During the latter part of the 20^th century，the averageamount of ultraviolet-B(UV-B)radiation reachingthe earth’s surface has increased as a result of thedepletion of stratospheric ozone(Butler et al.，1999).Over the past decade，stratospheric ozone depletionhas slowed and levels have even recovered slightly.However，complete recovery of the ozone layer willbe a slow process，and marine organisms will becontinuously exposed to high doses of UV-B radiationfor some time to come(Hu，2007). Interest in theeffects of UV-B radiation on macroalgae is increasing(Liu et al.，2008).

Macroalgae represent approximately 10% ofprimary productivity in the ocean(Smith，1981).They grow in the eulittoral and upper sublittoralzones，where they are exposed to increasing levels ofradiation. Chondrus ocellatus Holm(Rhodophyta)isa species of red algae that grows abundantly along rocky shores from the middle intertidal into thesubtidal zones of Qingdao，Sh and ong Province，China. It is the dominant species with the greatestbiomass in the macrobenthic algae community in therocky low intertidal zones of Qingdao(Tang et al.，2008). Chondrus ocellatus are widely distributedacross geographical areas and at different depths.

The effects of UV-B radiation on marinemacroalgae include damage to DNA，changes in theDNA repair capacity，and alterations to geneexpression，protein structures，photosyntheticpigments，secondary metabolism，morphology，and growth(Frohnmeyer and Staiger，2003; Xu et al.，2003; He et al.，2004; Bischof et al.，2006; Zhong et al.，2009; Pereira et al.，2014; Polo et al.，2014;Simioni et al.，2014). In macroalgae，large moleculescan be damaged by high levels of UV-B radiation.Increased UV-B radiation can phototransform DNA，leading to the production of cyclobutane pyrimidinedimers(CPDs) and pyrimidine(6-4)pyrimidinonedimers(Strid et al.，1994)，which inhibit DNAreplication and transcription(Buma et al.，1995，2000). Photosynthetic pigments(e.g.，chlorophylls，phycobilins，and carotenoids)show varyingsensitivities to UV-B radiation; phycobilins are themost sensitive，followed by chlorophylls，and thencarotenoids(Teramura，1983).

Damage to DNA，proteins，and pigments inhibitthe normal physiological processes of macroalgae. Inaddition to impacting photosynthesis and respiration，increased UV-B radiation also damages otherphysiological process，such as nutrient absorption and zoospore mobility(Renger et al.，1986; Allen et al.，1997; Karsten，2008). The negative effects of UV-Bradiation on these physiological processes c and ecrease growth rate and even cause death. Theseeffects can change the population size of a givenspecies，ultimately infl uencing the marine ecosystem(Duffy and Hay，2000; Sousa and Connall，1992).Species distributions can also be affected，as algaethat were distributed near the surface colonize deeperlayers(Wiencke et al.，2006).

Macroalgae have evolved various protection and repair mechanisms to reduce and reverse UV-Binduceddamage. The photosynthetic system respondsto UV-B radiation via two mechanisms: faster repairof photoinhibition and depressed photoinhibition(Bischof et al.，1999). In green algae，a mechanismexists by which UV damage to the D1 protein inphotosystem II can be detected and repaired(Yokthong et al.，2001). Over the long term，a series of antioxidantsystems has evolved to scavenge reactive oxygenspecies(Aguilera et al.，2002b). Algae have alsoevolved mechanisms to repair UV-B induced damageto DNA，such as light-dependent repair of CPDs inmany algal species(Pakker et al.，2000); dark repairalso occurs in many plants(Li et al.，2000; He et al.，2006). Some algae also synthesize mycosporine-likeamino acids(MAAs)，which can absorb UV radiation and emit heat or fl uorescence to prevent damage(Dunlap and Shick，1998; Karsten et al.，1998).

