Mercado-Burgos, Marianela

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    Reef accretion during the last 700 years in the outer insular shelf of southwest Puerto Rico
    (2012) Mercado-Burgos, Marianela; Ramírez-Martínez, Wilson R.; College of Arts and Sciences - Sciences; Santos, Hernán; Sherman, Clark; Department of Geology; Morell Rodríguez, Julio
    Previous studies reported ceased accretion for shelf edge reefs in southwest Puerto Rico after 6,000 yrs. Four cores were recovered from spur and groove reefs, on the outer shelf; to characterize changes in the reef stratigraphy and structure that could document reasons for changes in reef accretion. Three major constituents were found: Montastrea annularis complex (M. annularis, M. faveolata, M. franksi) coral fragments, Acropora palmata coral fragments and coral rubble. Total recovery from these reefs show most of the content composed of coral fragments (48%), followed by coral rubble (33%), in situ corals (17%) and crustose coralline algae (2%); being in situ corals relatively uncommon in the geologic record. The major reef builder is corals of the Mn complex while recoveries of A. palmata specimens were mostly in the form of fragments and not in place. Analyses of bioerosion processes documented removal of coral material mainly by Lithophaga sp., sponges and serpulid worms, responsible for up to 80% of microborings and 65% of macroborings. Recent radiocarbon ages (70 - 680 ± 25 yrs) in these corals show accretion rates ranging from 1.1 to 3.4 m/1,000 yrs in three of the four cores representing average values according to the literature. Average accretion rate is 2.3 m/1,000 yrs. The topography seen today of the spurs studied could have started about 1,000 to 2,000 years ago. The spur and groove "recent" Holocene reef sequence obtained in southwest Puerto Rico shows the natural variability of reef materials deposition and accretion. The new data documents recent reef accretion and bring important information about the platform development and history which was unknown until now.