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Water flow enhances coral photosynthesis by stimulating CO2 uptake

By Tim Wijgerde, Ph.D. Posted Apr 25, 2017 09:00 AM
"Go with the flow" can be good advice sometimes. This holds especially true for reef–building corals, which require constant water flow to stay healthy. This is because water flow affects many processes in corals, including gas exchange, heat dissipation and nutrient supply.
Water flow enhances coral photosynthesis by stimulating CO2 uptake

By incubating corals in so–called respiration cells, we can manipulate a host of factors to determine how corals respond to their environment.

A few years ago, scientists discovered that water flow enhances photosynthesis in the stony coral Favia veroni by removing excess oxygen produced under light conditions. When oxygen accumulates in coral tissue, it becomes toxic and disrupts photosynthesis via a complex process known as photorespiration.

This week, my colleagues from Wageningen University and I published yet another chapter about corals and water flow. We also discovered that increasing water flow around a stony coral (Galaxea fascicularis) enhances photosynthesis, but only when seawater pH is decreased by adding carbon dioxide (CO2). This makes sense, as carbon dioxide is used by the coral’s zooxanthellae to produce sugars and other nutritious compounds during photosynthesis. Thus, water flow can remove excess photosynthesis products such as oxygen, but at the same time provide substrates such as carbon dioxide. Although carbon dioxide is essential to corals and their symbiotic zooxanthellae, our increasing CO2 emissions are acidifying seawater too dramatically, with negative effects on coral growth.

We also discovered that G. fascicularis is one of the most efficient light collectors in the coral world, with efficient photosynthesis and high growth under low light levels (PAR of 39 μmol quanta m-2 s-1). Our results have been published by the Journal of Experimental Biology.

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Galaxea fascicularis is a highly efficient light collector, providing its symbiotic zooxanthellae with a effective environment for photosynthesis.

References

  1. Mass T, Genin A, Shavit U, Grinstein M, Tchernov D (2010) Flow enhances photosynthesis in marine benthic autotrophs by increasing the efflux of oxygen from the organism to the water. Proceedings of the National Academy of Sciences of the USA 107:2527–2531
  2. Osinga R, Derksen-Hooijberg M, Wijgerde T, Verreth JAJ (2017) Interactive effects of oxygen, carbon dioxide and flow on photosynthesis and respiration in the scleractinian coral Galaxea fascicularis. Journal of Experimental Biology 2017 : doi: 10.1242/jeb.140509
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