Combining O₂ Microsensors and Fiber-Optic Technology to Measure Photo-Physiological Responses of Symbiodinium

TY - ABST

T1 - Combining O2 Microsensors and Fiber-Optic Technology to Measure Photo-Physiological Responses of Symbiodinium

AU - Ulstrup, Karin Elizabeth

AU - Kühl, Michael

AU - Ralph, Peter

AU - Van Oppen, Madeleine

AU - Bourne, David

PY - 2008

Y1 - 2008

N2 - Corals associate with a diverse microbial assemblage of whichendosymbiotic and phototrophic microalgae, i.e. dinoflagellatesbelonging to the genetically diverse genus Symbiodinium, are bestknown. Traditional techniques to estimate photosynthesis activity suchas oxygen exchange and 14C-incorporation of Symbiodinium areconfounded by processes due to the coral host. In three case studies weemployed a novel approach using two technologies that enabledifferentiation of the photosynthesis activity of Symbiodinium, pulseamplitude-modulation (PAM) and O2 microsensors. The case studiesincluded i) monotypic Symbiodinium associating with a coral(Pocillopora damicornis), ii) a ciliate forming a brown band on the coralAcropora muricata, and iii) a genotypically diverse Symbiodiniumassociation with Acropora valida. In all instances, the combination offibre-optic technology and an O2 microelectrode enabled parallelmeasurements of gross photosynthesis rate and photosystem II quantumyield at the coral surface under steady-state conditions as a function ofincreasing irradiances. The studies showed large plasticity in photophysiologicalacclimation of Symbiodinium linked to light microclimateas well as motility (in the case of the ciliate) and Symbiodiniumgenotype (in the case of A. valida). In case i) and iii) there was nonlinearitybetween relative electron transport rate (rETR) and grossphotosynthesis measurements at moderate to high irradiances possiblydue to vertical heterogeneity of the symbionts in the tissue and/or theoperation of an alternative electron pathway such as cyclic electron flowaround PSII. Case ii) demonstrated that Symbiodinium ingested byciliates are photosynthetically competent and do not becomecompromised during the progression of the brown band zone. In contrastto case i) and iii) the symbionts produced relatively high grossphotosynthesis rate and rETR at moderate to high irradiance due togreater efficiency of light absorption caused by a higher density ofsymbionts in the ciliate.

AB - Corals associate with a diverse microbial assemblage of whichendosymbiotic and phototrophic microalgae, i.e. dinoflagellatesbelonging to the genetically diverse genus Symbiodinium, are bestknown. Traditional techniques to estimate photosynthesis activity suchas oxygen exchange and 14C-incorporation of Symbiodinium areconfounded by processes due to the coral host. In three case studies weemployed a novel approach using two technologies that enabledifferentiation of the photosynthesis activity of Symbiodinium, pulseamplitude-modulation (PAM) and O2 microsensors. The case studiesincluded i) monotypic Symbiodinium associating with a coral(Pocillopora damicornis), ii) a ciliate forming a brown band on the coralAcropora muricata, and iii) a genotypically diverse Symbiodiniumassociation with Acropora valida. In all instances, the combination offibre-optic technology and an O2 microelectrode enabled parallelmeasurements of gross photosynthesis rate and photosystem II quantumyield at the coral surface under steady-state conditions as a function ofincreasing irradiances. The studies showed large plasticity in photophysiologicalacclimation of Symbiodinium linked to light microclimateas well as motility (in the case of the ciliate) and Symbiodiniumgenotype (in the case of A. valida). In case i) and iii) there was nonlinearitybetween relative electron transport rate (rETR) and grossphotosynthesis measurements at moderate to high irradiances possiblydue to vertical heterogeneity of the symbionts in the tissue and/or theoperation of an alternative electron pathway such as cyclic electron flowaround PSII. Case ii) demonstrated that Symbiodinium ingested byciliates are photosynthetically competent and do not becomecompromised during the progression of the brown band zone. In contrastto case i) and iii) the symbionts produced relatively high grossphotosynthesis rate and rETR at moderate to high irradiance due togreater efficiency of light absorption caused by a higher density ofsymbionts in the ciliate.

M3 - Conference abstract for conference

T2 - 11th International Coral Reef Symposium

Y2 - 7 July 2008 through 11 July 2008

ER -