UV-radiation versus grazing pressure: long-term floating of kelp rafts (Macrocystis pyrifera) is facilitated by efficient photoacclimation but undermined by grazing losses
- 240 Downloads
Large quantities of floating macroalgae are traveling in coastal waters of the SE Pacific and in other temperate climate zones. While afloat, these algae are potentially exposed to full solar radiation, including UVA and UVB, which can have profound effects on their physiological and growth performance. Latitudinal variations in UV-radiation (UVR) are hypothesized to affect floating algae differently with higher impacts at low latitudes than at high latitudes. In addition, UVR together with grazing might accelerate the demise of floating kelps. This hypothesis was tested with outdoor laboratory experiments in which sporophytes of the giant kelp Macrocystis pyrifera (L.) C. Agardh were exposed to a combination of different UVR regimes (PAR only, PAR + UV) and grazing at three sites along the Chilean coast (20°S, 30°S, and 40°S). A latitudinal trend in irradiance was detected with increasing values from 40°S to 20°S. Surprisingly, floating M. pyrifera responded with a high acclimation potential within this latitudinal UVR gradient. At 20°S, floating kelps were slightly sensitive to UVR, which was reflected in reduced blade growth. At 30°S, physiological responses were hardly affected by the prevailing irradiance but sporophyte growth and thus persistence mainly depended on the presence or absence of amphipod grazers. At high latitudes, grazing had only minor impacts on algal biomass and blade growth, and kelps thrived well under all tested environmental conditions. Overall, our results reveal that floating M. pyrifera was only slightly affected by UVR and that sporophytes can efficiently acclimate over a latitudinal UVR gradient that spans from 20°S to 40°S. Given this high acclimation potential, we suggest that these (and possibly other) positively buoyant algae are important dispersal agents over a wide range of temperate latitude conditions.
KeywordsPhotosynthetically Active Radiation Electron Transport Rate Maximal Quantum Yield Macrocystis Pyrifera Northernmost Site
Financial support for this research was provided by FONDECYT 1060127 to MT, FT and IG. The first author is grateful to the German Academic Exchange Service (DAAD) and the FAZIT-Stiftung for financial support during her PhD thesis. We thank Ivan Hinojosa, Leonardo Miranda, Osvaldo Cerda, and Mario Villegas for their valuable help in the field and during the experiments. Finally, we are grateful to two anonymous reviewers who helped to improve this manuscript.
- Anderson MJ (2005) PERMANOVA: a FORTAN computer program for permutational multivariate analysis of variance. Department of Statistics, University of Auckland, New ZealandGoogle Scholar
- Franklin LA, Forster RM (1997) The changing irradiance environment: consequences for marine macrophyte physiology, productivity and ecology. Eur J Phycol 32:207–232Google Scholar
- Hinojosa I, González E, Ugalde P, Valdivia N, Macaya E, Thiel M (2007) Distribution and abundance of floating seaweeds and their associated peracarid fauna in the fjords and channels of the XI. Region, Chile. Cienc Tecnol Mar (Chile) 30:37–50Google Scholar
- Hoyer K, Karsten U, Wiencke C (2002) Induction of sunscreen compounds in Antarctic macroalgae by different radiation conditions. Mar Biol 41:619–627Google Scholar
- Mercado JM, Jiménez C, Niell FX, Figueroa FL (1996) Comparison of methods for measuring light absorption by algae and their application to the estimation of the package effect. Sci Mar 60:39–45Google Scholar
- Pavia H, Toth GB (2000) Inducible chemical resistance to herbivory in the brown seaweed Ascophyllum nodosum. Ecology 81:3212–3225Google Scholar
- Rothäusler E, Gómez I, Hinojosa IA, Karsten U, Tala F, Thiel M (accepted) Physiological performance of floating giant kelp Macrocystis pyrifera (Phaeophyceae): Latitudinal variability in the effects of temperature and grazing. J Phycol Google Scholar
- Schreiber U, Bilger W, Neubauer C (1994) Chlorophyll fluorescence as a non intrusive indicator for rapid assessment of in vivo photosynthesis. Ecol Stud 100:49–70Google Scholar
- Thiel M, Gutow L (2005a) The ecology of rafting in the marine environment I. The floating substrata. Oceanogr Mar Biol Annu Rev 42:181–264Google Scholar
- Underwood AJ (1997) Experiments in ecology. Their logical design and interpretation using analysis of variance. Cambridge University Press, CambridgeGoogle Scholar
- Von Ende CN (1993) Repeated-measures analysis: Growth and other time-dependent measures. In: Schreiner SM, Gurevitch J (eds) Design and analysis of ecological experiments. Chapman and Hall, New York, pp 113–137Google Scholar