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 2006occurs during vegetative growth.Size distribution observed in naturalpopulations throughout a 10-yeartime series shows cell lengthranging between 30 and 80 µm.Three sub-populations with sizemodes of ca 60, 45, and 35 µmalternate over the years. Based onsize reduction rates and growthcharacteristics, a model is proposedaimed at reproducing life cyclefeatures and the timing of sexualevents of P. multistriata at sea.O.13-04Asexual and sexual reproductionin Protoperidinium steidingerae(Dinophyceae)Session: O.13 - Life cyclesPresentation time: 10:10 - 10:30Kristin E Gribble 1 , D Wayne Coats 2 ,Donald M Anderson 11 Woods Hole Oceanographic Institution,WOODS HOLE, MA, United States ofAmerica2 Smithsonian Environ. Research Center,EDGEWATER, MD, United States ofAmericaProtoperidinium is a cosmopolitangenus of heterotrophicdinoflagellates with more than 200species. One species, P. crassipes,has been implicated as the sourceof azaspiracid shellfish toxin. In thisstudy, division, sexuality, mandatorydormancy and germination rates ofhypnozygotes, and identity lifehistorystages were revealed for thefirst time for any Protoperidiniumspp. Asexual division occurred byeleutheroschisis within a temporary,immotile cyst, yielding two daughtercells. Daughter cells were initiallyround and half to two-thirds the sizeof parent cells, then rapidlyincreased in size, forming hornsbefore separating. Sexualreproduction was constitutive inboth non-clonal and clonal cultures,indicating that the species may behomothallic. Gametes wereisogamous, approximately half thesize and lacking the pinkpigmentation of the vegetative cells,and were never observed to feed.Gamete fusion resulted in aplanozygote with two longitudinalflagella. Hypnozygotes had amandatory dormancy period of ca.70 days. Germination resulted inplanomeiocytes with twolongitudinal flagella. Protargolstainedspecimens indicate thatnuclear cyclosis may occur in theplanomeiocyte. Mis-identification ofmorphologically distinct life historystages and incomplete examinationof thecal plate morphology in fieldspecimens of P. steidingerae haveled to taxonomic confusion.O.14-01Physiological stress responsesof Daphnia magna tocyanobacteria and cyanobacterialcompoundsSession: O.14 - Food ChainsPresentation time: 09:10 - 09:30C WiegandLeibniz Institute of Freshwater Ecology,BERLIN, GermanyCyanobacteria frequently flourish ineutrophic aquatic systems andseveral species are capable ofproducing toxic secondarymetabolites, such as microcystinswhich specifically inhibitserine/threonine proteinphosphatases, and cyanopeptolinesand micropeptins leading toinhibition of trypsin, andchymotrypsin. Inhibition of grazingseems to be one of the ecologicalfunctions of the cyanobacterialbioactive compounds. With the helpof several mechanisms, the grazingzooplankter Daphnia magna59