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 2006toxicity were subsequently used infeeding preference experimentswith copepod grazers and differentnon-toxic alternative phytoplanktonprey. The results showed thatcopepods discriminated againstmore toxic A. minutum andsignificantly less A. minutum wasingested in treatments were induced(more toxic) A. minutum werepresent. Discriminate feeding ofcopepods resulted in a shift towardsA. minutum dominated speciescomposition in experiments withinduced, more toxic, A. minutum. Itis suggested that inducedresistance to grazers maycontribute to the formation ofharmful algal blooms.O.08-04The impacts of viral infection onHeterosigma akashiwo bloomsSession: O.08 - Population dynamics 2Presentation time: 12:00 - 12:20JE LawrenceUniversity of New Brunswick,FREDERICTON, CanadaA number of viruses infect theharmful bloom-forming raphidophyteHeterosigma akashiwo such asHaNIV, HaRNAV and a novelsystem in which two distinct virusesco-infect a host cell. These lyticviruses are distinct in theirbiochemical composition; theycontain different nucleic acids andproteins and are thereforegenetically diverse. Lytic infectionsin general are marked by a numberof events: replication of progeny,lysis of the host and theconcomitant release of progeny andorganic material. This cycleinherently means viruses impacthost abundance and nutrientcycling. However, a number offactors are specific to viruses andtherefore result in diverse impacts ofviral infection in phytoplanktonpopulation dynamics in situ. Forexample the lytic cycle length, burstsize and bloom density interact toinfluence the rate of propagation ofinfection, and therefore thedevelopment or demise of H.akashiwo blooms. In addition, thehost range of each virus clone andpermissiveness of each host strainshape the genetic composition of H.akashiwo populations. Thesefactors will be examined and usedto demonstrate the role of virus inphytoplankton blooms, and theimportance of isolating andcharacterizing novel viruses tounderstand the role of viruses inphytoplankton mortality.O.08-05Trigger factors of Alexandriumcatenella blooms in Hong KongSession: O.08 - Population dynamics 2Presentation time: 12:20 - 12:40KC HoOpen University of Hong Kong, HONGKONG, HongkongThe environmental data collected inHong Kong waters during the past20 years were reviewed andstatistically analysed. Resultsshowed that the ranges of watertemperature, solar intensity, salinityand wind and current directionsduring the periods of Alexandriumcatenella bloom were significantly(p