Microbes and mass extinctions: paleoenvironmental distribution of microbialites during times of biotic crisis

Abstract

Widespread development of microbialites characterizes the substrate and ecological response during the aftermath of two of the 'big five' mass extinctions of the Phanerozoic. This study reviews the microbial response recorded by macroscopic microbial structures to these events to examine how extinction mechanism may be linked to the style of microbialite development. Two main styles of response are recognized: (i) the expansion of microbialites into environments not previously occupied during the pre-extinction interval and (ii) increases in microbialite abundance and attainment of ecological dominance within environments occupied prior to the extinction. The Late Devonian biotic crisis contributed toward the decimation of platform margin reef taxa and was followed by increases in microbialite abundance in Famennian and earliest Carboniferous platform interior, margin, and slope settings. The end-Permian event records the suppression of infaunal activity and an elimination of metazoan-dominated reefs. The aftermath of this mass extinction is characterized by the expansion of microbialites into new environments including offshore and nearshore ramp, platform interior, and slope settings. The mass extinctions at the end of the Triassic and Cretaceous have not yet been associated with a macroscopic microbial response, although one has been suggested for the end-Ordovician event. The case for microbialites behaving as 'disaster forms' in the aftermath of mass extinctions accurately describes the response following the Late Devonian and end-Permian events, and this may be because each is marked by the reduction of reef communities in addition to a suppression of bioturbation related to the development of shallow-water anoxia.

Coexisting living stromatolites and infaunal metazoans

“…Metazoans certainly contributed towards the decline of the microbialites (Buatois et al 2014;Mata and Bottjer 2012), particularly the stromatolites, and their exclusion in modern habitats has enabled some microbialites to thrive (Eckman et al 2008). However, the surprising coexistence of clearly layered stromatolites with active burrowing and grazing metazoans ( Fig.…”

“…While the factors driving historical stromatolite decline have been debated (Riding 2000), both geological evidence (Mata and Bottjer 2012;Walter and Heys 1985) and comparisons with modern microbialite analogues (Feldmann and McKenzie 1998;Garrett 1970) suggest that metazoans have a negative effect on stromatolite formation through grazing and burrowing. This has also been experimentally demonstrated, whereby estuarine cyanobacterial benthic mats form Abstract Microbialites, bioaccretionary structures formed during the growth and metabolism of microorganisms (principally cyanobacteria) were the dominant lifeform in shallow late-Archean and Proterozoic oceans.…”

“…Consequently, most modern stromatolites are restricted to marginal, harsh environments where metazoans are largely excluded (Grotzinger and Knoll 1999;Riding 2011), whereas in the presence of metazoans, thrombolites (clotted microbialites) rather than laminated stromatolites may form (Feldmann and McKenzie 1998;Konishi et al 2001;Planavsky and Ginsburg 2009;Walter and Heys 1985). Recently-discovered peritidal stromatolites along the southern African coastline (Perissinotto et al 2014;Rishworth et al 2016;Smith et al 2011) were used in this study to further assess metazoan coexistence and lamination in comparison to other modern stromatolites (Edgcomb et al 2014;Garcia-Pichel et al 2004;Tarhan et al 2013) in light of the ecologically and evolutionarily relevant metazoanstromatolite exclusion hypothesis (Garrett 1970;Mata and Bottjer 2012;Riding 2000;Walter and Heys 1985).…”

Boreal earliest Triassic biotas elucidate globally depauperate hard substrate communities after the end-Permian mass extinction

“…Certainly, some filter feeding organisms such as crinoids seem to have re-diversified earlier in the Boreal Realm (at least after the latest Induan A. fassaensis bivalve zone equivalent63), yet typical encrusters including cyclostome bryozoans and serpulid polychaetes did not fully re-establish until the Rhaetian64. This conspicuous underrepresentation – which is likely not taphonomic because Palaeozoic encrusters possessed similar calcitic skeletons65 and cemented to the substrate throughout the sessile phase of their life cycle – accords with extreme fluctuations in oceanic salinity66, de-oxygenation94067, intense weathering and run-off that are thought to have promoted widespread eutrophication and the proliferation of stromatolite-forming microbial substrates10112668 in the absence of mat-grazing organisms5569. Moreover, these markedly atypical conditions apparently favoured microconchids, which were ubiquitous across marine to brackish and even freshwater habitats367071 and readily colonized microbial/algal substrates, perhaps because of their stability and immediate supply of nutrients and oxygen3472.…”

Ultrastructures of porostromate microproblematica from a Mulde Event (Homerian, Silurian) bioherm in Podolia, Western Ukraine

“…associated them with an increase in nutrient supply which allows microbial communities to reach ecological dominance. The presence of microbialites in the early aftermath of carbon isotope excursions has been observed in other Palaeozoic events, such as near the late Silurian Lau Event (Calner 2005b), as well as other mass extinction events such as those in the End-Permian and late Devonian (Radionova & Einasto 1986;Nose et al 2006;Kershaw et al 2007;Mata & Bottjer 2012 and included references). The sedimentary succession discussed in the present study is rich in microproblematica, but as their affinity is not known, we cannot be sure they represent a microbialite.…”