A microsensor study of light enhanced Ca2+ uptake and photosynthesis in the reef-building hermatypic coral Favia sp.

Abstract

The coupling between CO2 and Ca2+ exchange and photosynthesis by corals (Favia sp.) was studied with microsensors for Ca2+, 02, pH and COz. The profiles of these compounds, measured perpendicular on the coral surface, were strongly influenced by light. During illumination, the concentration of O2 and the pH at the polyp surface was higher than in the surrounding seawater, while the concentrations of Ca2+ and CO2 were lower. In the dark the inverse was observed. Furthermore, simultaneous recordmg of concentration changes at the coral surface, in response to light and inhibitors, were performed with pairs of the sensors. The concentration changes of CO2 and pH were slow, while those of Ca2+ and O2 were immediate and fast. The concentration changes of the O2 and Ca2+ concentrations at the coral surface were synchronous in response to changes in light condtions and to inhibition of the photosynthesis. Also, the spatial distribution of photosynthetic activity over a single polyp coincided with the distribution of CaZ' concentration changes. These results show that Ca2+ dynamlcs at the polyp surface is not an indirect effect of increased CaC03 precipitation at the skeleton, but ~n d icates the presence of a Ca2+ uptake mechanism that is directly correlated to photosynthesis. Inhibition of carbonic anhydrase strongly decreased photosynthesis, especially at higher light intensihes. This, comb~ned with the observed increase in CO2 concentration changes and absolute increase in CO2 concentration at the tissue surface, demonstrated the importance of carbonic anhydrase for C02/D1C uptake and transport to the site of photosynthesis.

Calcification acidifies the microenvironment of a benthic foraminifer (Ammonia sp.)

“…Temperature and pH (total scale) in the bulk seawater were measured using a micro-thermometer and a handheld pH meter (WTW pH 330i), respectively. pH LIX (precision 0.005), Ca 2+ LIX (precision 5 μM), and glass pH microelectrodes (precision 0.001) were prepared, calibrated and used as previously described (Ammann et al, 1987;De Beer, 2000;De Beer et al, 2000;Revsbech and Jorgensen, 1986). A detailed description of the measurement setup can be found in Polerecky et al (2007).…”

Evidence for water-mediated mechanisms in coral–algal interactions

“…Oxygen profiles were run at three positions in a random order along an axis perpendicular to the interaction boundary (i) apparently healthy Porites tissue 1 cm away from the interaction boundary ('coral'), (ii) the interface between Porites and the competitor ('interface'), and (iii) apparently healthy tissue of the competitor 1 cm away from the interface ('competitor'; electronic supplementary material, figure S1a). Measurements on coral tissue were exclusively conducted on the coenosarc (tissue between polyps) in order to minimize the influence of tissue movement [36] and the spatial heterogeneity of coral photosynthesis [25]. The microsensor was oriented vertically.…”

Effects of changing seawater temperature on photosynthesis and calcification in the scleractinian coral <i>Galaxea fascicularis</i>, measured with O₂, Ca²⁺ and pH microsensors

“…A better comparison of experiments became possible through the use of microcolonies originating from the same parent colony (Al-Moghrabi et al, 1993). The new application of microsensors permitted the measurement of many parameters at a µm scale and with high spatial and temporal resolution (De Beer et al, 2000;Kühl et al, 1995;Al-Horani et al, 2003a;Al-Horani et al, 2003b;Al-Horani et al, 2005). In this study, the two advancements were combined to investigate the impact of temperature on the physiology of the scleractinian coral Galaxea fascicularis.…”