Mineral formation in the primary polyps of pocilloporoid corals

Abstract

In reef-building corals, larval settlement and its rapid calcification provides a unique opportunity to study the bio-calcium carbonate formation mechanism involving skeleton morphological changes. Here we investigate the mineral formation of primary polyps, just after settlement, in two taxa of the pocilloporoid corals: Stylophora pistillata (Esper, 1797) and Pocillopora acuta (Lamarck, 1816). We show that the initial mineral phase is nascent Mg-Calcite, with rod-like morphology in P. acuta, and dumbbell morphology in S. pistillata. These structures constitute the first layer of the basal plate which is comparable to Rapid Accretion Deposits (Centers of Calcification, CoC) in adult coral skeleton. We found also that the rod-like/dumbbell Mg-Calcite structures in subsequent growth step may merge into larger aggregates by deposition of aragonite needles. Our results suggest that a biologically controlled mineralization of initial skeletal deposits (CoC) occurs in three steps: first, vesicles filled with divalent ions are formed intracellularly. These vesicles are then transferred to the calcification site, forming nascent Mg-Calcite rod/pristine dumbbell structures. During the third step, aragonite crystals may develop between these structures forming spherulite-like aggregates.

Optimization of skeletal protein preparation for LC-MS/MS sequencing yields additional coral skeletal proteins inStylophora pistillata

“…Vesicles were previously identified in corals [72, 73]; however, their origin and content was not detailed and they are sometimes attributed to preservation byproducts. These intracellular ion-rich vesicles may endocytose sea water [74], after which they are enriched in carbonate ions and then form hydrated ACC and anhydrous ACC precursors stabilized by acidic biomolecules including CARPs [75]. Using cell cultures, Mass et al [61] suggest that the vesicles, which contain Asp rich proteins, then transport their contents to the ECM, releasing their content by exocytosis.…”

Light-induced polyp retraction and tissue rupture in the photosensitive, reef-building coral Acropora muricata

“…Despite using low excitation power, Acropora muricata was particularly susceptible to CLSM. Quantitative comparisons to previous studies using conventional microscopy (WFM, CLSM and spinning disk confocal) for live imaging of Montipora capitata (Caldwell et al, 2017;Nielsen et al, 2018), Acropora digitifera (Ohno et al, 2017), Pocillopora damicornis and Stylophora pistillata (Mullen et al, 2016;Neder et al, 2019;Shapiro et al, 2016;Venn et al, 2009;Venn et al, 2011;Venn et al, 2013) was not possible as no power measurements were reported. Substantial differences in phototolerance may exist between different species.…”

“…They can also recover rapidly from environmental disturbances, making them important re-colonisers (Sweatman et al, 2011). Rather than using cell or tissue culture-based samples (Mass et al, 2012), single primary polyps (Neder et al, 2019;Ohno et al, 2017) or single polyps obtained through bail-out techniques (Shapiro et al, 2016), we here use small coral colonies with multiple polyps and a shared gastrovascular cavity. They allow the study of systemic responses in an unstressed, fully established colony.…”

“…In particular, fluorescence microscopy can reveal a lot, since it opens up the possibility to use coral tissue autofluorescence as a non-invasive, intrinsic marker of health and disease (Caldwell et al, 2017;Kenkel et al, 2011) and the monitoring of chlorophyll autofluorescence of the photosynthetic symbionts embedded in the coral tissue (Mullen et al, 2016;Shapiro et al, 2016). Fluorescent dyes can also be used in live imaging (Neder et al, 2019;Ohno et al, 2017;Venn et al, 2009). So far, only conventional techniques have been used to image live coral fluorescence on the cellular scale.…”

“…Confocal laser scanning microscopy (CLSM) of live polyps has been used in Montipora capitata at different spatial scales, to characterize overall diversity of natural fluorescence and to spatially localize the arrangement of fluorescent pigments (Caldwell et al, 2017). Inverted microscopy from below has been used to image several microns deep into the calcifying layers (Neder et al, 2019;Ohno et al, 2017;Shapiro et al, 2016;Venn et al, 2011). The approach works well when the main interest lies in the calcification of the flat bottom layer.…”