==== CHAPTER 15 ====

EFFECTS OF ULTRAVIOLET

RADIATION ON THE PELAGIC

ANTARCTIC ECOSYSTEM Marfa Vernet and Raymond C. Smith

ABSTRACT

Ultraviolet radiation (UVR) affects biotic and abiot ic factors in marine ecosystems. Effects on organisms are mostly deleterious due co dam­

age to DNA and cellular proteins that are involved in biochemical pro­cesses and which ultimately affect growth and reproduction. Differential sensitivity among microalgal species to UVR has been shown to shift community composition. As a result of this shift. the total primary pro­duction for the com munity may be maintained at pre-UVR levels . Simi­lar impacts and mechanisms are expected in Antarctic waters. The over­all effect of UVR on the ecosystem needs ro include relevant feedback mechanisms which can diminish, and sometimes reverse, deleterious ef­feers on population growth. For example. it has been speculated that UVR can increase iron-limited phytoplankton populations by photoin­duced reduction of Fe l - to Fe' -. a more soluble form of iron and readily avai lable for algal and bacterial uptake. An equally positive feedback can be attributed to diminished g razi ng by zooplankton . Thus. energy flow among [he troph ic levels can decrease as a result of damage to a certain trophic level. but overall biomass and ecosystem production might remain relatively unchanged .

Similar positive and negative feedbacks associated wit h UVR are re­lated to the dissolved organic matter (DOM) pool, known to be recycled by baererial activity. Although it cou ld be expected t hat bacterial pro­duction in Antarctic surface waters would decrease when exposed to UVR, this effect can be counteracted by increased substrate nutrient availabi l­ity. Photolysis of high-molecular weight molecules by UVR produces

The Effects of Ozone Depletion on Aquatic Ecosystems. edited by Donat-P. Hader. © , 997 R.G. Landes Company.

248 Tile E((ecls of Ozone Opp/etion on AqUcl tic ECOS~/5 tellls

higher availab ili ty of low-molec ul ar weight mo lec ul es readi ly ta ken up by bacrer ia . This step might be of greate r impOfWnCt

in high latit ude (:'(osys(:'ms where low bac­terial producrion has bten attributed to low su bstrate ava ilability.

Similarly, inc reased nutrients for bac­te ri a l act ivity originate fro m phocolys is of h igh-molecular weight moitcul es which are known to release NH.j • and am ino ac ids under UVR. T he DaM pool might also inc rease th rough phytoplankton excrerio n of organic maner, a process known to oc­cur under a lgal stress. On rhe ot her hand, a decrease in DaM by diffus io n from zoo­plankton fecal pell ers is ex peered in surface waters due [() decreased g razing.

In summary, we argue t hat rhe under­stand ing of the effecr of U VR on Anta rc­ric ecosystems is more t han the sum of the effect of radiation on ind ividua l spec ies, g iven t hat alteration of inte rspec ific inter­actions can exace rbate , dim ini sh and some­t imes reverse known physiological damage . This, p illS complex and nonlinea r feedback mechan isms associated wit h UV R effects m ake p rediction at the ecosystem leve l uncertai n .

INTRODUCTION A rt~cent characte ristic phenomenon of

the Antarctic ecosystem is the well-k now n springti me decrease in stratospheri c ozone, known as the ozone hole. It is confined to the po la r vo rtex over the Antarc ti c conti­nent , from September to December of each yea r. H owever, once the wintf: r/spring vor­tex breaks dow n, its effc:ns reach mid lat i­tudes, mostly during the mont h of Decem ­ber, I alt hough it has a lso been detected in s ub- an rarctic e nvi ronme n rs duri ng the sp ring . .! There has been sig nifi can t ann ual and intera nnua l var iab ility in Antarcti c ozone, and , conseq uen rl y, in changes in ozone-re la ted incident u lt rav ioler radiation (UVR). During the last two decades major internat ional efforts have focused o n the physics and chemi stry of the Eart h's atmo­sphere w ith emphasis on understanding processes that control the ozone layer, while

studies on the effects of UV on th t b iosphe re, in parti cular a t the co m munit}1 and ecosyst tm level, ha ve been re la ti ve ly lim ited. '

ln te res t in U V effects on aquatic eco­system s is in creasing because ozone deple­t ion is not restr icted to th e area over Ant­a rctica and signi fi can t reductions have been reported in the Nort hern H emisphere : I

. ';

Hemi spherical trends a rt superimposed on high in terannual variab ility, as poi nted our by Michaels Ct a i,' w here low ozone dur­ing 1992 can be assoc iated with a drop in sunspots, a strong EI Nino event and the erupti on of Mount Pinatubo, a ll of which can potentia ll y decrease ozone in the Strato­sphe re . Othe r popul a ted areas, such ns Sout h Ameri ca, Australia, New Zea land and Sout h Africa a re affected, in panicular at the t ime of [he vortex disappearance, probably as an effter of dilution.' ··'

It has been est im ated tha t aquati c eco­systems fix bttween 30 and 50 Gt of car­bon pe r yea r, whi ch is roug hl y half the ro­ta l g lo ba l fixation of ca rbon. H•

ltl

Consequently, the threat of increased UV R on surface layers of the ocean on mnrine product iv ity is of considerable conce rn . Es­timates fo r t he Sourhern Ocea n range frolll 1-5 Gt C y- '." For the Southern O cean, ice a lgae are esti mateu to contribute lip to

30 % of t he total pr im ary produCtion . I ..?

Traditionally, pred ic tion of U V efftcts on ecosystems have assumed a linear addition of U V effecrs on different level s of tht food chai n whe re t he f in a l effec r on h ig i1<:r troph ic Itve l p redators, s lIch as penguins. wha les and sea ls, have been in fe rred from t he cumul ative effeCt o n p ri ma ry produc­e rs and grazers. I ., I n other words, tht- roral effect of UV at a givf'n troph ic levc:l has bee n assumed co be the combinat ion of U V effeCts on the p revious trophi c level i1(.1ded to t he di rect effeCt of U V on t he leve l ic­self. For examp le, in itia l studies on UV effeCts o n marine nlga l communities rt'­po rted decreased [Ota l pr imary producriv-ity and shi fts between species rownrds It-ss UV -B -sensitive spec ies as well as l:I drop in total species diversity, assum ing consmnr

Effects of Ultraviolet Radiation on the Pelagic Antarctic Ecosystem

grazing.14"17 In contrast, recent trophic-level assessments suggest that differentialUV sensitivity between algae and herbivores may contribute to an increase in algae by exerting a stronger UV influenceon the grazers. 18-ly An analogous influenceon zooplankton, thus reducing zooplankton grazing, could counteract UV photo-inhibition on phytoplankton growth. Inaddition to biological factors, UVR affectsabiotic processes which affect directly orindirectly the food web. These factors areeither chemical (e.g. nutrients) or relatedto the dissolved organic matter (DOM)pool which is intrinsically related to themicrobial loop.20 Such an alteration of theecosystem functioning would result in a decrease of transfer of energy through thefood web.21

In this chapter we summarize what isknown of the UVR effects on different levels of the Antarctic food web, with emphasis on the relationships between trophicspecies, and what is known of the UV effects on abiotic processes affecting the foodweb. Several recent reviews on UVR effectson aquatic and Antarctic ecosystem13-22have given excellent summary of the UVphotobiology and that information will notbe rephrased here. We present evidence tosuggest that research required for understanding UV effects on Antarctic ecosystems will necessitate ecosystem studies inaddition to detailed determination of UVRon specific processes related to any giventrophic level.

