10th Larwood Meeting

THE Ca ISOTOPE COMPOSITIONS OF BRYOZOANS Marghaleray AMINI1, Dorrit E. JACOB1, Joachim SCHOLZ2 & Stephen J.G. GALER3 1Institut für Geowissenschaften, Joh.-Gutenberg-Universität Mainz, 55099 Mainz, Germany 2Forschungsinstitut Senckenberg, Senckenberganlage 25, Frankfurt/Main, Germany 3Max-Planck-Institut für Chemie, Postfach 3060, 55020 Mainz, Germany Inorganic carbonate precipitation experiments as well as laboratory culture experiments of biogenic carbonates indicate a thermodynamic control over the Ca isotope system. The Ca isotope systematic has been therefore proposed as a promising tool for the reconstruction of temperature and Ca content of ancient oceans, both of which associated with the global CO2 cycle. A number of studies to date are attempting to establish Ca isotopes as a paleo-thermometer by testing their sensitivity to temperature variations and by a calibration with established thermometers like oxygen isotopes and Mg/Ca ratios. Most of these studies are focused on the carbonate skeletons of corals and bivalves. However, corals and bivalves have gaps in their evolutionary history and are mostly restricted to tropical environments. Bryozoans, in contrast, provide a long, more than 400Ma old continuous evolutionary history and a wider geographic distribution, from polar to tropical regions. Although they have been recognized as important organisms through the Earth’s and oceans’ history, as yet, no Ca isotope data exist for bryozoans. Here we report first Ca isotope data on the carbonate skeletons of recent bryozoans. We compare cyclostome as well cheilostome species, in order to check for speciesdependent fractionation processes. Our results show a clear correlation between Ca isotopes and Mg concentrations with a decrease of Ca isotope fractionation with increasing Mg content. Also, we investigate potential Ca isotope variation along the growth axis in a colony specimen of the common and widespread Flustra foliacea. First data indicate a Ca isotope fractionation of 0.15‰ over a distance of 2 growth checks. We assume that this may also be related to an ontogenetic Mg decrease and/or to variations in growth rate. In order to better understand the calcification process, we are conducting analyses of the ultrastructure and mineralogy. Our first SEM and TEM analyses may suggest the presence of amorphous calcium carbonate (ACC) and/or vaterite. Both have been also proposed and recently shown as first phases in the biomineralisation sequence of bivalve shells. CALCIFICATION-INDUCING PROTEINS IN BRYOZOANS Michelle CARTER, Joanne S. PORTER & Peter MORRIS Centre for Marine Biodiversity and Biotechnology, School of Life Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, UK The biomineralic composition of bryozoan skeletons is highly variable consisting of calcite, magnesian-calcite, or aragonite. Aragonite and magnesian-calcite (Mg-calcite) are 50% more soluble in seawater than calcite thus bryozoans that form these types of calcium carbonate may be particularly vulnerable to ocean acidification. Therefore of critical concern is the impact of ocean acidification on bryozoans and their ability to produce a calcified skeleton under acidified conditions. One possible theory is that under such conditions, bryozoans will invest more heavily into the production of chitin. The objective of our research is to identify and locate the proteins involved in calcification in order to understand more clearly the underlying mechanisms of biomineralisation which will subsequently become a tool to understand the impact of ocean acidification on the biomineralisation process in bryozoans. RE-COLONIZATION OF THE SOUTHERN NORTH SEA WITH TRAVELING BRYOZOA: NATURAL AND HUMAN-MEDIATED VECTORS OF INTRODUCTION