Growth morphologies of modern marine stromatolites: A case study from Highborne Cay, Bahamas

Stromatolites are a uniquely coupled geo-biosphere system, which potentially records important paleoenvironmental and biological information. Characterizing and distinguishing between the biological and physical factors that control stromatolite morphogenesis, therefore, has important implications for the understanding of modern stromatolites and the interpretation of ancient systems. This paper documents the occurrence and distribution of stromatolites with distinct growth morphologies in the Highborne Cay reef system and other locations in Exuma Cays, Bahamas, and explores the relative contributions of physical and biological environmental factors controlling stromatolite shape. Our observations suggest that macro-scale growth morphologies of Exuma stromatolites are primarily controlled by accommodation space, hydrodynamics, and sedimentation patterns. The latter are critical for the stromatolite ecosystem in that the suspended sediment provides grains for trapping and binding and thus stromatolite accretion. Furthermore, sediment burial removes macroalgae, allowing the prokaryotic community to dominate. Changes in sedimentation patterns and frequency allow for the colonization of stromatolites by macroalgae and boring macrofauna, which, in time, destroy and degrade the stromatolite structure.