UV RADIATION IN THESOUTHERN OCEAN

Estimation of quantitative effects ofultraviolet radiation (UVR) on biologicalsystems requires knowledge of the incidentspectral irradiance and a biological weighting function (BWF), which provides thewavelength-dependency of biological action. Because BWFs are heavily weightedin the UV-B region of the spectrum, highspectral resolution is required for accurateestimation of effective biological doses.Smith et al23 have developed a high spec

tral resolution (1 nm) air and in-waterspectroradiometer and Booth et al24 havedeveloped the U.S. National ScienceFoundation UV Network which provideshigh resolution data at three locations inthe Antarctic continent. Alternatively, narrow band instruments (e.g. Bio-SphericalInstrument PUV series) can, in conjunction with an adequate full spectral model,be used to estimate incident spectral irradiance with adequate resolution. BWFs,specific to the target unit, have been developed. For Antarctica, stepwise functionsfor the BWF for photosynthesis have beendeveloped by Helbling et al,25 Lubin etal,26 Smith et al23 and Boucher et al27which have yielded results similar to themore detailed determination of Cullen etal.28 Other BWFs have been developed intemperate areas for plant chloroplasts29 andDNA.3(1 There is a paucity of BWFs forother processes, for other levels of the foodchain, not only for Antarctica but everywhere. This is a serious constraint formodeling and predictive purposes.

Actinometry (e.g. refs. 31, 32) has notbeen used extensively in Antarctic studies.On the other hand, a biological dosimeter,based on the response of an organism toUVR, has been used. This method providesa relative unit to assess potential effects ofUV exposure on a specific organism or target molecule. Once the response of theorganism to UV is evaluated under standard conditions, i.e. by exposure to natural UV radiation, we can say the organismhas been calibrated. A relative estimate ofpotential UV damage can then be estimated. The potential benefit of the biological dosimeter resides in being a relativelymore easy and inexpensive method, onceit has been carefully evaluated. The maindisadvantage is the exacting dosimetry required for quantitative calibration. It canalso be used to compare biological effectson very diverse environments with or without very different UV climatology. Although a biological dosimeter was carefullyevaluated for an Antarctic coastal site it hasnot been used extensively use in the

250 The £{(ecls or Ozone Depletion on Aquatic Ecosystems

regio n. H Both rh e acr inom erry and rhe biological dosimeter give broad band esti­mates of UV R unl ess rhe incident radia­cion is differentia ll y screened, usually with filrers. ,H

CLIMATOLOGY OF UV RADIATION U leraviolet radi ation (U VR) levels are

mostly controlled by atmospheri c ozone, cloud cover, and solar zenith angle with ozone concentration being relatively specific to the UV-B reg ion. )·' Natural variability in these env ironmental variables g ive ri se to a very high natural variabi lity in UVR , with ozone pri marily affcccing rhe relative ratios of UV-B to UVR, photosynthetic available radi at ion (PAR ), or rota I irrad i­anee. The dynamic nature of rhe polar vor­tex containing rhe ozone hole has given rise to large changes in these UV-B ratios on rim e sc al es of severa l days or less (Fig . 15. 1). The polar vortex, and corre­sponding ly , the ozone hole, is often elon­gated in shape, gi ving rise to an uneven di stribution of UV-B at locations within the Antarctic continent.35 The natural-short te rm variability (hours to days) due to

changes in cloud cover and solar zenith ang le compounds the diffi cu lty in assess­ing the innuence of increased UV-B levels on natu ral sys tems.B,Y; The resultant ef­fect is that natural variability (cloudi ness)

Fig. 15, J. Daily maximum UV·A irradiances (3 60· 400 nm) from J 5 Decem· ber / 989 10 7 Februa ry 199.3 ~1 r McMurdo Sta tion (77.5/ 'S, /66.40 ' £) shown (1S a fun ction of da}'s before and after solstice. Redrawn from Booth et ai, 1994.

~

'1' E

== ~

0 1::. CI> u c: co 'is CO ~

.!:::

3

2

can cou nteract UVR increases. Further, rc­cent work (Gautier et ai, Un iversity or Cal iforni a Sanra Barbara, U .S., personal com muni ca ti on) suggests that t he co m­bined influence of cloud cover and surface reflectance influences these UV -8 ratios. As not much is known w ith respect to the effen of th is variability on organi sms and processes, it is roo soon to predict t he ef­fect of thi s variabil ity either to enhance or decrease U V effects o n Antarcti c ecosystems.

TRANSMISSION OF UV IN SURFACE WATERS AND ICE

Transmi ss ion of UVR wi thin the wa­ter col umn is a key element in assess ing UV effeCts in marine sys tems. Light trans­mission is affected by wa ter itse lf, as well as particulate and dissolved organic mat­ter (POM and DOM, respect ively) within the water column , Water is known to be a relatively strong UV absorber37-39 and spec­tral attenuati on coefficients have been pub­lished for cleat natu ral wate rs. 3M H owever, in natura l waters, particulate and di ssolved o rgani c matte r strong ly absorb U VR and t hese in-water cons t ituents are hig hl y vari­able. In blue, more transparent oligotrophic waters, biolog icall y sign ifica nt UV doses (a n penetrate several tens of met ers. J n con trast, mort productive coastal waters,

o 125 Days before or after solstice

Effects of Ultraviolet Radiation on the Pelagic Antarctic Ecosystem

Fig. 15.2. Relationship betweenthe depth of 1% UV incidentradiation and dissolved organiccarbon (DOC) in lakes. Reprintedwith permission from Schindleret al. Nature 1996; 379:706,©1996 MacMillan MagazinesLimited.

with higher particle concentration (e.g.>3 mg chlorophyll a m-3) can have attenuation coefficients nearly an order of magnitude higher, limiting significant penetration depths to the order of meters.40 DOMshows an even stronger attenuation in theUVR'10,41 and can effectively limit significant penetration depths to a meter or less.For example, Kramer42 estimated that thecombination of high POM and DOM inDutch coastal waters would limit UVRtransmission in the water column to suchan extent that no UV effects or planktonicorganisms were expected. High POM absorption in Antarctic waters43 and probablyin ice-edge blooms,44 would limit UVtransmission in late spring and summerdue to high production, but not duringearly spring (e.g. October) where chlorophyll (chl) a levels are usually lower than0.5 mg m-3.45 The paucity of absorprionestimates for POM, and in particular forDOM, make it difficult to speculate ontheir effect in Antarctic waters, althoughsimilar levels of DOM as in other parts ofthe world would support the hypothesis ofimportant UVR absorption by DOM(Fig. 15.2).46 Estimated UV effects atdepths of about 20 m in the vicinity ofPalmer might be due in part to thecontribution of DOM absorption.'3-4^

The role of DOC in light attenuationis intimately related to other environmental changes. For example, in boreal lakes,the decreased amount of DOC, caused byan increase in average temperature and

acidification in the last 20 years, was related to increased UVR in the water column.48 In the case of Antarctic waters, acomplex mix of competing feedback mechanisms make estimating changes in UVR,due to environmental change, speculative.

