effects of ultraviolet radiation on the pelagic antarctic

= = = = CHAPTER
15 = = = =
EFFECTS OF ULTRAVIOLET
RADIATION ON THE PELAGIC
ANTARCTIC ECOSYSTEM
Marfa Vernet and Raymond C. Smith
ABSTRACT
U
ltraviolet radiation (UVR) affects biotic and abiotic factors in marine
ecosystems. Effects o n organisms are mostly deleterious due co damage to DNA and cellular proteins that are involved in biochemical processes and which ultimately affect growt h and reproduction. Differential
sensitivity among microalgal species to UVR has been shown to shift
communit y 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 growt h. 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 wa ters would decrease when exposed to UVR,
this effect can be counteracted by in creased substrate nutrient availabi lity. Photolysis of high-molecular weight molecules by UVR produces
The Effects of O zone Depletion o n Aquatic Ecosystems. edited by Donat-P. Hader.
© , 997 R.G. Landes Co mpany.
248
Tile E((ecls of Ozone Opp/e tion on AqUcl tic ECOS ~/5 t elll s
hig her availab ili ty of low-molec ul ar weig ht
m o 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 whe re low bacterial producrion has bte n attributed to low
su bstrate ava ilabilit y.
Similarly, inc reased nutrients for bacte ri al act ivity ori gina te fro m p hocolys is of
h igh-molecular weig ht moitcul es whi ch are
known to re lease NH.j • and a m ino ac ids
under UVR. T he DaM pool might also
inc rease th roug h phytoplankton excre ri o n
of organic mane r, a process k nown to occ ur under a lga l stress. On rh e ot her hand,
a decrease in DaM by diffus io n from zooplankton fecal pe ll ers is expeered in surface
waters du e [() decreased g razing.
I n summ ary, we argue t hat rhe understand ing of the effecr of U VR on Anta rcric ecosys t ems is more t ha n th e sum of th e
effect of radiation on ind ividua l spec ies,
g iven t hat alteratio n of inte rspec ific interactions can exace rbate, dim ini sh a nd somet imes reverse kn own p hysiological damage .
This, p illS complex and nonlin ea r feedback
mec han ism s associated wit h UV R effects
m ake p rediction at the ecosystem leve l
un certai n .
INTRODUCTION
A rt~cent c haracte ri sti c p he nom e non of
the Antarctic ecosys tem is the we ll-k now n
sprin gti me decrease in stratosphe ri c ozone,
kn own as th e ozo ne hole. It is confined to
t he po la r vo rtex ove r the Ant arc ti c co ntine nt , from Septembe r to Dece mber of eac h
yea r. H oweve r, once the wintf: r/spring vortex breaks dow n , its effc:ns reach mid lat itudes, mostly during the mont h of Dece m ber, I a lt hough it has a lso been detected in
s ub- an rarctic e nvi ronme n rs duri ng the
sp rin g ..! The re has bee n sig nifi can t ann ua l
and int era nnua l var iab ilit y in Antarcti c
ozone, a nd , co nseq uen rl y, in cha nges in
ozone- re la ted incide nt u lt rav ioler radiation
(UVR). During th e last two decades major
int ernat ional efforts have focused o n th e
physics a nd chemi stry of the Eart h' s atmosp here w ith emp hasis on understanding
processes that control the ozo ne layer, while
studies on the effects of UV on th t
b iosphe re, in parti cular a t th e co m munit}1
a nd ecosys t tm level, ha ve been re la ti ve ly
lim ited. '
ln te res t in U V effects on aquatic ecosyste m s is in creasing because ozone dep let ion is not restr icted to th e area ove r Anta rctica and signi fi can t reductions have been
reported in th e Nort hern H e misphere : I . ';
Hemi spherical trends a rt superimposed on
high in tera nnua l variab ilit y, as poi nted our
by Michaels Ct a i,' w here low ozone during 1992 can be assoc iated with a drop in
sunspo t s, a strong EI Nino event a nd the
erup ti on of Mount Pinatu bo, all of whi c h
ca n pote nti a ll y decrease ozone in t he Stratosp h e re . Othe r pop ul a t ed areas, suc h ns
Sout h Ameri ca, Australia, New Zea la nd
and Sout h Afri ca a re affected, in panicul ar
at th e t ime of [he vo rtex disappearance,
pro bab ly as an effter of dilution.' ··'
It has bee n est im ated t ha t aquati c ecosys tems fix bttween 30 and 50 Gt of carbon pe r yea r, whi ch is ro ug hl y half the rota l g lo b a l fixation
of ca rbon. H• ltl
Co nseque ntly, th e threat of inc reased UV R
on surface layers of th e ocean on mnrine
product iv ity is of consid erable conce rn . Estimates fo r t he Sourhern Ocea n range frolll
1-5 Gt C y- '." For the South ern O cea n , ice
a lgae are esti m ateu to contrib ute lip to
30 % of t he total pr im ary produCtion . I..?
