Aragonite infill in overgrown conceptacles of coralline Lithothamnion spp. (Hapalidiaceae, Hapalidiales, Rhodophyta): new insights in biomineralization and phylomineralogy

Abstract

New empirical and quantitative data in the study of calcium carbonate biomineralization and an expanded coralline psbA framework for phylomineralogy are provided for crustose coralline red algae. Scanning electron microscopy (SEM) and energy dispersive spectrometry (SEM-EDS) pinpointed the exact location of calcium carbonate crystals within overgrown reproductive conceptacles in rhodolith-forming Lithothamnion species from the Gulf of Mexico and Pacific Panama. SEM-EDS and X-ray diffraction (XRD) analysis confirmed the elemental composition of these calcium carbonate crystals to be aragonite. After spore release, reproductive conceptacles apparently became overgrown by new vegetative growth, a strategy that may aid in sealing the empty conceptacle chamber, hence influencing the chemistry of the microenvironment and in turn promoting aragonite crystal growth. The possible relevance of various types of calcium carbonate polymorphs present in the complex internal structure and skeleton of crustose corallines is discussed. This is the first study to link SEM, SEM-EDS, XRD, Microtomography and X-ray microscopy data of aragonite infill in coralline algae with phylomineralogy. The study contributes to the growing body of literature characterizing and speculating about how the relative abundances of carbonate biominerals in corallines may vary in response to changes in atmospheric pCO2 , ocean acidification, and global warming.

Eukaryotic Life Inhabits Rhodolith-forming Coralline Algae (Hapalidiales, Rhodophyta), Remarkable Marine Benthic Microhabitats

“…Because they precipitate calcium carbonate within their organic cell walls as Ca(Mg)CO 3 , a highly soluble, high-magnesium calcite polymorph123, coralline red algae are currently popular experimental subjects of many ecological and mineralogical studies that address the potential effects of ocean acidification and global warming on calcifying organisms2456. It is well known that the CaCO 3 in the cell walls provides the coralline algae several advantages such as rigidity, skeletal strength, protection from grazing and boring animals, and enhanced survivorship by increasing resistance to wave action7.…”

Anatomical structure overrides temperature controls on magnesium uptake – calcification in the Arctic/subarctic coralline algae <i>Leptophytum laeve</i> and <i>Kvaleya epilaeve</i> (Rhodophyta; Corallinales)

“…There is a burgeoning interest in using coralline crusts as environmental proxies for late Holocene temperature (Hetzinger et al, 2009;Gamboa et al, 2010;Halfar et al, 2010), Arctic ice sheet coverage (Halfer et al, 2013) and pH changes with time (Krayesky-Self et al, 2016). Typically magnesium content is used as a key indicator of late Holocene temperature fluctuations ).…”

Molecular and Morphological Diversity of Lithothamnion spp. (Hapalidiales, Rhodophyta) from Deepwater Rhodolith Beds in the Northwestern Gulf of Mexico

“…J (Fig. 15) illustrate the infill of spherical masses that were confirmed with analyses of SEM-EDS (energy dispersive spectrometry) and x-ray diffraction data to be aragonite (Krayesky-Self et al 2016). This infilling has been speculated to be associated with the development of the secondary hypothallium that grows over empty conceptacles (KrayeskySelf et al 2016), shown herein to be a common developmental pattern in Lithothamnion.…”

“…The NWGMx offshore Louisiana harbors subtidal rhodolith beds at depths of 45-80m comprising a diverse assemblage of non-geniculate coralline algae spanning all three orders Corallinales, Sporolithales and Hapalidiales , Krayesky-Self et al 2016, Richards 2016. These rhodolith communities consist of free-living marine nodules primarily accreted by coralline algae precipitating calcium carbonate, the biogenic rhodoliths (Foster 2001), and secondarily colonized nodules of geobiological origin, referred to as autogenic rhodoliths .…”