There are relatively few direct observations on the optical properties of Antarctic ice and snow. These observationssuggest that UV transmission in the ice ismaximum in October due to relativelyhigh transparency in spring. Based on theseobservations, it is expected that ice algae,associated with bottom communities in iceflows, potentially can be exposed to relatively high levels of UV-B. These UV-Blevels have increased by as much as an order of magnitude under the ozone hole.49

THE FOOD WEB

Phytoplankton

PhotosynthesisDeleterious effect of UV-B on photo

synthesis has been studied both in culturesand in the field, in particular for Antarctic phytoplankton. The reader is referredto reviews done in the last few years thatcover this subject extensively (e.g. refs. 22,36, 50, 51 and references therein). Overall, UV-B inhibits primary production by30-509? of shielded samples^2 with a strongdepth gradient from surface to about20-50 m.23-33-33 All these experiments arebased on 6-24 h incubations, either in situ

, - , -'-

Of in incuharors t'xposl·d ro sllnli,;.:hr. On rhe ;I\'l"r~l,!.!t' for rhe wafer column. primary producriCln <.I,.-creilses by (i- I 2';; ~'. ~! durin,!! spri nt!rime IlZUIlt" deplt'r ioll O\'f: r Anrarnir wafer resulring in ;t 2r;; fed unioll in rht' rt"arl y pri mary protlu([ ion {'Sf i nlil(:"S for rill:

l1lilrt.:inal ict' z() n l·. ~'H t' lbling e( ai " has(:d on dint-fene assumprions and mt'rhodol()~~y.

l'srimilrt' rhe: decrease in primary produc­{ion ro he n,I,) ';; for elu' en ri re iu:-frt't' wafers sourh of rht' Polilr From. A UV in­hibition fUllcr ion for pho{()synrhesis has been described by Cu lltn and Nealt. 'i'i Tht biol ogica l weighring funcrion for Anran.:­ric phytoplankton. I1tct'ssaQI to sca le UV R ro biological efTc:niv(: irratiianct', has been d(:,,[t'rm int'd for Il aru ral popu larions by Lubin e( ai, '" Helbling « ai," Smi(h or al,2 ; Buucher tr .. 12- ;Ind Nl'ale ef alY'

Nutrient uptake Very lin ll' is known or th t' c:ffen of

UVR on nutrient upwkt' in Anrarnic phy­roplankron. Srudit's on tempe ra te species sugt!:t's r (hat nirrogenast' , t he t' ll zy ml' rt'­lart'd co nirrogtn assimi lation in phy­ropiankwil. is acrivared by PAR '- anJ i l1-acrivnfed by UV -B rac1iarion. '~ In cont raSt, ammonium IIp[;d~t' seems less afft'<.:[(.·d. ~".f'O

Overall. amino acid (Ollct'lH rar iol1 in rhe ce ll dtt'reastd undtr UV-B. (01 Tht effect is also Idr on t'l1zymc:s rdartd (0 amino acid metaholism . UVR diminishes synrht'sis ilnd il1rra( .. ~ lI lIhir iln:umuiarion of alanint· ilnd va li nt"'! whi lt synrlll·sis ilnd acculllulat ion

of t!luramie ac id incr('· 'ISl' dul' {(I inhibition or g lu rama((:' synr hast ' .... or ,l.duram'Hl' de­hyd rogen;lst: , t,l! Tht'se rt:slIl tS are si m i lar ro

metabolic changes obsl'rvt'd in phrroplank­ron under nirroge:n streSS. suggesring rhar UV-B suppresses nirrogt'n assimilation inro ce:lls, t>; Decre;lsl,d N H I' uprakt' by PadM'a

spp, under UV-B and high intensity UV-A was interprered as rt'dllced supply of ATP and NA DPH from direre offeres of UV-B on rht: phorosynrheri <.: apparacus and pig­l11t'nt b le;tching, 1>4I Simi lar dTe(ts of UVR nn Anrarctic spec it's will havt ro bt as­sllmtd until t'xptrimtnrs are ca rried Ollt ror Anrarc..' ric, or at leasr, polar p hyroplankron,

Exudation Tht' amount of excrilcc: l lular c lrhu n

produced by phyroplankron has lx'ell ;1 COIi ­

tro\'ersial subjeL't for St:\,eral decades ,""

Excrerion of carbon hy pilOtosy ntht'ril' 01"

ganisms is a widespread process ;,lSSOl ial l,d with photosyn thtsi s,h~ On the: iI\'l' ra,l.!l·. phytoplankton txcrl'te:s 5-15'A' of rhl' C;II'­

bon in corporilted in parri c ulatt" maner. bot h in monospecific n ilrure:s and in nafU ­

rid populatiol1s(,'j ,t>:-! and tht' amOlllH e x­

crett'd is a conStant proportion oi' phtllo­synthetic: ratts, Several st lldi t's have poimnl OLit t hin a large: proportion of p llOwsyn ­chetic ca rbon got'S throug h a DOC phas("'" for at It'<lst shurr pt'riods of t ime:. - II Undl'!' chest' conditions. bt'tween 20-()OIfi oi' plw­rosynthiltt' must go inru rht' DOC pool l t l

explain the DOC ( ha n gc:s obser\' ed . I'

mainly dur ing spring bloom t'\'l'IltS in (('Ill ­

pt'riltl' waters, Additional organi( ('ar hon t'xCfetion in phytoplankton seem s associated with physiological imbalance due to ('V("ll['"

such as nitrogen limitation : I ,-; in particu­lar lIndtr high-light condit ions,-' III rill'

ritld. rhe transfer of ct'lls to higher irradi · anct" might produ<.:e excess phorosyn­thatt'. ('-'<'.'i Nutrient limitation is ohsl'fn·d

during !att' grow rh sragt's in batr h nLl­turc:s · I or at tht' e:nd or rht spring hlotlill .

High DOC c() llLenrrations havt' al so IWl' 1l

obse rvt'd after a Pb{((:IIIJ.flis sp. b loom, - ~, "

This t'xce:ss carhon t'xcre:red mi,ldn 11l' ;1 ... •

sociatni wirh increast'd in trace:llular Llrhll ­h)'<.iratt. as in diatoms -1.-- bur nor ohsl'f\'l'I1

in dinotlagellat(:s .--' Vt'r)' lit tle is known of ("xud,lrioll hy

Antarnic phyrophinkwn illld [he: l Oll'ol'· tillenr implicilrion for (il(: DOC pool. \{ l'­rent resulrs in the Arni c sllg,cesr ,I I. :r,~l '

,111101l1l( (If exrrace llular carb on Oh,'ol'r\'nl see mt'J to bt: rt' latc:d to phywplallkr tll l

composition (i,e. (ells w hi( h produ <.' l' 11111 -

c: ilal:e ror colonial forn"larion) .lntl (0 ;J It':-:-..t' r e:xr;IH {(l in sitU n itra te lim i(;lrion. · ... In Arnic Wa tt'r. Cbdt'/fIl't' I'IIS .fll(itl/i.l' a ll oc;nnl 4 0 '/f of total ca rbon incorporatt'tI ;IS ("st[.l ­ctllll iar under (ondit ions of low si lic ic acid (<<),2 PNf) and measurable nirril(t' concen­trations (0.5 -2.5 JlNO, Similar exrr;u.:l'lIuI:1r

carbon produccion was found in iI mixru rlo

Eifects of Ultrilvio/et Radiation on t/u" Pel.lgic Antarctic Ecos}lsrem 1.03

of C. l{J(ia/il and P. p'JlldJdii ar rh t Po la r Front and rhe ma rgina l ice zo nt wir h h ig her IlUrri e lH conct nrrarion s (5-1 0 ~tM n it rate ).