Traditionally, pred ic ti on of U V efftcts on
ecosystems have ass um ed a linear addition
of U V effecrs on different level s of t ht food
c h ai n whe re t he f in a l effec r on h ig i1<:r
trop h ic Itve l p redato rs, slI c h as penguins.
wha les a nd sea ls, have bee n in fe rred from
t he c umul ativ e effeCt o n p ri ma ry produce rs and grazers. I ., I n oth er words, tht- roral
effect of UV at a givf'n trop h ic levc:l has
bee n ass um ed 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 exa mp le, in itia l studies on UV
effeCts o n m a rin e nlga l communities rt'po rted decreased [O ta l pr ima ry produc ri vity a nd shi fts between species rownrds It-ss
UV -B -se nsitive spec ies as we ll as l:I drop
in total species diversity, assum ing consm nr
Effects of Ultraviolet Radiation on the Pelagic Antarctic Ecosystem
grazing.14"17 In contrast, recent trophiclevel assessments suggest that differential
UV sensitivity between algae and herbi
vores may contribute to an increase in al
gae by exerting a stronger UV influence
on the grazers. 18-ly An analogous influence
on zooplankton, thus reducing zooplank
ton grazing, could counteract UV photoinhibition on phytoplankton growth. In
addition to biological factors, UVR affects
abiotic processes which affect directly or
indirectly the food web. These factors are
either chemical (e.g. nutrients) or related
to the dissolved organic matter (DOM)
pool which is intrinsically related to the
microbial loop.20 Such an alteration of the
ecosystem functioning would result in a de
crease of transfer of energy through the
food web.21
In this chapter we summarize what is
known of the UVR effects on different lev
els of the Antarctic food web, with em
phasis on the relationships between trophic
species, and what is known of the UV ef
fects on abiotic processes affecting the food
web. Several recent reviews on UVR effects
on aquatic and Antarctic ecosystem13-22
have given excellent summary of the UV
photobiology and that information will not
be rephrased here. We present evidence to
suggest that research required for under
standing UV effects on Antarctic ecosys
tems will necessitate ecosystem studies in
addition to detailed determination of UVR
on specific processes related to any given
trophic level.
UV RADIATION IN THE
SOUTHERN OCEAN
Estimation of quantitative effects of
ultraviolet radiation (UVR) on biological
systems requires knowledge of the incident
spectral irradiance and a biological weight
ing function (BWF), which provides the
wavelength-dependency of biological ac
tion. Because BWFs are heavily weighted
in the UV-B region of the spectrum, high
spectral resolution is required for accurate
estimation of effective biological doses.
Smith et al23 have developed a high spec
tral resolution (1 nm) air and in-water
spectroradiometer and Booth et al24 have
developed the U.S. National Science
Foundation UV Network which provides
high resolution data at three locations in
the Antarctic continent. Alternatively, nar
row band instruments (e.g. Bio-Spherical
Instrument PUV series) can, in conjunc
tion with an adequate full spectral model,
be used to estimate incident spectral irra
diance with adequate resolution. BWFs,
specific to the target unit, have been de
veloped. For Antarctica, stepwise functions
for the BWF for photosynthesis have been
developed by Helbling et al,25 Lubin et
al,26 Smith et al23 and Boucher et al27
which have yielded results similar to the
more detailed determination of Cullen et
al.28 Other BWFs have been developed in
temperate areas for plant chloroplasts29 and
DNA.3(1 There is a paucity of BWFs for
other processes, for other levels of the food
chain, not only for Antarctica but every
where. This is a serious constraint for
modeling and predictive purposes.
Actinometry (e.g. refs. 31, 32) has not
been used extensively in Antarctic studies.
On the other hand, a biological dosimeter,
based on the response of an organism to
UVR, has been used. This method provides
a relative unit to assess potential effects of
UV exposure on a specific organism or tar
get molecule. Once the response of the
organism to UV is evaluated under stan
dard conditions, i.e. by exposure to natu
ral UV radiation, we can say the organism
has been calibrated. A relative estimate of
potential UV damage can then be esti
mated. The potential benefit of the biolog
ical dosimeter resides in being a relatively
more easy and inexpensive method, once
it has been carefully evaluated. The main
disadvantage is the exacting dosimetry re
quired for quantitative calibration. It can
also be used to compare biological effects
on very diverse environments with or with
out very different UV climatology. Al
though a biological dosimeter was carefully
evaluated for an Antarctic coastal site it has
not been used extensively use in the
The £{(ecls or Ozone Depletion on Aquatic Ecosystems
250
regio n. H Both rh e acr inom e rr y and rhe
biological dosimeter give broad band es timates of UV R unl ess rh e incident radiacion is differentia ll y screened, usually with
filrers. ,H
CLIMATOLOGY OF UV RADIATION
U leraviolet radi ati on (U VR ) levels are
mostly controlled by atmosp heri c ozone,
cloud cover, and solar zenith angle with
ozone co ncentration being rel ative ly specific
to th e UV-B reg ion. )·' Natural variability
can cou nteract UVR increases. Further, rccent work (Gautier et ai, Un iversit y
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 sur face
reflectance influences th ese U V -8 ratios. As
not much is kn own w ith respect to th e
effen of th is variability on o rga ni 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.