There are few studies which evaluated the effectsof UV-B radiation on early development stage and spores. Because the algae in juvenile stages aresmaller in size and simple in structures，different kinds of stress can affect the algae more evidently，asshown for various brown algae zoospores and germlings(Wiencke et al.，2000，2006 ; Altamirano et al.，2003)，unicells of Ulvales(Cordi et al.，2001) and early development of Gigartinales(Roleda et al.，2004). So the effect of UV-B radiation on themicroscopic life stages of the algae are essential torecruit. In this study，we evaluated the effects of UV-Bradiation on carpospore development，UV-Badaptability，and UV-B screening capacity in the earlydevelopmental stages of C. ocellatus . We alsoexamined the role of light quality during repair ofUV-B-induced damage. 2 MATERIAL AND METHOD 2.1 Algal material

C. ocellatus is abundant species of red alga alongthe coast of Qingdao，and inhabits the intertidal and upper sublittoral zones of rocky shorelines. It growsfrom a discoid holdfast and branches four or fi vetimes in a dichotomous. C. ocellatus with maturecarpogonium tissues was collected from rocks in theintertidal zone at Taipingjiao(a public beach)Qingdao，Sh and ong Province，China，in summer. Nospecifi c permissions were required. Experimentsusing about 200 fronds of gametophytes and werecarried out in the laboratory. Immature sporophytes ofC. ocellatus have the same morphological charactersas gametophytes.2.2 Release of carpospores

Sporangia with carpospores were washed insterilized seawater and cleaned using a banister brush.The washed gametophytes with carposporophyteswere dried in the shade for 4 h at 18°C to promote thespread of spores. Natural seawater was sterilized byfi ltering through 0.45-μm microporous fi ltering fi lm and then autoclaving. The three fronds of gametophyteswere placed in sterile Petri dishes containing 8 glassslides and 300 mL sterilized seawater. The disheswere kept in the dark until the carpospores attached tothe slides(20/3 mm²)，then the attached carposporeswere used for UV-B radiation experiments. Allcultures were maintained in modifi ed Provasoliculture solution consisting of sterilized seawaterenriched with nitrogen(8.24×10^-4 mol/L NaNO₃) and phosphorus(3.26×10^-5 mol/L NaH₂ PO₄ ·H₂ O)(Starr and Zeikus，1993). The cultures were kept at 18±1°Cunder a 12:12(L:D)photoperiod of 40 μmol photons/(m² ∙s)of photosynthetically active radiation(PAR)provided by 40-W daylight fl uorescent tubes(Philips，Ningbo，China). Each treatment consisted of fi vereplicates，one dish was one replicate. The culturesolution was replaced every 2 d until Day 48，when avertical branch had formed in each treatment. Thecarpospores were then assessed for physiological and biochemical indices.2.3 UV-B treatments

All experimental treatments occurred underlaboratory conditions. A rank of four fl uorescentUV-B lamps(Q-Lab，Clevel and ，OH，USA)providedsupplemental UV-B radiation. The UV-B intensitywas 7.2 μW/cm²，as measured with a UV-B type UVradiometer(Beijing Normal University PhotoelectricInstrument Factory，Beijing，China). The light wasfi ltered with the cellulose diacetate foil to achieve 0%transmission below 286 nm.

For these experiments，fi ve levels of UV-Bradiation(36，72，108，144，and 180 J/m²)wereemployed by adjusting the exposure time(5，10，15，20，and 25 min，respectively)(Table 1). The levels ofUV-B radiation were setting according to thepreliminary analysis. The tetraspores and germlingscould not development well as the dose of UV-Bradiation higher than 216 J/m² .The control consistedof carpospores kept under PAR with no UV-Bradiation(0 J/m²). The UV-B radiation treatmentswere applied each day at 09:00. The UV-B lampswere burned for 100 h before starting the experiment，as recommended by the manufacturer，and weresteadied 10 min before the start of each expose toachieve stable irradiance. To test the effects of lightquality on repair of UV-B-induced damage，thecarpospores were subjected to a 2-h recovery periodunder PAR，darkness，red light，or blue light after thedaily UV-B treatment(Table 1). Red and blue lightwere supplied at 40 μmol·photons/(m²·s)using three40-W Philips fl uorescent lamps. After the 2-h recoveryperiod，the carpospores were returned to their cultureconditions.

Table 1 UV-B radiation and light treatments during repair periods for carpospores released from Chondrus ocellatus blades

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To determine the UV-B radiation effects on thecarpospores，the experimental samples(PAR 36–180 J/m²)were returned to PAR after exposure toUV-B radiation; the control was not exposed to UV-Bradiation at all(Table 1，PAR group). To determinethe effects of light quality on repair of UV-B-induceddamage，experimental groups were subjected to fourdifferent light conditions immediately after UV-Bexposure. In these experiments，the group kept underPAR for 2 h was the ‘normal’ light repair group，whilethe group in darkness could not carry out light repair.These groups were compared with those kept in red orblue light for 2 h.2.4 Assessment of UV-B-induced damage toC. ocellatus 2.4.1 Carpospore diameters

