MEPS 270:103-116 (2004)  -  doi:10.3354/meps270103

Patterns of photosynthesis in 18 species of intertidal macroalgae from southern Chile

Iván Gómez1,*, Félix López-Figueroa2, Nancy Ulloa1, Viviana Morales1, Charlotte Lovengreen3, Pirjo Huovinen1,5, Susan Hess4

1Instituto de Biología Marina,
3Instituto de Física, and
4Instituto de Química, Universidad Austral de Chile, Casilla 567, Valdivia, Chile
2Departamento de Ecología, Universidad de Málaga, Teatinos s/n, 29071 Málaga, Spain
5Present address: Department of Biological and Environmental Science, University of Jyväskylä, PO Box 35, 40500 Jyväskylä, Finland

ABSTRACT: Photosynthetic characteristics of 18 macroalgal species, measured as chlorophyll a (chl a) fluorescence of photosystem II (PSII), pigment contents and susceptibility of photosynthesis to solar radiation, were studied in the field in southern Chile (Niebla, Valdivia) during mid-summer. Photosynthesis versus irradiance curves indicated that algae exhibited sun-adapted characteristics, with saturating points for photosynthesis (Ek) ranging between 50 and 400 µmol photon m-2 s-1. Under the solar radiation conditions that prevailed during the study period at this locality (daily doses of photosynthetically active radiation, PAR, close to 14000 kJ m-2 d-1, with instantaneous irradiances exceeding 2000 µmol photon m-2 s-1 at noon), algae were light saturated for periods (Hsat) between 11 and 14 h d-1. Daily courses of optimal quantum yield (Fv/Fm) of chl a fluorescence of PSII revealed the existence of photoinhibition of 46% at maximum relative to fluorescence measured in the morning. Similarly, the effective quantum yield ( ΦPSII) showed a decrease at noon coinciding with the peak of solar radiation. This reduction in ΦPSII was accentuated when algae were maintained in immersion for the whole measuring period; whereas, in algae measured in situ, i.e. subject to varying tidal height, chl a fluorescence decreased less. Although algae are currently exposed to very high doses of ultraviolet (UV) radiation, short-term exposures of 2.5 h around noon using specific cut-off filters did not result in high photoinhibition of Fv/Fm (rates < 25%), reinforcing the idea that these intertidal species are characterized by a marked tolerance to current solar UV radiation. Differences in the rates of photoinhibition of photosynthesis as well as in the photosynthetic characteristics were not related to functional-form group (e.g. thin vs thick morphs). Instead, the photosynthetic performance of algae was determined by their position in the shore: algae growing at mid-/infra-littoral zones had lower Ek and lower photoinhibition than algae from upper locations.

KEY WORDS: Macroalgae · Photoinhibition · Photosynthesis · Southern Chile · UV radiation

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