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

Research output: Contribution to conferenceConference abstract for conferenceResearch

  • Karin Elizabeth Ulstrup
  • Kuhl, Michael
  • Peter Ralph
  • Madeleine Van Oppen
  • David Bourne

Corals associate with a diverse microbial assemblage of which

endosymbiotic and phototrophic microalgae, i.e. dinoflagellates

belonging to the genetically diverse genus Symbiodinium, are best

known. Traditional techniques to estimate photosynthesis activity such

as oxygen exchange and 14C-incorporation of Symbiodinium are

confounded by processes due to the coral host. In three case studies we

employed a novel approach using two technologies that enable

differentiation of the photosynthesis activity of Symbiodinium, pulseamplitude-

modulation (PAM) and O2 microsensors. The case studies

included i) monotypic Symbiodinium associating with a coral

(Pocillopora damicornis), ii) a ciliate forming a brown band on the coral

Acropora muricata, and iii) a genotypically diverse Symbiodinium

association with Acropora valida. In all instances, the combination of

fibre-optic technology and an O2 microelectrode enabled parallel

measurements of gross photosynthesis rate and photosystem II quantum

yield at the coral surface under steady-state conditions as a function of

increasing irradiances. The studies showed large plasticity in photophysiological

acclimation of Symbiodinium linked to light microclimate

as well as motility (in the case of the ciliate) and Symbiodinium

genotype (in the case of A. valida). In case i) and iii) there was nonlinearity

between relative electron transport rate (rETR) and gross

photosynthesis measurements at moderate to high irradiances possibly

due to vertical heterogeneity of the symbionts in the tissue and/or the

operation of an alternative electron pathway such as cyclic electron flow

around PSII. Case ii) demonstrated that Symbiodinium ingested by

ciliates are photosynthetically competent and do not become

compromised during the progression of the brown band zone. In contrast

to case i) and iii) the symbionts produced relatively high gross

photosynthesis rate and rETR at moderate to high irradiance due to

greater efficiency of light absorption caused by a higher density of

symbionts in the ciliate.

Original languageEnglish
Publication date2008
Publication statusPublished - 2008
Event11th International Coral Reef Symposium - Fort Lauderdale, Florida, United States
Duration: 7 Jul 200811 Jul 2008

Conference

Conference11th International Coral Reef Symposium
CountryUnited States
CityFort Lauderdale, Florida
Period07/07/200811/07/2008

ID: 5467230