Through the Guam Ecosystems Collaboratorium for Corals and Oceans (GECCO) funded by NSF EPSCoR, University of Guam researchers are investigating the genetic diversity of reef builders at the species and population level. Mastophora is a broadly distributed genus of calcified red macroalgae and consists of three well-characterized species. Mastophora rosea (C.Agardh) Setchell is the type species of the genus with a type locality in Guam. So far, researchers have discovered a number of new Mastophora species for Guam. The morphology, anatomy, and genetics of these species are now being compared to known species using a variety of modern techniques, including micro-computed tomography.

X-Ray Microscopy Imaging of Calcified Algae

This month we imaged a sample of Mastophora rosea algae provided by the University of Guam using the SkyScan 2214 nano-CT. As can be seen from the view in Figure 1 above, the high-resolution setup of the SkyScan 2214 allowed us to microscopically examine the calcified algae sample. Specifically, reproductive conceptacles are visible with great detail, including visualization of each ostiole.

Unlike all our desktop systems, which utilize micro-focused sealed X-ray sources, the SkyScan 2214 utilizes a nano-focused X-ray source with the ability to switch between tungsten and Lab6 filaments. For the highest resolution applications, the Lab6 electron cathode utilizes a crystal of lanthanum hexaboride at the tip of the filament, which produces a higher flux of more focused electrons than a standard tungsten filament. The smaller the spot size of electrons striking the tungsten target within the X-ray source, the finer resolution achievable in the results.

As shown in Figure 2, while the sample is not particularly planar, DataViewer allows us to examine the fine porous structure present in the walls of the sample. The thin algae walls are highly porous but are well resolved using the SkyScan 2214.

In examining the dataset in 3D using CTVox, the ability to orient and rotate the sample as needed allows us to explore several conceptacles located within our imaging data (Figure 3). We also observe some calcified deposits present on the surface of the algae, which show up as bright protrusions from the surface of the sample.

Using CTAn, the thickness of the walls within the algae sample were examined (Figure 4). The results of this analysis were exported and visualized using a color-coded representation of thickness within CTVox. The thickest portions of the sample walls lie where the calcified deposits are present on the surface of the structure. The average thickness of the wall structures was determined to be 12.3 ± 6.1 µm for this region of the sample.

Conclusion

The introduction of the SkyScan 2214 nano-CT into the Micro Photonics imaging laboratory expands the scope of projects that can be examined via x-ray microscopy, especially for lower density samples where the highest resolutions are required. The Mastophora rosea algal sample examined in this project is a great illustration for the type of high-resolution imaging possible in examining the fine features present in the sample. We hope you found this Image of the Month informative and encourage you to subscribe to our newsletter and social media channels in preparation for the continuation of our image of the month series next month.

Scan Specifications

These scans were completed on our SkyScan 2214 nano-CT system at the Micro Photonics Imaging Laboratory in Allentown, PA. Reconstructions were completed using NRecon while visualization and volumetric analysis of the 2D and 3D results were completed using Dataviewer, CTVox, and CTAn.

Micro Photonics would like to thank the University of Guam for providing the sample used in this article.

For more information on the sample, please contact:

Tom Schils and Terry Donaldson, Guam NSF EPSCoR & Marine Laboratory, University of Guam
Sample: Mastophora rosea (C.Agardh) Setchell from Pago Bay, Guam

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