Photoinhibition of photosynthesis is reduced by water flow in the reef-building coral Acropora digitifera

Abstract

While photosynthesis of symbiotic algae is essential for reef-building corals, excess irradiance inhibits photosynthesis through photoinhibition, which can lead to coral bleaching under elevated temperature conditions. Here we show that water flow reduces photoinhibition of in hospite endosymbionts in the coral Acropora digitifera. Diurnal monitoring of chlorophyll fluorescence, under 2 different flow regimes (< 3 and 20 cm s -1 flow rates) in an outdoor aquarium, showed reduced photoinhibition, but only under moderate flow conditions (20 cm s -1 ). Experimental (laboratory) measurements, on time scales ranging from minutes to hours, showed that flow-mediated reductions in photoinhibition occurred not by enhancing recovery of the damaged photosystem, but rather through inducing differential photodamage. Moreover, experiments involving sequential light oscillations (500/20 and 1000/20 µmol photons m -2 s -1 ) at 3 flow regimes, < 3, 10, and 20 cm s -1 , on a time scale ranging from hours to days, revealed water-velocity-dependent reductions of dynamic photoinhibition. These results, on time scales ranging from minutes to weeks, confirm that reduced water flow amplifies photodamage of algal photosynthesis under strong irradiance, which in turn affects coral tolerance to strong irradiance and temperature.

Spectral Reflectance of Palauan Reef-Building Coral with Different Symbionts in Response to Elevated Temperature

“…This same trend was also observed after a thermal stress event in 2010 [51]. Increased heat and high irradiance can act synergistically to induce coral bleaching [2,[66][67][68][69][70]. Both studies attributed the relative resilience of the bay communities to thermal resistance in the animal and symbionts, and reduced irradiance due to high light attenuation in bay water compared to the clear oceanic waters found at fringe and patch reef sites.…”

Interactive effects of oxygen, carbon dioxide and flow on photosynthesis and respiration in the scleractinian coral Galaxea fascicularis

“…Several authors have reported positive effects of water flow on photosynthesis in corals (Dennison and Barnes, 1988;Lesser et al, 1994;Nakamura et al, 2005;Finelli et al, 2006;Mass et al, 2010;Schutter et al, 2011). In a flume experiment with Galaxea fascicularis, Schutter et al (2011) found an instantaneous increase in photosynthesis upon an increase in flow velocity from 5 to 20 cm s −1 , which supports the idea that the effects of flow on photosynthesis are related to an improved exchange of dissolved gases.…”

“…In a flume experiment with Galaxea fascicularis, Schutter et al (2011) found an instantaneous increase in photosynthesis upon an increase in flow velocity from 5 to 20 cm s −1 , which supports the idea that the effects of flow on photosynthesis are related to an improved exchange of dissolved gases. However, it remains unclear whether this flow effect relates to a higher influx of carbon dioxide into the coral tissue (Dennison and Barnes, 1988;Lesser et al, 1994) or to a higher efflux of oxygen out of the coral tissue (Nakamura et al, 2005;Finelli et al, 2006;Mass et al, 2010;Schutter et al, 2011). Mass et al (2010) demonstrated that the onset of flow led to a decrease of oxygen supersaturation from 500% to 200% inside illuminated tissue of the scleractinian coral Favia veroni.…”

Palau’s coral reefs show differential habitat recovery following the 1998-bleaching event

“…Recently, it has been shown that the interrelatedness of temperature and light has reciprocal effects, whereby the increase in temperature under high light conditions will be perceived by the symbionts as an increase in light stress, and vice versa (Iglesias-Prieto et al 2004;Takahashi et al 2004;Nakamura et al 2005). Figure 4 shows the considerably reduced scalar irradiance in Nikko Bay, compared with that at the Outer Eastern Reef site where the attenuation is more characteristic of a clear oceanic water type (Kirk 1994).…”