in these env ironmental variables g ive ri se
to a very hig h natural variabi lity in UVR ,
with ozone pri ma ril y affcccing rhe relative
ratios of UV-B to UVR, photosynthetic
ava ila ble radi at io n (P AR ), or rota I irrad ianee. The dynamic nature of rhe polar vortex containing rhe ozone hol e has give n ri se
to large c hanges in th ese UV-B ratios on
rim e sc al es of severa l days or less
(Fig . 15. 1). The pola r vortex, a nd corre-
TRANSMISSION OF UV
IN SURFACE WATERS AND ICE
Tran smi 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 we ll
as particulate and dissolved organic matter (POM and DOM, respect ive ly) within
spo ndin g ly , the ozone ho le, is often elonga ted in shape, gi ving rise to an uneven
di stribution of UV-B at locati ons within
the Antarctic continent.35 The natural-short
the water column , Water is kn own to be a
relatively strong UV abso rber 37 - 39 and spectral atten uati on coefficients have been published for cleat natu ra l wate rs. 3M H owever,
in natura l waters, parti cul ate and di ssolved
t e rm variabilit y ( hours to days) due to
o rga ni c matte r stro ng ly a bso rb U VR and
changes in cloud cover and solar ze nith
t hese in-water cons t it uents are hig hl y variable. In blue, more transparent oligo trophic
waters, biolog icall y sign ifica nt UV doses
(a n penetrate several tens of met ers. Jn
con trast, mort productive coastal waters,
ang le compounds the diffi cu lt y in assessing the innue nce of increased UV-B levels
on natu ral sys tems.B,Y; The resultant effect is th at natural variability (cloudi ness)
Fig. 15, J. Daily maximum
UV·A irradian c es (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 b efore
and after solstice. Redrawn
from Booth et ai, 1994 .
3
~
'1'
E
==
2
~
0
1::.
CI>
u
c:
co
'is
CO
~
.!:::
o
Days before or after solstice
125
Effects of Ultraviolet Radiation on the Pelagic Antarctic Ecosystem
Fig. 15.2. Relationship between
the depth of 1% UV incident
radiation and dissolved organic
carbon (DOC) in lakes. Reprinted
with permission from Schindler
et al. Nature 1996; 379:706,
©1996 MacMillan Magazines
Limited.
with higher particle concentration (e.g.
>3 mg chlorophyll a m-3) can have attenu
ation coefficients nearly an order of mag
nitude higher, limiting significant penetra
tion depths to the order of meters.40 DOM
shows an even stronger attenuation in the
UVR'10,41 and can effectively limit signifi
cant penetration depths to a meter or less.
For example, Kramer42 estimated that the
combination of high POM and DOM in
Dutch coastal waters would limit UVR
transmission in the water column to such
an extent that no UV effects or planktonic
organisms were expected. High POM ab
sorption in Antarctic waters43 and probably
in ice-edge blooms,44 would limit UV
transmission in late spring and summer
due to high production, but not during
early spring (e.g. October) where chloro
phyll (chl) a levels are usually lower than
0.5 mg m-3.45 The paucity of absorprion
estimates for POM, and in particular for
DOM, make it difficult to speculate on
their effect in Antarctic waters, although
similar levels of DOM as in other parts of
the world would support the hypothesis of
important UVR absorption by DOM
(Fig. 15.2).46 Estimated UV effects at
depths of about 20 m in the vicinity of
Palmer might be due in part to the
contribution of DOM absorption.'3-4^
The role of DOC in light attenuation
is intimately related to other environmen
tal changes. For example, in boreal lakes,
the decreased amount of DOC, caused by
an increase in average temperature and
acidification in the last 20 years, was re
lated to increased UVR in the water col
umn.48 In the case of Antarctic waters, a
complex mix of competing feedback mech
anisms make estimating changes in UVR,
due to environmental change, speculative.
