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 2006WILMINGTON, NC, United States ofAmericaThe toxic dinoflagellate Kareniabrevis forms extensive blooms inthe Gulf of Mexico, releasingbrevetoxins with implications forhuman health, mortalities of marinemammals and fishes. Historically, K.brevis was considered to formblooms above a salinity barrier of 24PSU. Recently, blooms in lowsalinity waters were recorded in theFlorida Panhandle and near theMississippi River outflow. In thisstudy K. brevis was cultured atsalinities of 15-40 at 5 PSU intervalsand N:P ratios (N:P = 16:1, 4:1 and80:1), to measure the influence ofsalinity and nutrients on growth andtoxicity. No growth of K. brevisoccurred at 20 PSU or below, butgood growth occurred at 25-40PSU. Growth varied from 0.36 to0.64 div day -1 . Highest growth ratesoccurred at 35 and lowest at 25PSU. Salinity was a primary factorregulating growth, with nutrients assecondary factors. Using an ELISAassay the highest per cellconcentration occurred in the 25 N-limited treatment with 100.0 and 40-Balanced with 99.2 pg toxin cell -1 .Similarly salinity was a primaryfactor regulating toxin productionparticularly at 25 and 40 PSU.Nutrient stress appears to stimulatetoxin production, prompting furtherinvestigation as to the relationshipbetween nutrients and toxins.PO.10-19Nutrient acquisition in theharmful dinoflagellateAlexandrium tamarense inresponse to different nitrogensupplySession: PO.10 - Ecophysiology &autecologySCY Leong, M Maekawa, S TaguchiSoka University, HACHIOJI, TOKYO,JapanNitrogen (N) is an essential variablecontrolling the bloom dynamics ofdinoflagellates in marineenvironments. The ability to take updifferent species of N readily andsimultaneously, and to switch Nsource rapidly is one of themechanisms that may enhance thebloom potential for dinoflagellates.In the present study, dinoflagellateAlexandrium tamarense grown on asingle N source was supplied withdifferent forms of N, and two Nspecies simultaneously to examinethe cellular nutrient uptake kineticsunder different supply mode. A.tamarense was able to take up Nreadily regardless of the previouslysupplied N source. Cells grown oneither nitrate or urea were observedto take up ammonium rapidly.However, with ammonium-growncells lower uptake rates of nitrateand urea were observed.Alexandrium tamarensedemonstrated the ability to take uptwo N species simultaneously.When ammonium and nitrate (orurea) were supplied in equalconcentrations, more ammoniumwas taken up and assimilated. Theability to take up different species ofN rapidly and also simultaneously isone of the advantages that mayallow A. tamarense to proliferateand form blooms in marineenvironments with complex Nsources.PO.01-20The distribution of Alexandriumspecies in British coastal watersSession: PO.01 - GeneticsJM Lewis, L Carter, L PercyUniversity of Westminster, LONDON,United Kingdom217