These resu lrs s tlt:t::esr ch.u species com­posicion and rheir p hys iolo,!-:ica l sta te may largtl y control extracel lular (;.\rbon produc­ti on in t he field. -'J Alt houg h low n itratt' is known to inlTt'ast' exudation. - ' thi s t'ffl'n

is not l'x pel'Cl'd in Ancarnic open watl'rs; however. t h is tffecr mig h t bt observed dur­ing o r after massive co;\sral b looms. 1'1.).;(1

In spite of the obviolls imporranct (If ph),top lank wn ex udacion o n tht carbon C},c!t and as subst rate for the microbial loop, no s tud it'S have bet'n ca rrit'd out on tht efftn of UV-B on txud;\ t ion, fo r ti­thtr tt'mpt'ratt' or pola r phytop lan k ton. In gtlleral, ex ud at ion illlTeast's wht n a lgat a rt' stressed and it can be specul attd chat UV -B stress wou ld act in a s imi lar way.

Respiration Changes in OHC in rCO.,! observed in

the Bt lli nghaust n Sea in the s pring of 19YO combined wit h changes in ce ll abull­dan ce in th t' colon ial prymnes iop h y te Pbm!O(}'llis sp. sugges t t hat under im:reased U V-B radia tion , as mtasu red undt' r dt­crt aseJ ozo nt (onctnt rat ion , t htrt is an increast in t ht' ratio of [0[;11 communi ty n:sp irat ion (0 p hotosynthes is.xl H etero­t rophic respiration increases were ;.ltuibuted co incrtased bantria l substrate du t' to (til lysis.

Growth Tht' effect of U V- B on marint ph y­

wpla nk w n grow th has btt n shown to be spt'c its-sptci fi c. For stveral cu lwres of tel11-ptratt sptci es, spec ific grow th rate was af­fecced negativ(·ly by U V_B. ~.!-N I In the dia­

com P b(((,(" /(/(/),/IIIII Iri(II/·IJIIIIIIII. no d tuease in UV R se ns it iv it y was observed wit h t illl t.~ .! Simi lar results were observed on .) 0

txper imtnrs on Anra rcric ph ytop la nkton dominated by C',rt'lbrrlJl (ri lll,b)/I1'" whe re .;..:rowrh rates d tcreasl'J by IOO'J on (t· ll s exposed to UV-A + UV- B + PAR and by SO'/( whe n ex posnl to UV- A + P,\R. as co mpared to conrrol s t'xpost'd to P ,\ R

onl y .'''~ O n rht other hanJ. act ivt grow rh of ( oasra l sptc ies was obst rvtJ for 12 days a t Pa lm e r Station whert d iarom ( u lrurt's wtre kept at in sit u sol'ar radi.niol1. sh No ditfere nc<:' was found also bttwee n t reat­

ments (UV R + PAR "s. PAR on ly) Ii" rh" colon i.li prym nes iophy rt P/;at IJIJ.fliJ sp .. al­thoutih tht'st' cu lwn:s did nor g row. T h is lack of ellel'( was observed in spitt' of tht' we ll -doc umented inhibirion of pho(Osy n­r h ts i s .!\·.!('-.!~ ti.)f Anrarcric ph}lroplankron in

ex pt' ri me nrs frol11 1-14 h and po inrs to­

wards di lh:rtnr conrro ls of p horosynr htsis

and growth and bttwetll sho rt - vs. lon,g­refm t:lltns of U V-B . Ir has been nott'J fi.lf some timt rh at cau tion must be used when inft rfing longe r tt' rm eco logical COI1-

St'lluencts from short-term obstrva rions.N-Mixing of (t lls in th t uppt r watt'r col ­

umn . in partic ular within rhe mixt d laye r, affens rht' avtragt irraJiance in whi ch a (t.1I is txposecl d uri ng rh t day. \"i.NS,""·) Sev­

t' ral s rud its havt spt'nlia[td aboU( rhe pos­s ib lt role of a lleviat ion fro m U VR in Ant­a rctic wate rs if ce ll s are mi xed detptr in rhe wate r colllmn . "i (j ·~tI ") 1 Expt rimt'nts where

U VR inre nsity was ma nipul ated to rt­stm ble m ix ing in the u pper water co lu mn showed increased product ion in cloud y days while rhe effect was opposirt on sunn y Jays. ~ 1 Phyroplankron dominattJ by t ht d iarom T ba/fl11;Olir(1 grarititl showed less phoroin h ibit ion when tx poseJ to va riable radiari on:''! supportin,!-: t ht' hypothtsis char mixing mi g ht provide UV-B protection. ,I,

Cell size Coastal wattrs have. on th t' avt' ragt_ a

hi ,!-: h t r proportion of htrge r ct' ll s chan ope n warers.''' For example. more than :-lO 'A of the nearshort p hyr(lp lan kcon biomass was assoc iated w ith ct ll s > 10 pm in T er re Ade li t' durin~ sum mer wh ilt 70 km off­short'. ct' li s > I () 11 m rep rt'st llted o n ly .)WJ of t ht, wra l b iomass and '51) r;1 of cht, (e ll s were be rwt'tn 1 _ 1()~lm . ' JI \'(Iithin coas ra l

wate rs. hit:h Chi (/ acc u m ul ar io n s ( i .e . b looms ) a rl- do min.Hed b~' lar~e n -lls (e.!! . > ~o pm ) while low Chi (f ( oncencrar iolls afe dominared by sm all er u : II S .. -l11.'1\ A differ­

enria l effect of UV R on (e l l size, as

Til(' [,.,.('(' (;; O( 0 1 0/)(;' Dt'p/t't ioll Oil AqU.Hie Ec.:os ~ ';; f< ·I1;'

obst" rvnl for diatom cultll rt"s.'Jh show hi~ h t' r

d;'lma~e on smalltr ct' lI s, and Wt m i!-dH spt'udatt' that oceani c ph ytoplankton rnay havt a hightr st' ns itiv ity to l1V-B . In ad­dition , U VR int:re<1sts ce ll s ize;.! assm:ia ttd with a concomltanr reducrio ll in specific growth ra tts.

Species composition In itia l t'xptrimtnts with ttmperatt

phytoplankton, showing difft' renri .1i se ns i­t ivi ty to UV-B by d iffc.: rt'nr spt:cies ,l - sug­ges t a change in spec ies composition in long-ttrm U V-B exposure with more UV­toleram spec ies ultimatel y dominating. I ('

As mentioned above. there is a wide range of interspeci fi c UV- B stns itivity on growth and surv iva l, with smaller ce ll s being mo re se nsitivt'. due to a hig htr surface to vol­u me ratio as a resul t of ce ll sizt' and ce ll shapt' Y6 In addi t ion to sizt, an increased UV-8 stns itivity in tlabe ll an:s, as compared with diatoms, was observtd in natural populat ions of AntarCtic phyroplankron . 'i •. 1)­

