Astrobiology Science Conference 2010 (2010) 5661.pdf

TWO YEARS IN THE LIFE OF A STROMATOLITE, HIGHBORNE CAY, BAHAMAS: SEDIMENTATION, ACCRETION, AND THE ROLE OF DIATOMS. R. P. Reid and E. M. Bowlin, Rosen- stiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Cswy, Miami, FL 33149; [email protected].

As the only known modern analogues to Pre- which are buried and unburied on daily to cambrian stromatolites that formed in open weekly basis. Stromatolite accretion in the marine environments, stromatolites in Exuma purely prokaryotic system is on the order of 1 Cays, Bahamas, have been the subject of in- mm per year. tense investigation for the past decade. Inte- grated studies relating stromatolite micro- Mixed prokaryotic-eukaryotic mat communi- structure to microbial populations and proc- ties, consisting of stalked diatoms overlying esses have provided a model for lamination filamentous cyanobacteria, are common on formation. The stromatolites are formed by columnar stromatolites which experience lithifying microbial mats, with each subsur- month-long periods of burial and exposure. face layer representing a community that was, The diatom communities trap sediment, at one time, at the stromatolite surface. which is subsequently bound by upward mi- gration of the underlying cyanobacteria. In 2003, the Research Initiative on Bahamian Stromatolite accretion by the mixed prokary- Stromatolites, or RIBS project, initiated a otic-eukaryotic community is on the order of comprehensive five-year program to investi- 1 cm per year. gate intrinsic and extrinsic factors causing cycling of the surface microbial communities The Highborne Cay monitoring program in- forming the stromatolites at Highborne Cay, dicates that cyanobacterial mats lacking dia- Bahamas. An important component of this toms are capable of trapping and binding study was an intensive field effort, which in- sand-size particles and building modern ma- cluded almost continuous monitoring of rine stromatolites. The addition of diatoms to sedimentation, microbial mat communities, cyanobacterial mats can increase stromatolite and accretion of Highborne Cay stromatolites accretion rates by an order of magnitude, but from Jan 2005 to Dec. 2006. the binding of diatom-accreted sand to form a wave resistant structure is accomplished by Results indicate that migration of sand waves cyanobacterial communites. These results across the stromatolite reef is a major control suggest that evolution of stromatolite- on the distribution of microbial communities. building communities to include eukaryotic Migrating sand waves bury and expose the algae does not explain the coarse grained na- reef episodically for periods of days, weeks, ture of modern marine stromtolites. and months. Microbial mat composition and resultant stromatolite accretion reflect the du- ration of burial and exposure events.

Stromatolite surfaces may be colonized by purely prokaryotic mats, or by mixed com- munities of prokaryotes and eukaryotes. The prokaryotic mats are dominated by gliding filamentous cyanobacteria and are found chiefly on low-relief stromatolite ridges,