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 20063 University of Tasmania, LAUNCESTON,AustraliaThe toxic dinoflagellateGymnodinium catenatum hasformed recurrent blooms in theHuon Estuary, south east Tasmaniasince the mid 1980s. Phytoplanktongrowth in the Huon Estuary isprimarily limited by nitrogen (N). Tobetter understand the bloomdynamics of G. catenatum,preference for and growth on:nitrate (NO3 - ), ammonium (NH4 + )and urea was investigated in aseries of laboratory experiments.Results demonstrated that G.catenatum grows equally well on:nitrate, ammonium and urea, buttakes them up in this order: NH4 + >NO3 - > urea. In addition, G.catenatum is capable of initialspecific N uptake rates ~20 times itsspecific growth rate i.e. 'surgeuptake'. The ability of G. catenatumto grow equally well using all threeN sources coupled with 'surgeuptake' capability are likely to playan important role in its dominance inthe Huon Estuary and otherecosystems.PO.13-33Prolonged toxicity ofScrobicularia plana after PSPevents and its relation toGymnodinium catenatum cystconsumption and toxindepurationSession: PO.13 - Regional eventsML Artigas 1 , A Amorim 2 , P Vale 3 , SSGomes 3 , MJ Botelho 3 , SM Rodrigues 31 University of Lisbon, PÓVOA DE STA.IRIA, Portugal2 Instituto de Oceanografia, LISBOA,Portugal3 IPIMAR/INIAP, LISBOA, PortugalIn contrast to other species ofbivalves such as blue mussels(Mytilus galloprovincialis) andcommon cockles (Cerastodermaedule), the clam Scrobicularia planahas been observed to retain PSPtoxicity for long periods (more than1 year) after a bloom event.Because this species is a depositfeeder, consumption ofGymnodinium catenatum cysts fromthe sediments was suggestedpreviously as one possibleexplanation for this fact. In autumn2005, a bloom of G. catenatum wasdetected along the NW coast ofPortugal. The gut contents of S.plana from affected areas wereexamined for dinoflagellate cystsduring and after the bloom. ThePSP content in bivalves wasfollowed by HPLC. The presence ofcysts was maximal during the bloomand then deminished, even thoughPSP toxicity never decreased tovalues below the regulatory safelimit. Depuration experiments withS. plana, blue mussels andcommon cockles revealed thatelimination of toxins in S. plana wasalmost non-observable within 1week, while in mussels or cocklesreduction to half the toxin level tookplace. These results suggest thatcysts are not responsible for theobserved prolonged toxicity, butinstead a slow depuration rate.PO.10-35Nitrogen dynamics of Pseudonitzschiacuspidata from the U.S.Pacific NorthwestSession: PO.10 - Ecophysiology &autecologyME Auro 1 , WP Cochlan 1 , VL Trainer 21 Romberg Tiburon Center, SFSU,TIBURON, United States of America2 Northwest Fisheries Science Center,NOAA, SEATTLE, United States ofAmerica129