We determined the diameters of carpospores undera fl uorescence microscope(CX31; Olympus，Tokyo，Japan)every 4 d from Day 0 until Day 48. Thediameters were measured from images using theoptical microscopy software package ImagePro Plusver. 6(Media Cybernetics，Silver Spring，Maryl and ，USA). Normal carpospores were approximately discshaped.The diameter of each was the average of 50carpospores diameter in each treatment.2.4.2 DNA extraction and ELISA of CPDs on Day 48

Total DNA was extracted from 0.1 g carposporesof C. ocellatus according to the method of Mayes etal.(2004). To avoid light repair during analysis，theDNA was extracted under dim red light. DNAconcentration was determined using a nucleic acidspectrophotometer(Ultrospec 4300 Pro，GEHealthcare，Little Chalfont，UK).

CPDs were quantifi ed by enzyme-linkedimmunosorbent assay(ELISA)as described by Moriet al.(1991)，with a monoclonal antibody，ab10347，supplied commercially(Abcam，Cambridge，UK).Absorbance of the reaction mixture at 490 nm was measured using a microplate reader(Multiskan MK3，Thermo Fisher Scientifi c，Massachusetts，USA).2.4.3 Concentrations of chlorophyll a and phycoerythrin on Day 48

Carpospores of C. ocellatus(0.1 g)washomogenized in 90% acetone with quartz s and on ice，then kept at 4°C for 24 h before centrifuging at8 944 × g at 4°C for 10 min. The absorbance of thesupernatant was measured at 647 nm and 664 nmaccording to the method of Ritchie(2006). Thechlorophyll a(Chl a)content was calculated as:

Click Browse formula

Carpospores of C. ocellatus(0.1 g)was washed withdistilled water，homogenized and extracted in 0.1 mol/Lphosphate buffer(pH 6.5)on ice，then centrifuged at8 944× g at 4°C for 10 min. The concentration ofphycoerythrin in the supernatant was determined usingthe method of Beer and Eshel(1985).2.4.4 Extraction and analysis of MAAs

0.1 g carpospores of C. ocellatus were oven driedat 100°C for 15 min，and MAAs were extracted for2 h in 25% HPLC-grade methanol(v/v)at 40°C. Thenthe samples were passed through a 0.22-μm membranefi lter. Tryamine hydrochloride(THC)was used as aninternal st and ard in this analysis(Whitehead and Hedges，2002). THC has a maximum absorption at280 nm，far lower than that of the MAAs，and arelatively low molecular weight，so it is easilydistinguishable from the common MAAs. Prior toliquid chromatograph/mass spectroscopy(LC/MS)analysis，100 μL of a solution containing 173 mgTHC dissolved in 1 mL of MeOH(1 mol/L)wasadded tO 400 μL of MAA st and ard.

The concentration of MAAs was analyzed withhigh-performance liquid chromatography(HPLC)(1120 Compact LC; Agilent，Santa Clara，CA，USA) and calculated from the peak area. The mobile phasewas 2.5% aqueous methanol(v/v)plus 0.1% aceticacid(v/v)in water，run isocratically at 1.0 mL/min for15 min. Sample volumes of 10 μL were injected intothe Sphereclone C column with precolumn(5 mpacking; 250 mm×4 mm I.D.). Peaks were detectedvia absorbances at 320 nm and 340 nm; samplescontaining the internal st and ard were monitored at280 nm and 320 nm.

MAA types were analyzed using an Agilent 1100LC/MS system with a diode array detector(DAD)interfaced to a quadrupole mass spectrometer at theFirst Institute of Oceanography，Qingdao，China. TheUV wavelengths monitored were 320 nm and 340 nm，except when the sample contained the internalst and ard，in which case 280 nm and 320 nm weremonitored. We used a C-8 column(250 mm×4.6 mmI.D.)with isocratic elution over a 15-min period. Themobile phase was 65:35 methanol/water acidifi ed topH 3.8 with acetic acid. The fl ow rate was 0.8 mL/min. The acquisition methods for LC/MS were basedon those of Whitehead and Hedges(2002)，and theconditions were optimized to produce positivemolecular ions(MH⁺)via electrospray ionization.Other LC/MS settings were as follows: gastemperature，350°C; sheath gas fl ow，11 mL/min;scan mode 50–600 amu. Each kind of MAA wasdetermined according to molecular weight from thetotal ion current. The structural formulae weredetermined by comparing the examined massspectrum with the st and ard mass spectrum and wereused to confi rm the MAA classes detected inC. ocellatus .2.5 Data analysis