There are relatively few direct obser
vations on the optical properties of Ant
arctic ice and snow. These observations
suggest that UV transmission in the ice is
maximum in October due to relatively
high transparency in spring. Based on these
observations, it is expected that ice algae,
associated with bottom communities in ice
flows, potentially can be exposed to rela
tively high levels of UV-B. These UV-B
levels have increased by as much as an or
der of magnitude under the ozone hole.49
THE FOOD WEB
Phytoplankton
Photosynthesis
Deleterious effect of UV-B on photo
synthesis has been studied both in cultures
and in the field, in particular for Antarc
tic phytoplankton. The reader is referred
to reviews done in the last few years that
cover this subject extensively (e.g. refs. 22,
36, 50, 51 and references therein). Over
all, UV-B inhibits primary production by
30-509? of shielded samples^2 with a strong
depth gradient from surface to about
20-50 m.23-33-33 All these experiments are
based on 6-24 h incubations, either in situ
,- ,
-'-
in incuharors t'xposl·d ro sllnli,;.:hr. On
rhe ;I\'l"r~l,!.!t' for rhe wafe r 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' lblin g e( ai " has(:d
on dint-fene assumprions and mt'rhodol()~~y.
Of
l'srimilrt' rhe: decrease in primary produc{ion ro he n,I,) ';; for elu' en ri re iu:-frt't'
wafers so urh 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.:ri c phytoplankton. I1tct'ssaQI to sca le UV R
ro biological efTc:niv(: irratiianct', has been
d(:,,[t'rm i nt'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 phyrop iankwil. is acrivared by PAR '- a nJ i l1acrivnfed by UV -B rac1iarion. '~ In cont ra St,
ammonium IIp[;d~t' seems less afft'<.:[(.·d. ~".f'O
Overall. amino acid (O ll ct'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.d uram '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 U V-B and hi gh intensity UV-A
was interprered as rt'dllced s u pply 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 rri ed 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 photos yn 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 monos pecific n ilrure:s and in nafU rid populatiol1s(,'j ,t>:-! and tht' amOlllH e xcrett'd is a conStant proportion oi' phtllosynt hetic: ratts, Several st lldi t's have poimnl
OLit t hin a large: proportion of p llOws yn chetic ca rbon got'S throu g h a DOC phas("'"
for at It'<lst shurr pt'riods of t im e:. - II Undl'!'
chest' co nditions. bt'tween 20-()OIfi oi' plwrosynthiltt' must go inru rht' DOC pool l t l
explain the DOC ( ha n gc:s ob ser\' ed . I'
mainly dur ing spring bloom t'\'l'IltS in (('Ill pt'riltl' waters, Additional organi( ('ar hon
t'xCfetion in phytoplankton see m s assoc iated
with physiological imbalance due to ('V("ll['"
such as nitrogen limitation : I ,-; in particular lIndtr high-light condit ions,-' III rill'
ritld. r he tran sfer of ct'lls to higher irradi ·
anct" might produ<.:e excess phorosynthatt'. ('-'<'.'i Nutrie nt 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 s p. b loom, - ~, "
This t'xce:ss carhon t'xcre:red mi,ldn 11l' ;1... •
sociatni wirh increast'd in trace:llular Llrhllh)'<.iratt. as in diatoms -1.-- bur nor ohsl'f\'l'I1
in dinotlagellat(:s .--'
Vt'r)' lit tle is known of ("xud,lrioll hy
A nt arnic 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 car b 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 in corporatt'tI ;IS ("st[.l ctllll iar under (ondit ions of low si lic ic acid
(<<),2 PNf) and measurable nirril(t' concentration s (0.5 - 2.5 JlNO, Similar exrr;u.:l'lIuI: 1r
carbo n produccion was found in iI mixru rl
o
1.03
Eifects of Ultrilvio/et Radiation on t/u" Pel.lgic Antarctic Ecos}lsrem
of C. l{J(ia/il a nd 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;
howeve r. t h is tffecr mi g h t bt observed during o r after massive co;\sral b looms. 1'1.).;(1
In spite of t he obviolls imporranct (If
ph),top lank wn ex udacion o n tht carbon
C},c!t and as s u bst rate for the microbial
loop, no s tud it'S have bet'n ca rrit'd out on
tht efftn of UV-B on txu d;\ t ion, fo r tit htr tt'mpt'ratt' or po la r phyto p lan k ton. In
gtlle ral, ex ud at ion illlTeast's w ht 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.
