LifeLife cyclecycle strategiesstrategies andand occurrencesoccurrences ofof redred tidestides ofof HeterosigmaHeterosigma akashiwoakashiwo andand ChattonellaChattonella spp.spp. inin temperatetemperate coastalcoastal seasea

Ichiro Imai (Kyoto University), Shigeru Itakura, Mineo Yamaguchi GlobalGlobal distributiondistribution ofof raphidophytesraphidophytes andand fish-killfish-kill (Edvardsen(Edvardsen andand ImaiImai 2006)2006) ContentsContents

1. Life cycle strategy of Chattonella antiqua and C. marina

2. Life cycle strategy of Heterosigma akashiwo

3. How do harmful raphidophyte blooms occur predominantly over diatoms in coastal sea? LifeLife cyclecycle strategystrategy ofof ChattonellaChattonella spp.spp. GrowthGrowth characteristicscharacteristics 1. Chattonella antiqua and C. marina are the summer red tide flagellates. 2. The optimum combination of temperature and salinity C. antiqua: 25°C and 25psu C. marina : 25°C and 20psu 3. Survival range of temperature C. antiqua: 11 ~ 31°C C. marina : 13 ~ 31°C

∴ C. antiqua and C. marina can not overwinter as vegetative cells in the Seto Inland Sea, and form cysts for overwintering. LifeLife cyclecycle ofof ChattonellaChattonella antiqua antiqua andand C.C. marinamarina basedbased onon DNADNA microfluorometrymicrofluorometry (Yamaguchi(Yamaguchi andand ImaiImai 1994)1994)

Chattonella antiqua and C. marina are the diploid organisms. CystsCysts ofof ChattonellaChattonella antiqua antiqua andand C.C. marinamarina (Imai(Imai andand ItohItoh 1988) 1988) AA && B:B: C.C. antiquaantiqua CC && DD:: C.C. marinamarina MPNMPN methodmethod forfor enumerationenumeration ofof ChattonellaChattonella cystscysts havinghaving germinationgermination abilityability inin sedimentssediments (Imai(Imai etet al.al. 1984).1984).

Feasible for the cysts without information on morphology ComparisonComparison ofof temperaturetemperature characteristicscharacteristics ofof germinationgermination andand maturationmaturation inin ChattonellaChattonella cysts.cysts. SeasonalSeasonal changeschanges inin germinabilitygerminability of of ChattonellaChattonella cystscysts inin sedimentssediments ofof collectedcollected atat 33 pointspoints inin Suo-Nada,Suo-Nada, thethe SetoSeto Inland Inland SeaSea (Imai(Imai andand ItohItoh 1987). 1987). AnnualAnnual lifelife cyclecycle ofof ChattonellaChattonella inin thethe SetoSeto Inland Inland Sea,Sea, includingincluding vegetativevegetative cellscells andand cystcyst phase.phase. (Imai(Imai andand ItohItoh 1987) 1987) SummarySummary forfor ChattonellaChattonella

ƒ 1. Chattonella spp. are diploid organisms (2n). ƒ 2. Chattonella has cyst stage for overwintering. ƒ 3. Cyst formation was induced by nutrient depletion such as nitrogen under low light conditions. ƒ 4. Cysts needs winter for maturation. ƒ 5. Cysts effectively germinate at 20°C or higher. ƒ 6. in situ germination of cysts show great seasonality. ƒ 7. Summer red tides are seeded by the germination of cysts in sea bottom. ƒ 8. Life cycle startegy of Chattonella is well adapted to temperate shallow coastal areas; changes between cysts and vegetative cells are easy. LifeLife cyclecycle strategystrategy ofof HeterosigmaHeterosigma akashiwoakashiwo SamplingSampling stationsstations forfor H.H. akashiwoakashiwo studystudy inin HiroshimaHiroshima Bay,Bay, thethe SetoSeto InlandInland Sea.Sea. CystsCysts ofof HeterosigmaHeterosigma akashiwoakashiwo discovereddiscovered fromfrom thethe sedimentssediments ofof thethe SetoSeto Inland Inland SeaSea (Imai(Imai etet al.al. 1993)1993) MPNMPN methodmethod forfor enumerationenumeration ofof H.H. akashiwoakashiwo cystscysts havinghaving germinationgermination abilityability inin sedimentssediments (Imai(Imai andand ItakuraItakura 1991).1991).

