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 2006lipid classes and fatty acids. Thetoxic strain consistently inhibitedgrowth in a dose-dependentmanner, relative to an Isochrysisgalbana control, leading to arresteddevelopment in D-stage, but yieldedvariable mortalities. Larvae did notrecover when returned to the controldiet after 2 wk-exposure to unialgalbrown tide; 20% of the populationrecovered following exposure to anA. anophagefferens/Isochrysisgalbana mixture, suggesting geneticvariability in susceptibility to browntide. Non-toxic Aureococcussupported growth rates comparableto I. galbana. Larvae exhibitedreduced filtration on unialgal browntide and selected against toxic cellsin mixed suspensions, as confirmedby gut autofluorescence and flowcytometry. Experimentalapproaches allowing discriminationbetween algal toxicity and nutritionaldeficiency are evaluated. Weconclude that brown tides will causemetamorphic failure of clam larvalpopulations primarily through toxinmediated,growth inhibition.Prolonged residence time in theplankton will increase vulnerabilityto secondary mortality factors. Inturn, hard clam larvae likely make anegligible contribution tomicrozooplankton grazing on browntide.PO.02-09Mating incompatibility:genotyping of Alexandrium cystsSession: GenomicsML Brosnahan 1 , DL Erdner 2 , DM Kulis 1 ,DM Anderson 11 Woods Hole Oceanographic Institution,WOODS HOLE, MA, United States ofAmerica2 Univ. of Texas at Austin, Mar. Sc. Inst.,PORT ARANSAS, TX, United States ofAmericaThough the ranges of toxic and nontoxicstrains of the dinoflagellateAlexandrium tamarense are notthought to overlap, these cell typesdo occur in close geographicproximity. Unpublished data (D. M.Anderson) show that toxic and nontoxicstrains of this species can fusesexually to form resting cysts(hypnozygotes). However, all hybridhypnozygotes die shortly aftergermination. Such post-zygoticlethality (PZL) may be a barrier torange expansion of toxic blooms. Itis not yet known whether suchhybrid fusions occur in nature; toxiccells may fuse only with other toxiccells if allowed a choice ofcompatible toxic and non-toxictypes. Here, a PCR method foranalysis of cysts resulting fromcompetitive crosses of toxic andnon-toxic strains is described. Withthis method, it is possible todifferentiate hypnozygotes arisingfrom two toxic, two non-toxic, andtoxic/non-toxic parents. Analysis ofsingle hypnozygotes and pellicle(non-zygotic) cysts, in conjunctionwith previously published data,suggests that pellicle cysts may beincompletely transformed zygotesrather than haploid cells. Aremaining obstacle to reliableobservation of mating selectivity isthe lack of a rapid and penetrantmethod for sexual induction of A.tamarense in culture.PO.13-62Seasonal diversity of Pseudonitzschiaspecies in the ShetlandIsles, ScotlandSession: PO.13 - Regional eventsLM Brown, E BresnanFisheries Research Services, ABERDEEN,United Kingdom140