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 2006and molecular mechanismsrequired for roseobacters toestablish and maintain theirsymbiosis with dinoflagellates.Recently, we discovered thatSilicibacter sp. TM1040 producesan antibacterial compound,tropodithietic acid, which inhibitsmany other marine bacteria. Agenetic analysis has revealed thebiosynthetic pathway, as well as theregulatory circuit controllingtropodithietic acid expression. Theimplications of these data and theeffect of the antibiotic on theinteraction of roseobacters with theirdinoflagellate hosts, the structureand composition of bacterialcommunities, and the sulfur cycleare discussed.PO.13-28Phytoplankton tidal populationin Sfax coasts (South Tunisia)Session: PO.13 - Regional eventsS. Ben Khedhir 2 , Asma Hamza 1 , M.Ben Hassen 21 Institut National des Sciences et Techno,SFAX, Tunisia2 INSTM, SFAX, TunisiaDiversity variation of phytoplanktonin relation to daily tidal movementswas studied during four seasons atthe Sfax coast, Tunisia. Diatomsthat adhere to the bottom move within the water column and can reachthe surface. The most abundantgroups of the phytoplankton weredinoflagellates and somecyanophytes. Diatom abundancehas a lunar as well as a seasonalvariability, with the highestabundance corresponding to thecoldest days of the lunar cycle.Dinoflagellate species occurredgenerally in summer andproliferated specially on the lastdays of the lunar cycle, showing apreference for decreasedturbulence.PO.10-46Influence of salinity on thedimensions of the dinoflagellateProrocentrum minimum undercontrolled conditionsA Beran 1 , M Monti 1 , M Berden Zrimec 2 ,L Drinovec 2 , F Tamberlich 3 , A Zrimec 21 OGS, TRIESTE, Italy2 Institute of Physical Biology,GROSUPLJE, Slovenia3 Osservatorio Alto Adriatico, ARPA FVG,TRIESTE, ItalyProrocentrum minimum is aplanktonic dinoflagellate, which isconsidered potentially toxic tohumans. Associations between P.minimum blooms and toxicity arerare, but harmful effects were onvarious occasions observed inareas of P. minimum blooms.Prorocentrum minimum is thereforeconsidered a HAB (Harmful AlgalBloom) species and a species to bemonitored.Prorocentrum minimum cell sizeand shape are highly variable, anddifferent factors, including salinity,temperature and light intensity, havebeen suggested as putative causesfor this variability. Various authorshave suggested that different formscould be treated as morphotypeswithin the species, and relationshipsbetween P. minimum morphology,geographical distribution and salinityhave been hypothesized. To studythe possible relation between celldimension and salinity, P. minimumstrains from different geographicalareas were maintained in cultureunder controlled conditions. Growthcurves were monitored at threesalinities (8, 16 and 32 PSU) andcell dimensions analyzed. Celldimensions varied in the differentphases of growth, and the average133