Each treatment consisted of fi ve replicates. Weused one-way analysis of variance and generalizedlinear model-univariate analysis to test the signifi canceof differences. We used SPSS 13.0 for statisticalanalyses(IBM，Chicago，IL，USA). Levene’s test wasused to assess homogeneity of variance. When the PP< 0.05).3 RESULT

The diameters of carpospores subjected to differentUV-B-radiation and light-repair conditions during theexperiment are shown in Fig. 1. The diameters differedafter Day 8 in the PAR group(Fig. 1a). Carposporediameters increased under 0 and 36 J/m² UV-Bradiation，but at higher UV-B radiation levels(72–180 J/m²)，carpospore growth was strongly inhibited.The diameters of carpospores exposed tO₃6 J/m²UV-B radiation were signifi cantly greater than thosein other treatments，including the control. On Day 48，the average diameter across the six UV-B treatmentsin the PAR was greater than the averages in the groups kept in darkness，blue light，or red light for the 2-hrepair period(P< 0.001). The lowest average diameterwas in the blue light group(P< 0.001). In the dark(Fig. 1b)，red-light(Fig. 1c) and blue-light(Fig. 1d)groups，the carpospore diameters differed on Day 4.In the dark group，the diameters of carpospores thatwere not subjected to UV-B radiation were the sameas those in the PAR group and signifi cantly greaterthan those in the red and blue groups on Day 48(P< 0.001). Carpospores subjected tO₃6 J/m² UV-Bradiation had slightly smaller diameters than those inthe control and 72 J/m² UV-B radiation treatments. Athigher UV-B doses，carpospore diameter wassignifi cantly smaller than in the control. Carposporediameter in the red light group(Fig. 1c)showed thesame trend as in the darkness group. In the blue light group(Fig. 1d)，at higher UV-B radiation levels，carpospore diameter decreased signifi cantly.

Fig. 1 Variation in carpospore diameters under different UV-B radiation and light conditions Diameters of Chondrus ocellatus carpospores kept under photosynthetically active radiation(a)，in the dark(b)，and under red(c) and blue(d)light afterexposure to different doses of UV-B radiation are shown. Diameters were measured every 4 d from Day 0 to Day 48. Letters(A–F)refer to the UV-B radiationdoses(0–180 J/m2)in Table 1. Data are mean values±SD(n=5).

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Inverted fl uorescence microscope images ofcarpospores on Day 48 after treatment with differentUV-B radiation levels are shown in Fig. 2. Normalcarpospores were approximately disc-shaped，with asmooth edge and dark color(Fig. 2a). Carposporesexposed tO 36 J/m² UV-B radiation(Fig. 2b)grewmore rapidly than those in the control，but had rougheredges. When UV-B radiation levels exceeded 72 J/m²(Fig. 2c，d)，carpospore growth was inhibited and theirdiameters were smaller than those in the control and low-dose(36 J/m²)UV-B treatment. In addition，carpospores subjected to UV-B levels greater than72 J/m² had indistinct edges，irregular shapes，incompactly-arranged cells，and a light color. The inverted fl uorescence microscope images clearlyshow that in the control，carpospores grew better inthe PAR(Fig. 3a) and darkness(Fig. 3b)treatmentsthan in the other two groups(Fig. 3c，d). When theUV-B radiation level was 180 J/m²(Fig. 4)，UV-Bradiation adversely affected carpospores in all fourlight treatments，as described above. Carpospores inthe blue light group also showed signs of damage;they had hyaline vesicles at the edges and were verylight in color.

Fig. 2 Carpospores in UV-B radiation plus PAR treatmentson Day 48 Chondrus ocellatus carpospores exposed to photosyntheticallyactive radiation(PAR)after normal culture without UV-B radiation(a) and after UV-B radiation treatment with 36 J/(m2· d)UV-B(b)，72 J/(m2· d)UV-B(c)，and 180 J/(m2· d)UV-B(d)were observedunder an inverted microscope. Scale bar: 100 μm.

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Fig. 3 Carpospores exposed to PAR，dark，red light，and blue light after non-UV-B treatment Chondrus ocellatus carpospores were observed under an invertedmicroscope on Day 48 after a non-UV-B radiation treatment(0 J/(m2· d)UV-B)followed by exposure to photosynthetically activeradiation(PAR)(a)，dark(b)，red light(c)，and blue light(d). Scalebar: 100 μm.