onl y .'''~ O n rht other ha nJ. act ivt grow rh
of ( oasra l s ptc ies was obst rvtJ for 12 days
a t Pa lm e r Station w hert d iaro m ( u lrurt's
wtre kept at in sit u so l'a r radi.niol1. sh No
ditfere nc<:' was found also bttwee n t reat-
ments (UV R
+
PAR "s. PAR on ly) Ii" rh"
Respiration
Changes in OHC in rCO.,! obse rved in
th e Bt lli nghau st n Sea in the s pring of
19YO co mbined wit h chan ges in ce ll abulldan ce in th t' colon ial prymnes iop h y t e
Pbm!O(}'llis sp. s ugges t t hat under im: reased
U V-B radia tio n , as mtasu red undt' r dtcrt aseJ o zo nt (o nctnt rat io n , t htrt is an
increast in t ht' ratio of [0[;1 1 communi ty
n:sp irat ion (0 p hotosynthes is. xl H eterot rop hi c resp iration increases we re ;.ltuibuted
co incrtased bantria l s u bstrate du t' to (t il
lysis.
colon i.li prym nes iophy rt P /;at IJIJ.fliJ sp .. althoutih tht'st' cu lwn:s did nor g ro w. T h is
lack of ellel'( was observed in s pitt' of tht'
we ll -doc um ented inhibirion of pho(Osy nr h ts i s .!\·.!('-.!~ ti.)f Anrarcric ph}lropla nkron in
ex pt' ri me nrs frol11 1-14 h an d po inr s towards 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 so me timt rh at cau tion mu st be used
when inft rfing longe r tt' rm eco logical COI1St'lluen cts from short-ter m obstrva rio ns. NMixing of (t lls in th t uppt r watt'r col umn . in partic ular within r he mix t d laye r,
affens rht' avtragt irraJiance in whi ch a
(t.1I is txposecl d uri ng rh t day. \"i.NS,""·) Sevt' ral s rud its ha vt spt'nlia[td aboU( rh e poss ib lt role of a ll eviat ion fro m U VR in Anta rctic wate rs if ce ll s are mi xed detptr in
rhe wate r c olllmn . "i (j ·~tI ") 1 Expt rim t'nts where
U VR inre nsit y was ma nipul ated to rtstm ble m ix ing in th e u pper water co lu mn
sho wed in creased product ion in clo ud y da ys
while rhe effect was opposirt on s unn y
Ja ys. ~ 1 Phyroplankron dominattJ by t ht
d iarom T ba/fl11;Olir(1 grarititl s howed less
pho roin h ibit io n w hen tx poseJ to va ria ble
radiari o n :''! s up portin,!-: t ht' hy poth tsis char
mixing mi g ht provide U V-B protection. ,I,
Growth
Cell size
Th t' effect of U V- B on marint ph ywpla nk w n grow th has btt n sho wn to be
spt'c its-s ptci fi c. For stve ral cu lwres of tel11ptratt sptci es, spec ific grow th rate was affecced neg ativ(·ly by U V _B. ~.!-N I In the di acom 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 re sult s were observed on .) 0
txper imtnrs on Anra rcric ph yto p la nkton
dominated by C',rt'lbrrlJl (rilll,b)/I1'" whe re
.;..:rowrh rates d tcrea sl'J by I OO'J on (t· ll s
Coastal wattrs have. on th t' avt' ragt_ a
hi ,!-: ht r proportion of htrge r ct'll s cha n ope n
warers.''' For example. more t han :-lO 'A of
the nearshort p hyr(lp lan kcon biomass was
ass oc iated w ith ct ll s > 10 pm in T er re
Ad e li t' durin~ sum me r wh ilt 7 0 km offsho rt'. 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 C hi (f ( oncencrar iolls afe
dominared by sm all er u : II S..-l 11.'1\ A differenria l effect of UV R on (e l l size, as
exposed to UV-A + UV- B
+
PAR and by
SO'/( w he n ex posnl to UV- A + P,\R. as
co mpar ed to conrrol s t'xpost' d to P ,\ R
Til(' [,.,.('('(;;
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 yto plankton rna y
ha vt a hi ghtr st' ns itiv it y to l1V-B . In addition , U VR int:re<1sts ce ll s ize;.! assm:ia ttd
with a co nco mlt anr redu crioll 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 UV toleram spec ies ultimatel y dominating. I ('
As me ntioned above. there is a wide range
of interspeci fi c UV- B stns itivity on grow th
and surv iva l, with smaller ce ll s being mo re
se nsitivt'. due to a hi g htr surface to vo lu me ratio as a res ul 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 co mpared
with diatoms, was observtd in n a tural
pop ul at ions of AntarCtic phyroplan kron . 'i •.1)Thi s di fft'rence ( an be att ri bmed in parr
to si ze (fla g ell a t es ar e on the av erage
smaller than Anrarct ic diatom s) and to increased UV-absorbing propercit's of diatoms l)1 rt'lat e J to the presenct' o f
m ycospo rint-like a mino acids whi c h are
bt' li evt'd to reduce dt' lt'te ri om effects by
UV-B on g row th :'" The predict ed sh ift
from less to more resistant spec its (e.g.
