Stabilization Role of Crustose Coralline Algae During Late Pleistocene Reef Development on Isla Cerralvo, Baja California Sur (Mexico)

TIERNEY, P.W. and JOHNSON, M.E., 2012. Stabilization role of crustose coralline algae during Late Pleistocene reef development on Isla Cerralvo, Baja California Sur (Mexico). Crustose coralline algae played a fundamental role in reef establishment during the Late Pleistocene (122,143 ± 175 YBP) on Isla Cerralvo in the southern Gulf of California. Transported cobbles with a generally elongated clast shape (mean sphericity: 0.6) were encrusted by coralline red algae before locking in a N–S alignment (mean N2°W) and providing a fixed substrate for colonization by Porites and Pocillopora corals. A fringing reef grew on this pavement of clast-encrusting rhodoliths and was succeeded by additional cobble-coral cycles. Out of five stratigraphically repetitive cycles, only the second and third offer sufficient exposure to be quantified with any confidence. Census data, cobble orientations, and measurements of algal rinds were collected to characterize the transition from rhodoliths to corals. Clasts in the second cycle (mean dimensions 7.4 × 4.6 cm) have rinds that average 5.4 mm (standard deviation, or SD, 4.2 mm) at their thickest and 0.9 mm (SD 0.8 mm) at their thinnest. Directly overlying corals reflect an average height of 16.2 cm. Clasts within the third cycle (mean dimensions 7.2 × 4.6 cm) have rinds that average 3.1 mm (SD 2.5 mm) at their thickest and 0.9 mm (SD 0.8 mm) at their thinnest. Directly overlying corals reflect an average height of 15.4 cm. Coralline algae helped cement both underlying cobble pavement and reef corals.