View source for Impacts of instrumental period climate change on macroalgae

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[[File:Figure 4.53 - Physiological temperature adaptation of Antarctic macroalgae.png|thumb|'''4.53''' Physiological temperature adaptation of Antarctic macroalgae (after Wiencke and Clayton, 2002<ref name="Wiencke and Clayton, 2002">Wiencke, C. and Clayton, M.N. 2002. Antarctic Seaweeds, (Synopses of the Antarctic Benthos. Ed.: J. W. W&auml;gele and J. Sieg ; Vol. 9), Ruggell : Gantner ; K&ouml;nigstein : Koeltz Scientific Books., 239 pp.</ref>)]]
Many Antarctic macroalgae, especially from the subtidal zone, are adapted to low temperatures (Wiencke et al., 1994<ref name="Wiencke et al, 1994">Wiencke, C., Bartsch, I., Bischoff, B., Peters, A.F. and Breeman, A.M. 1994. Temperature requirements and biogeography of Antarctic, Arctic and amphiequatorial seaweeds, ''Botanica Marina.'', '''37''', 247-259.</ref>, 2007<ref name="Wiencke et al, 2007">Wiencke, C., Clayton, M. N., G&oacute;mez, I., Iken, K., L&uuml;der, U. H., Amsler, C. D., Karsten, U., Hanelt, D., Bischof, K. and Dunton, K. 2007. Life strategy, ecophysiology and ecology of seaweeds in polar waters, Reviews in Environmental Science and Biotechnology, 6(1/3), 95-126.</ref>), especially those endemic to the Antarctic. For example, the red algae ''Georgiella confluens'' ([[:File:Figure 4.53 - Physiological temperature adaptation of Antarctic macroalgae.png|Figure 4.53]]), ''Gigartina skottsbergii'' and ''Plocamium cartilagineum'' grow only at 0&deg;C and not at 5&deg;C, and exhibit upper survival temperatures (USTs) as low as 7 to 13-14&deg;C, respectively (Bischoff-B&auml;smann and Wiencke, 1996<ref name="Bischoff-B&auml;smann and Wiencke, 1996">Bischoff-B&auml;smann, N. and Wiencke, C. 1996. Temperature requirements for growth and survival of Antarctic Rhodophyta, ''Journal of Phycology'', '''32''', 525-535.</ref>). Other Antarctic red algae grow at temperatures up to 5 or 10&deg;C and have USTs of up to 19&deg;C. Macroscopic growth stages of endemic Antarctic brown algae grow up to 5&deg;C and exhibit USTs of 11 to 13&deg;C. Their reproductive microscopic stages grow up to 10 or 15&deg;C and have USTs between 15 and 18&deg;C (Wiencke and tom Dieck, 1989). Antarctic cold-temperate species (especially from the intertidal) are characterised by higher temperature requirements (Wiencke and tom Dieck, 1990).