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Fig. 4 Carpospores exposed to PAR，dark，red light，and blue light after UV-B treatment Chondrus ocellatus carpospores were observed under an invertedmicroscope on Day 48 after a 180 J/(m2· d)UV-B radiation treatmentfollowed by exposure to photosynthetically active radiation(PAR)(a)，dark(b)，red light(c)，and blue light(d). Scale bar: 100 μm.

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The absorbance of CPDs in C. ocellatus changedwith UV-B radiation level. As shown in Fig. 5，UV-Bsignifi cantly affected DNA and accumulation of CPDs in the PAR group(P< 0.001; Fig. 5a). As theUV-B radiation level increased from 0 J/m² to 72 J/m²，the CPD absorbance increased，peaking at a value of1.0，then decreased after exposure to 108 J/m² UV-Bradiation. At 144 J/m² UV-B，the absorbance of CPDs(0.35)was signifi cantly lower. The control groupsalso formed some CPDs. In the group kept in darkness(Fig. 5b)，CPD absorbance increased with the level ofUV-B radiation(P< 0.001). In the red-light group(Fig. 5c)(P< 0.001)，the absorbance of CPDs increasedas the level of UV-B radiation increased to 72 J/m²，where the peak value of 1.76 was seen; at 108 J/m²UV-B radiation，CPD content decreased(0.64absorbance)then increased. In the blue-light group(Fig. 5d)，CPD absorbance did not differ signifi cantlyamong the 36，108，144，and 180 J/m² UV-B treatments(P =0.384). The average absorbance values in theblue-light groups(0.5791)were lower than those inthe PAR，darkness，and red-light groups. Carposporesin the red-light group had the highest CPD contents.

Fig. 5 CPD concentrations in carpospores under different UV-B radiation and light conditions Concentrations of cyclobutane pyrimidine dimers(CPDs)in Chondrus ocellatus carpospores were determined on Day 48 after different doses of UV-Bradiation followed by photosynthetically active radiation(a)，dark(b)，red light(c)，and blue light(d). Data are mean values±SD(n =5). Different letters abovecolumns indicate signifi cantly different mean values(LSD test，P <0.05).

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As shown in Fig. 6，UV-B radiation signifi cantlydamaged some pigments in C. ocellatus in the PARgroup(P< 0.001)(Fig. 6a). The low level of UV-Bradiation(36 J/m²)increased Chl-a synthesis，and Chl-a content rose to 2.29 mg/L. As the level of UV-Bradiation increased further，the Chl-a contentdecreased signifi cantly. In the group kept in darkness(Fig. 6b)，the Chl-a content increased with the UV-Bradiation level from 36 to 108 J/m²，peaking at1.05 mg/L，then decreasing at higher UV-B levels(P< 0.001). The Chl-a content in the red-light(P< 0.001; Fig. 6c) and blue-light(P< 0.001; Fig. 6d)group showed the same trends as observed in the PARgroup，with peaks of 1.35 and 1.36 mg/L，respectively.

Fig. 6 Chl-a concentrations in carpospores under different UV-B radiation and light conditions Concentrations of Chl-a in Chondrus ocellatus carpospores were determined on Day 48 after different doses of UV-B radiation followed by photosyntheticallyactive radiation(a)，dark(b)，red light(c)，and blue light(d). Data are mean values±SD(n=5). Different letters above columns indicate signifi cantly-differentmean values(LSD test，P<0.05).

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There were signifi cant changes in the phycoerythrincontents in response to UV-B radiation，as shown inFig. 7. The trends in phycoerythrin contents were thesame as those observed for Chl-a contents in the PAR(P< 0.001; Fig. 7a) and blue-light(P< 0.001; Fig. 7d)groups. A low level of UV-B radiation(36 J/m²)resulted in increased phycoerythrin synthesis，and thephycoerythrin content increased to 0.02 and 0.012 mg/L，respectively，in the two groups; at higherUV-B levels，the phycoerythrin content decreasedsignifi cantly. The phycoerythrin contents decreasedsignifi cantly with increasing levels of UV-B radiationin the darkness(P< 0.001; Fig. 7b) and red-light(P <0.001; Fig. 7c)groups. The average phycoerythrincontent was lowest in the blue-light group.