Thi s di fft'rence ( an be att ri bmed in parr to si ze (fla g ell a tes are on the average smaller than Anrarct ic diatom s) and to in­creased UV-absorbing propercit's of dia­tomsl)1 rt'lat eJ to the presenct' o f mycospo rint-like amino acids whi ch are bt' li evt'd to reduce dt' lt'te ri om effects by UV-B on g row th :'" The predicted sh ift from less to more resistant spec its (e.g. from fbgellarts ro diawms) was obsNvt'd in a 2-wt"t"k experimtnt of nar ura l Anrarc­tic populations t"xpost"d ro amnienr U VR, although si milar ChI tI and parricuhue car­bon acc umularion were ohserved undtr UVR and UVR + PAR ." Unde r lIV R the amount of U V ahsorhing compound s (t.t!. m y<:ospori ne-l i ke a 111 i no .. It'ids) increased as well. As a result of rhi s shift in speci es composition. a decreased sensiriv iry of pho­tosynthe s is wa s obse rv ed in rhe ph y­roplankton t"x posed to U VR . The hi g her res isranct" by d iarnms, as cornpared wit h fiage ll a rts ( in parricu lar the colonia l prymnc:siophyte. P /)rft'{JI),JliJ jJOIlc/Jf!lii, ref. R I ), see ms to be rehHed [() a lower efft"([ on phorosynt hes is as wtl l as nitrat t' uprake. $·)

Few sw d its a re a\'a ilablt' on d"(tc£ s Ill' UV R at lon,!-!t"r rime sca les. rvldvl inn t't ill' " docllmt"med no changts in diatom spl' r il'., co mpos ition in laminared sed im enrs ill Anrarctic anox ic fio rds for t ht las( 20 year,. coincidin,g w it h t he dtcre;lst' of OZOIll' . Howeve r, as nored by Bothwell and co­workers ls the limi ted data provided hy McMinn et <1 1'/1' do no r subsrami <1rt" rill' ir implied lack or a UV-B eHtcr.

ZOOPLANKTON UV t'ffec£s on zooplankton , under nor­

mal and decreased ozone conditions in rem­pt'rare waters, afftct zooplankton su rvival. reproduct ion and grazing .'}'} It is nor cif.'ar fro m these res ults if d t"c reastd g ra zi n,t: would resu lt in a reversa l of UV ent-crs 011

phyrop lankton, as observed for a chrnnomid/diilwm interaction in te mpl'ract.' freshwatt'r strt"am beds (Fi g, 15, .1 ), \Y/ t' call expecc that a 50 '/{ mortality of a g razer would decrease g razi ng p ress ure and fa vor phyroplankron growth. The poss ibi lity of grazing revtrs ing delttt"riulis effeCts of UV on phyroplankron and rhe relarivt' impor­ulIlce of grazing in controll ing phytoplank ­ton popu lat ion growth in any ,g ivt"n com­f11uniry is currtntly a mar rer of specula rioll . U ndt"r current U V irradinllce. ovt'fall tll'­creast' in primary production by U V in rill' Antarcti c t"up hotic zone is t'st ir1"wted .11

6-2Y/f of marg inal ice zone production .:" :' Th e ovtra ll rt"su lt would depend on rill' dft'Ct of UVR on Anrarct ic graze rs, an'r­aged for rhe t uphor ic ZOIlt". and on rilllt' .sca les represen tative of phywplankro n ;I t­

clll'nulatioll at ambienr tempt'rctrurl' (d.IY:­[(l wtl'ks. if Wt' assume i t spt'cifi c ~ro\\,lh ra rt' of 0.1-0, ,) d- I), ll

SEDIMENTATION Pottnria l changes in g razing prt'ssufl'

wi ll affect st"dimelltatiol1 of particu l:lIl' matter. In areas whert:· organic matter snli· men rar ion OU t of rhe euphoric zone is d Ul '

to g ra zt r ( i,e, k rill ) ftcal pe l lt'r s . II ~ ' Wl'

m ig- In ex pen a shifr ro cdl st d imt'ntation. assuming no change in p rima ry p roduction . Thus, rhe pulse of orbani c matte r after a bloom could consist mainl y of intilCt cell s.

Effects of Ultraviolet Rae/;alion on tile Pelagic Antarctic Ecosys tem 255

PAR 100 600

A • 90% .. B .. '" 75 0 50% .c =~ .a N" 400 > N .c ' "0 ' a.E .- E o '"

50 E . (; E o 0

:;:-25

e oS 200 U :c

U

0 0

PAR + UV-A 100 100

C .. 0 .. '" 75 .c 75

" >'N" ; ~ .c ' a.E .- E 50 0", 50 E .

(; E 00 c: c:

:;:-25 e- 25 U :c

U

0 0

PAR + UV- A + UV-B 100 100

E .. F ttl

.. 75 .c 75

~N" " .c ' ; ~ a.E 50 .- E 50 o '"

E . (; E o 0

c: c: :;:-25 e- 25 U :c

U

0 0 0 • • 12 16 20 • 10 12 ,. 16 ,.

Fig. 15.3. Changes in pi1ytopl.lnktoll (chlorophyll a conce/Hr.ltiofl, left pclnels) and chirollolllid larval abundance (cilironomid wbps, right panels) with tim e> in streams. Expprimenls carried Qut at two irradiance levels (filled s}'mbols, 90'1./ of inciden t irradi.lIlce, .1fld open circles, 5()% of incident irradiatlce} at three treatments (PAR: top panels: PAR + UV·A: middle parll'/s; and PAR + UV·A + UV·13: low pclnels). Reprinted with permission from Bothwell et aI, Science 26.5:97·/ 00. [) 1994 American Association [or the Ad va ncem ellt o f Science.

T his tffecr w ill be maxil11um in coasral art'as where larger ce ll s') I and hight f pro­duct ion art fO Ll nu. ''j Secondary effects wil l include alrt'r<lriol1 of t' lel11t'nral rar ios . her­trorroph ic subsr rare and IllHrienr recycling below rhe euphoric zone. If, on rhe m htr hand. a large p roportion of stdim (.' nrin .c manef is due [0 cell si nking rhen rhe lJual ­iry of orga ni c ma[[e r co deprh wou ld nor bt" subs ranriall y alrered. 1I 1! The q uan r iry and riming mighr bt afte:ctt"d if. as Jis-

cussed before , UV R wou ld a lre r speCies composirion and /or specit"s s ize.

THE M ICROBIAL LOO P

B ACTERIA

Bant'fi.d biomass in Anrarn ic warers can reach 9 '/f of rhl' nee plan kcon biomass in rhe rop 50 m and increase wirh deprh lip co 507r . as Illeilsurt"d in Bransfield Srrai r and Drakt Passage in summer. 1(' DitYt" rtlH

from othtr parts o( rhe oceall, th l' n: is no correlarion hl"twl'L'n phyropl.inkron and bacterial biomass in Anran.:t ic warers'l l,li l

,;

and rhe reasoll (or this differt'nct' I S

unclear. 1(1;

UV R reduces hacrni;ll acriv:ry III remperare (oastal waters in rhe rop 5 m of the water co lumn, with no indirarion of higher resisran(e in surfan' popu lations as opposed ro chose from depth .1II1 Inhibit ion was observed at an irradi<1 nce equal to

0. 7 W 111 -'; . UV-B was also found to pho­tochem ically degrade bacterial extrace llular t'nzymes . I!H The com bination of decreased bacterial activity and the degradarion of ex ­tracellular enzymes redu ct'S t he flow or energy through rhl" microbial loop. Thi s ('ffeer is COLI l1[eracred , or at leasr dimin­ished , by rhe increase in bacterial subsrrate due to phorodegradat ion of DOM. In­creased bacteria l activity at low UV -8 ir­radian ce wirh respect to da rk up t akt· (F ig. 15.4) was attributed to this process.

