Modern stromatolite phototrophic communities: a comparative study of procaryote and eucaryote phototrophs using variable chlorophyll fluorescence

Abstract

Stromatolites are laminated organosedimentary structures formed by microbial communities, principally cyanobacteria although eucaryote phototrophs may also be involved in the construction of modern stromatolites. In this study, productivity and photophysiology of communities from stromatolites (laminated) and thrombolites (nonlaminated) were analysed using fluorescence imaging. Sub-samples of mats were excised at Highborne Cay, Bahamas, and cross-sectioned to simultaneously analyse surface, near-surface (1-2 mm), and deeper (2-10 mm) communities. Rapid light curve parameters and nonphotochemical downregulation showed distinct differences between phototroph communities, consistent with the reported quasi-succession of classic stromatolite mat types. Greater productivity was shown by cyanobacteria in Type 1 and Type 3 mats (first and final stage of the succession, Schizothrix gebeleinii and Solentia sp. respectively) and lower productivity within Type 2 mats (intermediate mat type). Eucaryote mat types, dominated by stalked (Striatella sp. and Licmophora sp.) and tube-dwelling (e.g. Nitzschia and Navicula spp.) diatoms, showed greater productivity than cyanobacteria communities, with the exception of Striatella (low productivity) and an unidentified coccoid cyanobacterium (high productivity). Findings indicate comparative variability between photosynthetically active procaryote and eucaryote sub-communities within stromatolites, with a pattern logically following the succession of 'classic' mat types, and lower than the productivity of eucaryote dominated 'nonclassic' mat types.

Environmental influences on living marine stromatolites: insights from benthic microalgal communities

“…The result has been comparatively few studies portraying the ecological role of stromatolite communities in their modern environments. Perkins and colleagues () investigated this ecological dynamic in terms of the physiology of stromatolite algal communities. They, informatively, demonstrated that pioneer and successional cyanobacterial mat types had higher productivity than their intermediate mat communities, but still lower productivity than eukaryote‐dominated (diatoms, specifically) stromatolite mats (Perkins et al ., ).…”

“…Perkins and colleagues () investigated this ecological dynamic in terms of the physiology of stromatolite algal communities. They, informatively, demonstrated that pioneer and successional cyanobacterial mat types had higher productivity than their intermediate mat communities, but still lower productivity than eukaryote‐dominated (diatoms, specifically) stromatolite mats (Perkins et al ., ). This suggests an important role for stromatolite communities in coastal systems, especially in terms of the productivity input from different algal groups.…”

“…Understanding the factors controlling the relationship between these two autotroph groups is important from a geological perspective in terms of stromatolite layering (Bowlin et al ., ) as well as community succession in intertidal versus sub‐tidal habitats (Awramik and Riding, ). Additionally, the observed variability in prokaryote and eukaryote productivity in stromatolite communities (Perkins et al ., ) highlights the importance of these two algal groups in terms of trophic dynamics in these rare coastal ecosystems.…”

“…Knowledge of the drivers controlling algal composition in these pools will contribute towards contextualizing the modern South African stromatolites compared with marine stromatolites elsewhere in the world, particularly those in the Bahamas and Shark Bay. This would be expected to provide insight into how the dynamic environmental conditions of the intertidal zone affect the structure of the algal stromatolite community, and thereby its productivity (Perkins et al ., ) and sediment trapping efficiency (Awramik and Riding, ; Frantz et al ., ).…”

Comparative metagenomics unveils functions and genome features of microbialite‐associated communities along a depth gradient

“…Comparatively, microbial eukaryotes are less-well studied. Nonetheless, metabarcoding and imaging approaches suggest that they are moderately abundant and diverse in microbialites from Cuatro Ci enegas (Breitbart et al, 2009), lake Alchichica (Couradeau et al, 2011;Sagha€ ı et al, 2015), and several marine stromatolites (Al-Qassab et al, 2002;Perkins et al, 2012;Bernhard et al, 2013;Mobberley et al, 2013;Edgcomb et al, 2014). Metagenomics can, via the direct sequencing of environmental DNA, inform about the metabolic potential of natural communities (Tringe and Rubin, 2005;Dinsdale et al, 2008).…”