Fig. 7 Phycoerythrin concentrations in carpospores under different UV-B radiation and light conditions Concentrations of phycoerythrin in Chondrus ocellatus carpospores were determined on Day 48 after different doses of UV-B radiation followed byphotosynthetically active radiation(a)，dark(b)，red light(c)，and blue light(d). Data are mean values±SD(n=5). Different letters above columns indicatesignifi cantly different mean values(LSD test，P<0.05).

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MAAs were analyzed by LC/MS(Fig. 8). Thecarpospores of C. ocellatus contained three kinds of MAAs: palythine(245.112 9)，asterina-330(289.138 1)，and shinorine(333.129 2). These MAAswere quantifi ed by HPLC. We observed the sameretention times of compounds extracted fromcarpospores subjected to different treatments in thefour groups，implying that their chemical compositionswere identical in the different samples. The MAAcontents in the carpospores from the four groups areshown in Fig. 9. The MAA contents of the PAR groupincreased(0.115 mg/g)，decreased(0.018 mg/g)，and then increased again with increasing doses of UV-Bradiation(P< 0.001; Fig. 9a). A similar trend wasobserved in the groups kept in darkness(P< 0.001;Fig. 9b) and red light(P< 0.001; Fig. 9c); the MAAcontents peaked in response tO 36 J/m² UV-B radiationat 0.087 and 0.139 mg/g，respectively，but decreasedat higher UV-B levels. In the red-light group，theMAA content of carpospores subjected tO₃6 J/m²UV-B was signifi cantly greater than that in the PAR，darkness，or blue-light groups(P< 0.001). In the bluelightgroup(P< 0.001; Fig. 9d)，MAA contentsincreased with UV-B radiation level from 0 to 72 J/m²(0.148 mg/g)，but decreased at 108 J/m² UV-B to thelowest value of 0.28 mg/g. The highest average MAAcontent was in the blue-light group(P< 0.001).

Fig. 8 Extracted ion current of MAAs in carpospores of Chondrus ocellatus Extracted ion currents of mycosporine-like amino acids(MAAs; a. palythine(245.112 9); b. asterina-330(289.138 1); c. shinorine(333.129 2))in carposporesof C . ocellatus are shown. Molecular weights were determined by LC/MS.

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Fig. 9 MAA concentrations in carpospores under different UV-B radiation and light conditions Mycosporine-like amino acid(MAA)concentrations in Chondrus ocellatus carpospores were determined on Day 48 after different doses of UV-B radiationfollowed by photosynthetically active radiation(a)，dark(b)，red light(c)，and blue light(d). Data are mean values±SD(n =5). Different letters above columnsindicate signifi cantly-different mean values(LSD test，P<0.05).

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In some rhodophytes，UV-B radiation negativelyaffected growth，photosynthetic pigments，and photosynthetic parameters and caused someultraviolet-absorbing/screening substances toaccumulate(Eswaran and Rao，2001; Hoyer et al.，2001; Eswaran et al.，2002; Schmidt et al.，2009;Schmidt et al.，2010a，b，c; Schmidt et al.，2012a，b).Our results show that UV-B signifi cantly stressedC. ocellatus carpospores. The low dose of UV-B radiation promoted growth and development ofC. ocellatus ; carpospore diameters were signifi cantlyhigher in this treatment than in the other treatments(including the control)in the PAR group on Day 48.The low UV-B dose may have promoted the activitiesof some protection and repair mechanisms in thecells，so the algae could acclimatize better to theconditions. According to Liu et al.(2008)，a low-doseUV-B promoted zoospore germination and theformation of male and female gametophytes. Ourresults showed that when the UV-B radiation exceeded72 J/m²，carpospore growth decreased signifi cantly. Inaddition，morphological changes induced by UV-Bradiation were very signifi cant; at high UV-B levels，the discoidal body of C. ocellatus had indistinctedges，irregular shapes，incompactly-arranged cells，and a light color. According to Scariot et al.(2013)，UV-B radiation induced morphological changes intetrasporelings，such as altered length-to-width ratio，twisted thalli，loss of pigmentation，and differentiation of more than one apical cell. As well as in younggametophytes of Gelidium floridanum，theultrastructure also changed by UV-B radiation(Simion et al.，2014). These changes may be due tothe negative effects of UV-B radiation，includingbleaching of photosynthetic pigments，damage tophotosystem II，and the formation of CPDs and reactive oxygen species. These changes inhibitphysiological and biochemical reactions，ultimatelydelaying the development of the carpospores.