from fbgellarts ro di awms) was obsNvt'd
in a 2- wt"t"k experimtnt of nar ura l Anrarcti c populations t"xpost"d ro amnienr U VR,
although si milar C hI tI and parric uhu e carbon acc umularion were ohse rved undtr
UVR and UVR
+
PAR ." Unde r lIV R the
amount of U V ah sorhing co mpo u nd 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
co mposition. a d ecreased se nsiriv iry of photosynthe s is wa s obse rv ed in rhe ph y roplankton t"x posed to U VR . The hi g her
res isran ct" b y 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 m s to be re hH ed [() a lower efft"([
on phorosynt h es is as wtl l as nitrat t'
uprake. $·)
O( 0 1 0/)(;' D t'p/t'tioll Oil AqU.Hie Ec.:os ~ ';; f< ·I1;'
Few sw d its a re a\'a ila blt' on d"(tc£ s Ill'
UV R a t lo n,!-!t"r rime sca les. rvldvl inn t't ill'"
docllmt"med no c han gts in diatom spl' r il'.,
co mpos ition in laminared sed im enrs ill
Anrarctic anox ic fio rd s for t ht las( 20 year,.
coincidin,g w it h t he dtcre;lst' of OZOIll' .
Howeve r, as nor ed by Bothwell and coworkers ls the limi ted data provided hy
Mc Minn et <1 1'/1' do no r subsra mi <1rt" rill' ir
implied lack or a UV-B eHtcr.
ZOOPLANKTON
UV t'ffec£s on zooplan kton , und er normal and decreased ozone conditions in rempt'rare waters, afftct zooplankton su rvival.
reproduct ion a nd 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
c hrnn o mid /diilwm inte raction in te m pl'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 lit y of
gra zing revtrs ing delttt"riulis effeCts of UV
on phyroplankron and rhe re larivt' imporulIlce of grazing in co ntroll ing phytoplank ton popu lat ion growth in any ,g ivt"n comf11unir y is currtntly a m ar re r of spec ula rioll .
U ndt"r c urrent U V irradinllce. ovt'fall tll'creast' in primary production by U V in rill'
Ant a rcti c t"up hotic zone is t'st ir1"wted .11
6-2Y/f of marg inal ice zo ne production .:" :'
Th e ovtra ll rt"su lt would depend on rill'
dft'Ct of UVR on Anrarct ic gra ze rs, an'raged for rhe t uphor ic ZOIlt". and on rilllt'
.sca les represen tative of phywplankro n ;I tclll'nulatioll at ambienr tempt'rctrurl' (d.IY:[(l wtl'ks. if Wt' assume it spt'cifi c ~ro\\,lh
ra rt' of 0.1-0, ,) d- I), ll
SEDIMENTATION
Pottnria l changes in g ra zing prt'ssufl'
wi ll affect st"dimelltatiol1 of particu l:lIl'
matter. In areas wh e rt:· organic matter snli·
men rar ion OU t of rhe e uphori c zo ne 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 im t'ntation.
ass uming no c hange in p rima ry p rodu ction .
Thus, rhe pulse of orbani c m atte r after a
bloom could consist mainl y of intilCt cell s.
Effects of Ultraviolet Rae/;alion
255
on tile Pelagic Antarctic Ecosys tem
PAR
...
100
A
'>" N
=~
• 90%
0 50%
75
50
U
25
:;:-
B
.c
.a N" 400
.-"0 'E
E .
o 0
.c '
a.E
(;o '"
E
600
eoS
200
:c
U
0
0
PAR + UV-A
100
...
.c
C
'"
75
"
>'N"
.- E
E .
00
a.E
(; E
0 " , 50
U
0
75
;~
.c '
:;:-
100
50
c: c:
e-
25
:c
U
0
25
0
PAR + UV- A + UV-B
100
..
E
ttl
.c
75
"
~N"
F
75
;~
.c '
a.E
(;o '"
E
50
U
25
:;:-
100
.- E
E .
o 0
c: c:
e:c
50
25
U
0
0
•
•
12
16
20
0
•
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 o pen circles, 5()% of incident irradiatlce} at three
treatments (PAR: top panels: PA R + 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 A ssociation [or the A d va ncem ellt
o f Science.
T his tffecr w ill be maxil11um in coas ral
art'as w here larger ce ll s') I and hight f product ion art fO Ll nu. ''j Second ary effects wil l
include alrt'r<lriol1 of t' lel11t'nral rar ios . hertrorrop h ic sub sr rare a nd IllHrienr recycling
below rhe euphoric zo ne. If, on rhe m htr
hand. a large p ro po rtion of stdim (.' nrin.c
manef is du e [0 cell si nking rhen rhe lJual iry of orga ni c ma[[e r co d eprh wou ld nor
bt" subs ranriall y alrered. 1I1! The q uan r iry
and riming mi ghr bt afte:ctt"d if. as Jis-
c ussed before , UV R wou ld a lre r speCies
co mposirion and /or specit"s s ize.