This adaptation of Antarctic macroalgae to low temperatures is also reflected in photosynthesis. The photosynthetic capacities of endemic Antarctic species measured at 0&deg;C are as high as in temperate algae measured at higher temperatures (Thomas and Wiencke, 1991<ref name="Thomas and Wiencke, 1991">Thomas, D.N. and Wiencke, C. 1991. Photosynthesis, dark respiration and light independent carbon fixation of endemic Antarctic macroalgae, ''Polar Biol.'', '''11''', 329-337.</ref>; Wiencke et al., 1993<ref name="Wiencke et al, 1993">Wiencke, C., Rahmel, J., Karsten, U., Weykam, G. and Kirst, G.O. 1993. Photosynthesis of marine macroalgae from Antarctica Light and temperature requirements, ''Botanica Acta'', '''106''', 78-87.</ref>; Weykam et al., 1996<ref name="Weykam et al, 1996">Weykam, G., G&oacute;mez, I., Wiencke, C., Iken, K. and Kl&ouml;ser, H. 1996. Photosynthetic characteristics and C:N ratios of macroalgae from King George Island (Antarctica), ''Journal of Experimental Marine Biology and Ecology'', '''204''', 1-22.</ref>; Eggert and Wiencke, 2000<ref name="Eggert and Wiencke, 2000">Eggert, A., Wiencke, C. 2000. Adaptation and acclimation of growth and photosynthesis of five Antarctic red algae to low temperatures, ''Polar Biol.'', '''23''', 609-618.</ref>). However, optimum temperatures for photosynthesis are clearly above the Antarctic water temperatures. The lowest temperature optima have been recorded in ''Ascoseira mirabilis'' (1 to 10&deg;C). The other species tested so far are characterised by higher values between 10 and 20&deg;C. Temperature optima for dark respiration are higher than those for photosynthesis (Drew, 1977<ref name="Drew, 1977">Drew, E.A. 1977. The physiology of photosynthesis and respiration in some Antarctic marine algae, ''Br. Antarct. Surv. Bull.'', '''46''', 59-76.</ref>; Wiencke et al., 1993<ref name="Wiencke et al, 1993">Wiencke, C., Rahmel, J., Karsten, U., Weykam, G. and Kirst, G.O. 1993. Photosynthesis of marine macroalgae from Antarctica Light and temperature requirements, ''Botanica Acta'', '''106''', 78-87.</ref>; Eggert and Wiencke, 2000<ref name="Eggert and Wiencke, 2000">Eggert, A., Wiencke, C. 2000. Adaptation and acclimation of growth and photosynthesis of five Antarctic red algae to low temperatures, ''Polar Biol.'', '''23''', 609-618.</ref>).

Due to global warming the geographic distribution of stenothermal cold water species will be limited in future to the coasts of the Antarctic continent itself. Species presently occurring today predominantly in the cold-temperate region and rarely in the Antarctic will become more established in the Antarctic region (M&uuml;ller et al., submitted). This can cause unforeseeable changes in the ecology of Antarctic shallow water communities.

Light determines significantly the depth zonation and survival of macroalgae. Antarctic seaweeds are able to tolerate dark periods of up to one year without suffering damage, and their light requirements for growth are very low (Wiencke, 1990<ref name="Wiencke, 1990">Wiencke, C. 1990. Seasonality of brown macroalgae from Antarctica - a long-term culture study under fluctuating Antarctic daylengths, ''Polar Biol.'', '''10''', 589-600.</ref>). In juvenile sporophytes of Antarctic ''Desmarestia''les, growth is light saturated at &le; 20 &micro;mol photons/m<sup>2</sup>/s1 (Wiencke and Fischer, 1990<ref name="Wiencke and Fischer, 1990">Wiencke, C. and Fischer, G. 1990. Growth and stable carbon isotope composition of cold-water macroalgae in relation to light and temperature, ''Mar. Ecol. Prog. Ser.'', '''65''', 283-292.</ref>). The low light requirements for completion of the life cycle and for growth of Antarctic seaweeds are based on the low light requirements for photosynthesis (Wiencke et al., 1993<ref name="Wiencke et al, 1993">Wiencke, C., Rahmel, J., Karsten, U., Weykam, G. and Kirst, G.O. 1993. Photosynthesis of marine macroalgae from Antarctica Light and temperature requirements, ''Botanica Acta'', '''106''', 78-87.</ref>; Weykam et al., 1996<ref name="Weykam et al, 1996">Weykam, G., G&oacute;mez, I., Wiencke, C., Iken, K. and Kl&ouml;ser, H. 1996. Photosynthetic characteristics and C:N ratios of macroalgae from King George Island (Antarctica), ''Journal of Experimental Marine Biology and Ecology'', '''204''', 1-22.</ref>; Eggert and Wiencke, 2000<ref name="Eggert and Wiencke, 2000">Eggert, A., Wiencke, C. 2000. Adaptation and acclimation of growth and photosynthesis of five Antarctic red algae to low temperatures, ''Polar Biol.'', '''23''', 609-618.</ref>). As a result, light compensation (Ic) and saturation (Ik) points are very low in Antarctic species and mostly range between 1 and 15 and between 14 and 52 &micro;mol photons/m<sup>2</sup>/s1, respectively (Wiencke et al., 1993<ref name="Wiencke et al, 1993">Wiencke, C., Rahmel, J., Karsten, U., Weykam, G. and Kirst, G.O. 1993. Photosynthesis of marine macroalgae from Antarctica Light and temperature requirements, ''Botanica Acta'', '''106''', 78-87.</ref>; Weykam et al., 1996<ref name="Weykam et al, 1996">Weykam, G., G&oacute;mez, I., Wiencke, C., Iken, K. and Kl&ouml;ser, H. 1996. Photosynthetic characteristics and C:N ratios of macroalgae from King George Island (Antarctica), ''Journal of Experimental Marine Biology and Ecology'', '''204''', 1-22.</ref>; Brouwer, 1996<ref name="Brouwer, 1996">Brouwer, P.E.M. 1996. In situ photosynthesis and estimated annual production of the red macroalga Myriogramme mangini in relation to underwater irradiance at Signy Island (Antarctica), ''Antarct. Sci.'', '''8''', 245-252.</ref>; Eggert and Wiencke, 2000<ref name="Eggert and Wiencke, 2000">Eggert, A., Wiencke, C. 2000. Adaptation and acclimation of growth and photosynthesis of five Antarctic red algae to low temperatures, ''Polar Biol.'', '''23''', 609-618.</ref>). These low light requirements allow Antarctic macroalgae to grow down to considerable depths. Theoretically, growth of some species is possible at water depths down to approximately 75 m (Wiencke, 1990<ref name="Wiencke, 1990">Wiencke, C. 1990. Seasonality of brown macroalgae from Antarctica - a long-term culture study under fluctuating Antarctic daylengths, ''Polar Biol.'', '''10''', 589-600.</ref>; Wiencke et al., 1993<ref name="Wiencke et al, 1993">Wiencke, C., Rahmel, J., Karsten, U., Weykam, G. and Kirst, G.O. 1993. Photosynthesis of marine macroalgae from Antarctica Light and temperature requirements, ''Botanica Acta'', '''106''', 78-87.</ref>).