In this study，UV-B radiation induced CPDformation in the DNA，and we observed the patternsof repair under different light conditions. DNA is amain target molecule of UV-B radiation. Inrhodophytes，UV-B-induced damage can be remediedvia light repair(photoreactivation)，dark repair(nucleotide excision repair)，and recombination repair(Britt，1999). Here，when the UV-B radiation level increased to 144 J/m²，the CPD content decreasedsignifi cantly. Tetraspores may have several repairmechanisms that are induced by serious DNA damage.In some bacteria have some repair mechanisms inresponse to UVR-induced damage. These mechanismsare usually classifi ed into dark repair and photoreactivation. All mechanisms are inducible aspart of the SOS regulon，and the induction is dependenton the level of DNA damage.Some bacteria can repairUVR-induced damage via dark repair and photoreactivation mechanisms that are induced aspart of the SOS regulon upon DNA damage(Zenoff et al.，2006). These SOS repair mechanisms may alsoexist in the tetraspores of C. ocellatus . If so，theycould have repaired the CPDs that accumulated inC. ocellatus cells，decreasing the CPD content. As theUV-B radiation increased further，the rate of CPDformation would have exceeded that of DNA repair，and /or the DNA photolyase would be damaged byUV-B radiation，explaining the increases in CPDsunder high levels of UV-B radiation.

UV-B radiation also decreased the concentrationsof phycoerythrin and Chl-a in C. ocellatus .Phycoerythrin，which absorbs at 498–565 nm，is themost important light-harvesting protein inphotosystem II in red algae(Sui and Zhang，1998 ;Munier et al.，2014)，and also plays important roles inmany physiological and biochemical reactions. Insome red algae，a high dose of UV-B radiation leadsto a sharp decrease in phycoerythrin content(Aguilera et al.，1999; Schmidt et al.，2010a，b，c; Schmidt et al.，2012a，b). Recently，Xu and Gao(2009)reported thatphycoerythrin contents decreased signifi cantly inresponse to UV-B radiation in Gracilarialemaneiformis . In our experiments，the phycoerythrincontents in carpospores were signifi cantly lower athigh UV-B doses(>36 J/m²). Under these conditions，there were also signifi cant decreases in Chl-a content，consistent with previous reports on the effects of UV-B radiation on Chl-a content(Sinha and Häder，1998; Eswaran et al.，2002).

MAAs，which comprise a cyclohexenone or-hexenimine core conjugated with the nitrogen moietyof an amino acid，are strong antioxidants(Shick and Dunlap，2002). These compounds also function asimportant UV-absorbing sunscreens in red algae(Karsten and Wiencke，1999). Total MAA levels inPalmaria palmata were greater in samples fromshallow waters(1.5 m depth)than in those fromdeeper waters(3 m). Furthermore，MAA contents inP . palmata and Devaleraea ramentacea were lowerin samples collected in spring or when covered withice than in samples collected in summer，when theUV-B radiation level was higher(Aguilera et al.，2002a). In this experiment，the MAA contentsincreased rapidly when the alga was exposed to a lowdose of UV-B radiation(36 J/m²). We speculated thatthere is a threshold of UV radiation for MAAsynthesis. As the UV-B radiation level increased，MAA synthesis was promoted，and the cellular contents increased signifi cantly. As UV-B levels rose，MAA contents signifi cantly decreased，suggestingthat MAAs are consumed as UV-B protectants or asantioxidants more rapidly than they can be synthesizedunder these conditions. In red algae，MAAs hadimportant antioxidant activity and provided someprotection against UV-B radiation(Dunlap and Yamamoto，1995). In cyanobacteria，MAA contentsincreased signifi cantly with UV-B dose(Rajeshwar et al.，2003; Rastogi and Incharoensakdi，2014).

In general，UV-B radiation negatively affectedearly development of C. ocellatus carpospores，eventhough their growth was promoted at lower doses.The results prove that low-dose UV-B radiationpromotes MAA synthesis，but at higher doses，UV-Bradiation inhibited carpospore growth，induced CPDs，bleached pigments，and consumed MAAs.4.2 Effects of light quality on repair of UV-Binduceddamage

