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 2006macrophytes. In sheltered areasextensive masses containingmixtures of green algae can befound, among which three maintypes can be distinguished: thosepredominantly made up of speciesof Ulva (including Enteromorpha),entangled filaments of Cladophora,and elongate masses ofChaetomorpha linum. High numbersof microscopic algae can be foundattached to these substrates ordwelling close to the macroalgalsurfaces, forming diverse epibenthiccommunities. Attached diatomsmake up the greatest abundance ofepibenthic organisms, especially inmore exposed areas, but a varietyof dinoflagellates, including toxinproducingspecies, are regularmembers of the community insheltered areas. The composition ofthese communities in the threedifferent types of green algalmasses was examined everyfortnight in two sheltered localities,using a quantification method thatinvolves the forced detachment ofthe organisms from a known weightof macroalgal mass, followed bycounting in sedimentationchambers. Differences in theabundance of epibenthic species inthe different types of substrateswere noted and may be useful fordirecting efforts for finding toxicspecies in other areas of thisextensive lagoon.PO.04-08An individual-based modelsimulates the effects of browntide on larval recruitment of hardclamsSession: PO.04 – Food chainsEileen E. Hofmann 1 , Eric N. Powell 2 , V.Monica Bricelj 3 , John M. Klinck 1 , JohnN. Kraeuter 21 Old Dominion University, NORFOLK,United States of America2 Haskin Shellfish Research laboratory, In,PORT NORRIS, United States of America3 Institute for Marine Biosciences, Nation,HALIFAX, CanadaExperimental data were used tomodify an individual-based modelthat simulates growth, development,and metamorphosis of hard clam,Mercenaria mercenaria, larvae toinclude the effects of brown tide(Aureococccus anophagefferens).The coupled model was applied topredict brown tide effects on clamlarvae in a USA estuary (GreatSouth Bay, New York) whereblooms of varying magnitude haveoccurred for 20 yrs coincident withthe period of clam spawning andlarval development. Initialsimulations showed thattemperature and food quantityvariations produce small changes inoverall larval survivorship, whereaschanges in food quality (especiallyreduced lipid content) have thelargest effect on larval survival.Simulations that include brown tideeffects show inhibition of M.mercenaria larval growth that isobserved in laboratory experimentswith a toxic A. anophagefferensstrain. When brown tide occurs over2 wks of development, followed by aperiod of no exposure, the modelpredicts considerably reducedpostlarval recruitment success. Thesimulated genetic structure of thepopulation shows that brown tideaffects the genotypic characteristicsof hard clam populations. Forexample, simulations show thatbrown tide exposure selects againstfast growing larvae derived fromlarge eggs that attain competencewithout the necessary lipid reservesto sustain metamorphosis.191