12th International Conference on Harmful Algae

INTERNATIONAL SOCIETY FOR THE STUDY OF HARMFUL ALGAE12 th <strong>International</strong> <strong>Conference</strong> on Harmful Algae, Copenhagen, Denmark, 4-8 September 2006the Baltic Sea. At the beginning ofthe bloom (June 29th 2004), 27.43% of the D. norvegica cellscontained food vacuoles. A monthlatter (July 27th), 49.67 % of the D.norvegica cells in the whole watercolumn had food vacuoles, thewater column was well stratified andnitrogen limited. The highest celldensity (341 cells/l) was recorded inthe aphotic zone (30 m depth),where 71% of the D. norvegica cellscontained food vacuoles. Real-timePCR assay and microscopeobservations showed that part ofthe population (5%) was in a latestage of cell division. These resultssuggest that phagotrophy was themain nutritional pathway for D.norvegica, supporting the formationand maintenance of sub-surfaceblooms of D. norvegica in the BalticSea during the summer.PO.13-15Didymosphenia geminata: a newinvasive diatomSession: PO.13 – Regional eventsS.C. Cary 1 , B.J.F Biggs 2 , C. Kilroy 2 ,C.C. Vieglais 3 , M. Bothwell 4 , S.A.Spaulding 11 University of Delaware, LEWES, UnitedStates of America2 Nat.Inst. of Water and Atm. Res.,CHRISTCHURCH, New Zealand3 Biosecurity New Zealand, WELLINGTON,New Zealand4 Environment Canada, NANAIMO,BRITISH COLUMBIA, CanadaThe freshwater benthic diatomDidymosphenia geminata (Lyngbye)Schmidt (Didymo) is emerging asan organism with an extraordinarycapacity to impact streamecosystems. This stalked diatom isable to dominate stream benthos bycovering 100% of substrates withthicknesses of up to 20 cm, greatlyaltering physical and biologicalconditions within streams. Aparadox exists in that these denseblooms occur in streams that wouldotherwise be considered extremelyoligotrophic. In recent years,streams and rivers in New Zealand,North America, Europe, and Asiahave been colonized byunprecedented masses of Didymoand its extra cellular stalks. Thepattern of expansion of thegeographic range of Didymo bloomsaround the globe suggests thathuman activity is an importantvector. Although nuisance bloomsof Didymo are increasingly reportedby the public and local media therehas been little scientific investigationof the phenomenon outside of NewZealand. Recent work on the globaldistribution, ecology, genetics andon-going mitigation efforts will bepresented.PO.07-07Control of toxic algal bloom by atiny parasitoidSession: PO.07 - Ecology andoceanographyA Chambouvet, L GuillouBiological station, ROSCOFF, FranceSince 1988, an invasive harmfulblooming species Alexandriumminutum Halim has been repeatedlyrecorded along the Atlantic Frenchcoast in the Penzé Estuary. Firstdetected as massive toxic bloomsduring the first years of occurrence(about 10 7 cells/l), this species isstill detected every year, but it nolonger foms blooms (about 10 5cells/l). At the same time, two noveleukaryotic lineages belonging to theAlveolata (Group I and Group II)were detected by cultureindependent methods (geneticdiversity from total genomic DNA)collected from a large array of148