THE M ICROB IAL LOO P
B ACTE RIA
Bant'fi.d biomass in Anrarn ic ware rs
can reac h 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 su mmer. 1(' DitYt" rtlH
lar wei ,~.dH DOM (e.g. Fig. 15 . ) ) 111 '1 1
which is readily ilvailab le for bacrni ;d
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;
01.
(()nsumprion. ICI~.IIlS
The imporrance of rhe s izt da ss 011
bantrial produnivity is srill a ma rr<: r Ill'
debart. as Amon and Benner lll'l found r hat
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-mo lt'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 whic h UV pllOr() ~
oxidat ion of DOM would be
impOrrallll"
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.lne rial metabo lism, ll l r he 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()c hemi 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
the solar spe([rum for this process whi(h
cou ld be due both (0 high t r e nergy <Ind
hi g 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
UV R reduce s 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 s urfan' popu lations as
opposed ro chose from depth . 1II1 I nhibit 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
energy through rhl" microbial loop. Thi s
('ffeer is COLI l1[eracred , or at leasr diminished , by rh e increase in bacterial subsr rate
due to phorodegradat ion of DOM. Increased bacteria l activity at low UV -8 irradian ce wirh respect to da r k up t akt·
(F ig. 15.4) was attributed to this process.
or
or
PHOTO-OXIDATION OF
DOM
UV-B inreranion wit h DOM is known
to produce oxyge n radica ls a nd hydrogen
peroxide (H,;O ,! ) which call be co nsidered
oxidarive agell[s of biologica l membranes
and have a negat ive impaer on plankton ic
comI11L1nities.l!l ~ In addirion , mulrip le studies have documenred rhe photo-ox idat ion
of nOM responsib le for degrading highmo lt'nilar weighr DOM inro low-l11olecuFig . IS . ..J. /3a Cfl'ri.1/ s(' c ondclr~ ' produc·
tion fB SJJ ) ,J.s a (unction o( UV·/3 (,leliatioll. No tl-' hight·,. prod uclion ,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/.
140
~ 120
'"
Co 100
or
y = 52.7 - 40.7· log( x)
n = 75, r = 0.605, P < 0.001
••
• ....
,..
..-~....
.
~
-" . . ... . . :-."• •.
. ..
.. •
0
80
c..
en
m
60
i•
::::
••
~e
• :1 • •
...........
• • !
•
40
•
!
~
20~~~~~~~~~~~~~~
0.0
0. 2
0. 4
0.6
0.8
UV-B [W m·2 j
1.0
1.2
1.4
EfI"ects of Ultraviolet Radiation on the Pe/<lgic Antarctic Ecosys tem
c hem ical characttr ist ics p rtv iously assoc iated on ly w ith humi c s ubs tan ces. Th e
so urce of thi s pool of DOM see m to be
degradation of ctllul ar mt'mbranes and can
be assumt'd ro bt' prouuced a nywhe re in t ht'
occ-;m .
NUTRIENTS
MACRO NUTRI ENTS
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 larg er availabi lity of a mm onium, of
majo r im porranct in areas of nitrogt ll li m ica rion , can counteract dtcreast'd N upcake
and mecabo l ism by ph ytop lan kto n, W.6' and
potenria lly bacrt ria , as a rtsu lr of U V-B
inhibition . In spite of h igh nitrate co nct ntrarion s in m os t Anta rnic open wattrs
d uring the growth seaso n , phytop lank ton
h as shown low spec ific nitrate lIptakt
rates l ! ') and differentia l uptak e of NH j '
wht n p rese nt, ll(' suggesting that a portnrial efferr of UV-B in releas ing N H .,· may
be of inte rts t in tht Southern Ocea n .
M ICRON UTRI ENTS
The pote ntia l inreract ion of iron ( Fe)
a nd UV-B as a source of di ssolved iron is
imporca nr in t he Southern Ocean as it has
betn hypoth esized that Fe limitation may
be con troll ing primary product io n in Antareri c open waters c haracte ri zed with low
c hl orop hyll acc umul at ion and hi g h ma c ronutr ient conct nrrat ion . ll - For tx ample . t he
g radient of hightr productivity in coasta l
wa(t'rs as opposed to optn W;l(t rS obse rved
in th t' \'(/tstern Antarctic Pen insu la 1').1"11 is
co rr e laet d wit h observe d iron concen tration s (4.7 nM a nd 0. 1() nM, res pectiv e ly). lIS A sim ila r approach was tak en by
de Baar et al II,) to explain h igh primary
productivity at tht Po lar f ront ( 12 0() .1 000 m g C 01-' d- ') wit h hi g h Fe co n centratIOn in surfa ce waee rs (2-4 nM a t
60- 100 m) as opposed to lowe r primary
production (80- ., 00 mg C m -' d- ') a t the
Antarctic Ci rcumpo lar Curn: nt with su bnan o molar co n centra tion s (0. 17 nM a t
4 0 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 ad di tio n wit h respect
2.5 '--'--'-"--'--"----'--"-IT--'
.2!..
