Pinckney, J. L.. Texas A&M University, pinckney@ocean.tamu.edu
Steppe, T. L.. University of North Carolina, tfs6030@email.unc.edu
Paerl, H. W.. University of North Carolina, hpaerl@email.unc.edu
Reid, P. University of Miami, preid@rsmas.miami.edu

 
MICROALGAL MEDIATION OF LITHIFICATION IN BAHAMIAN STROMATOLITES
 
Stromatolites (the earliest known macrofossils) are laminated sedimentary structures thought to be of cyanobacterial origin. Modern-day stromatolites in the Bahamas are composed of successive layers of lithified laminae that result from microbial processes. The close association between microalgae and laminae suggests that microalgae mediate processes that lead to stromatolite formation and growth. Understanding this association involves the characterization of microalgal community composition and ecophysiology (primary productivity, respiration, N fixation). In a collaborative study of the geomicrobiology of stromatolites at Highborne Cay, Exuma, Bahamas, we examined microalgal community structure and function during four cruises in 1997-98. Filamentous cyanobacteria (Schizothrix/Phormidium) were the most abundant algal group. However, diatoms, chlorophytes, and purple photosynthetic bacteria were common community components. The relative abundance of different algal groups varied seasonally and may explain the non-lithified layers between laminations. Production to respiration ratios (P/R) were usually greater than 3. The proposed mechanism for the formation of lithified laminae is related to the production of extracellular polysaccharides (EPS) by microalgae. High P/R ratios may reflect the production of copious amounts of EPS within the mat layers. Calcium ion binding by EPS and release during EPS decomposition by bacterial heterotrophs may result in the formation of lithified laminae.
 
Day: Friday, Feb. 5
Time: 12:15 - 12:30pm
Location: Eldorado Hotel
 
Code: SS46FR1215E