Stromatolites made by photosynthetic cyanobacteria and other microorganisms.

iBase ID

181150

Creator

Edgcomb, Virginia P.

Title

Stromatolites made by photosynthetic cyanobacteria and other microorganisms.

Type

Still Image

Date

08/05/2011

File name

graphics/Australia_Genny_Edgcomb/DSC_2025.JPG

Notes

Microbial mats are conspicuous components of many benthic marine and aquatic settings. A subset of these microbial mats binds sediments to form potentially fossilizable structures, often called stromatolites or microbialites. While much is known about microbialite autotrophs, little is known about their heterotrophic eukaryotes. The lack of understanding is surprising given that stromatolites have an extensive geologic record spanning most of Earths history. Stromatolites are layered sedimentary structures formed by a combination of microbial activities, abiotic carbonate precipitation, and sedimentary processes. Details of stromatolite formation and preservation are poorly understood, and a drastic decline in stromatolite occurrence and diversity in the late Precambrian has long been a conundrum. A popular hypothesis to explain this decline at ~1 billion years ago is that eukaryotic organisms evolved to become predators on stromatolites. To date, the most commonly proposed predatory culprit is an unidentified metazoan, although evidence of such an organism is lacking from the fossil record. Protists, most of which are not expected to leave an obvious fossil record, are additional possible stromatolitic predators, but they have been largely ignored in this context. In light of preliminary results, we hypothesize that (1) Heterotrophic protist activity caused the textural change from stromatolites (layered sediment fabric) to thrombolites (clotted sediment fabric) and (2) Heterotrophic protists caused the decimation of Neoproterozoic stromatolites. It is impossible to recreate the Neoproterozoic, so studies of modern analogs must serve to indirectly test our hypotheses. The overall goal of this project is to describe the eukaryotic communities associated with modern stromatolites and thrombolites from the Bahamas and Australia, compare the communities from the two sites, and to relate the communities to stromatolitic / thrombolitic sediment fabric and biomarker signatures. The overall goal will be achieved by addressing the following specific aims: (1) Identify, via morphologic and molecular approaches, the eukaryotic community of modern stromatolites and thrombolites; (2) Analyze modern and fossil stromatolites and thrombolites for their eukaryotic lipid biomarkers using solvent extraction, chromatographic and mass spectrometric methods; (3) Using the Fluorescently Labeled Embedded Core (FLEC) method, document the sub-millimeter distributions of the heterotrophic eukaryotic community inhabiting modern stromatolites and thrombolites in conjunction with fine-scale sediment fabric; (4) Using solvent extraction, chromatographic and mass spectrometric methods, analyze cultures of allogromiid foraminifers to survey for lipid biomarkers unique to them; (5) After incubation of modern stromatolites with heterotrophic protists, use FLEC methodology to determine how their activity affects sediment fabric and conduct preliminary comparisons of these modern fabrics to those of stromatolite fossils.

Intellectual Merit: The oldest fossil stromatolites are &gt;3.4 billion years old and are the most visible manifestations of pervasive microbial life on the early Earth. The changes in stromatolite abundance and morphology document complex interplays between biological and geological processes. This project addresses multiple aspects of stromatolite genesis and pre-fossilization alteration but, at its core, focuses on one of the greatest geological enigmas: the possible connection between stromatolite decline and the rise of complex life.
Image Of the Day caption:
These rocky formations, called stromatolites, are made by photosynthetic cyanobacteria and other microorganisms. The microbes secrete compounds that bind sediment grains, creating a fine-layered mineral microfabric. Stromatolites were among the earliest life on Earth, and massive formations dominated shorelines starting about 3.5 billion years ago. About 1 billion years ago, their populations mysteriously plummeted; now they exist in only a few locations, like this one in Shark Bay, Australia. WHOI scientists Joan Bernhard and Virginia Edgcomb have investigated that decline, which occurred as more complex life forms were emerging.

Microbial mats are conspicuous components of many benthic marine and aquatic settings. A subset of these microbial mats binds sediments to form potentially fossilizable structures, often called stromatolites or microbialites. While much is known about microbialite autotrophs, little is known about their heterotrophic eukaryotes. The lack of understanding is surprising given that stromatolites have an extensive geologic record spanning most of Earths history. Stromatolites are layered sedimentary structures formed by a combination of microbial activities, abiotic carbonate precipitation, and sedimentary processes. Details of stromatolite formation and preservation are poorly understood, and a drastic decline in stromatolite occurrence and diversity in the late Precambrian has long been a conundrum. A popular hypothesis to explain this decline at ~1 billion years ago is that eukaryotic organisms evolved to become predators on stromatolites. To date, the most commonly proposed predatory culprit is an unidentified metazoan, although evidence of such an organism is lacking from the fossil record. Protists, most of which are not expected to leave an obvious fossil record, are additional possible stromatolitic predators, but they have been largely ignored in this context. In light of preliminary results, we hypothesize that (1) Heterotrophic protist activity caused the textural change from stromatolites (layered sediment fabric) to thrombolites (clotted sediment fabric) and (2) Heterotrophic protists caused the decimation of Neoproterozoic stromatolites. It is impossible to recreate the Neoproterozoic, so studies of modern analogs must serve to indirectly test our hypotheses. The overall goal of this project is to describe the eukaryotic communities associated with modern stromatolites and thrombolites from the Bahamas and Australia, compare the communities from the two sites, and to relate the communities to stromatolitic / thrombolitic sediment fabric and biomarker signatures. The overall goal will be achieved by addressing the following specific aims: (1) Identify, via morphologic and molecular approaches, the eukaryotic community of modern stromatolites and thrombolites; (2) Analyze modern and fossil stromatolites and thrombolites for their eukaryotic lipid biomarkers using solvent extraction, chromatographic and mass spectrometric methods; (3) Using the Fluorescently Labeled Embedded Core (FLEC) method, document the sub-millimeter distributions of the heterotrophic eukaryotic community inhabiting modern stromatolites and thrombolites in conjunction with fine-scale sediment fabric; (4) Using solvent extraction, chromatographic and mass spectrometric methods, analyze cultures of allogromiid foraminifers to survey for lipid biomarkers unique to them; (5) After incubation of modern stromatolites with heterotrophic protists, use FLEC methodology to determine how their activity affects sediment fabric and conduct preliminary comparisons of these modern fabrics to those of stromatolite fossils.

Intellectual Merit: The oldest fossil stromatolites are >3.4 billion years old and are the most visible manifestations of pervasive microbial life on the early Earth. The changes in stromatolite abundance and morphology document complex interplays between biological and geological processes. This project addresses multiple aspects of stromatolite genesis and pre-fossilization alteration but, at its core, focuses on one of the greatest geological enigmas: the possible connection between stromatolite decline and the rise of complex life.
Image Of the Day caption:
These rocky formations, called stromatolites, are made by photosynthetic cyanobacteria and other microorganisms. The microbes secrete compounds that bind sediment grains, creating a fine-layered mineral microfabric. Stromatolites were among the earliest life on Earth, and massive formations dominated shorelines starting about 3.5 billion years ago. About 1 billion years ago, their populations mysteriously plummeted; now they exist in only a few locations, like this one in Shark Bay, Australia. WHOI scientists Joan Bernhard and Virginia Edgcomb have investigated that decline, which occurred as more complex life forms were emerging.

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Photo by Ginny Edgcomb

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