PAR，the b and of solar radiation from 400 nm to700 nm，is used for photosynthesis. Our resultsshowed that carpospore diameters in the PARtreatment were signifi cantly higher than those in otherthree groups. We hypothesize that the carposporeskept in the dark after exposure to UV-B radiationwere unable to repair UV-B-induced damage，whichred light inhibited some repair processes，and thatblue light enhanced the effects of UV-B radiation. Thediameters of carpospores differed after Day 8 in thePAR group and after Day 4 in the three other groups;thus，the damage induced by UV-B radiation appearedlater in the PAR group，indicating that PAR plays animportant role in repair. In other studies，PARpromoted adaptive mechanisms of plants exposed toUV-B radiation(Teramura，1980; Cen and Bornman，1990). Pradhan et al.(2006)reported that the degreeof damage to the photosynthetic apparatus of wheatleaves subjected to UV-B treatment was more severethan that in a UVB+PAR treatment. In this study，weobserved a decrease in CPD content during DNArepair in the PAR treatment. These results indicatedthat light repair was active in carpospores. Britt(1995)indicated that UV-B damage to DNA wasmainly repaired by photoreactivation.

In the groups kept in darkness after exposure toUV-B radiation，CPD absorbance decreased in thetreatment exposed to low UV-B doses(36–108 J/m²).We hypothesize the existence of a repair mechanismother than photoreactivation in carpospores，becausewithout PAR，the light-dependent repair process could not operate. Dark(nucleotide excision)repair isthought to operate in carpospores. It may be inhibitedunder PAR when the DNA damage is mild，while indarkness，it is activated to repair the DNA damagedby UV-B radiation. He et al.(2006)studied the effectsof UV-B radiation on CPD contents in mung bean and observed that dark repair occurred to DNA，but thatphotoreactivation did not in darkness. Furthermore，the results of the present study suggest that，as thelevel of UV-B radiation increased，CPD formed morerapidly，exceeding the rate of DNA repair and accumulating in carpospores. The variation of Chl-awas different from that in other groups. So the darkcondition may aggravated the damage of UV-Bradiation on Chl-a . The content of Chl-a in 36 J/m²treatment decreased signifi cantly.

Our experimental results showed that CPD contentswere higher in the red-light group than in the othergroups. The light-repair process may not be able tooperate under red light，allowing a large number ofCPDs to accumulate in the carpospores. Some studyindicated that dim red light could inhibit DNAphotorepair(Freeman et al.，1989). With the CPDsaccumulated to a dose in the algae，there may someanother repair mechanism activated，so the CPDscontents decreased. The phycoerythrin content of thegroup subjected to no UV-B followed by red light washigher than that in the groups kept in PAR，darkness，or blue lightgroups not subjected to UVB . In otherwords，during carpospore culture，red light couldpromote phycoerythrin synthesis. Similarly，ourresults indicated that red light also promoted MAAssynthesis.

In the blue-light group，the carpospores had smalldiameters on Day 48 of the experiment，suggesting asynergism between blue light and UV-B radiation thatexacerbates damage. The blue light dose may notactivate light-dependent repair mechanisms exceptDNA photolyase after UV-B exposure. Other studieshave reported on the wavelengths of light thatdifferent plant photoreceptors absorb. Because onlytrace amounts of blue light were absorbed byphotoreceptors，Arabidopsis growth was inhibitedunder this color of light(Shao，2001). Blue light hasbeen reported to promote the activity of DNAphotolyase(Britt，1995; Zhong et al.，2009). Inanother study，the lethal and mutagenic effects ofCPDs induced by far-UV(200–300 nm)were reversedby irradiation with near-UV/blue-light(300–500 nm);this photoreactivation was catalyzed by photolyase，ablue-light-activated DNA repair enzyme(Thompson and Sancar，2002). Our results showed that CPDcontents were lower in the blue-light group than inother groups. Blue light also decreased the sensitivityof MAAs synthesis to UV-B radiation. In the bluelightgroup，the highest MAA content occurred incarpospores exposed to 72 J/m² UV-B radiation，whilein the PAR，darkness，and red-light groups，the highestMAA contents were in carpospores exposed tO₃6 J/m²UV-B radiation.

In general，PAR was best for repairing of UV-Binduceddamage. The activity of DNA dark repair waspromoted in darkness and inhibited by PAR. Red lightpromoted phycoerythrin synthesis but inhibited DNAlight repair，allowing a large number of CPDs toaccumulate. Blue light promoted the activity of DNAphotolyase，greatly improving remediation effi ciency，but carpospore growth was inhibited.5 ACKNOWLEDGMENT

The authors would like to acknowledge the staff ofthe First Institute of Oceanography(SOA)(Qingdao，Sh and ong，China)for the use of their LC/MS.