PHOTO-OXIDATION OF DOM UV-B inreranion wit h DOM is known

to produce oxygen radica ls and hydrogen peroxide (H,;O,! ) which call be considered oxidarive agell[s of biologica l membranes and have a negat ive impaer on plankton ic comI11L1nities.l!l ~ In addirion , mulriple stud­ies have documenred rhe photo-ox idat ion of nOM responsib le for degrading high­molt'nilar weighr DOM inro low-l11olecu-

140

lar wei ,~.dH DOM (e.g. Fig. 15 . ) ) 111 '1 101.

which is readily ilvailab le for bacrni ;d (()nsumprion. ICI~.IIlS

The imporrance of rhe s izt dass 011

bantrial produnivity is srill a ma rr<: r Ill' debart. as Amon and Benner lll'l found rhat although bacter ial growth effi(it'l1(il's WL"rl'

hightr ,t[ low-mo lecular we ight DOM , rll~

tal baneri;.11 growth and respirarion wa ~ h igher at high-molt'cu lar wt'ight DOJ\I ( > I UOO da lrons). n:,sulring in a hi gher Clr~ bon based rilre of ut il ization. It is ((){) <:arlr to assess the degree to which UV pllOr() ~

oxidat ion of DOM would be or impOrrall ll" in Anrarnic surface waters. Given rhe dl' ~

bart' on whether bacterial aniviry is de ~ pressed at low temperature, I 111. 11 I and rill' potential ro le of substrate on po lar h.lne­rial metabo lism, ll l rhe role of phy[()plallk ~

ron as providers of labi Ie DOC and p lw('o­oxidation of DOM by UVR ',Ht' hoth critica l to An t:.1n: tic ecosystems.

Phor()chemi ca l p roduction of d isso lvl'll am ino ilc ids from hum ic substances hav t· been shown co increase bacterial prmllJ r ~ tion in temperare coasta l warers. 11 \ UV-B was found to be t he most anive porrion or the solar spe([rum for this process whi(h cou ld be due both (0 high t r energy <Ind hig her absorption by the targt'r moIL-cull'. A lthough no or low humic acids are ex­pected in Anrarctica, Lara and Thol1l;IS III have ident ified recalcirrant DOM produl..·· rion by marine p h ytoplankcon w irh

y = 52.7 - 40.7· log(x)

Fig . IS . ..J. /3aCfl'ri.1/ s('condclr~ ' produc· tion fB SJJ ) ,J.s a (unction o( UV·/3 (,lelia­tioll. Notl-' hight·,. produclion ,J( low u\I·n wilh rpspl-'c/ 10 rldr}.. U/)/tlkl'. Rl" drdwn (rolll /-h-' mell p i .1/. t"I,IIl1fl' H, /:7 f 7·7 1'). COfJ rrigIJI, A/d c/\/ifl.ln

Mdg.17.iIH'.s l.imi/('c/.

•• ~ 120

n = 75, r = 0.605, P < 0.001

• '"

, .. .... Co 100 ~ . ~ .... " -0

c.. en m

80 .- . i •• ~e

" • • :1 •• • .. :::: ........... • • 60 . . ... . ... :-. ! • • ! . .... ~ .. • 40 • 20~~~~~~~~~~~~~~

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 UV-B [W m·2j

EfI"ects of Ultraviolet Radiation on the Pe/<lgic Antarctic Ecosys tem 257

chem ical characttr ist ics p rtv iously assoc i­ated on ly w ith humi c subs tan ces. Th e source of thi s pool of DOM see m to be degradation of ctllul ar mt'mbranes and can be assumt'd ro bt' prouuced anywhe re in tht' occ-;m .

NUTRIENTS

MACRONUTRIENTS

DOM exposed to U V-B re leases NH .. in to dle su rround ing watNS, thus becom­ing a nllcritnr sOlln.:t' in coastal wate rs. ll' Thi s larger availabi lity of ammonium, of major im porranct in areas of nitrogt ll li m i­ca rion , can counteract dtcreast'd N upcake and mecabol ism by ph ytoplan kton, W.6' and potenria lly bacrtria , as a rtsu lr of U V-B inhibition . In spite of h igh nitrate conct n­trarion s in mos t Anta rnic open wattrs d uring the growth season, phytop lank ton has shown low spec ific nitrate lIptakt rates l

! ') and differentia l uptake of NH j '

wht n p resent, ll(' suggesting that a portn­rial efferr of UV-B in releas ing N H ., · may be of interts t in tht Southern Ocea n.

M ICRON UTRIENTS The potentia l inreract ion of iron ( Fe)

and UV-B as a source of dissolved iron is imporcanr in t he Southern Ocean as it has betn hypothesized that Fe limitation may be con troll ing primary product io n in Ant­areric open waters characte ri zed with low chl orophyll acc umul at ion and hig h macro­nutr ient conct nrrat ion . ll - For txample . t he g radient of hightr productivity in coasta l wa(t'rs as opposed to optn W;l(t rS observed in th t' \'(/ts tern Antarctic Pen insu la 1').1"11 is co rre laetd wit h observe d iron concen ­tration s (4.7 nM a nd 0. 1 () nM, res pec­tively). lIS A sim ila r approach was taken by de Baar et a l II,) to explain h igh primary productivity at tht Po lar f ront ( 120() ­.1 000 mg C 01-' d- ') wit h hi g h Fe co n­centratIOn in surface waee rs (2-4 nM at 60- 100 m) as opposed to lowe r primary production (80- .,00 mg C m-' d- ') a t the Antarctic Ci rcumpolar Curn: nt with su b­nan o molar co ncentra tion s (0. 17 nM a t 40 m ). On the other hand , de Baa r e t all.!o and Burna tt al 12 1 did not fin d rapi d C hi fl

accumu lation with Fe addi tion wit h respect

2.5 '--'--'-"--'--"----'--"-IT--'

Fig. / .5.5. Photochemical production ofpyru· va te after irradidtion of di$solved organic matter (DOM ) plotted agaimt the ra te of uptake of fJ}' fl lV.1U· by b,lCteria in coastal waters (tilled circles) and in the Sarg.15so Spa (op en circles). ReprinfE>d with permiSSion from Kie/)C'r t'l aI, Na tllre 19119; 341 :637· 639,!D /989 Mac/!"Iiflan M.lgazines Limited.

.2! .. 1.5 ~

~ E. :::l 1.0 .. " .0, o o 0.5 iii

• °0~~--2~~-~4~-L-~6~-L-~8

Photoproduction [nM h-1]

I ,

258 The E[fects of OlOnt~ De:'pletion on Aqucl t ic Ecos~/s t(:,lll s

1.0,--,--,--,--,----;,----;,----;,----;,----;n

i' 0.8 .;;.

~ 0.6

"C ~ 0.4 ::J

"C

~ 0.2

•

30 60 Time [min)

to controls in t he Wedde ll/Scotia Seas (both ueatments g rew at simi lar leve ls). The authors concluded t hat incubation ef­fects overrode meta l, and in part icula r, Fe add it ion d ut' in pare to rhe excl usion ur large grazers from the t'xperi mental vessels. Iron add itions shifts phyroplankton com­position from flage llates to diatoms, both in Antarct ic l1 1 and in eq uatoria l Pac ific waters. I 11 The ir rt'sults were nor as dra­matic as t hose obse rved by Helbli ng et al 1'! \ who found increased pr imary produc­t ivity and m icrozooplankton population in surface pe lag ic waters afte r addit ion of Fe. No effect was obse rved in deep pe lagic waters or coas tal wate rs off Seal Island . A sh ift to la rger cells is si milar to orher ex­peri mentS of phytop lankton exposed to UVR I IJ.91'l whic h were attributed to differential cell su rvival and DNA damage.