Feasible for the cysts without information on morphology DistributionDistribution ofof cystscysts ofof HeterosigmaHeterosigma akashiwoakashiwo inin bottombottom sedimentssediments ofof HiroshimaHiroshima Bay,Bay, thethe SetoSeto Inland Inland SeaSea (Imai(Imai andand ItakuraItakura 1991). 1991).

Cysts were abundant in the coast. EffectsEffects ofof temperaturetemperature onon thethe germinationgermination ofof HeterosigmaHeterosigma akashiwoakashiwo cystscysts inin sedimentssediments determineddetermined byby thethe MPNMPN methodmethod (Imai(Imai andand ItakuraItakura 1999).1999).

Vigorous germination at 15°C or higher temperature SeasonalSeasonal fluctuationsfluctuations ofof thethe highesthighest cellcell densitiesdensities ofof H.H. akashiwoakashiwo cellscells inin waterwater columnscolumns atat 33 stationsstations inin HiroshimaHiroshima BayBay (Imai(Imai andand ItakuraItakura 1999). 1999).

Blooms in May ~ June with great seasonality SeasonalSeasonal fluctuationsfluctuations ofof germinablegerminable cysts cysts (MPN)(MPN) inin thethe surfacesurface sedimentssediments (0(0 -- 1cm) 1cm) ofof HiroshimaHiroshima BayBay (Imai(Imai andand ItakuraItakura 1999). 1999).

Many cysts are always physiologically germinable. SeasonalSeasonal fluctuationsfluctuations ofof surafacesuraface (open (open circle)circle) andand bottombottom (closed(closed circle)circle) waterwater temperaturestemperatures atat 33 stationsstations inin HiroshimaHiroshima Bay.Bay. WeeklyWeekly changeschanges inin waterwater temperature,temperature, H.H. akashiwoakashiwo inin surfacesurface water,water, andand thethe totaltotal H.H. akashiwoakashiwo livelive cystscysts inin surfacesurface sedimentssediments (0-1cm)(0-1cm) atat Stn.1Stn.1 inin HiroshimaHiroshima BayBay (Imai(Imai andand ItakuraItakura 1998).1998). TotalTotal livelive cystscysts increasedincreased justjust afterafter thethe peakpeak ofof bloombloom andand neededneeded 11 weekweek forfor maturation.maturation. HeterosigmaHeterosigma redred tidestides usuallyusually occuroccur atat 2020°°CC oror higherhigher withwith widewide rangerange ofof salinitysalinity (Honjo(Honjo 1993). 1993). ProcessProcess andand keykey factorsfactors forfor thethe occurrenceoccurrence ofof HeterosigmaHeterosigma akashiwoakashiwo redred tidetide (Smayda(Smayda 1998). 1998). SummarySummary forfor HeterosigmaHeterosigma akashiwo akashiwo

