Seminar Title 1:  Toward an understanding of coral calcification   

Presented by:  Michael Holcomb, ARC Centre of Excellence in Coral Reef Studies, School of Earth and Environment & Oceans Institute The University of Western Australia

Abstract: Calcification, as carried out by corals, is responsible for forming the structural frame work for some of the most diverse ecosystems on earth.  Despite the importance of this process for building and maintaining reefs, our understanding of calcification remains limited.  I will present evidence which supports calcification being an active (energy requiring) process carried out by corals.  Although calcification occurs at a site isolated from the external environment, its dependence on external environmental conditions varies widely study to study, and even between conditions within a given study.  Using a simple box model and constraints from abiogenic aragonite growth I will attempt to explain how energy investment and tissue permeability may explain much of the range of observed responses of calcification to environmental variables, with a focus on ocean acidification.

Biography:  Michael obtained a BS in Biology and Chemistry from the University of Idaho in 2004, where he worked on reproductive biology in fish.  Michael completed his PhD in 2010 in the MIT/WHOI Joint Program in oceanography working on biomineralization in corals.   He went on to a postdoc at the Centre Scientifique de Monaco where he worked on the energetics of coral calcification, and has recently started a postdoc at the University of Western Australia where he is working on the boron isotope pH proxy in corals.

 Seminar Title 2:  Modelling the spatial variability of nutrient and alkalinity in coral reef systems using a coupled physical-biogeochemical approach                           

Presented by:  Zhenlin Zhang, ARC Centre of Excellence in Coral Reef Studies, School of Earth and Environment & Oceans Institute The University of Western Australia

Abstract: We investigate the combined effect of hydrodynamic forcing and biogeochemical processes on the distribution of nutrients, benthic nutrient fluxes and alkalinities across a shallow-water fringing coral reef system.  A new benthic biogeochemical module was first developed using relationships from the coral reef literature relating convective nutrient mass transfer velocities to total bottom drag and integrated it in a coupled three-dimensional numerical ocean circulation model (ROMS) and numerical spectral wave model (SWAN). The coupled model showed high spatial variation in nutrient concentration and successfully reproduced the nutrient concentration across a section of Ningaloo Reef at Sandy Bay. The coupled physical-biogeochemical model was further extended to investigate the system-scale response to reef calcification within a section of Ningaloo Reef at Coral Bay. We modelled the spatial distribution of both the residence time and the deviation in total alkalinity (TA) from offshore values of this reef-lagoon. While residence time was calculated from the hydrodynamic model alone using a conservative tracer, TA was modeled as a reactive tracer whose ‘release’ was driven by light-dependent community calcification through a relationship derived from measurements made on an adjacent reef flat. Results showed that 1) the coupled model was capable of reproducing the observed spatial variability of TA on a scale much larger than the ~100 m control volume where the calcification measurements were made; and 2) that both residence time and TA varied strongly as a function of the incident wave forcing and location within the reef lagoon system. This new modeling approach provides a framework for accurately estimating nutrient uptake and calcification rates across entire reef systems based on observed gradients in nutrient and TA within a coral reef system, thus providing a new powerful tool for coral reef research and monitoring.

Biography:  Dr. Zhenlin Zhang completed her PhD degree in oceanography at the University of Western Australia in 2011. Her current research focuses on developing spatial-explicit biogeochemical models in coral reef systems and investigating how the physical and pelagic biogeochemical processes offshore influence nutrient dynamics and water chemistry within coral reef systems nearshore.