In marine ox ic waters, Ft: " is the more stable form while Fe ':!' is mort' solub le and readily ava ilable to phytoplankton and bac­ter ial uprake .l'?-I T he concent ration of Ft: (111 ), (the sum of dissolved inorganic spe­c it'S) is t he relevant fac£O r ro cons ider with respect to the uptakt' of inorganic iron. I.? '

Its conce ntration va ri t's from lO-H to t 0-')

M. Rect'nt data indicates that 99.9% of t he dissolved iron in surface warers is bound with in organic co mplexes, resulting in subpicomolar concent ration of disso lved Fe(l II ). It is be lieved that the ligands for iron may orig inate from phytoplankton_ L!~

90

Fig. 15.6. Photoreduction of Fe(lII) in sealvaler (p/-I B.O·a.1 1 in the presence o( the diatom Phaeodactylum tricornu tunl under UVR. Fe(lI/) concerHr<l· lion of 5 JIM; diatom cOIlC(~n · Ira tion of I O~ cells mI' J. Re:" dra~·vn (rom Klima et ai, Marin(' Chemistry J 7: 15-27. Com/right 1992, with kind permission (rom Elsevier NL.

Sun light inc reases rates of oxidarion and reduction of iron , enhancing labile Ft· concentrations and p hytop lankton uptake. A lrhoug h UV-B photoreduces Fe(l ll ) to Fe(lI ) associated to inorgan ic ligand COI11-

p lexes, a larger reduction power is expecrnl from organic chromophores. 115 ReduCtion of organic l igands may occu r by rhe p horoproduced superoxide radical (0'-). In addit ion, ox idation of Pe(lI) can occur with p hotoproduced H 10 .! .

Photo-reducr ion of Fe( I1I ) to Fe(ll) is also attr ibuted to the act ion of marine p hytop lankton (F ig. 15.6). H igh conce n­trations of Pe( II ) were observed during p hytoplan kton spri ng blooms in J apal1(~se coastal waters. l Ui Experimt'nts wit h filrrare from a d iatom cult ure resu lted in photo­red uction of Fe(l l ) after addition of 5 pM Ft'(J lI ). T hi s proct'ss was attr ibured to rhe re least' of hydroca rboxylic acids by phy­toplankto n, know n co reduce Fe(l ll ) ro Fe( Il ) in t he prt'st'nce of sun light 1.!·! and is more pronounced at lowt'r temperawres (5 0

vs. 20°C), important for Antarctic warers (su rface water tem peraturt' va ries from - 1.Bo to +2.5°C).

CONCLUSIONS Two important conc lus ions ca n be

d rawn from this discussion . First , evicit'nce has accumulatt'd to indicate that an aSSt"SS ­mt'nt of UV effects on Antarctic ecos}'s­terns or marine ecosystems in genemi, will

Effects of Ultraviolet Radiation on the Pelagic Antarctic Ecosystem 259

,---MACRONUTRIENTS --~

-+ ~ MICRONUTRIENTS -

OH-~ ... ; H20 2 '~... ::

'4' I I

uv , DOM~

'b::~;~~.ta.t \~Pta~ PHYTOPLANKTON ) le.kage BACTERIA

gr.1lng h~zlng \ 1 Fig. 151 Scheme showing biotic (fu lf line) and abiotic (dashed line) relationships in the upper water column in the ocean, based on inter­actions discussed in the text. The arrow shows the direc­tion of energy flow.

. • I~kag. "'"

MACROZOOPLANKTON • MICROZOOPLANKTON grazing

require experimenmtion on the ecosystem as a whole, or at least , isolate pares of it which include several interactions (i.e. the microbial loop). The predictive capability of adding effects on individual pools in the system is limited and experiments in tem­perate areas suggest that this can even be erroneous. Each level or species is not act­ing in a vacuum and biocic and abiot ic in­teractions will modify its genotypic re­sponse to UVR. Second, it is not possible to est imate UV effects on ecosystems with­Out concurrent effort toward understand­ing environmental and biological forces which drive the system. Thus, UV effects are an added stress upon the system and need to be considered in conjunction with other potential limiting factors, such as nu­trients, and other driving forces, such as mixing and ice cover.

In general, we speculate that a more profound and permanent effect of UVR might be the alteration of interaction be­tween singular elements in the ecosystem than the direct effect of UV in inhibition of that same element (Fig. 15.7) . For ex­ample , changes in species composition might overshadow decrease in total primary producrion;16.19 increased substrate for het­erotrophic activity might balance UV in­hibition of bacterial growth; IO~ changes in iron availabili ty l 25 could counteraCt pho­tosynthetic photoinhibition. The conse-

quences are far reaching in that the over­all carbon balance might change due to

different proportions of carbon burial re­lated to potential changes in cell size, graz­ing and subsequent sedimentation altering the CO2 interaction between atmosphere and oceans.

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Effects of Ultraviolet Radiation on the Pelagic Antarctic Ecosystem 26 1

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ENVIRONMENT Ai

INTELLIGENCE UNIT

THE EFFECTS OF OZONE DEPLETION ON AQUATIC ECOSYSTEMS

Donat-P. Hader Friedrich -Alexander -U niversirar

Insritut ftir Botanik und Pharmazeutische Biologie Erlangen, Germany

Academic Press R.G. LANDES COMPANY

AUSTIN

r;:====== CONTENTS ========il

1. Stratospheric Ozone Depletion and Increase in Ultraviolet Radiation .............. ......... .... ............................... .... 1 Donat-P. Hader How Is the Ozone Layer Affected? ........................................................ I UV Increase Was Partially Masked by Air Pollution ........... ........ ........... 2 Negative Effects of Increased Solar UV Radiation on Life ..... ..... ........... 4

2. Making Links: From Causes to Effects to Action ........................ 5 Canice Nolan

3. Consequences of the Effects of Increased Solar Ultraviolet Radiation on Aquatic Ecosystems .... ... ........... .. ... .... ... .... ...... .... . 11 Donat-P. Hader and Robert C. Worrest Importance of Aquatic Ecosystems ...................................••................. II Effects of Solar UV-B on Aquatic Ecosystems .. ... .. .. .. ........ ............ .... .. II Global Distribution of Phytoplankton .... ..... ............ ... ... ....... .............. 12 Penetration of Solar Radiation into the Water Column ..... ..... ..... .. ... ... 12 Macroalgae and Seagrasses ................................ .. ....................... .......... 18 Cyanobacteria ..... ....... ........... .. .... .... ............... ...... ........... ...... .. ............ 19 Screening Pigments ............ ...... ... ....... ... ......... .......... .. ........ ... .............. 21 Carbon Dioxide Uptake and Its Role in Global Warming ................... 2 1 Consumers ........ .... .. ... ... .... .......... ................... .................... ....... .. .. ... .. . 21 Substitutes of CFCs and Their Degradation Products .... .. ......... .... .. .... 25 Consequences .. .. ..... ... .... ..... ....... ..... .. ....... .... ............ .. ..... .. .............. ... . 25

