Distribution of Algal Photosynthates As Seen Using Planar Optodes Allison Gregg 3/5/11

Background on Coral-Algal Interactions  Coral reefs filled with great diversity of organisms  Corals around the world are succumbing to environmental stressors  How is algae playing a part? Top: Bottom:

What is Really Going On?  Microprobes have shown that coral-algae interaction zones are hypoxic  Leads to coral disease  What is the mechanism behind this? -microbe mediated? -or something else?  Planar optodes as a way to visualize what is happening Jennifer Smith,

What Are Planar Optodes?  a type of optical sensor used for visualizing various analyte concentrations  Able to visualize two dimensional space as opposed to electrodes  used for O 2, CO 2, pH, temperature ~2 cm

^Oxygen bubbled water^ ^Nitrogen bubbled water^ How Do Oxygen Optodes Work?  Oxygen optode is made from a cocktail consisting of PtOEP indicator and coumarin antenna dye, immobilized in a polystyrene matrix  PtOEP signal is chemically dependent on analyte concentration; coumarin signal is independent of analyte  Analyte concentration calculated from ratio of fluorescence intensity of indicator: antenna

Experimental Design  Original Hypothesis: Increase of flow leads to increased rates of photosynthesis in coral and macro algae  First, turf algae was placed in a chamber with no flow to determine baseline measurements of photosynthesis  What we found was surprising…

Algae After Being Exposed to Light for Two Hours:

Would We Get the Same Outcome with Flow?  Macro algae was put in front of optode sheet too see how oxygen was distributed in response to flow  Was there more diffusion through environment?

When a Photosynthesizing Algae is Exposed to Flow

What Does This Mean?  Oxygen released from algae during photosynthesis in discrete region- no diffusion  Respiration of algae from all around surrounding area  New Hypothesis: The distinct oxygen gradients produced from algae suggest that the position of coral to algae relative to direction of flow could play a part in the hypoxia along an interface.

The Next Step  Does this pattern of distribution occur in other algae species or coral?  Glucose optode to see if DOC is released in same pattern as oxygen  Field work to see if these patterns at interaction zones can be seen in situ  Can a relationship between prevalence of coral disease and positioning of algae up current or down current from coral be found?

Acknowledgements  Thanks to:  Forest Rohwer  Rohwer Labbies  Andi Haas  Morten Larsen  Ronnie Glud  Sergey Borisov  Jen Smith  Mark Hatay  Peter Salamon  Anca Segall  Undergraduate Biomath group  Funding:  NSF-funded STEM Scholarship  National Science Foundation

Ratio to Concentration  Ratio= (R-G)/G  This ratio is then used to determine the concentration using the Stern-Volmer equation:  C= (R 0 -R)/(Ksv(R 0 -R*  )

How Does Math Come into Play?  Actual concentration of oxygen is determined by using the modified Stern- Volmer equation: - R/R 0 =(f/1+Ksv 1 [O 2 ] + (f-1)/ 1+Ksv 2 [O 2 ]) Where f is the unquenchable fraction of the optode, R is the ratio at a certain [O2], R0 is ratio at anoxia, Ksv2=0, and Ksv1 is the slope of the line R0/R vs [O2]