Calcein labelling and electrophysiology: insights on coral tissue permeability and calcification

Abstract

The mechanisms behind the transfer of molecules from the surrounding sea water to the site of coral calcification are not well understood, but are critical for understanding how coral reefs are formed. We conducted experiments with the fluorescent dye calcein, which binds to calcium and is incorporated into growing calcium carbonate crystals, to determine the permeability properties of coral cells and tissues to this molecule, and to determine how it is incorporated into the coral skeleton. We also compared rates of calcein incorporation with rates of calcification measured by the alkalinity anomaly technique. Finally, by an electrophysiological approach, we investigated the electrical resistance of coral tissues in order to better understand the role of tissues in ionic permeability. Our results show that (i) calcein passes through coral tissues by a paracellular pathway, (ii) intercellular junctions control and restrict the diffusion of molecules, (iii) intercellular junctions should have pores of a size higher than 13 Å and lower than 20 nm, and (iv) the resistance of the tissues owing to paracellular junctions has a value of 477 + 21 Ohm cm 2 . We discuss the implication of our results for the transport of calcium involved in the calcification process.

Multiple driving factors explain spatial and temporal variability in coral calcification rates on the Bermuda platform

“…Though experiments employing calcein dye to measure intra-annual extension are becoming increasingly common in laboratory experiments, application of this method to in situ experiments has remained relatively limited until recently (Tambutte et al 2011;Holcomb et al 2013). To and dark (dashed) treatments for the two sample species Porites astreoides (light gray) and Diploria strigosa (dark gray).…”

Corals concentrate dissolved inorganic carbon to facilitate calcification

“…Corals were analysed in duplicate (indicated by 1 or 2 annotation). Analyses (7)(8)(9)(10)(11)(12)(13)(14)(15)(16) were collected on each sample (Table 1) with the exceptions of RR 3.7 mM 2 and RR 5.3 mM 1 where only 2 and 1, respectively, credible d 11 B analysis (exhibiting the 42 Ca spike throughout the analysis) were obtained. Errors are calculated as for the field corals and horizontal lines denote seawater concentrations calculated from observations of pH and TA in the culture seawater 22 .…”

“…There are no known active transport mechanisms for boron in corals and we assume that dissolved boron is transported to the ECF in seawater. Seawater transport to the ECF is a passive process 8 and as such the transport rate is likely to be constant. At equilibrium, B(OH) 3 is enriched in 11 B compared with B(OH) 4 À (ref.…”

Reconsidering the role of carbonate ion concentration in calcification by marine organisms

“…Some foraminifera and coral species have been reported to transfer calcification-relevant ions to the site of CaCO 3 precipitation by means of seawater transport (Bentov et al, 2009;de Nooijer et al, 2009;Gagnon et al, 2012;Tambutté et al, 2012). In the case of foraminifera, seawater is engulfed in membrane vesicles, transported to the site of calcification, and on its way alkalized to increase [CO 2− 3 ] (Bentov et al, 2009;de Nooijer et al, 2009).…”

“…In the case of foraminifera, seawater is engulfed in membrane vesicles, transported to the site of calcification, and on its way alkalized to increase [CO 2− 3 ] (Bentov et al, 2009;de Nooijer et al, 2009). In the case of corals, seawater (or at least its constituents smaller than 20 nm; Tambutté et al, 2012) may pass epithelia and reach the CaCO 3 skeleton via the paracellular pathway. For both processes (seawater endocytosis and seawater leakage along the intercellular space), all DIC species are potential inorganic carbon sources to fuel calcification.…”