Meeting Abstract

S1-1.14  Jan. 4  The effects of coral morphology and ambient flow on mass transfer in coral communities REIDENBACH, M.A.*; KOEHL, M.A.R.; GENIN, A.; MONISMITH, S.G.; KOSEFF, J.R.; University of California, Berkeley; University of California, Berkeley; The Hebrew University of Jerusalem; Stanford University; Stanford University mattr@berkeley.edu

Water flow over benthic communities, such as coral reefs, controls many biologically important processes, including food capture by benthic organisms, uptake of dissolved nutrients, larval dispersal, and waste removal. How are these transfer processes affected by the physical flow environment and the morphology of the coral? The fine-scale dynamics of turbulent mixing and mass transport between a Porites compressa reef and the overlying water were studied in a laboratory flume where unidirectional currents could be compared to wave-dominated flows. The flow velocities and wave characteristics used in the flume were based on field measurements of water velocities above and within P. compressa reefs in Kaneohe Bay, HI. Turbulent shear and rates of mixing were measured using laser-Doppler anemometry, while planar laser-induced fluorescence was used to create a 2-dimensional map of the flux of dissolved materials from the reef. We found that wave action dramatically increased intermittent shear and mixing events, thus enhancing mass transfer rates up to three-fold over those in equivalent unidirectional currents. We also compared mass transfer rates of P. compressa to two other coral species with different branching structure: Stylophora pistillata and Pocillopora verrucossa. Mass transfer rates, which increased with flow velocity and with wave frequency, were lower in species with closely-spaced branches. Our results showed that the vertical mixing of the water within the reef and the boundary layer thickness along reef surfaces both affect the rate of transport between the reef and the overlying water.