Antarctic algae are not only low light adapted but can also cope with high light conditions in summer due to their ability for dynamic photoinhibition, a photoprotective mechanism by which excessive energy absorbed is rendered harmless by thermal dissipation. The capability for dynamic photoinhibition is related to the depth distribution of the individual species. Species from the eulittoral, upper and mid sublittoral show a more or less pronounced decrease in photosynthetic activity during high light stress, and full recovery during subsequent exposure to dim light. In contrast, deep water and understory species recover only slightly and slowly indicating photodamage, especially after exposure to UV radiation. Recent studies indicate that the effect of UV radiation is not limited to the physiological and organism level. Rather, it influences the biodiversity, structure and function of macroalgal communities (Zacher et al., 2007<ref name="Zacher et al, 2007">Zacher, K., Wulff, A., Molis, M., Hanelt, D. and Wiencke, C. 2007. Ultraviolet radiation and consumer effects on a field-grown intertidal macroalgal assemblage in Antarctica, ''Global Change Biology'', '''13'''(6), 1201-1215.</ref>; Campana et al., submitted). The effects on the community level depend on the UV susceptibility of the unicellular propagation units of the seaweeds (Roleda et al., In Press; Zacher et al., 2009<ref name="Zacher et al, 2009">Zacher, K., Roleda, M.Y., Wulff, A., Hanelt, D., and Wiencke, C. 2009. Responses of Antarctic Iridaea cordata (Rhodophyta) tetraspores exposed to ultraviolet radiation. Phycological research, 57(3), 186-193.</ref>). So UV radiation represents an important factor for the determination of the upper distribution limit on the shore. The obtained results are of great importance for the estimation of the effects of enhanced UV radiation due to stratospheric ozone depletion. UV induced changes in algal zonation and biodiversity make changes in the trophic relations of coastal ecosystems very probable.
==References==
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[[Category:The instrumental period]]
[[Category:Antarctic biology]]
[[Category:Marine biology]]