~
1.5
~
E. 1.0
.
"
:::l
.0,
o
o
0.5
iii
•
°0~~--2~~-~4~-L-~6~-L-~8
Photoproduction [nM h-1]
257
Fig. /.5.5. Photochemical production ofpyru·
va te after irradidtion of di$solved organic
matter (DOM ) plotted agaim t the ra te of
up take of fJ}' fl lV.1U· by b,lCteria in coastal
waters (tilled circles) and in th e 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.lgazin es Lim ited.
I ,
The E[fects of OlOnt~ De:'pletion on Aqucl tic Eco s ~/s t(:,lll s
258
1.0,--,--,--,--,----;,----;,----;,----;,----;n
i' 0.8
.;;.
~
•
Fig. 15.6. Photoreduc tion of
Fe(lII) in sealvaler (p/-I B.O·a.1 1
in the presence o( the diatom
0.6
"C
~ 0.4
Phaeoda ctylum tri co rnu tunl
::J
under UVR. Fe(lI/) concerHr<l·
lion of 5 JIM; diatom cOIlC(~n ·
Ira tion of I O ~ cells mI' J. Re:"
"C
~ 0.2
dra~·vn
30
60
Time [min)
90
(rom Klima et ai, Marin('
Chemistry J 7: 15-27. Com/right
1992, with kind permission
(rom Elsevier NL.
to controls in t he Wedde ll/Scotia Seas
(both ueatments g rew at simi lar leve ls).
The aut hors concluded t hat incubation effects overrode meta l, and in part icula r, Fe
add it ion d ut' in pare to rhe excl usio n
large graze rs from the t'xpe ri mental vessels.
Iron add itions shifts phyroplankton composition from flage llates to diatoms, both
in A ntarct ic l1 1 and in eq uato ria 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
wate rs or coas tal wate rs off Seal Island . A
sh ift to la rge r cells is si m ilar to orher experi m entS 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 wate rs, Ft: " is the more
stable form w hile 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 inorga nic spec it'S) is t he relevant fac£O r ro cons ider wit h
respect to the uptakt' of ino rganic 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
subpicomo lar concent ration of disso lved
Fe(l II ). It is be lieved that the ligands for
iron may orig inate from phytoplankton_ L!~
ur
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 COI11p lexes, a large r reduction power is expecrnl
from o rganic chromophores. 115 ReduCtion
of organic ligands 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 m arine
p hytop lankto n (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 wa ters. 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 rbox ylic 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 wa ter tem peraturt' va ri es from - 1.Bo
to +2.5°C).
CONCLUSIO NS
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 U V effects on Anta rctic ecos}'sterns or marine ecosystems in genemi, will
Effects
of Ultraviolet
Radiation
on
259
the Pelagic Antarctic Ecosystem
, - - - MACRONUTRIENTS --~
~
-+
MICRONUTRIENTS OH-~
... ;
H20 2 '~...
::
'4' I I
, DOM~
uv
'b::~;~~.ta.t \~Pta~
PHYTOPLANKTON )
gr.1lng
.
•
h~zlng
I~kag.
le.kage
\
"'"
MACROZOOPLANKTON •
grazing
Fig. 151 Scheme showing
BACTERIA
1
MICROZOOPLANKTON
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.
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 tempe rate 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 estimate UV effec ts 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 examp le , changes in species composition
might overs hadow 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 CO 2 interaction between atmosphere
and oceans.
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ENVIRONMENTAi
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
R.G. LANDES COMPANY
Academic Press
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 Aq uatic 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 ...... ...................... .......... ....................................... .... ...... 3 1
Spectral Leakage ........ ...... ............. .... ....... .. ............. ..... ...................... .. 34
Artificial Sources .... ................... ................ .......................................... 36
Cosine Collector Design ..................................................................... 37
Dark Corrections .............. .. ....................... .................... ..................... 39
Conclusion ............................... .............. ......................... ............ ....... . 4 1
Appe ndix 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
il
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 AssemblagesThree 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. G reece) ...... 223
Discussion ........................ .......................................................... ... .... 224
Conclusions ........... ....... ................................................................ .... 227
14. Effects ofUV-B on Ciliates ..................................................... 229
Roberto Marangoni, B,atriu Martini and Giuliano Colombetti
Introduction ..................................................................................... 229
Early Studies and General Considerations ......................................... 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
I
I
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