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 20061 Finnish Environment Institute, HELSINKI,Finland2 Finnish Institute of Marine Research,HELSINKI, Finland3 Institute of Nutrition, University of Jena,JENA, GermanyDinophysis acuminata, D. norvegicaand D. rotundata are commonlyfound in the late summer planktoncommunities of the northern BalticSea. Dinophysis-derived toxinshave previously been found inbenthic organisms, but noinformation on toxin transport viathe planktonic food webs exists. Toinvestigate the role of copepods asgrazers of Dinophysis spp. a seriesof experiments were carried out atthe SW coast of Finland.Grazing activity and prey selectivityof Eurytemora affinis and Acartiabifilosa were experimentally studiedwith field collected, concentratedplankton assemblages containingDinophysis spp. offered as food.The experimental water wasmanipulated to establish bothspecies diverse, and Dinophysisspp.– dominated microplanktonassemblages. The copepodingestion rates and selectivity ineach experiment were estimated.Toxin content of copepods used inthe incubations and field collectedzooplankton were analysed.The overall ingestion rates inDinophysis - dominated units were30.5 – 130 cells ind -1 d -1 . When foodavailability increased, otherorganisms were preferred, and theingestion rates on Dinophysis spp.were more variable (0.9 – 149 cellsind -1 d -1 ).PTX-2 (142 pg ind -1 ) was found inE. affinis after 24h incubation.Moreover, traces of PTX-2 and itsseco acid were found from fieldcollected zooplankton samples fromthe study area.O.14-04Karlotoxins mediate interactionsbetween the mixotrophicdinoflagellate, Karlodiniumveneficum, its prey, and itspredatorsSession: O.14 - Food ChainsPresentation time: 10:10 - 10:30JE Adolf, D Krupatkina, TR Bachvaroff,AR PlaceUMBI Center of Marine Biotechnology,BALTIMORE, United States of AmericaLittle is known about the ecologicalmechanisms that allow the toxicdinoflagellate, K. veneficum, tobloom. Here, we tested hypothesesthat the cytotoxic and ichthyotoxickarlotoxins produced by K.veneficum (1) allow greater feedingby K. veneficum on cryptophyteprey, Storeatula major, and (2) haveanti-grazing properties against acommon predator of K. veneficum,the heterotrophic dinoflagellateOxyrrhis marina. Of 14 strains of K.veneficum offered S. major as preyonly the non-toxic strains, MD5 and‘G. corsicum’, did not feed. Oxyrrhismarina feeding rate on K. veneficumwas reduced significantly when fedtoxic compared to non-toxic strainsor when a sub-lethal dose of purifiedtoxin was added to a non-toxic preyculture. The feeding rate of O.marina on non-toxic K. veneficumwas reduced in mixed culturescontaining both toxic and non-toxicstrains. We suggest karlotoxin ispart of an ecological strategy thatincreases K. veneficum cellulargrowth rate via mixotrophy whileminimizing grazing losses. Thesemechanisms will work together tooptimize population growth rates,increasing the likelihood of bloomformation. Further experiments arebeing conducted to test the ability ofK. veneficum to compete with O.61