis in the mid-eulittoral strain (a) and the low eulittoral strain (b) of Corallina officinalis. (After Hader et al., 2003.)

to possess the xanthophyll cycle. This indicates that the inhibitor should be used with caution since it seems to have strong side effects.

5. Presence and Dynamics of UVR-Absorbing Compounds in Patagonian Macroalgae

Macroalgae constitute a source of UV-absorbing compounds, typically mycosporine-like amino acids (MAAs). These compounds are known to protect organisms against UVR stress because of their ability to absorb short wavelengths, but other ecophysiological functions such as protectors against desiccation or as osmotic regulators, antioxidants, and even as accessory pigments have been reported (Korbee Peinado et al., 2006). Therefore, the capacity of synthesizing and accumulating these compounds would provide an adaptive advantage for organisms exposed to different ambient stressors. This is especially important for Patagonian macroalgae that are subjected to high radiation levels and suffer desiccation, especially during low tides and at summer time. Studies dealing with these compounds in Patagonian macroalgae have focused on two main aspects: (a) to determine their presence and abundance in key species of the community and (b) to assess their dynamics throughout daily cycles and considering the tide effects. These studies are particularly important in the context of climate change, as they give insight into the capacity of different algae to cope with increasing solar radiation.

Specific studies were carried out with the two strains of the Rhodophyte Corallina officinalis (i.e., low- and mid-eulittoral forms). High-performance liquid chromatography (HPLC) analysis indicated the presence of two MAAs, shinorine and palythine, with the absolute concentration of the latter being about tenfold higher than that of the former (Fig. 4). The amount of MAAs in low-eulittoral samples was significantly lower than that in the mid-eulittoral strain. Significant diurnal changes in the MAAs concentration and in the ratio between shinorine and palythine of the low-eulittoral Corallina algae were also observed (Richter et al., 2006): Both MAAs concentration increased around local noon, but the ratio between shinorine and palythine decreased during midday owing to a higher increase in palythine over shinorine (Fig. 4). In the afternoon, the MAAs concentration decreased again. In the mid-eulittoral strain, MAAs dynamics showed an opposite pattern so that around noon the palythine concentration decreased compared with shinorine, whereas in the afternoon the palythine concentration tended to increase. Although the data indicate a strong influence of solar radiation on MAAs synthesis in C. officinalis, it is still an open question, whether endogenous circadian or circatidal rhythms are also involved in this process.

Concentration of UV-absorbing compounds and photosynthetic pigments as a function of different radiation treatments throughout daily cycles were done with the Rhodophyte Porphyra columbina. Five MAAs were identified: mycosporine-glycine, shinorine, porphyra-334, palythine, and asterina. Porphyra-334 was the most abundant MAA (~80% of the total concentration) and it was always present regardless of the conditions under which the algae were exposed. Shinorine was also present in high concentrations (~20%), whereas the remaining MAAs occurred at much lower concentrations. UV-absorbing compounds in P. columbina generally decreased throughout the daily cycles in the two radiation treatments implemented (i.e., PAR+UVR and PAR only) but, in contrast to Corallina officinalis, higher values were determined at night; also, and in general, slightly lower values at the end of the experiment were determined in samples exposed only to PAR. The concentration of photosynthetic pigments, on the other hand, remained low throughout the experiment. Results from ammonium-enrichment experiments on the synthesis of MAAs and photosynthetic pigments (Korbee Peinado et al., 2004) showed no significant increase in the concentration of MAAs during a 6-day exposure at concentrations of 0 and 50 mM NH4+. On the other hand, samples a 0.4—1

ir 1

ir 1

Figure 4. Diurnal changes in concentration (mg/g DW) of the MAAs shinorine and palythine in Corallina officinalis growing in the low eulittoral (a) and in the mid-eulittoral (b) zones. Data are the means and standard deviation of five independent measurements of different samples collected at the corresponding time. Differences between midday low eulittoral samples and morning or evening samples in shinorine are significant (P < 0.05) and highly significant (P < 0.001) in palythine. Differences between midday samples and morning or evening samples were only significant (P < 0.05) for palythine but not for shinorine. (After Helbling et al., 2004.)

Figure 4. Diurnal changes in concentration (mg/g DW) of the MAAs shinorine and palythine in Corallina officinalis growing in the low eulittoral (a) and in the mid-eulittoral (b) zones. Data are the means and standard deviation of five independent measurements of different samples collected at the corresponding time. Differences between midday low eulittoral samples and morning or evening samples in shinorine are significant (P < 0.05) and highly significant (P < 0.001) in palythine. Differences between midday samples and morning or evening samples were only significant (P < 0.05) for palythine but not for shinorine. (After Helbling et al., 2004.)

b grown at 300 mM NH4+ had a significant increase compared with the initial value and other treatments at day 6. In addition, and after 3 days of exposure, the content of MAAs was significantly lower in thalli exposed only to PAR compared with treatments receiving additionally UV-A and UVR, indicating a stimulation of MAA synthesis in these treatments.

The daily variations of UV-absorbing compounds in Ceramium sp. exposed to full solar radiation followed approximately the daily irradiance cycle, with high concentrations during the day and decreasing in the evening; during the day, their concentration in samples exposed to UVR was significantly higher than in those exposed only to PAR. Callithamnion gaudichaudii displayed high variability in the concentration of UV-absorbing compounds in algae exposed to full solar radiation, with significantly higher values during early morning and decreasing during the day.

A comparison of the co-variation of UV-absorbing compounds as a function of chlorophyll a in seven macroalgae species is shown in Fig. 5. UV-absorbing compounds had a wide range of responses according to the species: In C. officinalis and P. columbina exposed to full solar radiation, a significant positive correlation was observed. On the other hand, in Ceramium sp and in C. gaudichaudii a poor correlation between these compounds was found. Small amounts of UV-absorbing compounds were found in Ulva rigida, Dictyota sp., and Enteromorpha linza. Carotenoids, however, showed a significant positive correlation with chlorophyll a in species studied (carotenoids = 0.9 * chl a, R2 = 0.89, P < 0.0001).

♦ Ceramiun

□ Calithamnion

■ Corallina

0

0 Enteromorpha

9 Dictyota

A

A Porphyra

+

+ Ulva

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