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 2006to model, and further the number ofsampling stations. Our results showthat ANN models, with a lownumber of input variables, are ableto reproduce trends in D. acuminatapopulation dynamics.O.05-03Temporal changes inmicrocystin-producing and nonmicrocystin-producingMicrocystis populations of aJapanese LakeSession: O.05 - Population dynamics 1Presentation time: 09:50 - 10:10Mitsuhiro YoshidaFukui Prefectural University, OBAMA,JapanTemporal changes in hepatotoxinmicrocystin-producing and nonmicrocystin-producingMicrocystisaeruginosa populations wereexamined in Lake Mikata, Japan. Tomonitor densities of the total M.aeruginosa population andpotentially microcystin-producingcells, we used quantitative real-timePCR assays targeting thephycocyanin intergenic spacer (PC-IGS) and the microcystin synthetasegene (mcyA), respectively. Duringthe sampling period, the ratios ofcell numbers of mcyA genotypes tothe total M. aeruginosa variedconsiderably with the range from0.005 to 0.35. When surface nitrateconcentrations increaseddramatically, there was an apparentrise in cell number ratios of mcyAgenotypes. As an alternativeapproach, the 16S-23S rDNAinternal transcribed spacer (16S-23S ITS) genotyping was employedfor the identification of potentiallymicrocystin-producing and nonmicrocystin-producinggenotypes innatural communities. Thephylogenetically closely related butdistinct microcystin genotypes werefound between different sampleswhen ratios of cell numbers of mcygenotypes were relatively high.Thus, our data suggest that multipleecotypes, which are adapted toecological parameters, mightcoexist within the M. aeruginosacommunity.O.05-04Vertical migration: an keystrategy for the ecologicalsuccess of the toxicdinoflagellate Gymnodiniumcatenatum in south eastTasmania, AustraliaSession: O.05 - Population dynamics 1Presentation time: 10:10 - 10:30SIE Blackburn 1 , K Wild-Allen 1 , MADoblin 2 , PA Armstrong 3 , CJ Bolch 4 , PAThompson 1 , GM Hallegraeff 41 CSIRO, HOBART, Australia2 University of Technology, SYDNEY,Australia3 University of Tasmania, Aquafin CRC,LAUNCESTON, Australia4 University of Tasmania, LAUNCESTON,AustraliaThe toxic dinoflagellateGymnodinium catenatum hasformed recurrent blooms in theHuon Estuary, south east Tasmaniasince the mid 1980s. The estuary ischaracterised by humic-ladensurface river flow and micro-tidalsalt wedge estuarine circulation. Adistinctive feature of the blooms isdiurnal vertical migration (DVM), upto 20 metres of the water column.Laboratory studies using verticallystratified columns demonstrate thatDVM facilitates nutrient retrieval atdepth. In addition, G. catenatumgrows equally well on nitrate,ammonium or urea and, in the field,G. catenatum utilises whichever ofthese nitrogen sources are availableduring DVM. This indicates an38