4. Instrumentation and Methodology for Ultraviolet Radiation Measurements.in Aquatic Environments ..... ... ... .... ..... ..... ........ . 31 John H. Morrow and Charles R. Booth Introduction ...... ................... ... .......... ................. ........ .............. .... ...... 31 Spectral Leakage ........ ...... ............. .... ....... .. ............. ..... .... .................. .. 34 Artificial Sources .... ........... .... .... .... .. .......... ... ....................................... 36 Cosine Collector Design ......... ................. ........................................... 37 Dark Corrections .............. .. .... ... .......... .. .... ........ ........ .... .. ... ................ 39 Conclusion ............................... ......... ..... .............. ........... ............ ....... . 4 1 Appendix 4.1: Commonly Available Commercial Instruments .. .......... 4 1

5. Penetration of Solar UV and PAR into Different Waters of the Baltic Sea and Remote Sensing of Phytoplankton ........... 45 Helmut Piazma and Donat-P. Hader Introduction ........... .... ......................................................••......... ....... 45 Materials and Methods .......... ... .......... .. ..... ... ..... .. ... .... ... .. .............. ... .. 47 Basic Parameters, Definitions and Equations ....................................... 48 Results ...... ..... ... ....... ..... ......................................................... ............. 53 Spectral Backscattering and Passive Remote Sensing .... ... .... ..... .... ... ... . 65 Summary and Conclusions ........... ...... ... .. ....... ....... ........ .. .... ............... 76

6. Biological Weighting Functions for Describing the Effects of Ultraviolet Radiation on Aquatic Systems .......................... ... 97 John! Cullen and Patrick j. Neale Introduction ....... ..... ..... .... ............... ... ........... .. .......... .. ... .................... 97 QuantifYing Radiant Exposure ...... .. ... .. ...... ... .. ............................... ..... 98 Biological Weighting Functions ... .... ... ... ......... .. ... .... ... .... .... .... ............ 99 The Importance of a Good Weighting Function .... ... ...... ............ .. .... 100 Temporal Dependence and Reciprociry ofUV Effects .. ...... .. ......... ... 104 Lineariry of the Exposure vs. Response Curve ................. .... .. ......... ... 105 Methods for Determining Biological Weighting Functions .. ........... .. 107 Summary and Conclusions ............................................................... 109 Appendix 6.1: Procedures for Calculating Biological

Weighting Functions ...... ...... ....... ........... .. ... ... .............. ............ .. ... 110

7. Biological UV Dosimetry ....... ..... .. .......... ..... .... ... ... .. ...... ... ...... 119 Gerda Horneck The Biological Effectiveness of Solar UV Radiation ..... .. ...... .... ..... ... . 119 Quantification of the Biological Effectiveness of Solar Radiation .... .. 120 Characteristics of Biological Dosimeters ...................... ......... .. ...... .... . 125 Scope of Application of Biological Dosimeters .................................. 134

8. Role of Uhraviolet Radiation on Bacterioplankron Activity .... 143 Gerhard! Herndl Introduction ........................................... ........... ............. .................. 143 Role of Ultraviolet Radiation on Bacterioplankron Cells ................... 144 Role of Ultraviolet Radiation on Dissolved Organic Matter ..... .. ...... . 148 Interaction Between Bacterioplankron Activiry and DOM

in the Upper Mixed Water Column .. ......................... ... ...... ... .. ... .. 150 Future Research Directions ..... .... ....................... .. .......... ... ................ 150

'I

ill

9. Optical Properties and Phytoplankton Composition in a Freshwater Ecosystem (Main-Donau-Canal} .......... ................ . 155 Maria A. Hiider and Donat-P. Hiider Introduction ....................... .. ....... ....................... ......... .. .. .......... ...... . 155 Materials and Methods ...... ...................... .. ................... ............ ........ 156 Results ............................................................................... ..... .. ........ 157 Discussion ... .......................... ... ..... .................... ..... ..... ...... ................ 168

10. The Effects ofUltraviolet-B Radiation on Amphibians in Natural Ecosystems .. .. ...... ......................... 175 Andrew R. BIa"stein and j oseph M. Kiesecker Initial Laboratory Studies ............................ ..... ...... ....... .. ........ .......... 176 Field Studies ...................... .... .... ................................................. ...... 176 Field Experiments at Relatively High Elevation Sites in Oregon ...... . 177 Field Experiments at Low Elevation Sites in Oregon ..... .................. .. 178 Synergism ofUV-B Radiation with Other Agents .. ........ ................... 180 Discussion ........ .... .. ............ .. ......... .............. ..... ................ .. ..... .. ........ 182 Conclusions ........ ... .......... ......................... ....... .. ......... .. ....... ............. 185

II. Impacts of UV-B Irradiation on Rice-Field Cyanobacteria .... . 189 Rajeshwar P. Sinha and Donat-P. Hiider Introduction .. ....................... ........... ................ ..... ................... ...... ... 189 Conclusion .......... .. .............. ..... .. .......................... .... ...... ... ....... .. ....... 195

12. Studies of Effects of UV-B Radiation on Aquatic Model Ecosystems ................................................ 199 Sterz-Ake Wiingberg arid j ohmme-Sophie Selmer Introduction ......... ............................................... ....... ... ............ ....... 199 Model Ecosystems Used for Assessing Effects ofUV-B Radiation

on Aquatic Ecosystems .. ............... .................................................. 20 I Reported Effects .... ........ .. ........................................................... .. .. .. . 206 Effects on Primary Producers ............ ... ...... .... ..... ....... ....... .... .......... .. 207

13. Solar UV Effects on Benthic Marine Algal Assemblages-Three Case Studies .................... .. ............................ ...... .. .. ..... 215 Regas Santas Abstract ..... ............................. ... .................. ................. .. ................... 2 15 Introduction .......... ....... ... ... ................... .. .. ... ................ ... ....... .. ........ 2 I 5 Case Study I-Laboratory Mesocosm Experiments ... .... .......... .. ...... . 217 Case Study 2-Tropical Assemblages (Caribbean) .......... .................. 221 Case Study 3-Mediterranean Assemblages (Korinrhos. Greece) .. .... 223 Discussion ........................ ..... ..................................................... ... ... . 224 Conclusions ......... .. ....... ................... .......... ................................... ... . 227

I I

I' ,.,

14. Effects ofUV-B on Ciliates ........ .... .. .. ..................................... 229 Roberto Marangoni, B,atriu Martini and Giuliano Colombetti Introduction ..... ..... ... ... ..... .... .. .. ... ... ... .. .............. ............................... 229 Early Studies and General Considerat ions ...... ..... .......... .................... 230

15. Effects of Ultraviolet Radiation on the Pelagic Antarctic Ecosystem .. ... .... .......... .. .................... 247 Marfa V.met and Raymond C Smith Abstract .............. ........ .... ... .... .... .... ....... .. .... .. ...... ... .. ..... .... ................. 247 Introduction ...... .... .... ... ....... ... .... ..... ... ..... ................. ........ ....... ...... .. . 248 UV Radiation in the Southern Ocean ............................................... 249 The Food Web ..... .... .................... ... ...... ... ..... .. ... ............... ..... ........ ... 251 The Microbial Loop ............. ........................ .. ...... ..... .. ....... ......... .... .. 255 Nutrients ............................... ..... .... ... ... ...... .............. ......... ... .... ........ 257 Conclusions ....... .. ... ..... ......... .. ............. .................. ... ........ ....... ........ . 258

Index .... .... ..... .. ............ ... .. .. ............. ...... ...... ...... ......... ............... ..... 267