Pulse Amplitude Modulation Fluorometry - Coral Reef Targeted ...

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depart from each other at higher levels of light (Geel et al. 1997). Such an effect ismost likely due to non-assimilatory electron flow through PSII such as that due toMehler activity, which can change between different algae or under different physicalconditions. Likewise, current evidence suggests that coral absorptance can changesubstantially during bleaching (Enriquez et al. 2005), thus rendering anymeasurement of “relative” ETR that does not account for such absorptance changeshighly suspect to gross error.ReferencesEnriquez S, Mendez ER, Iglesias-Prieto R (2005) Limnol Oceanogr 50: 1025-1032Franklin DJ, Hoegh-Guldberg P, Jones RJ, Berges JA (2004) Mar Ecol Prog Ser 272:117-130Geel C, Versluis W, Snel JFH (1997) Photosynth Res 51: 61-70Iglesias-Prieto R, Beltran VH, LaJeunesse TC, Reyes-Bonilla H, Thome PE (2004)Proc Royal Soc London 271: 1757-1763Kromkamp J, Forster RM (2003) Eur J Phycol 38: 103-112Lesser MP, Farrell JH (2004) Coral Reefs 23: 367-377Warner ME, Fitt WK, Schmidt GW (1999) Proc Nat Acad Sci 96: 8007–801220
Diel Cycling of Nitrogen Fixation in Corals withSymbiotic CyanobacteriaMichael P. Lesser 1 , Luisa I. Falcón 2 , Aimé Rodríguez-Román 3 , SusanaEnríquez 3 , Ove Hoegh-Guldberg 4 , and Roberto Iglesias-Prieto 31 Department of Zoology and Center for Marine Biology, University of NewHampshire, Durham, New Hampshire 03824, USA; 2 Instituto de Ecología,Universidad Nacional Autónoma de México, Circuito Exterior s/n CiudadUniversitaria, CP 04510 México, D. F. México, 3 Unidad Académica Puerto Morelos,Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma deMéxico, Cancún QR 77500, México, 4 University of Queensland, Centre for MarineSciences, 4072, St. Lucia, Queensland, AustraliaCorals in mutualistic symbiosis with endosymbiotic dinoflagellates (zooxanthellae)are essential components of the ecological diversity of tropical coral reefs.Zooxanthellate corals also exist in an environment where inorganic nitrogen limits thegrowth and abundance of zooxanthellae in hospite 1-3 . Many colonies of theCaribbean coral, Montastraea cavernosa, contain endosymbiotic cyanobacteria 4 .These cyanobacteria co-exist with the zooxanthellae and express the nitrogen fixingenzyme nitrogenase 4 . Here we show that the percentage of colonies containingsymbiotic cyanobacteria increases with increasing depth, and that measurements ofnitrogen fixation show a diel pattern with the highest rates of nitrogen fixation in theearly morning and evening. No nitrogen fixation was measurable in non-symbioticcon-specifics. The δ 15 N stable isotope data show a strong nitrogen fixation signal inthe zooxanthellae fraction of corals with cyanobacterial symbionts suggesting thatzooxanthellae use fixed nitrogen products. The timing of nitrogen fixation avoidsmaximum periods of photosynthesis to avoid severe hyperoxia, and nitrogen fixationdoes not occur when the coral experiences hypoxia or anoxia. These cyanobacteriarequire low oxygen tensions to support the respiratory processes that provide theenergy required to fix nitrogen. Nitrogen fixation in these corals provides animportant supplemental source of a limiting element for this novel microbialconsortium.Figure 1. Green-brown (left) and red morphs of Montastraea cavernosa under Bluelight and viewed through an orange filter set. Photo: O. Hoegh-Guldberg21
Page 1: Theme 1: Pulse Amplitude Modulation
Page 6 and 7: Iglesias-Prieto R (1996) Biochemica
Page 8 and 9: Variation in light absorption prope
Page 10 and 11: Mark E. Warner 1An overview of the
Page 14 and 15: Figure 2 Percent abundance ofMontas
Page 16: Figure 4. a) The relationship betwe
Page 21 and 22: Imaging-PAM: Operation and Possibil
Page 24 and 25: Seasonal fluctuations in the physio
Page 26 and 27: Optimal quantum yield of PSII (Fv/F
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