ƒ 1. Heterosigma a akashiwokashiwo has cyst stage for outliving such as overwintering. ƒ 2. Cyst formation was induced at the end of blooms and completed in the dark (Itakura et al. 1996). ƒ 3. New cysts need ca. 1 week for maturation. ƒ 4. Cysts effectively germinate at 15°C or higher. ƒ 5. in situ germination of cysts can always occur. ƒ 6. Red tides show great seasonality, and hence seeded by the germination of cysts in sea bottom. ƒ 7. Life cycle startegy of H. akashiwo is also well adapted to temperate shallow coastal areas; changes between cysts and vegetative cells are easy. HowHow dodo harmfulharmful raphidophyteraphidophyte bloomsblooms occuroccur predominantlypredominantly overover diatomsdiatoms inin coastalcoastal sea?sea? ChangeChange ofof bloomsblooms fromfrom diatomsdiatoms toto H.H. akashiwoakashiwo andand toto diatoms.diatoms. GrowthGrowth parametersparameters ofof diatomsdiatoms andand raphidophytesraphidophytes ------Species Nutrients μmax (division/day) Ks (μM) ------Diatoms Chaetoceros didymum NO3-N 1.82 1.29 PO4-P 2.16 0.48 Ditylum brightwellii NO3-N 2.02 0.73 PO4-P 2.00 0.16 Thalassiosira rotula NO3-N 1.69 1.28 PO4-P 1.70 0.23 ------Raphidophytes Chattonella antiqua NO3-N 0.74 0.87 PO4-P 0.74 0.29 Heterosigma akashiwo NO3-N 1.7 – 1.9 1.99 - 2.45 PO4-P 1.7 – 1.9 1.00 – 1.98 ------RaphidophytesRaphidophytes havehave cysts.cysts. DiatomsDiatoms havehave restingresting stagestage cells.cells. SeedsSeeds ofof diatomsdiatoms andand raphidophytesraphidophytes areare abundantabundant inin sedimentssediments ofof coastalcoastal sea.sea. GerminationGermination ofof raphidophyteraphidophyte cystscysts inin thethe darkdark

Chattonella spp. Heterosigma kashiwo DiatomDiatom restingresting stagestage cellscells needsneeds lightlight forfor germinationgermination andand rejuvenationrejuvenation GerminationGermination experimentexperiment

H. akashiwo cysts 330 / g sedimedt

Diatom resting stage cells 1.6 x 105 / g sed.

Light: 110µE/ m2/ sec 14hL : 10hD

Temperature: 20ºC EffectsEffects ofof lightlight intensityintensity onon germinationgermination and/orand/or rejuvenationrejuvenation ofof diatomdiatom restingresting stagestage cells.cells.

DiatomDiatom restingresting stagestage cellscells needneed lightlight forfor germination.germination.

Open circle: total diatoms Closed circle: S. costatum Black triangle: Chaetoceros Star: Thalassiosira Comparison of the effects of light intensity to cysts and diatom resting stage cells on dominancy of H. akashiwo.

InIn surfacesurface water:water:

1)1) DiatomsDiatoms dominateddominated inin higherhigher light.light. 2)2) H.H. akashiwoakashiwo dominateddominated inin lowlow lightlight VerticalVertical profilesprofiles ofof lightlight intensityintensity inin coastalcoastal seasea Harima-Nada, Seto Inland Sea ChaetocerosChaetoceros spp.spp. formform soressores inin lowlow nitrogennitrogen concentrationconcentration

Chaetoceros curvusetus, C. distans, C. lauderi

Harima-Nada: July 14 - 18, 1991 DiatomDiatom restingresting hypothesishypothesis

Nutrient depletion after stratification induce resting stages of diatoms. SummarySummary

ƒ 1. Diatoms are stronger than raphidophytes i inn vegetative growth. ƒ 2. Raphidophytes h haveave cyst stage and diatoms have resting stage in their life cycles. ƒ 3. Raphidophyte cysts can germinate in the dark and diatom resting stage cells need light for germination. ƒ 4. Nutrient depletion induce resting stage in diatoms. ƒ 5. Low light irradiation to sediments induced predominancy o off raphidopyhtes in water columns. ƒ 6. The diatom resting hypothesis is presented for the mechanism of occurrences of raphidophyte red tides. AA proposalproposal ofof ideaidea forfor preventionprevention ofof harmfulharmful bloomsblooms byby bottombottom irradiationirradiation

No toxic effects on environments

Problems for feasibility 1. Timing, period, and intensity of irradiation 2. Scale of irradiation