12th International Conference on Harmful Algae

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INTERNATIONAL SOCIETY FOR THE STUDY OF HARMFUL ALGAE12 th <strong>International</strong> <strong>Conference</strong> on Harmful Algae, Copenhagen, Denmark, 4-8 September 2006Gambierdiscus toxicus were grownin N- (nitrate, ammonium, freeamino acids, urea, or putrescine) orP-limited (phosphate, ß-glycerophosphate, or nucleotides)xenic batch cultures. Growth ratesranged from 0.11- 0.18 d -1 excepton urea (no growth). Cellular N andP pools were uncoupled fromconditions in the water and celldivision continued after the limitingnutrient was below detectable limits.N:P varied from 3-34 (1651) and 2-37 (strain 1655) with no relationshipbetween cellular N:P and totaltoxicity. Strain 1655 was roughlyfive-fold more toxic than strain 1651.The N source had no effect ontoxicity in either strain. The Psource had no effect on toxicity instrain 1651, but strain 1655 cellsgrown on ß-glycerophosphate weremore toxic. Stationary phase cellswere more toxic than exponentialphase cells in both strains underboth N- and P-limitation. In P-limited semi-continuous cultures,the toxicity of strain 1655 decreased(43.7-79.3 fg C-Ctx1Eq cell -1 ) as thegrowth rate increased (0.02-0.15 d -1 ). Toxicity differences were afunction of growth phase (batchculture) or growth rate (semicontinuousculture). Nutrient sourceand type of nutrient limitation havinglittle to no effect.PO.13-58Involvement of cyanobacteria inthe tropical ecotoxicologicalphenomenon of ciguatera fishpoisoningSession: PO.13 - Regional eventsD Laurent, AS Kerbrat, I de Fremicourt,T Darius, M Chinain, S PauillacIRD, NOUMEA, New CaledoniaDuring 2005, a cyanobacterialproliferation (Hydrocoleumlyngbyaceum) was found to inducea severe ciguatera outbreak in Lifou(Loyalty Islands, New Caledonia).Lipid-soluble extracts ofcyanobacteria and giant clams werefound to contain CTX-likecompounds, as assessed byneuroblastoma cell bioassays andcompetitive membrane-bindingassay using tritiated brevetoxin-3.According to the mouse bioassay,water-soluble extracts of bothsamples appear to contain the wellknownalkaloid neurotoxinsproduced by cyanobacteria andresponsible for Paralytic ShellfishPoisoning (PSP).This is the first demonstration ofsimultaneous occurrence of PSPtoxins and CTX-like toxins inextracts of marine cyanobacteria.The chemical identification of thesetoxins is currently underway byliquid chromatography coupled withmass spectrometry (LC/MS).Although long-term observations willbe necessary to decipher the trendsin dinoflagellate and cyanobacteriapopulations as well as thefavourable environmentalparameters, the new findingsrequire that CFP risk assessmentprograms must now includemonitoring of cyanobacteria besidesthe usual screening fordinoflagellates. In the perspective ofglobal warming, such events wouldprobably arise more frequently.PO.11-02Effect of bicarbonate addition onallelopathy in OscillatoriaagardhiiSession: PO.11 – AllelopathyLA Lawton 1 , GA Akin-Oriola 2 ,1 The Robert Gordon University,ABERDEEN, United Kingdom2 Lagos State University, LAGOS, Nigeria215
INTERNATIONAL SOCIETY FOR THE STUDY OF HARMFUL ALGAE12 th <strong>International</strong> <strong>Conference</strong> on Harmful Algae, Copenhagen, Denmark, 4-8 September 2006Phytoplankton species competewith each other for limitingresources especially nutrients. Thishas led to the evolution of differentstrategies ensuring their competitiveadvantage over other species inresource utilization. An example ofsuch a strategy is allelopathy – therelease of organic compounds byplants into the medium, whichaffects competiting species. Thisstudy investigates the effect ofbicarbonate-enriched spent mediaof non-toxic O. agardhii CYA 29 ongrowth and toxin concentration in M.aeruginosa PCC 7820.Bioassays were carried out in BG11 media to which were addedeither i) 15mM of bicarbonate ii) 0.1% (v/v) spent medium of O. agardhiior iii) 15mM bicarbonate and 0.1 %(v/v) spent medium of O. agardhii.The cultures were incubated at 25°C and sampled for biomass andtoxin concentration.A statistical analysis using Tukey’shonestly significant difference testshowed that after 3 weeks, biomassand total microcystin concentrationwere higher in cultures with spentmedia than those with bicarbonateand spent media. In contrast,microcystin concentrationdecreased six-fold in cultures withbicarbonate.Conclusion: addition of bicarbonateand/or spent media of O. agardhiihas a significant impact on growthand toxin production in M.aeruginosa.PO.11-14Epilithics biofilms: effect ofallelopathic compound onstructure and algal productionSession: PO.11 - AllelopathyJ Leflaive, L Ten-HageUniversité Paul Sabatier, TOULOUSE,FranceProduction of allelochemicals maybe considered as a competitor- andpredator-exclusion process. Epilithicbiofilms are benthic microbialaggregates formed by anassociation of autotrophs andheterotrophs, prokaryotes as well aseukaryotes. With the relativelycohesive organization ofmicroorganisms, theseagglomerates are quite auspiciousfor allelopathic interactions. The aimof this study is to show the effects ofthe presence of an allechemicalproducingstrain on biofilm structureand production. The experimentalset-up was based on artificialbiofilms, grown in microcosms andcomposed of a limited number ofalgal species (cyanobacteria anddiatoms, isolated from naturalbiofilms). Non-destructivetechniques of biofilm investigationswere used in order to elucidate bothspatial structure and functioning(laser-scanning confocalmicroscopy, microelectrodes). Toeliminate the effects of competition,extracts containing cyanobacterin,an allelopathic compound producedby the cyanobacteria Scytonemahofmannii, were added to thebiofilms. In a more general context,epilithic biofilm is an example ofcomplex integrated system whosedynamic functioning involves manysignalisation and regulationnetworks. This study aim tounderstand how allelopathicinteraction can modify biofilmfunctioning and structure.PO.06-13Effects of varying salinity andN:P ratios on the growth andtoxicity of Karenia brevisSession: PO.06 - Population dynamicsDK Lekan216
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12th International Conference on Harmful Algae

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